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.

January 8, 1999 -- Vol. 3 Number 2

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There is no national science just as there is
no national multiplication table; what is national
is no longer science.
-- Anton Chekhov (1860-1904)

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Contents of This Issue:

1. Sharp Criticism of US Science Education Effort
2. An Explanation for Low-Latitude Glaciation
3. A New Model for Proterozoic Ocean Chemistry
4. Selective Amplification in a Replicating Peptide System
5. Intracellular Sodium and Gain Control of the NMDA Receptor
6. On Neural Processes and Conscious Experience
 
Following the main text: Notices, subscription information,
editorial contacts, etc.

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1. SHARP CRITICISM OF US SCIENCE EDUCATION EFFORT
In the US, a companion to the ever-present question of how to
fund scientific research is the question of how to manage science
education. Two recent reports indicate that science education in
the US continues to be considered a dismal scene. ... ... Jeffrey
Mervis presents an extensive review of a major effort by the US
National Science Foundation (NSF), the so-called Statewide
Systemic Initiatives, an effort launched in 1991 in 10 states,
and which "grew out of a bipartisan political promise to make US
elementary and secondary students the best in the world in
science and math." The author calls this NSF program a bold
attempt to achieve reform on many fronts at the statewide level,
the program ranging from training teachers and developing new
curricula to rewriting state laws and reshuffling school
management. The conclusion of the author is that after 7 years
and considerable expenditure of money, the proposed
transformations in the teaching of science sought by NSF have not
materialized, and "the National Science Foundation is still
looking for answers."
... ... W.H. Schmidt and C.C. McKnight (2 installations, US)
present a review of the results of the Third International
Mathematics and Science Study, the purpose of which was to
provide data on the practices and results of national education
systems. The study involved analysis of the education systems of
over 40 countries, including analysis of textbooks and several
achievement tests. The results of the study are complex, but in
general, concerning the US, the results apparently indicate that
science and mathematics abilities in the US decline between the
4th and 8th grades, that 4th grade US students are better trained
than the international average, while 8th grade US students are
below the international average. For example, in 8th grade
geometry achievement tests, 33 countries place above the US,
while only Iran, Kuwait, Colombia, and South Africa place below
the US. Science education in the US was found to be particularly
weak in the physical sciences. The authors conclude that although
there are difficulties with some of the analyses and methods of
this study, many of the findings are "robust" and have
implications for education policy.
-----------
Jeffrey Mervis: Mixed grades for NSF's bold reform of statewide
education.
(Science 4 Dec 98 282:1800)
QY: Jeffrey Mervis 
-----------
W.H. Schmidt and C.C. McKnight: What can we really learn from
TIMSS?
(Science 4 Dec 98 282:1830)
QY: William H. Schmidt 
-------------------
Summary by SCIENCE-WEEK  8Jan99
-------------------
Related Background:
ON POPULAR CULTURE AND THE THREAT TO RATIONAL INQUIRY
In an essay on current popular attitudes toward science and
scientists, Douglas R. Hofstadter (Indiana University
Bloomington, US) makes the following points: 1) Science is
currently presented to children and teens combined with
irrelevancies such as action-packed stories, rock music, amusing
quipsters, sassy jokes, sexual innuendoes, or up-to-date teen
slang -- as if science is a "bitter pill" that needs sugar-
coating. 2) Society today seems to be pervaded by a deep,
unconscious, anti-science bias. Scientists are represented in
movies, television, and books as heartless, humorless nerds who
would sooner kill than smile, sooner write abstruse formulas than
make love. 3) There is a dismissive attitude toward science as an
explanatory framework for the world, and the welcoming of so-
called "mysteries" such as after-death experiences, alien
abductions, crystal channeling, crop circles, telekinesis,
clairvoyance, extrasensory perception, or remote viewing. 4)
Movie and television viewers and readers of serious literature
are given the tacit message that the line between the natural and
supernatural is blurry, and perhaps even nonexistent. 5) The
general public no longer views science with a sense of awe and
mystery, but instead considers it conservative and mundane,
"trapped" in logical thinking. 6) The implicit message of popular
culture is that science is boring, conservative, closed-minded,
devoid of mystery, and a negative force in society. The author
concludes: "I have no quick fixes. I do not know how to quickly
and easily repair decades of damage. I do not fully understand
why the sands have shifted so radically. All I can do is look on
in sadness and worry about the future of rational inquiry,
bemoaning the loss of awe toward genuine mysteries that our
society was once lucky enough to possess."
QY: Douglas R. Hofstadter, Indiana Univ. Bloomington 812-855-4848
(Science 24 Jul 98 281:512) (Science-Week 14 Aug 98)
-------------------
Related Background:
AN ESSAY ON SCIENTIFIC ILLITERACY
In an essay on the scientific illiteracy of the general public,
N. Augustine (Princeton University and Lockheed Martin Corpor-
ation, US) notes the apathy concerning science and technology
that is apparently rampant in the US, and that "an indifference
toward scientific understanding is almost considered a badge of
honor." A recent US National Science Foundation survey indicates
that less than half of American adults understand that the Earth
orbits the Sun yearly; only 21% can define DNA; only 9% know what
a molecule is; 25 million Americans cannot locate the US on an
unlabeled world map. The public attitude toward science and
scientists is consistently negative. The great irony is that the
American economy and standard of living are based on a foundation
of rapid scientific advances. Augustine suggests that modern
scientists and engineers "must become as adept in dealing with
societal and political forces as they are with gravitational and
electromagnetic forces." QY: Norman Augustine, Princeton
University 609-258-3000 (Science 13 Mar 98)


2. AN EXPLANATION FOR LOW-LATITUDE GLACIATION
*Paleomagnetic data suggest that the Earth was glaciated at low
latitudes during the Paleoproterozoic Era (approximately 2.4 to
2.2 billion years ago), and also during the Neoproterozoic Era
(approximately 820 to 550 million years ago), although there is
evidently some dispute concerning the Neoproterozoic data. An
apparently straightforward explanation for low-latitude
glaciation is that the climate was very cold in *Precambrian
times as a consequence of *reduced solar luminosity uncompensated
by high levels of *greenhouse gases. A problem with this idea
(sometimes called the "snowball Earth" hypothesis) is that it is
difficult to explain how the ice caps could have extended to low
latitudes without causing the extinction of most or all surface
life. An alternative explanation for low-latitude glaciation is
that rather than the polar ice caps extending to the Equator, the
zonation of climate with respect to latitude was reversed. It has
been suggested, for example, that the *obliquity of the Earth may
have been greater than 54 degrees during most of its history,
which would have made the Equator the coldest part of the planet.
But this idea would require a mechanism to bring the obliquity
down to its present value of 23.5 degrees. ... ... D.M. Williams
et al (3 installations, US AU) now propose that "*obliquity-
oblateness feedback" could have reduced the obliquity of the
Earth by tens of degrees in less than 100 million years if the
continents were situated so as to promote the formation of large
polar ice sheets. The authors suggest a high obliquity for the
early Earth may also provide a natural explanation for the
present inclination of the lunar orbit with respect to the
*ecliptic (5 degrees), which is otherwise difficult to explain.
-----------
D.M. Williams et al: Low-latitude glaciation and rapid changes in
the Earth's obliquity explained by obliquity-oblateness feedback.
(Nature 3 Dec 98 396:453)
QY: Darren M. Williams 
-----------
Text Notes:
... ... *Paleomagnetic data: In general, paleomagentics is the
study of the direction and intensity of the Earth's magnetic
field throughout geologic time. The essential method of
paleomagnetics is the measurement of *remanent magnetism and the
application of analysis of the data to various questions in 
paleo-geophysics and paleo-geology.
... ... *remanent magnetism: Remanent magnetism is that component
of a rock's magnetization whose direction is fixed relative to
the rock and which is independent of moderate applied magnetic
fields. The significance of remanent magnetization in rocks is
that the polarity fixation occurs during the cooling of molten
rock or the sedimentation of sedimentary rocks in response to the
magnetic field of the Earth at that particular geological time.
Thus, remanent magnetization of rocks provides a history of
Earth's magnetic field.
... ... *Precambrian: In general, the time-frame between the
consolidation of the Earth's crust and the beginning of the
Cambrian period approximately 590 to 550 million years ago. The
Cambrian explosion of life forms, the rather sudden appearance of
numerous invertebrate fossils, has been a long-standing puzzle
for paleobiologists, and at present there is apparently no single
generally accepted explanation. Among the ideas proposed have
been, 1) that the explosion of new forms resulted from a sudden
increase in atmospheric oxygen; 2) that the explosion is only
apparent, and the Precambrian, the period previous to the
Cambrian, lacks fossils because of heat and pressure associated
with important geological changes; 3) that living forms evolved
mostly in freshwater areas, and are therefore absent in
Precambrian sediments, which are primarily marine; 4) that
changes in the shape and extent of shorelines produced by
continental drift dramatically transformed climate and
environment; 5) that the previous evolution of DNA recombination
and regulatory genes culminated in and sparked the diversity and
anatomical complexity manifested in the explosion; 6) that an
exponential increase of species could become significant only
after attaining a threshold value at the start of the Cambrian;
7) that once multicellular organisms appeared, the intrinsic
possibilities for variation increased enormously with a resultant
explosion of evolved forms. Unfortunately, there is no evidence
to suggest a selection of one of these proposals, although some
of them are less convincing than others. And of course the truth
may be that more than one factor was involved. No matter the
origin, the Cambrian explosion is apparently accepted by most
paleobiologists as a real discontinuity, a period that saw the
sudden emergence of dozens of new orders and phyla.  
... ... *reduced solar luminosity: There is apparently good
geophysical evidence that the brightness of the Sun (solar
luminosity; the "solar constant") has increased approximately 25
percent over the lifetime of Earth. The impact on climate of a
Sun supplying only 75 percent of its present heat is considered
by most paleoclimatologists to have been considerable (some
believe the impact would be "spectacular").
... ... *greenhouse gases: The physical basis of the so-called
"*greenhouse effect" is essentially simple: carbon dioxide gas is
transparent to visible light but relatively opaque to infrared
radiation. The same is true of glass. Relatively high-energy
visible light radiation from the sun passes inward through the
atmosphere, warms the surface of the Earth, which then radiates
lower energy in the form of infrared radiation (heat) back to the
atmosphere. But if the atmosphere has a concentration of infrared
impenetrable gases such as carbon dioxide, the infrared radiation
cannot pass out, and the surface of the Earth underlying the
atmosphere cannot cool, and the surface of the Earth thus will
continue to grow hotter.
... ... *obliquity: The "obliquity" of the Earth is the angle
between the plane of the equator and the plane of the Earth's
orbit, and it is quite important in determining climate belts
around the Earth's sphere.
... ... *obliquity-oblateness feedback: The term "oblateness"
refers to the flattening of a star or planet at the poles, caused
by its rotation. Quantitatively, oblateness is measured by
subtracting the polar diameter from the equatorial diameter, then
dividing by the equatorial diameter. The "obliquity-oblateness
feedback" (sometimes called "climate friction") referred to in
this report involves a feedback loop: Earth's obliquity drives
variations in oblateness by changes in continental ice volume and
sea level, and oblateness itself affects the rate at which
obliquity varies.
... ... *ecliptic: The plane of the orbit of the Earth around the
Sun, presently forming an angle of 23.5 degrees with the Earth's
equator.
-------------------
Summary & Notes by SCIENCE-WEEK  8Jan99
-------------------
Related Background:
EARTH'S OBLIQUITY AND THE SHRINKAGE OF THE TROPICS
... ... Rubincam et al (National Aeronautics and Space
Administration, US) review the periodic shrinkage of Earth's
tropical zone. In the past year, the Earth completed one
revolution around the Sun, the Moon went through its phases 13
times, and the tropic of Cancer moved another 14.7 meters south.
The tropic of Cancer is the latitude at which the Sun is overhead
at the June solstice, and that latitude is moving toward the
equator. Similarly, the tropic of Capricorn, where the Sun stands
at the December solstice, moved 14.7 meters northward. Almost
1100 square kilometers move from the tropics into the temperate
zone each year. The reason for the shrinkage is the changing
obliquity of the Earth, which is getting progressively smaller by
approximately 47.5 arc-seconds per century. Various gravitational
torques of the Sun, Moon, and other planets cause the Earth's
obliquity to oscillate with a period of approximately 41,000
years. QY: David P. Rubincam, NASA Goddard Space Flight Center,
Greenbelt, MD 20771 US.
(Sky & Telescope June 1998) (Science-Week 8 May 98)


3. A NEW MODEL FOR PROTEROZOIC OCEAN CHEMISTRY
The time-frame of what is called the "Proterozoic" era is the
period from approximately 2.5 billion years ago to 590 million
years ago, and the consensus is that it was during this time
frame that life on Earth underwent a significant expansion, in
particular the appearance of multicellular forms. The early
atmosphere of the Earth apparently differed from the present
atmosphere mainly by its lack of free oxygen, and this absence of
free oxygen is believed to have made possible the synthesis of
many compounds indispensable for the origin of life. One of the
central problems in earth science is to explain the apparent
transition from a primitive atmosphere free of oxygen to the
present atmosphere which holds 21 percent of the gas. The idea is
that only after all accessible surface iron had been deposited as
ferric oxide, all carbon transformed into carbon dioxide, all
hydrogen oxidized to water, and all sulfur converted into sulfate
and sulfide, was it possible for free oxygen to accumulate. The
extant data indicate a significant oxidation of the surface of
the Earth approximately 2 billion years ago, with direct evidence
for this oxidation provided by geological records of the
oxidation-reduction sensitive elements Fe and U, the records
reflecting the conditions prevailing during weathering. The idea
is that the oxidation event was probably driven by an increased
sedimentary burial of organic matter between 2.3 and 2.0 billion
years ago. It is generally believed that banded iron formations
precipitated from an ocean whose bottom waters contained
significant concentrations of ferrous iron, and that this
sedimentation process terminated when aerobic bottom waters
developed, which oxidized the iron and thus removed it from
solution. ... ... D.E. Canfield (Odense University, DK) now
proposes that anoxic bottom waters probably persisted until well
after the deposition of banded iron formations ceased, and that
sulfide, rather than oxygen, was responsible for removing iron
from deep ocean water. The author suggests the sulfur isotope
record supports this hypothesis, and that approximately 1.8
billion years ago the increase in sulfide production became
sufficient to precipitate the total flux of iron into the oceans.
The author proposes that aerobic deep-ocean waters did not
develop until the Neoproterozoic era (1.0 to 0.54 billion years
ago), in association with a second large oxidation of the surface
of the Earth. The author further suggests this new model is
consistent with the emerging view of *Precambrian sulfur
geochemistry and the chemical events leading to the evolution of
animal forms, and that the model is fully testable by detailed
geochemical analyses of preserved deep-water marine sediments.
The author concludes: "The development of a middle-Proterozoic
sulfide ocean, as proposed here, best explains the available
geochemical and biological information on the course of Earth-
surface change during the Proterozoic era."
-----------
D.E. Canfield: A new model for Proterozoic ocean chemistry.
(Nature 3 Dec 98 396:450)
QY: D.E. Canfield 
-----------
Text Notes:
... ... *Precambrian: The time-frame of the Precambrian period is
4.5 billion years to approximately 545 million years ago (when
the Cambrian period begins). The Precambrian is divided into 3
eras, characterized as follows:
 -- Hadean (4.5 - 3.9 billion years ago): From the formation of
the Earth until the first appearance of sedimentary rocks, with
no record of fossil organisms.
 -- Archaen (3.9 - 2.5 billion years ago): Appearance of
sedimentary rocks, *stromatalites, and *benthic prokaryotes.
 -- Proterozoic (2.5 -0.545 billion years ago): Appearance of
*planktonic prokaryotes, followed by appearance of *eukaryotic
cells, followed by appearance of multicellular organisms.
... ... *stromatalites: A laminated calcium carbonate fossil
structure formed principally by bacteria and algae.
... ... *benthic prokaryotes: Prokaryotes are cells lacking
internal membrane-bound structures (such as a nucleus), and
benthic prokaryotes are prokaryotes living on the sea floor.
... ... *planktonic prokaryotes: These are prokaryotes that float
passively on surface water.
... ... *eukaryotic cells: Cells with internal membrane-bound
structures (such as a nucleus)
-------------------
Summary & Notes by SCIENCE-WEEK  8Jan99
-------------------
Related Background:
EVOLUTION: 1 BILLION YR OLD FOSSILS OF TRIPLOBLASTIC ANIMALS
There are two contradictory views concerning the early history of
*metazoans. The "*Cambrian explosion" hypothesis is based on
Cambrian shell fossils and *Burgess-type exceptionally well-
preserved fossil deposits ("lagerstatten"). This hypothesis
suggests that animal phyla originated rather suddenly
approximately 580 million years ago during the *Proterozoic-
Phanerozoic transition. The alternative hypothesis (called "slow
burn") suggests that animals developed more slowly, first
appearing, according to some molecular analyses, more than 1
billion years ago. ... ... A. Seilacher et al now report data
from the Mesoproterozoic Chorhat Sandstone site in central India.
The authors report that certain *bedding plane features are
biological and can be interpreted as the burrows of wormlike
undermat miners (i.e., *infaunal animals that excavated tunnels
underneath *microbial mats). The authors suggest these burrows
indicate that *triploblastic animals existed more than a billion
years ago. The authors further suggest their evidence indicates
that the diversification of animal designs proceeded very slowly
before the appearance of organisms with hard skeletons during the
Cambrian evolutionary explosion, and that the diversification
occurred before the ecological changes that accompanied that
explosion.
-----------
A. Seilacher et al (3 installations, DE IN US)
Triploblastic animals more than 1 billion years ago: Trace fossil
evidence from India.
(Science 2 Oct 98 282:80)
QY: Friedrich Pfluger, Yale University, 203-432-4771.
-----------
Text Notes:
... ... *metazoans: In general, the term "metazoa" refers to all
multicellular animals. Among important distinguishing
characteristics of metazoa are cell differentiation and
intercellular communication. For certain multicellular colonial
entities such as sponges, some biologists prefer the term
"parazoa".
... ... *Cambrian: Refers to the approximate general time-frame
500 to 600 million years ago (but often considered as 505 to 545
million years ago).
... ... *Burgess-type: The Burgess Shale fossil deposit site in
British Columbia (CA) is apparently a geological accident of
superb preservation, and one that has revealed to paleontologists
the limitations of their views of the varieties of life in the
*Cambrian period. All the fossils expected for the Cambrian are
found in the Burgess Shale, but studies have demonstrated in
addition a remarkable array of perfectly preserved soft-bodied
animals, including a variety of worms, *arthropods, sponges,
*brachiopods, and some bizarre forms seemingly unrelated to any
known groups. The consequence was a new appreciation among
paleontologists of the tremendous increase in metazoan diversity
that apparently occurred during the Cambrian period, and indeed
this increase is now considered one of the most important events
in the history of life on Earth. 
... ... *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).
... ... *brachiopods: A phylum of bivalve coelomate invertebrates
resembling bivalve molluscs. The term "bivalve" refers to the
presence of a hinged shell; the term "coelomate" refers to the
presence of a true body cavity.
... ... *Proterozoic-Phanerozoic transition: The Proterozoic eon
is the time-frame 2600 million years ago to 600 million years
ago. The Phanerozoic eon is the time-frame 600 million years ago
to the present. During the Phanerozoic, atmospheric oxygen
apparently increased by a factor of 10 to its present value.
... ... *bedding plane: A distinct surface separating two
strata, the bedding plane marking a break in the continuity of
sedimentation, a break that can be caused by a period of erosion
or a cessation of sediment supply.
... ... *infaunal: Refers to an organism that burrows into the
substrate.
... ... *microbial mats: A dense microbial layer. The authors
propose this served as a food source for wormlike animals
exploiting its decaying base.
... ... *triploblastic animals: These are animals with a body
organization derived from 3 germ layers (ectoderm, endoderm,
mesoderm). The category includes all metazoans except
*coelenterates, which are diploblastic.
... ... *coelenterates: A phylum of mostly marine multicellular
animals. (e.g., jellyfish).
-------------------
Summary & Notes by SCIENCE-WEEK  30Oct98
-------------------
Related Background:
DISCOVERY OF 3-DIMENSIONAL ALGAE AND ANIMAL EMBRYO FOSSILS
A phosphorite is a sedimentary rock composed chiefly of phosphate
minerals. The Proterozoic era (also called the Algonkian) is the
geologic time between the Archean and the Paleozoic, with the
Archean beginning about 3.9 billion years ago and involving the
first appearance of sedimentary rocks and the first primitive
organisms at the bottom of the oceans. In paleontology, the term
"radiation" refers to a diverging and diversifying spread of
animals or plants into new environments with a resultant
production of new evolutionary forms, and the Ediacaran radiation
refers to an assemblage (until now the oldest) of soft-bodied
marine animals, the assemblage first discovered in the Ediacara
Hills in Australia. The algae comprise a large mixed group of
photosynthetic and essentially single-celled plants, and are
considered ancestral to modern green plants. Thalli are primitive
types of plant bodies not differentiated into stems, leaves, and
roots; the term also refers to the gametophyte generation (the
phase of the plant life cycle producing reproductive cells) of
some ferns and lichens. The term "cleavage stages" refers to the
early stages of embryo formation when the egg cell rapidly
divides into smaller and smaller cells. The "Bilateria" are a
major division of the animal kingdom comprising all forms with
bilateral symmetry, and the term "bilaterians" refers to the
first such forms appearing after the emergence of protozoa. The
term "phylogeny" refers to the evolutionary history of an
organism or group of organisms. ... ... Xiao et al (3 authors at
2 installations, US CN) report the discovery of phosphorites of
the late Neoproterozoic (570 +- 20 million years ago) in the
Doushantuo Formation, southern China, an apparent exceptional
record of multicellular life from just before the Ediacaran
radiation of macroscopic animals. Abundant thalli with cellular
structures preserved in 3-dimensional detail show that late-
Proterozoic algae already possessed many of the anatomical and
reproductive features seen in modern marine flora. Embryos
preserved in early cleavage stages indicate the divergence of
lineages leading to bilaterians may have occurred well before
their macroscopic traces or body fossils appear in the geological
record. The authors suggest that discovery of these fossils shows
that the early evolution of multicellular organisms is amenable
to direct paleontological inquiry, and that paleontological
observations, together with insights from molecular phylogeny and
developmental genetics, can facilitate a modern integration of
phylogeny, development, and paleontology that extends deeply into
evolutionary history to address the early evolution of
multicellular life.
QY: Andrew H. Knoll, Botanical Museum, Harvard University,
617-495-1000
(Nature 5 Feb 98) (Science-Week 20 Feb 98)
-------------------
Related Background:
PRECAMBRIAN SPONGES WITH CELLULAR STRUCTURES
The sponges (Porifera) are a phylum of primitive multi-cellular
animals (Metazoa), always attached at one point to a substrate,
usually without a definite symmetry, and usually marine. The
sponge body is a loose aggregation of cells with little
intercellular coordination, but the cells are specialized into
various types with various functions important to the viability
of the entire organism. There is also in sponges an internal
"skeleton" of chalk, silica, or protein, and "calcareous sponges"
are sponges containing a relatively large amount of calcium
carbonate. In this report, "spicules" are the hard internal
structures in sponges composed primarily of silica or calcium
salts, and a "monoaxonal" spicule is a spicule having essentially
only one dimension (e.g., needle-like). The term "epidermis"
refers to the outermost layer of cells in any multicellular
organism; "porocytes" are tubular cells that constitute the walls
of certain sponges; "amoebocytes" are freely moving cells (sponge
cells in this context) within a metazoan tissue; "sclerocytes"
are cells involved in the formation of the sponge skeleton;
"spongocoel" refers to the branching internal cavity of a sponge,
the cavity having a connection in one place or another to the
external aqueous environment; "flagella" are long and thin
cellular organelles that protrude from the surfaces of cells and
are specialized to produce locomotion. The Cambrian period
extended from 545 to 505 million years ago, and was the time
during which many multicellular organisms first arose, and the
Vendian period is the Precambrian metazoan fossil period. The
term "Cambrian explosion" refers to the apparent relatively
sudden appearance of an enormous number of living forms during
the Cambrian period. ... ... Li et al (3 authors at 2 install-
ations, TW CN) report the identification of sponge remains in the
Early Vendian Doushantuo phosphate deposit (cf. previous report,
this  issue) in south China. The skeletons consist of siliceous
monoaxonal spicules, with preserved soft tissues including the
epidermis, porocytes, amoebocytes, sclerocytes, and spongocoel,
and among thousands of metazoan embryos a sponge larva having a
shoe-shaped morphology and dense peripheral flagella. The authors
suggest the data indicate the calcareous sponges may have an
extended history in the Late Precambrian, and that animals lived
40 to 50 million years before the Cambrian explosion. They
further suggest these Doushantuo rocks provide a potentially
inexhaustible resource for understanding the early evolution of
animal life.
QY: Chia-Wei Li, National Tsing Hua Univ., Hsinchu, Taiwan, China
(Science 6 Feb 98) (Science-Week 20 Feb 98)


4. SELECTIVE AMPLIFICATION IN A REPLICATING PEPTIDE SYSTEM
One of the central questions in research concerning the origin of
life on Earth involves the primordial development of replicating
prebiotic chemical systems. Self-replication has been
demonstrated in synthetic chemical systems based on
oligonucleotides, peptides, and complementary molecules without
natural analogues. But within a living cell virtually no molecule
catalyzes its own formation, and the search for chemical systems
in which both auto- and cross-catalysis can occur has therefore
attracted wide interest. One such system, consisting of 2 self-
replicating peptides that catalyze each other's production, has
been reported ... ... S. Yao et al (4 authors at Purdue
University, US) now describe a 4-component peptide system that is
capable of auto- and cross-catalysis and that allows for the
selective amplification of one or more of the products by
changing the reaction conditions. The authors suggest that the
ability of this system to selectively amplify one or more
molecules in response to changes in environmental conditions such
as pH or salt concentration supports the idea that self-
replicating peptides may have played a role in the origin of
life.
-----------
S. Yao et al: Selective amplification by auto- and cross-
catalysis in a replicating peptide system.
(Nature 3 Dec 98 396:447)
QY: Jean Chimielewski 
-------------------
Summary by SCIENCE-WEEK  8Jan99
-------------------
Related Background:
VIRTUAL SYMBIOSIS IN HIGHER-ORDER PEPTIDE SELF-REPLICATION
In biology, symbiosis is an intimate and protracted association
of individuals of different species, and mutualism is a type of
symbiosis in which both participants receive benefits from the
association. The two terms are sometimes used interchangeably,
with symbiosis referring to a mutually beneficial association.
The concept of a "hypercycle" was first formulated by Manfred
Eigen (in collaboration with P. Schuster) 20 years ago. A
hypercycle is essentially an interrelationship of two or more
self-replicating molecular species interlinked through a cyclic
catalytic network. In a bipartite arrangement, for example, self-
replicating molecule A may produce as a by-product X, and X
catalyzes the self-replication of B, which produces the by-
product Y, and Y catalyzes the self-replication of A, and so on.
Many permutations of the idea are possible, and if one considers
the bipartite arrangement outlined above as a single system, it
is evidently a higher-order single system that is reproducing via
autocatalysis. In the replication of biological macromolecules,
genotypic replication refers to the genomic replication of DNA
and RNA, while phenotypic replication refers to the replication
of the proteins said to be "expressed" by the genomic elements
(genes), i.e., the expression of the nucleic acid information.
Lee et al (Scripps Research Institute, US) report a chemical
system that is an apparent example of a minimum hypercyclic
network, the system involving two otherwise competitive self-
replicating peptides "symbiotically" catalyzing each other's
production. The authors suggest this example of a hypercyclic
peptide network supports the idea that peptides could play a role
in early darwinian evolution involving selection based on
feedback processes of genotypic replication, and that molecular
genotypes and phenotypes may have been the same molecules.
QY: M. Riza Ghadiri 
(Nature 11 Dec 97) (Science-Week 2 Jan 98)


5. INTRACELLULAR SODIUM AND GAIN CONTROL OF THE NMDA RECEPTOR
It has been known for 50 years [*Note #1] that the influx of
sodium ion into the nerve cell is fundamental to electrical
signalling in the nervous system, the influx essential for such
basic signals as *action potentials and *excitatory postsynaptic
potentials in neurons. During periods of impulse bursting or high
levels of discharge activity, large increases in intracellular
sodium ion concentration are apparently produced in the neuron
cell body and *dendrites, and a central question is what is the
intracellular signalling function, if any, of this increased
postsynaptic intracellular sodium ion concentration?
... ... X.-M. Yu and M.W. Salter (2 installations, CA) now report
that intracellular sodium ion concentration regulates the
function of *NMDA (N-methyl-D-aspartate) receptors, a principle
subtype of *glutamate receptor. The authors report that NMDA-
receptor-mediated whole-cell electric currents and NMDA-receptor
*single channel activity were increased by raising intracellular
sodium ion concentration, and that channel activity decreased
upon lowering intracellular sodium ion concentration. The authors
conclude from this that the activity of NMDA channels tracks
changes in intracellular sodium ion concentration. They report
that the sensitivity of the channel to sodium ion is apparently
set by an enzyme (a *kinase) known to be associated with the
channel. Increasing intracellular sodium ion concentration
selectively increased synaptic responses mediated by NMDA
receptors, but did not increase synaptic responses mediated by
non-NMDA receptors. The authors suggest their results indicate
the change in postsynaptic intracellular sodium ion concentration
that occurs during neuronal activity is a signal for controlling
the gain of excitatory synaptic transmission, and that this
mechanism may be important for NMDA-receptor-dependent
*plasticity and toxicity in the central nervous system.
-----------
X.-M. Yu and M.W. Salter: Gain control of NMDA-receptor currents
by intracellular sodium.
(Nature 3 Dec 98 396:469)
QY: Michael W. Salter 
-----------
Text Notes:
... ... *Note #1: The first direct evidence in single nerve
fibers that an influx sodium ion electrical current is the major
event during the nerve impulse was provided by A.L. Hodgkin and
B. Katz in 1949. In the 1950s, Hodgkin was joined by A.F. Huxley,
and together they developed a quantitative model to explain the
ion currents involving sodium and potassium. Also in the 1950s,
J.C. Eccles provided the first comparable evidence for the
*excitatory postsynaptic potentials of neuron synapses, and
during the same period B. Katz provided the first evidence for
the role of sodium ion currents during events at the
neuromuscular junction. Hodgkin, Huxley, and Eccles received the
Nobel Prize in Physiology and Medicine in 1963; Katz received the
Nobel Prize in Physiology and Medicine in 1970 (primarily for his
work involving chemical transmitter events at the neuromuscular
junction). For an introductory review of ion movements in nerve
cells, see the SW Focus Report "The Neuron", available at URL
.
... ... *action potentials: In general, the term "action
potential" refers to the potential change produced by current
flow resulting from a transient increase in sodium ion
permeability, a transient change that is propagated along the
nerve axon to the axon terminal(s). In most vertebrate nerve
cells, the nerve axon is a long extension of the cell, an
extension that can attain lengths as much as a meter, the
extension originating from a cell body approximately 50 microns
in diameter.
... ... *excitatory postsynaptic potentials: Neurotransmitters
are chemical substances released at the terminals of nerve axons
in response to the propagation of an impulse to the end of that
axon. The neurotransmitter substance diffuses into the synapse,
the junction between the presynaptic nerve ending and the
postsynaptic neuron, and at the membrane of the postsynaptic
neuron the transmitter substance interacts with a receptor.
Depending on the type of receptor, the result may be an
excitatory or an inhibitory effect on the postsynaptic nerve
cell. In each case, the effect is associated with a transient
electrical change in the postsynaptic membrane, the excitatory
effect associated with an "excitatory postsynaptic potential", a
transient depolarizing current flow involving an influx of sodium
ions.
... ... *dendrites: The general input extensions of nerve cells
are called "dendrites", and they may also be extensively
branched. In general, dendrites are considered to receive input
and axons to propagate output, but the electrical architecture of
most neurons is complicated, and in many types of nerve cells
activation of the axon produces electrical activity that not only
propagates down the axon but also propagates backward through the
cell body and dendrites.
... ... *NMDA (N-methyl-D-aspartate) receptors and glutamate
receptors: Glutamate is a major excitatory amino acid
neurotransmitter, accounting for an estimated 40 percent of all
nerve signals in the human brain, and involved in phenomena such
as neural development, learning, and memory formation. Glutamate
is ordinarily released under close cellular biochemical control
and reuptake, and in excess amounts it is an intense excitant of
nerve cells and potentially toxic. Glutamate is suspected as an
important contributor to the pathogenesis of a number of
neurodegenerative disorders, including amyotrophic lateral
sclerosis and parkinsonian dementia. The glutamate receptor is
the molecular site that mediates the actions of glutamate
neurotransmitters, and this receptor has been a focus of
intensive research and has been differentiated into N-methyl D-
aspartate (NMDA), kainate, and quisqualate subtypes [see
background material below]. Neurons that release glutamate are
called "glutamatergic", and they have been located in many
important areas of the human brain. 
... ... *single channel activity: (single ion channel activity)
Ion channels are protein channels in cell membranes that allow
ions to pass from extracellular solution to intracellular
solution and vice versa. Most ion channels are selective,
allowing only certain ions to pass, and an individual cell has
ion channels with various ion selectivities. The selectivity of
an ion channel can be "gated", the channel effectively opened or
closed, and ion channels are said to *voltage-gated or *ligand-
gated, depending on how the change in selectivity is provoked.
... ... *kinase: In general, a "kinase" is any enzyme involved in
the transfer of a phosphate group.
... ... *plasticity: In neurobiology, the term "plasticity" is
the name given to the capacity of neural tissue to adjust to
change.
-------------------
Summary & Notes by SCIENCE-WEEK  8Jan99
-------------------
Related Background:
CALCIUM SENSING OF METABOTROPIC GLUTAMATE RECEPTORS
L-glutamate (derived from the amino acid, glutamic acid) is
considered the principal excitatory neurotransmitter in the
vertebrate central nervous system, and is one of the neuro-
transmitter substances that interact with ion channels that are
switched on or off by specific ligands (i.e., they are "ligand-
gated"). Glutamate is known to act on 3 classes of receptors, one
of which is a slow-acting receptor type coupled to G-proteins and
called "metabotropic". (The G-proteins are membrane-bound
proteins that act as transducers between messenger molecules
interacting with the cell surface and the intracellular messenger
system). Frog oocytes are frog egg cells, and they are a common
laboratory vehicle for expressing the proteins of genetically
engineered material from other species and coupling this
expression with electrophysiological measurements of frog oocyte
membrane behavior. "Transfection" is the uptake of exogenous
(foreign) DNA fragments in solution directly into animals cells
in laboratory culture, and is one method of introducing foreign
genes into cells. ... ... Kubo et al (3 authors Tokyo
Metropolitan Institute for Neuroscience, JP) report
investigations of the behavior of rat metabotropic glutamate
receptors as calcium ion sensors in a frog oocyte expression
system, and that some types of these receptors are indeed
activated not only by glutamate but also by extracellular
Ca(sup2+). A single amino acid residue was found to determine the
sensitivity of these receptors to calcium ion, and one of the
receptors caused morphological changes when transfected into
mammalian cells. The authors suggest that in cells under
physiological conditions, the sensing of extracellular calcium
ion by metabotropic glutamate receptors may be an important
aspect of neuron cell regulatory processes.
QY: Yoshihiro Kubo 
(Science 13 Mar 98) (Science-Week 27 Mar 98)
-------------------
Related Background:
SECRETION OF GLUTAMATE BY BRAIN ASTROCYTES
Glial cells are more numerous than neurons in the brain, but
their function has been generally characterized as "metabolic" or
"supportive", without much discussion of details, and more is
known about peripheral glial cells than glial cells in the
central nervous system. Astrocytes are the largest glial cells,
with many extensions radiating outward like a starburst, and at
least one of their functions is apparently to maintain the so-
called "blood-brain barrier" effectively separating neural tissue
from blood. ... Kainic acid, an algal neurotoxin, is a structural
analogue of glutamate, and it has been extensively used in
research, since at high concentrations it selectively destroys
glutamate receptor neurons (glutaminergic neurons). Glutamate is
known to act on 3 classes of receptors, one of them called the
kainate receptor because at low concentrations of kainic acid the
action of glutamate on this receptor is enhanced. The chemistry
of this kainate receptor is not yet well-characterized, mainly
because selective ligands for it are not known. Another class of
glutamate receptor is the AMPA receptor [AMPA = (RS)-alpha-amino-
3-hydroxy-5-methyl-4-isoxazoleproprionic acid], and the third is
NMDA (N-methyl-D-aspartate). These 3 receptors are ionotropic,
i.e., their activation produces changes in membrane ion permeab-
ility. According to another and more recent scheme of glutamate
receptor classification, one receptor type is AMPA/kainate
(ionotropic), another receptor type is NMDA (ionotropic), and a
third receptor type is a slow-acting receptor type coupled to G-
proteins and called metabotropic receptors. (The G-proteins are
membrane-bound proteins that act as transducers between messenger
molecules interacting with the cell surface and the intracellular
messenger system). Prostaglandins are fatty acids secreted by
cells that have hormone-like actions in the immediate vicinity,
and one circumstance that produces their release is tissue
injury. ... ... Bezzi et al (8 authors at 2 installations, IT)
report that coactivation of the AMPA/kainate and metabotropic
glutamate receptors on astrocytes stimulates these cells to
release glutamate through a calcium-dependent process mediated by
prostaglandins. The authors suggest their results reveal a new
pathway of regulated transmitter release from astrocytes, and
that interactions between neurons and astrocytes may play a
critical role in synaptic plasticity and neurotoxicity. They also
suggest that the prostaglandin-mediated glutamate release from
astrocytes may be involved in the pathophysiology of various
brain diseases and injuries.
QY: Andrea Volterra 
(Nature 15 Jan 98) (Science-Week 30 Jan 98)


6. ON NEURAL PROCESSES AND CONSCIOUS EXPERIENCE
Identifying the material substrate of conscious experience has
been a subject of intellectual inquiry for nearly three thousand
years, and a focus of scientific investigation for more than two
centuries. Research has clarified the material substrate as a
neural substrate, but the details are still quite murky, and the
formulation of useful questions remains uncertain. In general,
each generation of neurobiologists reformulates the relevant
questions in its own context, which is the way with most long-
extant problems. Each reformulation has the potential of leading
to new methods of experiment and analysis, and to a possible step
forward in unraveling what continues to be one of the most
profound scientific and philosophical enigmas. ... ... G. Tononi
and *G.M. Edelman (Neurosciences Institute San Diego, US) present
a review of what the authors call a new approach to the question
of the neural substrate of conscious experience, the authors
making the following points: 1) *Classical approaches that
attempt to determine an anatomical locus of consciousness are
heuristically useful, but they leave a fundamental problem
unresolved: How could the possession of some particular
anatomical location or biochemical feature render some neurons so
privileged that their activity gives rise to subjective
experience? 2) The authors state they choose an alternative
approach, a strategy to characterize "the kinds of neural
processes that might account for key properties of conscious
experience," and that two properties are emphasized: a) conscious
experience is integrated: each conscious scene is unified; b) at
the same time, conscious experience is highly differentiated:
within a short time one can experience any of a huge number of
different conscious states. 3) The authors propose that a group
of neurons can contribute directly to conscious experience only
if it is part of a distributed functional cluster that achieves
high integration in hundreds of milliseconds. To sustain
conscious experience, the authors propose it is essential that
this functional cluster be highly differentiated, as indicated by
high values of complexity. 3) The authors propose that a large
cluster of neuronal groups that together constitute, on a time
scale of hundreds of milliseconds, a unified neural process of
high complexity be termed the "dynamic core". The dynamic core is
a functional cluster: its participating neuronal groups are much
more strongly interactive among themselves than with the rest of
the brain. The dynamic core must also have a high complexity: its
global activity patterns must be selected within less than a
second out of a very large repertoire. The authors state that the
term "dynamic core" deliberately does not refer to a unique and
invariant set of brain areas: the core may change in composition
over time and may vary significantly across individuals. [*Note
#1] 5) The authors suggest that a strong prediction based on
their hypothesis is that the complexity of the dynamic core
should correlate with the conscious state of the subject. The
authors also predict that neural processes underlying automatic
behaviors, no matter how sophisticated, should have lower
complexity than neural processes underlying consciously
controlled behaviors. Another prediction is that a systematic
increase in the complexity of coherent neural processes is
expected to accompany cognitive development. The authors
conclude: "The evidence available so far supports the belief that
a scientific explanation of consciousness is becoming
increasingly feasible."
-----------
G. Tononi and G.M. Edelman: Consciousness and complexity.
(Science 4 Dec 98 282:1846)
QY: Giulio Tononi 
-----------
Text Notes:
... ... *Classical approaches: Both primary visual cortex and
prefrontal cortex have been considered to be involved in
conscious experience. In the mammalian brain, the primary visual
cortex is the area of the cerebral cortex containing nerve cells
and neural circuits responsible for primary visual sensation. The
prefrontal cortex is the part of the cerebral cortex found at the
anterior portion of the frontal lobes, and there is evidence that
this region is involved in planning complex cognitive behaviors,
and in the expression of personality and appropriate social
behavior.
... ... *G.M. Edelman: Gerald M. Edelman received the Nobel Prize
in Physiology and Medicine in 1972, the prize awarded primarily
for his work in determining the sequence of 1330 amino acids that
constitute human immunoglobulin, a protein entity essential to
the function of the human immune system.
... ... *Note #1: The adjective "dynamic" is a key term here: An
essential aspect of the Tononi-Edelman approach is that the
neural substrate of consciousness varies within an individual and
from one individual to the next, a marked divergence from the
classical search for a fixed anatomical locus of conscious
experience.
-------------------
Summary & Notes by SCIENCE-WEEK  8Jan99
-------------------
Related Background:
HUMAN NEUROCOGNITIVE ARCHITECTURE: A PLASTICITY MODEL
In human neurobiology, the term "cognition" refers to
intellectual functions that include perceiving, remembering,
imagining, conceiving, understanding, judging, and reasoning. And
one of the central problems of human neurobiology is to
understand the neurological substrates for all of these aspects,
and also to understand the evolution of these aspects where such
evolution can be delineated. In other words, from a neurological
standpoint, the questions in this context are how does the mind
work and how did it get that way? From any research perspective,
that is what is called a tall order. One view, proposed by
evolutionary psychologists, is based on the presumption that the
demands on *hunter-gatherer life during the *Pleistocene epoch
generated a vast array of evolutionary cognitive adaptations that
determine current human cognition and behavior. But many
neurobiologists disagree with this approach, and instead focus on
the intrinsic *plasticity of the human brain, and in particular
on the intrinsic plasticity of the human neocortex, an intrinsic
plasticity manifested during individual development -- a response
to the individual's physical and psychological environment. These
two approaches are in essence restatements of the classical
nature vs. nurture controversy, but the classical character of
the question does not make the question less important. ... ...
P. La Cerra and R. Bingham present a critique of the evolutionary
psychology approach to the understanding of cognitive processes
and offer an alternative model which they propose is more in
agreement with the current evidence in neurobiology. The authors
make the following points: 1) An extensive literature underscores
the enormous functional plasticity of the *neocortex, a
distinguishing characteristic of mammals. This evidence supports
the position that cortical representational features are
systematically constructed by the dynamic interaction between
environmentally derived neural activity and intrinsic neural
growth mechanisms. 2) The information-processing capacities of
the neocortex are largely constructed in response to the problem
domains confronting the individual throughout development, and
these constructions remain modifiable throughout the life
history. 3) This neurobiological account of the ongoing
construction of the human neurocognitive architecture contrasts
sharply with the account of evolutionary psychologists, who
conceive of the mind as a confederation of information-processing
adaptations, each of which evolved in response to a problem posed
by Pleistocene selection pressures. 4) Numerous methodological
problems and theoretical flaws call the validity of the
evolutionary psychological paradigm into question... Evolutionary
psychologists have suggested that investigation of the neural
correlates of behavior is not mandatory for the study of
cognitive adaptations. This failure to reconcile theoretical
claims with neurobiological data has veiled from evolutionary
analyses the functional organization of the information-
processing circuits that comprise the human neurocognitive
architecture. 5) The authors propose that the problems faced by
ancestral *hominids and their mammalian predecessors would have
required an adaptively flexible online information-processing
system, and would have driven the evolution of a functionally
plastic neural substrate, the neocortex, rather than a
confederation of evolutionary prespecified social cognitive
adaptations. 6) The authors propose that human cognitive
processes result from the activation of constructed cortical
representational networks, which reflect probabilistic
relationships between sensory inputs, behavioral responses, and
adaptive outcomes. The construction of these networks throughout
development, and their modification throughout experience, are
mediated by subcortical circuits that are responsive to the life
history regulatory system. The authors conclude: "The model we
have outlined emphasizes individual differences as the product of
an evolved self-adapting system, a neurocognitive architecture
that is unique by design." In summary, the La Cerra and Bingham
idea is essentially that human neurocognitive systems (the
neurocognitive "architecture") are "constructed" during
individual development and experience, rather than inherited as
preformed circuits (structures) selected by evolutionary
pressures during and before the Pleistocene epoch. The authors
term their approach "constructivist".
-----------
P. La Cerra and R. Bingham (Calif. Inst. of Tech., US)
The adaptive nature of the human neurocognitive architecture: An
alternative model.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11290)
QY: Roger Bingham 
-----------
Text Notes:
... ... *hunter-gatherer life: The consensus among
paleoanthropologists is that sometime between the beginning of
*hominid bipedalism (the "hominini") and the appearance of Homo
sapiens, perhaps about 2 to 3 million years ago, there occurred a
divergence from essential ape-like behavior and the emergence of
a hunter-gatherer existence, the hunting of animals and the
gathering of plants, both for food.
... ... *hominids: In general, any primate in the human family.
... ... *Pleistocene epoch: A geological epoch with the time-
frame 2.5 million years ago to 11,000 years ago. This was the
epoch of rapid hominid evolution, and the appearance of cattle
and the modern horse.
... ... *plasticity: 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".
... ... *neocortex: The most recently evolved part of the
cerebral cortex.
-------------------
Summary & Notes by SCIENCE-WEEK  23Oct98
-------------------
Related Background:
ON MODULAR COGNITIVE SYSTEMS IN THE HUMAN BRAIN
One of the central challenges of cognitive neuroscience is to
unmask the apparent unitary nature of perceptual, memorial, and
cognitive systems. Neuropsychological analyses, functional brain-
imaging methods, and analyses of normal reaction times have
revealed that apparently unitary processes consist of multiple
components. Frequently, these multiple components are distributed
across the cerebral hemispheres, but appear unified because of
the integration possible via the corpus callosum.
... ... Baynes et al (4 authors at 3 installations, US) report a
case of elective surgery for a severe epileptic disorder, the
surgery involving a resection of the corpus callosum in a left-
handed woman with left-hemisphere dominance for spoken language.
The patient demonstrated a dissociation between spoken and
written language. Words flashed to the dominant left hemisphere
were easily spoken out loud, but could not be written. When words
were flashed to the patient's right hemisphere, she could not
speak them out loud but she could write them with her left hand.
The authors suggest this marked dissociation supports the view
that spoken and written language output can be controlled by
independent hemispheres, even if before hemispheric disconnection
spoken and written language appear as inseparable cognitive
entities.
QY: Kathleen Baynes 
(Science 8 May 98 280:902) (Science-Week 29 May 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 neuro-
biologists 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 Univ-
ersity, 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)


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