ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy makers.

November 12, 1999 -- Vol. 3 Number 46

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Man's destiny is to know, if only because societies with
knowledge culturally dominate societies that lack it.
Luddites and anti-intellectuals do not master the differential
equations of thermodynamics or the biochemical cures of illness.
They stay in thatched huts and die young.
-- Edward O. Wilson

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Contents of This Issue:

A ScienceWeek Editorial

1. Time-Scale of Disappearance of Stellar Dust Disks
2. On the Peaking of World Population Growth
3. Clonal Interference and the Evolution of RNA Viruses
4. Origins of Insect Metamorphosis
5. Plasticity of Auditory Cortex in Congenitally Deaf Animals
6. Traumatic Brain Injuries in High School Athletes

In Focus: On Riemann's Geometry

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A ScienceWeek Editorial:
------------------------
     This is the first explicit editorial ever to appear in
ScienceWeek, and we are presenting it because we are extremely
annoyed at a front page article in the New York Times of 
November 3, 1999. The lengthy article, in addition to the front
page paragraphs, occupies a full internal page, and is concerned
with genetically engineered agriculture and foods, in particular
with a squash plant genetically engineered to be resistant to
destructive plant viruses. The headline of the article is:
"Squash With Altered Genes Raises Fears of 'Superweeds'". Of
course, the provocation of the headline (which is all most people
will read) is a common modus operandi in journalism (see
background material below): in the absence of a cause for fear,
there is nothing to write about the squash plant or food
production, certainly nothing that will sell newspapers. The New
York Times article, as do most popularized accounts of this
subject, gathers quotations from various sources to support the
notion that extreme concern about genetic engineering in
agriculture is warranted, in other words, to sustain and provoke
public fear. Little space in the article is devoted to
counterarguments, or to the actual and potential benefits of
genetic engineering in agriculture; the gist is to emphasize
risks, with words like "may", "could", "might" appearing in
nearly every paragraph.
     Since the New York Times is the most influential newspaper
in the US, and since certain other US media have been publishing
similar articles, the prospect is that the US will soon have the
problem already experienced in the UK -- a strong, vocal, and
militant protest movement against genetically engineered
agriculture and foods -- against so-called "Frankenstein foods".
The sociological energy loop is apparent: the media provokes
public fear, which in turn produces public interest in the
subject, which in turn produces more media provocation, and so
on, with an ongoing result an increase in media market share. In
the instance of genetically engineered agriculture, the emphasis
is always on risk: may, could, might -- provocation by
articulation of possibilities.
     We agree there is risk. There is always risk in any new
technology, precisely because the technology is new. In the past,
this was true for the first explorations of the human species
with fire, with the wheel, with the use of metals, with sea
travel, with the introduction of the steam engine, the
automobile, immunization, air travel, and television. We are what
are because in the past we took risks.
     But the most important point, and the one almost always
avoided by the media, is that it is not possible in principle to
prove a null hypothesis -- in particular, it is not possible to
prove that any drug or vaccine or food or technology is harmless,
i.e., risk-free. All that one can do is demonstrate that under
certain experimental circumstances there is no apparent harm; one
cannot make a proof of no harm for all circumstances. For
example, it has not been proved (and it cannot be proved) that
the inks now used by the New York Times and other print media are
not carcinogenic. All inks contain dye molecules, many dyes are
known to be carcinogenic, and many substances interact with
biological cells at extremely small concentrations. Should we
provoke public fear concerning these media inks? Is it in the
public interest to do so? The article in the New York Times
essentially castigates the US Department of Agriculture for not
requiring agricultural companies that produce genetically
modified products to prove their products are harmless. Since no
such proof is possible, this is what is called a "bad rap"
against the US Department of Agriculture.
     Undoubtedly, there will in the future be various real side
effects of genetically engineered agriculture that will be
recognized as undesirable for one reason or another. There is
indeed an element of risk. But genetic engineering in agriculture
is of such great potential importance for world food production
that we must go forward with it. If we are a rational society, we
will use the technology and deal with consequent problems as they
arise. The scientific community must advise the public to
recognize the media ballyhoo against genetic engineering for what
it is -- provocation for profit.
----------
Dan Agin
Editor/Publisher
ScienceWeek
dpa@scienceweek.com
-------------------
Related Background:
AN UNCERTAIN STAND BY MIT JOURNAL ON BIOTECH AGRICULTURE
The application of genetic engineering to agriculture has caused
intensive debate and militant protests in the UK and Europe, but
so far the debate in the US has been comparatively subdued.
Perhaps one reason for the lower level of protest in the US is
that US media in general have not been excessively alarmist. It
is thus strange to see a prominent publication of a first-rank US
engineering university, the Massachusetts of Technology, treating
the subject of genetically modified agricultural products in a
manner one would expect from a UK tabloid. The cover of the
July/August 1999 issue of the _Technology Review_ blares:
"Biotech Goes WILD", the headline on a background of metallic-
looking plants shaped into barbed wire. Inside the magazine
(which is now in its 100th year of publication), the lead article
of the same title is by noted science writer Charles C. Mann.
What is striking is that the text itself is rather even-handed,
while the title and blurbing appear deliberately alarmist:
"Biotech Goes Wild" is the title. The lead blurb: "Genetic
engineering will be essential to feed the world's billions. But
could it unleash a race of 'superweeds'? No one seems to know.
And nobody's in charge of finding out." Another blurb: "The worry
is that biotech crops will spontaneously breed with wild
relatives creating 'superweeds'". The editorial in the issue, by
Editor-in-Chief John Benditt, is also even-handed, which makes
both the magazine cover and the blurbs in the Mann article even
more surprising. Perhaps the explanation is that MIT's
_Technology Review_ is now a newsstand publication, and the cover
is deliberately designed to be provocative. The editors would
perhaps point out that since the actual content is even-handed,
the content will counteract the effect of the cover.
Unfortunately, most people who approach a newsstand and see the
cover of _Technology Review_ will not buy the magazine or even
open it: they will merely be left with "Biotech Goes WILD"
ringing in their heads, reinforcing other misinformation and
fears of the unknown. (It is ironic that in the context of
genetics, the term "wild" denotes the "normal" and unmodified
plant.) In the UK, the tabloids call genetically engineered
agricultural products "Frankenstein Foods". Years ago,
_Technology Review_ of the Massachusetts Institute of Technology
was a publication seriously devoted to the accurate communication
of new science and technology to the public. Apparently, that
focus has been overwhelmed by other considerations.
(Technology Review Jul/Aug 1999) (ScienceWeek Bulletin 11 Aug 99)
[For more information: http://scienceweek.com/search/search.htm]
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1. TIME-SCALE OF DISAPPEARANCE OF STELLAR DUST DISKS
The current nebula theory of planet formation proposes that
star-planet systems begin as a contracting cloud of gas and dust
that flattens into a rotating disk. The center of this cloud
becomes the star, and the planets eventually form in the disk of
the nebula. In the inner part of the nebula, the hottest part,
only high density minerals can form solid grains. The outer
regions are cooler, and in those regions icy materials of lower
density are formed. Planets grow from these solid materials,
beginning as dust grains, which grow by condensation and
accretion into planetesimals that range from a few centimeters to
a few kilometers in diameter. These planetesimals settle into a
thin plane around the star and accumulate into larger bodies, the
largest of which grow the fastest and eventually become
protoplanets. Once the star becomes a luminous object, the
remaining nebula is cleared as the star's radiation and the
stellar-wind (powerful streams of charged particles from the
star's surface) push the remnants out of the system. Thus ends
the phase of planet-building. As might be expected, the above
theory is also the current view of the history of our own Solar
System. Since the details of disk formation, and the physical
properties of protoplanetary disks, can be modelled by
quantitative theory, the general idea is to investigate such
disks that are apparent around stars to test the theoretical
models. There is no way to do that with our own solar system,
because the protoplanetary disk is long gone: one needs
relatively young stars. 
... ... H.J. Habing et al (10 authors at 4 installations, NL FR
ES) report infrared observations of 84 nearby *main-sequence
stars using the *ISOPHOT instrument aboard the ISO satellite. The
authors report their observations indicate that most stars
younger than 300 million years have dust disks, while most stars
older than 400 million years do not: 90 percent of the disks
apparently disappear when the star is between 300 and 400 million
years old. The authors suggest that several events related to the
apparent "clean up" of debris in the early history of our own
Solar System have a similar time-scale.
-----------
H.J. Habing et al: Disappearance of stellar debris disks around
main-sequence stars after 400 million years.
(Nature 30 Sep 99 401:456)
QY: H.J. Habing [habing@strw.leidenuniv.nl]
-----------
Text Notes:
... ... *main-sequence stars: The Hertzsprung-Russell diagram is
a plot of stellar absolute magnitude against spectral type, and
is one of the most useful diagrammatic aids in astrophysics. The
Main Sequence is a region on the Hertzsprung-Russell diagram
where most stars, including our own Sun, are situated. The course
of a star's evolution can be traced as a particular path in the
H-R diagram, with the paths of various types of stars showing
significant differences.
... ... *ISOPHOT instrument aboard the ISO satellite: The
Infrared Space Observatory (ISO) is a European Space Agency
satellite for infrared astronomy launched in 1995. ISO carries a
telescope, a camera, an imaging photopolarimeter, and two
spectrometers. ISOPHOT is the multi-band photometer-polarimeter
aboard ISO. Using 23 infrared filters, the polarimeter operates
over the band 2 to 200 microns.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 12Nov99
[For more information: http://scienceweek.com/search/search.htm]
-------------------
Related Background:
DUST DISKS AND EXTRASOLAR PLANETS
Paul Kalas (Max-Planck Institute for Astronomy Heidelberg, DE)
reviews current investigations concerning dust disks around stars
and the implications of the data for the existence of planets
around these stars. The author makes the following points: 1) One
of the important discoveries of the 1980s was the existence of
circumstellar disks of dust around some stars, the disks
apparently replenished by unseen parent bodies such as comets and
asteroids. 2) Some of these disks have recently been spatially
resolved by a new generation of ground-based instruments. An
example is the disk surrounding the star HR 4796, discovered in
1991 to have thermal emission from warm circumstellar dust. Two
observing teams have now mapped the emission from this dust disk
and revealed a peanut-shaped disk with the waist of the disk due
to an apparent central cavity (papers by Jayawardhana et al and
Koerner et al, in press). The data are interpreted by the authors
as indicating the existing of planets in formation around the
star, and so announced in news headlines (press releases by US
Harvard-Smithsonian Center for Astrophysics, US Jet Propulsion
Laboratory). Kalas, however, says the interpretation is premature
and not warranted by the data. 3) At about the same time as the
previous reports, maps of dust around the stars Vega, Fomalhaut,
and Beta Pictoris were published (Holland et al, *Nature*,
392:788 1988), and these maps were also interpreted as indicating
the presence of planets, but with differing bases for the
interpretations. Of the four stars, the data from HR 4796 and
Fomalhaut are interpreted as indicating planets creating central
cavities in dust formation, whereas the data from Vega and Beta
Pictoris are interpreted as indicating planets producing local
concentrations in their dust disks. The two interpretations are
apparently inconsistent. 4) Kalas asks: "Could the apparent
discrepancy result from 'planet mania', a bias among astronomers
in which every cavity and blob, even a wiggle, in circumstellar
dust disks is taken as evidence for extrasolar planets? Which
dust-planet relation does theory favor?" 5) Kalas says
theoretical arguments are available for both interpretations: one
can show that gravitational perturbations from a planetary object
will eventually create a cavity in a dust disk, but one can also
show that a planet can create a dust wake that looks like a large
blob following the planet in its orbit. 6) Kalas says: "At
present, therefore, we cannot uniquely identify the cause of the
dust blobs and dust cavities near these four stars. Planet-mass
objects are just one of the physically possible ideas."
QY: Paul Kalas [kalas@mpia-hd.mpg.de]
(Science 10 Jul 98 281:182) (Science-Week 31 Jul 98)
[For more information: http://scienceweek.com/search/search.htm]


2. ON THE PEAKING OF WORLD POPULATION GROWTH
In theory, the growth of a biological population is a geometrical
progression. If the resources necessary for maintaining
organismic viability are infinite, the population growth curve
will be exponential. On the other hand, if vital resources are
limited, growth will follow a sigmoid curve ("S-curve"). Since
limited resources is the usual parameter for real biological
populations, it is the sigmoid curve which is the norm. The early
part of the sigmoid curve, however, the so-called "J" section, is
essentially exponential in character, and if an examined
population is in this phase of its growth, it is often difficult
to determine where the upper bend to a sigmoid shape will occur.
In 1798, the economist Thomas Robert Malthus (1766-1834)
published anonymously his _Essay on Population_, in which he
maintained that since human population growth is a geometric
progression, and any increase in food supply perforce an
arithmetic progression, human population would always outrun the
food supply, and the various known population limiters such as
famine, disease, and war were therefore essential for the
survival of the species. This, of course, created a furor, and in
the second edition of his work in 1803, Malthus suggested that
the moral restraints of delayed marriage and sexual abstinence
might counter the increase in population. Thus did the adjective
"Malthusian" enter the language of social and political
discourse. No matter the validity of the analysis of Malthus, his
idea sparked heated debates throughout the next two centuries,
debates that in one form or another continue today. One major
characteristic of all of these debates has been the lack of
knowledge about when the "J" section of the curve will turn to
form the "S-curve".
... ... Vaclav Smil (University of Manitoba, CA) presents an
essay on the human population growth rate, the author making the
following points:
     1) Some time in the first half of the 17th century, after
thousands of years of stagnation or very slow annual growth
amounting to a small fraction of 1 percent, the global population
passed through the "J-bend" of the exponential growth curve and
began its still unfinished ascent.
     2) During the late 1960s, the relative rate of global
population growth peaked at just over 2 percent per year, the
rate then falling to approximately 1.7 percent by 1990. In the
early 1990s, the natural increase of the global population fell
below 1.5 percent.
     3) As with other species, the exponential growth of humanity
will end and the other bend of the growth curve will form,
creating an S-shaped curve -- but neither the onset of the S-bend
nor the eventual maximum population count can be predicted with
great certainty. The author suggests it is highly probable that
we are already beyond the mid-point of the S-curve, and that the
current global total of 6 billion may not double again. The high
variant of the latest (1998) long-range forecast by the United
Nations has the global population growing to no more than 10.7
billion by the year 2050, while the low-growth scenario forecasts
only 7.3 billion people by that year.
     4) The medium forecast of the United Nations of a world
population of 8.9 billion by 2050 is based on the assumption that
by the year 2050 total fertilities will be almost universally no
higher than the replacement ratio of 2.1 children per woman,
compared to the current global mean of approximately 2.7. But
this assumption of a reduction in replacement ratio may be wrong,
given that some countries (e.g., Ethiopia and Nigeria) still have
replacement ratios as high as 6 to 7 children per woman.
     5) The author concludes: "The world population may, after
all, undergo one more doubling to 12 billion. Even so, we may be
seeing the beginning of the end of the growth of our species.
Children born today may be thinking about their retirement at a
time when the global population count will have stabilized -- or
even begun to decline."
-----------
Vaclav Smil: How many billions to go?
(Nature 30 Sep 99 401:429)
QY: Vaclav Smil, Dept. of Geography, University of Manitoba,
Winnipeg, Manitoba R3T2N2 CA.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 12Nov99
-------------------
Related Background:
ON AMMONIA AND THE POPULATION EXPLOSION
Ammonia [NH(sub3)], a nitrogen hydride, is a colorless gas with a
rather interesting human history that ranges from its discovery
by the remarkable chemist Joseph Priestley (1733-1804) to the
first large-scale synthetic production and use of ammonia in
synthetic fertilizers and explosives in the 20th century. The
human requirement for synthetic fertilizers and explosives is an
instance of irony in the application of science, since the major
use of synthetic fertilizers is in the production of crops to
feed people, and the major use of explosives is in the production
of weapons to kill people. Nitrogen compounds are essential to
fertilizers and explosives, but in the early 20th century the
best large-scale source of such compounds was in the nitrate
deposits of Chile [*Note #1], which at that time was quite remote
from Europe. Another possible source of nitrogen compounds, only
theoretical at the time, was Earth's atmosphere, since the
atmosphere is mostly nitrogen gas and therefore constitutes an
inexhaustible supply. If atmospheric nitrogen could be converted
to ammonia, the ammonia could be used in the synthesis of various
nitrogen compounds, including fertilizers and explosives. Fritz
Haber (1868-1934) and Carl Bosch (1874-1940) are credited with
the discovery of the Haber-Bosch process for the synthesis of
ammonia from its elements, a discovery that literally altered the
course of 20th century history. The basis of the process is the
combining of nitrogen and hydrogen at high pressure over a
catalyst. Haber, who first demonstrated the synthesis in 1909,
received the Nobel Prize for Chemistry in 1918; Bosch, who
engineered the application of the method to the large-scale
production of ammonia, received the Nobel Prize for Chemistry in
1931 [*Note #2]. ... ... Vaclav Smil (University of Manitoba, CA)
presents an historical essay on the Haber-Bosch discovery, the
author making the following points:
     1) The author poses the question: What is the most important
invention of the 20th century? The usual answers include
airplanes, nuclear energy, space flight, television, and
computers, but none of these are critical to human well-being.
The synthesis of ammonia from its elements, however, is critical:
the world's population could not have grown from 1.6 billion in
1900 to the 6 billion of today without the Haber-Bosch process.
     2) The synthesis of ammonia belongs to that special group of
discoveries -- including Edison's light bulb and the Wright
brothers' flight -- for which we can pinpoint the date of the
decisive breakthrough. The archives of Badische Anilin-Und Soda-
Fabrik (BASF) contain a letter from Haber, at that time Professor
of Physical Chemistry at Technische Hochschule in Karlsruhe, to
the company directors, a letter in which Haber recounts how the
previous day the first demonstration to company scientists of the
synthesis of ammonia from nitrogen and hydrogen was made: "All
parts of the apparatus were tight and functioned well, so it was
easy to conclude that the experiment could be repeated."
     3) Although a number of company officials lacked confidence
in the application of Haber's method because of the high pressure
(over 100 atmospheres) required, Carl Bosch, who managed the BASF
nitrogen-fixation research, was apparently confident: "I believe
it can go. I know exactly the capability of the steel industry.
It should be risked." It was Bosch who was responsible for the
development of the proper steel housing necessary for large-scale
ammonia production.
     4) The present world output of ammonia amounts to
approximately 130 million metric tons per year, and 80 percent of
this goes into fertilizers, of which urea is the most important.
The ammonia is absolutely essential to sustain today's
population: rich countries might fertilize much less by cutting
excessive food production and by eating fewer animals, but even
the most assiduous recycling of organic wastes and the widest
planting of *nitrogen-fixating legumes could not supply enough
nitrogen for land-scarce, poor and populous nations. For several
decades now, virtually all the fixed nitrogen added to the fields
of China, Egypt, and Indonesia has come from synthetic
fertilizers.
     5) The author concludes: "Without this [the Haber-Bosch
process], almost two-fifths of the world's population would not
be here -- and our dependence will only increase as the global
count moves from 6 to 9 or 10 billion people."
-----------
Vaclav Smil: Detonator of the population explosion.
(Nature 29 Jul 99 400:415)
QY: Vaclav Smil, Dept. of Geography, University of Manitoba,
Winnipeg, CA.
-----------
Text Notes:
... ... *Note #1: During World War I (1914-1918) access to the
Chilean nitrate deposits by Germany was almost impossible, with
imports of nitrates blocked by the British navy. The German
military needed explosives, which required nitrates, which
required a source of usable nitrogen. This was the main impetus
for the development of the large-scale production of ammonia by
Bosch and BASF. Many historians believe that if Germany had had
to depend only on Chilean nitrates for explosives, World War I
would have ended in 1916, with several million lives saved.
... ... *Note #2: The personal story of Fritz Haber is
interesting. Haber became a prominent chemist following his
discovery of the synthesis of ammonia from nitrogen and hydrogen.
He was extremely patriotic, and during the war he devoted great
efforts to the development of gas warfare, directing the first
warfare use of chlorine gas in 1915, and of mustard gas in 1917.
In the history of war, the beginning of gas warfare is dated as
April 22, 1915, "the day at Ypres when Haber's gas blowing
process surprised and overpowered the enemy lines for the first
time." Because of his work in gas warfare, there were many
protests when Haber was awarded the Nobel Prize after the war
ended. Following the war, and the huge reparations demanded from
Germany by the Allies, Haber worked to isolate gold from seawater
in order to pay the reparations. The yield was too small and
research failed. In 1933, when the Nazis came to power in
Germany, Haber's patriotic services in ammonia synthesis for
explosives, gas warfare, and the attempted isolation of gold from
seawater were dismissed as irrelevant because Haber was a Jew,
and Haber was forced to give up his post and flee Germany. He
went first to England, then decided to go to Palestine, but he
died in Switzerland on his way south. Carl Bosch had a different
fate: Bosch, who was not a Jew, remained in Germany as a
prominent scientist. In 1933, Bosch actually cautioned Hitler
against the policy of dismissing non-Aryan scientists, pointing
out to Hitler the severe damage which this policy threatened to
inflict on the pursuit of chemistry and physics in Germany.
Hitler's response: "Then we'll just get along without physics and
chemistry for a hundred years!" In 1935, as the Nazi era
continued, Bosch succeeded Max Planck as head of the Kaiser
Wilhelm Society (now called the Max Planck Society).
... ... *nitrogen-fixating legumes: In leguminous plants such as
beans and peas, the symbiotic bacteria Rhizobium form
characteristic root nodules, the bacteria supplying the plant
with usable nitrate obtained from atmospheric nitrogen, while the
bacteria obtain carbohydrates from the plant. In general, the
term "nitrogen-fixation" refers to any fixation of nitrogenous
compounds from atmospheric nitrogen. In nature, this is achieved
by the normal metabolism of specialized soil bacteria (e.g.,
Rhizobium), and also by the electric discharges of lightening in
the atmosphere. The Haber-Bosch process is industrial nitrogen-
fixation.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 20Aug99


3. CLONAL INTERFERENCE AND THE EVOLUTION OF RNA VIRUSES
     Studies of the dynamics of evolution indicate that
populations adapt through the appearance and subsequent fixation
of beneficial mutations. In large populations, beneficial
mutations may arise frequently enough so that two or more are
simultaneously present in independent lineages. Once beneficial
mutations have arisen, there is a certain probability of losing
them by "*genetic drift" while their frequency is low, but after
an early period dominated by genetic drift, beneficial mutations
reach a substantial frequency in the population. In a sexual
system, these beneficial mutations will eventually combine,
ensuring their fixation together. But if the system is asexual,
the lineages created by beneficial mutations will compete, and
only the mutation with the largest effect will be fixed. This
competition of beneficial mutations in asexual populations is
called "*clonal interference", and it is a phenomenon that
ensures that beneficial mutations that do achieve fixation are of
large effect.
     Excluding *prions, whose categorization is still uncertain,
viruses are the smallest infectious agents, ranging from
approximately 20 to 300 nanometers in diameter, and containing
only one kind of nucleic acid (RNA or DNA) as their genome. In
general, the nucleic acid is encased in a protein shell, which
may be surrounded by a lipid-containing membrane, and the entire
infectious unit is termed a "virion". Viruses are inert in the
extracellular environment, replicating only in living cells, and
they are essentially genetic-level parasites: the viral nucleic
acid contains information necessary for programming the infected
host cell to synthesize various virus-specific macromolecules
required for the production of viral progeny [*Note #1].
     RNA viruses are viruses whose genome consists of RNA, and
they are involved in a number of serious human diseases,
including hemorrhagic fevers and human immune deficiency syndrome
(AIDS). One important characteristic of RNA viruses is that as a
group they show the highest mutation rates in nature. This,
together with their potentially large effective population sizes,
and the fact that their reproduction can be asexual, suggests
that clonal interference may play an important role in their
adaptive evolution.
... ... R. Miralles et al (4 authors at 2 installations, ES US)
report a study of clonal interference in an RNA virus population
(*vesicular stomatitis virus), the study involving two variants
differing only in their ability to grow in the presence of a
*monoclonal antibody. The authors report their results provide
evidence that clonal interference does indeed occur in viral
populations, and that this evidence along with models of clonal
interference allows certain properties of the adaptive evolution
of RNA viruses to be inferred. The authors suggest the following:
     1) Adaptive substitutions appear as discrete rare events,
regardless of mutation rate or population size. They often do not
occur simply as the result of a single mutation but instead
represent the best of several competing mutations. The authors
suggest this fact has consequences for the dynamics of drug
resistance and the search for resistance mutations.
     2) In medium to large populations, the rate of fitness
increase is hardly affected by changes in either mutation rate or
population size.
     3) Resident populations are protected from invaders simply
because of their numerical advantage. A high-fitness vesicular
stomatitis viral clone seeded at low frequency into a resident
population of low-fitness variants was displaced by the low-
fitness competitors. When its initial frequency was above a
certain threshold, however, the high-fitness clone always
outcompeted the low-fitness variants in the resident population.
The authors suggest that the existence of a frequency threshold
for dominance imposes an element of uncertainty in virus sampling
during disease outbreaks.
-----------
R. Miralles et al: Clonal interference and the evolution of RNA
viruses.
(Science 10 Sep 99 285:1745)
QY: Santiago F. Elena [santiago.elena@uv.es]
-----------
Text Notes:
... ... *genetic drift: The term "genetic drift" refers to the
random fluctuations of gene frequencies due to sampling errors.
Genetic drift occurs in all populations, but its effects are most
evident in populations that are small.
... ... *clonal interference: In this context, a "clone" is a
lineage derived from a single ancestor.
... ... *prions: Prions are a class of poorly understood proteins
implicated in a number of exotic human neurological diseases and
in some common animal diseases such as sheep scrapie and bovine
spongiform encephalopathy in cattle ("mad cow disease").
... ... *Note #1: Over 4000 animal and plant viruses have been
identified (as of 1995), these entities categorized into 71
families, 11 subfamilies, and 164 genera, with hundreds of
viruses still unassigned. 24 families contain viruses that infect
humans and animals. Classical categorizations of viruses were
based on the diseases they produces, but modern categorizations
are based on molecular biological parameters.
... ... *vesicular stomatitis virus: This virus causes a disease
of cattle. The viral entity is bullet-shaped, approximately 75
nanometers in diameter, 180 nanometers in length, the genome
single-stranded RNA, 13-16 kilobases in size. The virus
replicates in cell cytoplasm, with viral assembly involving
budding from the cell membrane.
... ... *monoclonal antibody: In general, a monoclonal antibody
is an immunoglobulin protein derived from a single clone of
plasma cells. Such antibodies are chemically and structurally
identical and constitute a pure population with highly specific
antigen-binding properties. In general, an "antigen" is any
chemical entity that activates an immune response, especially an
entity originating outside the body, and an "antibody" is a
specific immunoglobulin protein produced by an immune cell, the
protein specifically binding a particular antigen. In the context
of this report, a typical antigen would be a moiety in the
surface coat of the virus.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 12Nov99
[For more information: http://scienceweek.com/search/search.htm]


4. ORIGINS OF INSECT METAMORPHOSIS
     In biology, the term "metamorphosis" refers to a process in
which an animal undergoes a relatively rapid change from a pre-
adult form (larval form) to an adult form. The process is under
*hormonal control, and is most notable in the life histories of
the majority of insects and in the amphibia.
     In general, however, insect and amphibian metamorphosis are
qualitatively quite different: whereas amphibian metamorphosis is
characterized by the remodeling of existing tissues, insect
metamorphosis often involves the destruction of larval tissues
and their replacement by an entirely different population of
cells.
     Insects (hexapods) are a class of *arthropods whose members
have a body with a distinct head, thorax, and abdomen. The head
bears one pair of antennae and paired mouthparts, the thorax
bears 3 pairs of legs and frequently either one or two pairs of
wings, and the abdomen bears no legs but other appendages may be
present. Fossil insects have been dated from the *Devonian period
onward. 750,000 different insect species have been recognized,
and it is believed that at least that many different species are
still unrecognized.
     The focus of this report is insect development, which in
general is distinguished by 3 major patterns:
... ... 1) A few insects, such as *springtails, have no larval
stage and undergo direct development (ametabolous development).
... ... 2) Other insects, notably grasshoppers and *bugs, undergo
a partial or gradual metamorphosis (hemimetabolous development)
in which adult organs are formed without any profound
discontinuity. The rudiments of the wings, genital organs, and
other adult structures are present at hatching, and they become
more mature with each *molt. At the last molt, the emerging
insect is a winged and sexually mature adult. The stages between
molts (and the final adult stage) are called "instars". The
larval form of a hemimetabolous insect is called a "nymph". In
general, the nymph resembles the adult but is sexually immature.
... ... 3) The 3rd pattern is that of "holometabolous
development", as seen in flies, beetles, moths, and butterflies,
and in this pattern there is a dramatic and sudden transformation
between the larval and adult stages. The juvenile larva, which is
a feeding entity (e.g., caterpillar, grub, maggot), undergoes a
series of molts as it becomes larger. After the last larval
instar stage, the larva undergoes a metamorphic molt to become a
"pupa". The pupa does not feed, its energy being derived from the
food ingested during the larval stages. During the pupa stage
(pupation), the adult structures are formed, and these structures
replace the larval structures.
     Homometabolous insects apparently evolved after the
appearance of hemimetabolous insects. Ancestral insect species
did not undergo metamorphosis, and there are still some existing
species that lack metamorphosis (ametabolous) or undergo only
partial metamorphosis (hemimetabolous). One of the major
questions in insect evolutionary biology is essentially this: How
did the 3-part life cycle that characterizes the holometabolous
insects evolve from the nymph and adult stages of the
hemimetabolous insects?
... ... J.W. Truman and L.M. Riddiford (University of Washington
Seattle, US) present a review of the question that includes a new
hypothesis, the authors making the following points:
     1) The authors point out that two opposing hypotheses have
been advanced to explain the evolution of homometabolous insects.
The first hypothesis was formulated by A. Berlese in 1913, who
noted a similarity between different larval body forms of
homometabolous insects and the morphological transitions seen
during embryogenesis of hemimetabolous insects. Berlese proposed
that the homometabolous larva arose by a process of "de-
embryonization", so that the larva was essentially a free-living
feeding embryo. The premature hatching was believed to be caused
by a reduction in the amount of yolk stored in the egg, and
hatching at different times generated a diversity of larval
forms. As the larva took over the feeding responsibilities, the
nymph was reduced to a single instar that became the pupa.
     2) The alternative hypothesis (1914, 1948) for insect
metamorphosis held that larvae and nymphs were equivalent, and
that the pupal stage arose de novo as the disparity between larva
and adult widened. This second hypothesis, which considers larvae
and nymphs as equivalent stages, has been the more accepted
hypothesis during the past 50 years.
     3) The authors state that their own examination of the
endocrine control of embryonic and postembryonic insect
development suggests that the roots of metamorphosis are to be
found in embryonic stages, more in line with the views of Berlese
and the more recent similar views of V. Novak (1975).
     4) The authors consider the form and function of the
"pronymph stage". In many arthropods, the stage that hatches from
the egg has unique features that distinguish it from subsequent
life stages. The entity (hatchling) in this stage does not feed,
and is often helpless and the object of maternal care. It
subsists on its yolk supply and represents a continuation of
embryonic development, but outside the confines of the egg shell.
The first post-embryonic molt finally transforms this entity into
an active feeding juvenile. There are corresponding hatchling
stages in both ametabolous and hemimetabolous insects, a general
stage the authors term the "pronymph stage". In ametabolous
insects, the pronymph stage lasts for 3 to 4 days. In
hemimetabolous insects, the pronymph stage is passed primarily in
the egg and lasts for minutes to a few hours after hatching. The
authors' hypothesis essentially proposes that the hemimetabolous
pronymph has become the homometabolous larva.
     5) In this new hypothesis, changes in the endocrinology of
development are central. The 3 stages of the ancestral insect
species -- pronymph, nymph, and adult -- are proposed to be
equivalent to the larva, pupa, and adult stages of insects with
complete metamorphosis.
     6) Concerning the implications of their hypothesis, the
authors point out that the hormone -- "*juvenile hormone" -- that
regulates insect metamorphosis has structural similarities with
the *retinoids that regulate aspects of embryogenesis in
vertebrates. The authors conclude: "In both groups of animal,
these types of compound may be ancient regulators of embryonic
growth and development, but in the insects they have achieved a
postembryonic, hormonal function as greater portions of embryonic
development were deferred until the end of larval growth."
-----------
J.W. Truman and L.M. Riddiford: The origins of insect
metamorphosis.
(Nature 30 Sep 99 401:447)
QY: James W. Truman [jwt@u.washington.edu]
-----------
Text Notes:
... ... *hormonal control: In general, a "hormone" is a chemical
messenger, a molecular entity secreted by one part of an
organism, and which affects the growth, development, behavior,
etc. of other parts.
... ... *arthropods: The largest phylum in the Animal Kingdom in
terms of both number of taxa and biomass, but the taxonomy has
undergone revision, and it is now essentially an informal
classification. In general, the arthropods are characterized by a
tough chitinous protective covering (exoskeleton) flexible only
at the joints (e.g., insects).
... ... *Devonian period: From approximately 400 million to 345
million years ago. Sometimes called the Age of the Sea, since
more of the Earth was underwater than is now.
... ... *springtails: (Collembola) An order containing almost
2000 species of blind, primitively wingless insects with short
antennae and mostly less than 6 millimeters in length.
... ... *bugs: In biology, the term "bugs" refers specifically to
the insect order Hemiptera, examples of which are aphids,
cicadas, bed bugs, leaf hoppers, scale insects.
... ... *molt: (ecdysis) In general, periodic shedding of an
outer layer. In insects, the process is controlled by the hormone
ecdysone ("molting hormone").
... ... *juvenile hormone: In general, "juvenile hormone" is a
hormone found in insects that prevents metamorphosis into the
adult form and maintains larval characteristics. This hormone
functions antagonistically to the hormone "ecdysone", which
promotes molting and differentiation into the adult. Juvenile
hormone is produced in specialized secretory cells in the corpus
allatum, a structure near the insect brain. At least 3 varieties
of juvenile hormones have been chemically identified: all are
derivatives of farnesoic acid.
... ... *retinoids: A group of diterpenoids that includes
retinoic acid and Vitamin A. Retinoic acid, a naturally occurring
oxidation product of Vitamin A, is apparently involved in
vertebrate morphogenesis, and in the growth and maintenance of
certain tissues.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 12Nov99
[For more information: http://scienceweek.com/search/search.htm]


5. PLASTICITY OF AUDITORY CORTEX IN CONGENITALLY DEAF ANIMALS
In general, the brains of animals and humans are organized in
layers, the most recently evolved structures added on top of the
older structures. The cerebral cortex is the most exterior part
of the human brain, and also the most recently evolved region.
The cortex is a thin surface layering of nerve cells, the region
only several millimeters thick but covering all of the brain
surface. This is the part of the central nervous system most
intimately involved with the so-called "higher faculties",
although the cortex operates in concert with other parts of the
brain. The structure is primitive in lower mammals, and is found
progressively more pronounced and with greater surface area in
primates and man. In addition to involvement with higher
faculties, the cerebral cortex also contains several primary
receiving areas for various sensory modalities, these regions of
the cortex essentially acting as topographic maps of sensory
input, maps that apparently organize input data into patterns
meaningful for connected analytical regions. Two outstanding
features of the cerebral cortex are its capacity for self-
organization ("self-wiring") and its plasticity (in general, the
ability of specific loci to alter function in response to
previous experience). In all sensory modalities, self-
organization and plasticity depend on external stimuli. During
development of the nervous system in a single individual,
critical periods apparently exist during which an external
influence is required to trigger the subsequent steps of central
development. The criticality of these periods is made clear by
the demonstrated arrested development that results from sensory
deprivation during the critical periods. This aspect of
neurological development is of particular importance in
congenitally deaf patients, whose deafness can now in certain
cases be treated by implants in the auditory sensory organ
(cochlear implants). When adults who are congenitally or
prelingually deaf receive cochlear implants, the results are
disappointing: these patients never gain language competence and
often request that the implants be removed. In contrast, early
cochlear implantation in congenitally or prelingually deafened
children can lead to nearly perfect acoustic communication and
language competence. What is not known, however, is the
neurological basis underlying this phenomenon. Since certain
types of experiments in humans are obviously not feasible, much
research in the area has focused on animal models. In
congenitally deaf cats, the central auditory system is deprived
of acoustic input because of degeneration of the auditory sensory
organ cell system (the organ of Corti) before the onset of
hearing. But auditory neurons that propagate activity to the
brain (primary auditory afferents) survive under these conditions
and can be stimulated electrically in appropriate experiments.
... ... R. Klinke et al (5 authors at University of Frankfurt,
DE) now report that by means of an intracochlear implant and an
accompanying sound processor, congenitally deaf kittens were
exposed to sounds and conditioned to respond to tones. After
months of exposure to meaningful stimuli, the cortical activity
in chronically implanted cats (i.e., cats with chronically
implanted recording electrodes) produced electric field
potentials of higher amplitudes and expanded in area, developed
long latency responses indicative of intracortical information
processing, and showed more evidence of neuron connection
efficacy than was observed in naive and unstimulated deaf cats.
This activity established by auditory experience in congenitally
deaf animals resembles activity found in hearing animals. The
authors suggest their results indicate that although without
afferent input the auditory cortex remains rudimentary, this
deficiency can be overcome by reafferentation (i.e, rewiring of
input) to the deprived auditory channel by substitution of the
missing cochlear activity. After implantation, a continuous input
of relevant acoustic stimuli mimicking normal conditions results
in animals displaying exploratory behavior, and animals that are
attentive and motivated, factors known to strengthen cortical
plasticity. The authors suggest a similar recruitment (i.e.,
organized activation) of the auditory cortex is likely to be the
basis of demonstrated hearing acquisition in prelingually deaf
human infants after early cochlear implantation.
-----------
R. Klinke et al: Recruitment of the auditory cortex in
congenitally deaf cats by long-term cochlear electrostimulation.
(Science 10 Sep 99 285:1729)
QY: Rainer Klinke [klinke@em.uni-frankfurt.de]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 12Nov99
[For more information: http://scienceweek.com/search/search.htm]
-------------------
Related Background:
PLASTICITY OF CEREBRAL CORTEX AFTER PERIPHERAL INJURY
The term "plasticity" in the context of brain research refers in
general to the ability of the brain to alter its connections or
dynamics as a result of experience or changes in conditions. So,
for example, the ability of certain parts of the brain,
particularly the cerebral cortex, to assume new functions
following destruction by disease or trauma of other parts is an
example of brain plasticity. The various parts of the brain do
not show the same degree of plasticity, and in general the degree
of plasticity of any part may change with the life history of the
individual. The brains of infants and young children, for
example, are extremely plastic. The mammalian brain region called
"somatosensory cortex" is the part of the cerebral cortex
functionally involved in the analysis of sensory input from
various body parts. The reorganization of somatosensory cortex
has been observed in monkeys with forelimb amputation or forelimb
sensory deafferentation (loss of neural input from the forelimb),
and in human amputees, and this reorganization is presumed to be
the basis for the sensation of *phantom limbs and perhaps for
*phantom pain. An important question is how such large-scale
changes are mediated in the adult brain. ... ... S.L. Florence et
al now report a study of the distributions of *thalamic and
cortical connections in 4 *macaque monkeys with long-standing
accidental trauma to a forelimb, the purpose of the study to
determine whether the growth of new connections plays a role in
the reorganization of somatosensory cortex known to occur after
major alterations in peripheral somatosensory inputs. The authors
report that microelectrode recordings demonstrated massive
reorganizations of the cortex related to the affected limb.
Tracer injections revealed normal patterns of thalamo-cortical
connections, but markedly expanded lateral connections ("cortico-
cortical" connections; also, "intracortical" connections) in
somatosensory cortex. The authors suggest their results indicate
that the growth of intracortical connections but not thalamo-
cortical connections could account for much of the reorganization
of the *sensory maps in cerebral cortex.
-----------
S.L. Florence et al (3 authors at Vanderbilt University, US)
Large-scale sprouting of cortical connections after peripheral
injury in adult macaque monkeys.
(Science 6 Nov 98 282:1117)
-----------
Text Notes:
... ... *phantom limbs: In general, the term "phantom limb"
refers to the sensation that an amputated limb is still present.
Also called "stump hallucination".
... ... *phantom pain: Phantom limb is often associated with
painful sensations of burning, prickling, tickling, or tingling
in the missing part of the limb.
... ... *thalamic and cortical connections: The thalamus is a
deep brain structure that consists of groups of nerve cells that
project to various other regions of the brain. In general, these
groups of nerve cells are specific relay stations for sensory
information (e.g., visual, auditory, pain, temperature, etc.) The
"connections" referred to here are those from the thalamus to the
cortex and those inside the cortex from cortical neurons to other
cortical neurons.
... ... *macaque monkeys: Macaca is a large genus of Old World
monkeys that includes macaques, rhesus monkeys, and the Barbary
apes.
... ... *sensory maps: The mammalian cerebral cortex is
essentially a multilayered surface, highly convoluted in the
higher forms, and it is into the layers of this surface that
sensory information input from the various sensory systems is
projected for analysis. Depending on the sensory system involved,
these projections are more or less isomorphic with the
distribution of the sensory receptors of the system. Thus, for
example, there is in effect a "map" of the hand in the
somatosensory cortex, and there is a "map" of each retina of the
eye in the visual cortex, and so on. The mapping in somatosensory
cortex is of the entire body.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 11Dec98
-------------------
Related Background:
THE ROLE OF VISUAL EXPERIENCE IN DEVELOPMENT OF VISUAL CORTEX
The visual system of vertebrates, especially that of the higher
vertebrates, is highly organized. The retina of the eye, for
example, which is essentially a surface upon which photons
impinge to be absorbed by chemical photosensors, is "mapped" by
exiting nerve fibers, and light-induced activation of the retinal
map are relayed with some transformations to various levels of
the central nervous system and finally to what is called the
"primary visual projection area" of the cerebral cortex (also
called "primary visual cortex"). The processing of this mapping
information is, in fact, the key to how we perceive the world
around us. ... ... Crair et al (3 authors at 2 installations, US)
report a study of the development of cortical maps for
orientation and eye preference in the primary visual cortex of
normal and binocularly deprived cats. These cortical maps were
present by 2 weeks after birth, and developed until nearly 3
weeks of age whether or not the eyes were open. With continued
visual deprivation, responses to both eyes deteriorated. The
authors suggest that the basic structure of visual cortical maps
is innate, but experience is essential for specific features as
well as for maintaining the responsiveness and selectivity of
cortical neurons.
QY: Michael P. Stryker [stryker@phy.ucsf.edu]
(Science 23 Jan 98)
-------------------
Related Background:
EVIDENCE OF CROSS-MODAL PLASTICITY IN BLIND HUMANS
In neurobiology, the term "plasticity" is the name given to the
capacity of neural tissue to adjust to change. One variant of
this concerns the dependence of the "wiring" of the nervous
system on its input. Another variant concerns the degree to which
one region can under certain conditions assume the function of
another region. Plasticity does not occur everywhere in the
nervous system, but it is often evident in the cerebral cortex of
the brain, the cortex being the thin layer of cells apparently
responsible for higher analysis of sensory input, language,
ideation, and other so-called higher functions lumped together in
the category "cognitive processes". Last week Leonardo G. Cohen
et al (11 authors at 4 installations in US, AR, JP) reported the
results of studies of cross-modal plasticity in blind humans.
These studies involved non-invasive interference with cortical
activity by applying transient magnetic stimulation from outside
the skull. It has been demonstrated that such stimulation can
affect brain activity, and in this study the apparatus threshold
for stimulation of the motor cortex was first determined, and
then transient magnetic stimulation 10% above that threshold
applied to the occipital lobes of the brain through the overlying
skull to interfere with electrical activity in the visual cortex.
The experiments involved various location and procedural
controls, and also a group of sighted individuals. Essentially,
what was found is that in people blind from an early age, the
visual cortex is apparently involved in somato-sensory function
(fingertip reading of individual Braille characters), while the
same is not true for sighted subjects.
QY: L.G. Cohen [lcohen@codon.nih.gov] (Nature 11 Sep 97)
-------------------
Related Background:
... One striking example of plasticity concerns the so-called
"critical period" for histological development of the visual
system in mammals. This is a period between birth and a later
time during which the neuron circuits in the visual areas of the
cerebral cortex are being developed. Once the system is
completely developed, keeping one or both eyes closed has no
effect on vision. For example, an adult human can develop a
cataract in one eye, not have it removed for years, but once it
is removed and a lens substitute in place, the vision in that eye
is normal. The critical period for vision in humans lasts from
birth to about 6 years, and there is much histological evidence
that the visual cortex is changing during that time. A similar
critical period exists in other mammals. If both eyes are kept
covered from birth throughout the critical period in cats and
monkeys, and the eyes are then uncovered, the animals remain
functionally blind. It can be shown there is a gradation of the
effect of the absence of input from the eyes: the effect is
greater during the early part of the critical period than later
on. And damage can also be demonstrated by keeping only one eye
covered. In all of this, the eyes themselves are optically normal
after they are uncovered, the cells in the retina and in the
lower visual centers appear to function normally in their
response to visual input. But the deprived eye or deprived eyes
are "blind", and the changes or lack of development responsible
for this loss of visual function are in the visual cortex and are
due to its plasticity, its dependence on appropriate input for
the formation of working connections.
(from Science-Report 26 Sep 97)
-------------------
Related Background:
PHANTOM SENSATIONS EVOKED BY HUMAN THALAMIC MICROSTIMULATION
One of the most fascinating phenomena in human neurobiology is
the so-called "phantom limb", the essentials of which are as
follows: Our sensations are based on sensory information arriving
at the higher centers of the central nervous system, the
connections being for the most part "hard-wired" through
embryology and early development. The sensory cerebral cortex, in
fact, quickly develops a hard map of all the peripheral sensory
receiving elements in the body, and the map is thus fixed. Now
consider the amputation of a leg. The relevant peripheral sensory
neurons have cell bodies close to the spinal cord and long axons
that extend to the lower leg. If the lower part of the leg is
removed, the sensory axons are cut at the stump, but the sensory
neuron cell bodies are still intact and most of these cells
survive the amputation. But input from these particular neurons
is hard-wired in the brain to represent input from the lower leg.
So although the lower leg is now absent, anything that excites
the axons of these particular neurons will be interpreted by the
central nervous system as an input from the lower leg as if the
lower leg had not been removed at all. Hence, the term "phantom
limb". In particular, amputees can often feel pain in part or all
of a limb that no longer exists. A stereotaxic device is a rigid
metal coordinate frame into which the head of an animal or human
is fixed so that microscale positioning of electrodes at any
particular coordinate position can be effected without
displacement caused by movement of the subject and with some
fidelity as far as the locus of placement at a point is
concerned. "Functional stereotactic mapping" refers to using a
stereotactic device to map a particular region of the brain under
conditions in which that particular region is functional. The
thalamus is an important part of the sub-cortical brain relaying
sensory information to the cerebral cortex, and the ventrocaudal
thalamus is a subregion of the thalamus. ... ... Davis et al (6
authors at University of Toronto, CA), in experiments designed to
assist the treatment of severe phantom or stump pain, report that
microelectrode recordings and microstimulation during functional
stereotactic mapping of the ventrocaudal thalamus in human
amputees reveals an unusually large thalamic stump representation
consistent with the findings from animal experiments. The authors
suggest their results support the hypothesis that the thalamic
representation of the amputated limb remains functional in
amputees with phantoms.
QY: Karen D. Davis [kdavis@playfair.utoronto.ca]
(Nature 22 Jan 98)
-------------------
Related Background:
BRAIN PLASTICITY IN CHILDREN AFTER HEMISPHERECTOMY
Epilepsy is a term unhappily applied to several dozen different
seizure disorders, their commonality being central nervous system
seizures rather than identical pathological processes causing the
seizures. From a neurophysiological standpoint, a seizure is the
end result of a massive discharge of nerve cells, often the motor
neuron pathways that activate muscle cells. Seizures can be
produced by various central nervous system infections, metabolic
disturbances, toxic agents, cerebral oxygen deficiency, expanding
brain lesions, cerebral trauma, cerebral hemorrhage, and so on.
In general, any physiological event or series of events that
produces a wide disruption of central nervous system activity has
the potential for production of seizures of one sort or another.
Most patients who for reasons known (symptomatic epilepsies) or
unknown (idiopathic epilepsies) are chronically subjected to
seizures can be helped with various pharmacological agents such
as phenytoin or cloneazepam, but 10% to 20% of patients have
seizures that cannot be managed by drugs. If the seizures are due
to a specific damaged locus in the brain (the "epileptic focus"),
the recourse for these patients, if the locus can be determined,
is surgery. What is done is to completely remove the epileptic
focus, sometimes an area no larger than a small coin, and if the
surgery is successful the cure is immediate and permanent. There
are cases, however, in which the affected part of the brain is
quite large, the seizures completely unmanageable, and the only
recourse is radical surgery. Since severe chronic epilepsy due to
brain lesions is usually first diagnosed in young children, it is
such children who are the usual patients in radical brain surgery
for epilepsy. The most radical and fairly common procedure is
hemispherectomy, removal of an entire half of the brain, and the
most remarkable aspect of this is that when the surgical
procedure is successful, not only are the seizures eliminated,
but the child can function as well or almost as well as any other
child. It is an example of a phenomenon well-known to
neurobiologists called "brain plasticity", the ability of the
brain to recover the function of a damaged or removed region by
assignment of the function to an undamaged location. The language
area of the brain, for example, is often considered to be fixed
on the left side of the brain by genetics, but in truth it is not
so fixed, and if the left side of the brain is removed at an
early age, the right side of the brain will quickly develop a
language center and there will be little functional impairment.
In a recent publication, Eileen P. G. Vining (Johns Hopkins
University, Baltimore MD US) reports the progress of 54 children
who underwent hemispherectomy for recurrent severe epileptic
seizures. The majority of the patients were seizure-free
following surgery, no longer needed drugs, and many of the
patients are now in school. One of the most significant facts
about the human brain is that its histological development
continues at least until adolescence, and the dynamism of this
histological development is what is responsible for its
remarkable plasticity.
QY: E. Vining, Johns Hopkins University (410) 516-8171
(Pediatrics August 1997) (Science-Week 22 Aug 97)
[For more information: http://scienceweek.com/search/search.htm]


6. TRAUMATIC BRAIN INJURIES IN HIGH SCHOOL ATHLETES
High school students who choose to participate in sports place
themselves at risk for a sports-related injury, and of particular
concern is injury that may result from a rotational or linear
force applied to the head and brain. Such forces may result in a
minimal injury to the brain, or they may cause permanent
disability or death.
... ... J.W. Powell and K.D. Barber-Foss now present a study to
identify the type, frequency, and severity of mild traumatic
brain injury in selected high school sports activities. In this
study, "mild traumatic brain injury" was defined as an injury for
which the injured player was removed from participation and
evaluated for a traumatic brain or head injury by the athletic
trainer, physician, or both, prior to the student returning to
sport participation. The study involved 246 certified athletic
trainers recording injury and exposure data for high school
varsity athletes participating in boys' football, wrestling,
baseball, and field hockey, girls' volleyball and softball, boys'
and girls' basketball, and boys' and girls' soccer. 235 US high
schools during 1 or more years of 1995-1997 participated. The
authors report that of the 23,566 reported injuries in the 10
sports during the 3-year period, 1219 were classified as mild
traumatic brain injuries, with football accounting for 63.4
percent of the cases. There were 6 cases of *subdural hematoma
and intracranial injury reported in football. The authors suggest
that based on their data, an estimated 62,816 cases of mild
traumatic brain injury occur annually among high school varsity
athletes in the US. The authors state that although rates of mild
traumatic brain injury vary among sports, none of the 10 popular
sports in their study was without the occurrence of mild
traumatic brain injury. The authors conclude: "Continued
involvement of high school sports sponsors, researchers, medical
professionals, coaches, and sports participants is essential to
help minimize the risk of mild traumatic brain injury."
-----------
J.W. Powell and K.D. Barber-Foss: Traumatic brain injury in high
school athletes.
(J. Amer. Med. Assoc. 8 Sep 99 282:958)
QY: John W. Powell [john@med-sports-systems.com]
-----------
Text Notes:
... ... *subdural hematoma: The "dura" (dura mater) is a
relatively thick membrane covering the brain. In general, a
"hematoma" is a collection of blood which has escaped from blood
vessels as the result of injury. A "subdural hematoma" is a
hematoma between the dura and the brain, and as such it can cause
either temporary or permanent damage to the underlying cerebral
cortex.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 12Nov99


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

IN FOCUS: ON RIEMANN'S GEOMETRY
"In 1854 Riemann became a professor at Gottingen, at which time
he was required to deliver an introductory lecture for the
faculty. His paper entitled, "On the Hypotheses Which Lie at the
Foundations of Geometry," may well have been the most influential
lecture ever given in mathematics. The notion that other
geometries existed besides Euclidean geometry had already been
determined, for the Russian mathematician Nicolai Ivanovitch
Lobachevsky (1793-1856) had delivered a paper as early as 1826 on
the characteristics of at least one non-Euclidean geometry. Yet,
non-Euclidean geometries were still considered somewhat in the
backwaters of mathematics. Riemann's paper changed all that. He
proposed that geometry not be thought of as collections of points
and lines, but as sets of ordered n-tuplets and the rules for
determining the distances between elements in the set. An n-
tuplet is simply an ordered set of n numbers. For example, in
two-dimensional Euclidean space, every point is uniquely defined
by an ordered pair of real numbers (x,y). In three-dimensional
space every point is uniquely defined by three numbers (x,y,z).
In n-dimensional space, each point has a unique address given by
an n-tuplet (x,y,z,...,n). The rules for determining the
distances between elements in the set are the geometry's metric,
and they define space's curvature. Classical geometry studied
curves and surfaces in their entirety, but modern geometry was
concerned with the microscopic shape of space that surrounded
each point of the space... Riemann generalized the idea of
geometry as the study of possible manifolds, rather than any
rigidly defined metric. In the broadest sense, a manifold is
nothing more than a collection of objects of a set. Geometry then
becomes the study of the conditions placed upon the objects of
sets, rather than implying the characteristics of space by
visualizing the shape of the space. Riemann was not interested in
just the study of three-dimensional space or even four-
dimensional space, but the more general characterization of n-
dimensional spaces... Riemann not only has the distinction of
delivering possibly the most profound lecture on geometry, but he
repeated his accomplishment by delivering in 1858 an equally
profound eight-page paper on number theory. Whether he could have
produced a third such thunderous paper the world will never know,
for he died tragically from tuberculosis when he was only 39."
[*Note #1]
-----------
Calvin C. Clawson: _Mathematical Sorcery: Revealing the Secrets
of Numbers_.
(Plenum, New York 1999, p.207,210)
-----------
Text Notes:
... ... *Note #1: Georg Friedrich Bernhard Riemann (1826-1866)
was the son of a Lutheran pastor and his original ambition was to
follow in his father's footsteps. Riemann studied Hebrew and
attempted to prove the truth of the Book of Genesis by
mathematical reasoning. After he failed in this, his ambitions
shifted to mathematics. The most famous application of Riemann's
geometry is that of Albert Einstein (1879-1955) in the general
theory of relativity. The metric equation (the equation defining
distances between elements) in that theory is developed directly
from the general metric equation first proposed by Riemann in his
1854 lecture. It is often said that Riemann's geometry is "non-
Euclidean". This is not quite correct: Riemann's geometry is
simply more universal than Euclid's, with Euclidean geometry a
special case of Riemannian geometry.


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