ScienceWeek

SCIENCEWEEK

ScienceWeek
September 26, 2003
Vol. 7 Number 39A

An Online Digest of Research in the Sciences

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For the real amazement, if you wish to be amazed, is this
process: You start out as a single cell derived from the coupling
of a sperm and an egg; this divides in two, then four, then
eight, and so on, and at a certain stage there emerges a single
cell which has as all its progeny the human brain. The mere
existence of such a cell should be one of the great astonishments
of the Earth. People ought to be walking around all day, all
through their waking hours calling to each other in endless
wonderment, talking of nothing except that cell.
-- Lewis Thomas (1913-1993)

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Section 1

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Part A - Symposium: Cognitive Neuroscience

1. Introduction
2. Emotion, Cognition, and Behavior
3. Memory and the Memory Consolidation Hypothesis
4. Consciousness and Complexity
5. Naturalizing Consciousness: A Theoretical Framework
6. Organization of Cell Assemblies in the Hippocampus
7. On the Neuronal Coding of Number
8. Tactile Perception, Cortical Representation, and the Bodily
Self
9. Grammar vs. Language in Neurolinguistics
10. Neuropsychiatric Symptoms in Dementia and Cognitive
Impairment

Notices and Subscription Information

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Section 2

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1. INTRODUCTION

HISTORICAL ANTECEDENTS OF MODERN BRAIN SCIENCE

During the sixteenth and seventeenth centuries, scientific
advances gave rise to accurate descriptions (but not actual
explanations) of electricity. And as seventeenth-century
explorers spread out around the world, a more complete notion of
the surface of the Earth was gained. The principles of both
electricity and geography were eventually applied to concepts of
how the brain worked. However, change was slow. When the
important properties of the nervous system ceased to be regarded
as the flow of "humors", this explanation was temporarily
replaced by the theories of the "ballonists", who considered the
nerves to be hollow tubes through which the flow of gases excited
the muscles. How did one disprove such a view? Scientists
dissected animals under water. When no gases were observed to
bubble up during muscle contractions, the theory went flat.

What new insight was gained from this gruesome experiment?
(Remember that although electricity was known, its powers had yet
to be applied to practical uses. The industry of this era, mid-
seventeenth century, received its power from windmills, flowing
rivers, and waterfalls.) Something had to flow from the nerves to
cause muscles to contract, so a "vital fluid" theory replaced the
gas theory. It was reasoned that an "essence" of the hollow
nerves flowed into the muscle, mixed with its fluids, and caused
explosive contractions. This "fluid" hypothesis was one of the
first to be issued from the newly formed Royal Society of
England, around 1661.

The vital-fluid concept eventually gave way to the view, proposed
by the physicist Isaac Newton (1642-1727) around the beginning of
the eighteenth century, that activity was transmitted by a
vibrating "aetherial Medium", one which had all the properties
later found to hold for biological electricity. Even with the
primitive instruments of the eighteenth and nineteenth centuries,
it was rather easy to show that both nerves and muscles were
electrically excitable. However, the view that the nerves and
muscles themselves actually worked by generating animal
electricity was not immediately grasped. The Italian anatomist
and physiologist Luigi Galvani (1737-1798) solved this problem
near the end of the eighteenth century, and the German
physiologist Emil du Bois-Reymond (1818-1896) reexamined it early
in the next century. Du Bois-Reymond was the first scientist to
attempt an explanation of all functions of the brain on the basis
of chemical and physical grounds. He and his coworkers were the
first to measure in a convincing way the electrical properties of
living, active nerves and muscles.

Adapted from: F.E. Bloom and A. Lazerson: Brain, Mind, and
Behavior. 2nd Edition. W.H. Freeman 1988, p.14
More information at:
http://www.amazon.com/exec/obidos/ASIN/0716718634/scienceweek

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ON LOCALIZATION OF FUNCTION IN THE HUMAN BRAIN

For more than 200 years, neurobiologists have been concerned with
the general problem of what is called "localization of function"
in the human brain. That there is considerable localization of
function is indisputable: there are brain regions involved with
specific primary inputs such as vision, audition, taste, etc.,
brain regions for specific primary outputs to various muscle
systems, and brain regions for speech and the understanding of
language. The still unclear aspects concern anatomical
localization of other so-called "higher faculties", e.g.,
learning, memory, perceptual analysis, motivations, various other
cognitive abilities, etc.

Classical studies of localization of function in the human brain
essentially began with Franz Joseph Gall (1758-1828), who
postulated that the shape of the human brain, especially its
convolutions, was related to "mental capacity", and that
different parts of the brain were involved with different parts
of the human body. This latter proposal concerning the relation
between different parts of the brain and different parts of the
body was essentially a correct view. But Gall also believed he
could correlate the shape of the human brain with various
emotional and temperamental qualities, and that the shape of the
brain, particularly its convolutions, could be deduced from the
irregularities existing in the topology of the overlying skull.
Thus began the 19th century pseudoscience of "phrenology", a
quackery that postulated that various human character traits
could be identified by literally feeling bumps on the head. The
public adored the idea, and so-called "phrenologists" continued
to bamboozle the public long after Gall was dead. What started as
a useful view that correlated brain anatomy with function, ended
in a popular pseudoscience that still had the public confused and
misled 100 years later.

The next most important figure in this field was Pierre Paul
Broca (1824-1880), a neurosurgeon who in 1861 discovered the
motor area of the brain responsible for speech, and who studied a
series of patients with traumatic injuries in this area. As a
result of Broca's work, the idea that at least certain brain
functions are localized was put on a firm scientific footing, and
a long history of research by clinical neurologists attempting to
correlate traumatic brain injury to loss of specific brain
function began. Beginning in the 1950s, evidence from localized
electrophysiological studies was added to the data resulting from
studies of traumatic brain injury, and in the 1990s an entirely
new set of data from functional magnetic resonance imaging of the
human brain in action became available to researchers studying
localization of brain function. This field is now intensely
active and of signal importance in neurology and cognitive
science. But the human brain is profoundly complex, and there are
still more questions than answers about how things get done in
this 1400-gram mass of tissue that makes us what we are.

The term "cortex" (cerebral cortex), in this context, refers to
the thin surface layering of nerve cells of the brain, 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 generally 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. Many contemporary
neurobiologists who study the brain emphasize precise "mapping"
of the cerebral cortex into "areas" associated with specific
functions.

The following points are made by Jonathan C. Horton (Nature 2000
406:565):

1) Given the limitations of histology, researchers often
designate areas in brain cortex by topography. For example, any
region that contains its own representation of the visual world
qualifies for "area" status. Unfortunately, topographic order in
other than primary visual areas ("higher" visual areas) is often
too crude to provide a reliable definition of boundaries. Another
limitation is that topography may not be meaningful outside
sensory and motor cortices. The author asks: "What constitutes
topography in regions concerned with language, motivation, or
personality?"

2) The author points out that relentless experimental efforts and
a battery of technical advances have provided us with better maps
of the brain. But much of the cortex stubbornly refuses to be
mapped, and the author suggests it is worth questioning the
assumption that the cerebral cortex consists of a finite number
of areas with sharp borders. An alternative is that only certain
regions -- mostly motor and sensory cortex -- are organized in
this way. Other regions might be diffuse fields separated by
gradual transitions in function, properties, and connections. As
Broca said in 1861: "Although I believe in the principle of
localization, I have asked and still ask myself within what
limits this principle can be applied." The author (Horton)
concludes: "For brain cartographers, the last frontier is in
their heads."

Nature http://www.nature.com/nature

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2. EMOTION, COGNITION, AND BEHAVIOR

The following points are made by R. J. Dolan (Science 2002
298:1191):

1) An ability to ascribe value to events in the world, a product
of evolutionary selective processes, is evident across phylogeny
(1). Value in this sense refers to an organism's facility to
sense whether events in its environment are more or less
desirable. Within this framework, emotions represent complex
psychological and physiological states that, to a greater or
lesser degree, index occurrences of value. It follows that the
range of emotions to which an organism is susceptible will, to a
high degree, reflect on the complexity of its adaptive niche. In
higher order primates, in particular humans, this involves
adaptive demands of physical, socio-cultural, and interpersonal
contexts.

2) The importance of emotion to the variety of human experience
is evident in that what we notice and remember is not the mundane
but events that evoke feelings of joy, sorrow, pleasure, and
pain. Emotion provides the principal currency in human
relationships as well as the motivational force for what is best
and worst in human behavior. Emotion exerts a powerful influence
on reason and, in ways neither understood nor systematically
researched, contributes to the fixation of belief. A lack of
emotional equilibrium underpins most human unhappiness and is a
common denominator across the entire range of mental disorders
from neuroses to psychoses, as seen, for example, in obsessive-
compulsive disorder (OCD) and schizophrenia. More than any other
species, we are beneficiaries and victims of a wealth of
emotional experience.

3) Progress in emotion research mirrors wider advances in
cognitive neurosciences where the idea of the brain as an
information processing system provides a highly influential
metaphor. An observation by the 19th-century psychologist,
William James (1842-1910), questions the ultimate utility of a
purely mind-based approach to human emotion. James surmised that
"if we fancy some strong emotion, and then try to abstract from
our consciousness of it all the feelings of its bodily symptoms,
we find we have nothing left behind, no mind-stuff out of which
the emotion can be constituted, and that a cold and neutral state
of intellectual perception is all that remains" (2). This
quotation highlights the fact that emotions as psychological
experiences have unique qualities, and it is worth considering
what these are. First, unlike most psychological states emotions
are embodied and manifest in uniquely recognizable, and
stereotyped, behavioral patterns of facial expression,
comportment, and autonomic arousal. Second, they are less
susceptible to our intentions than other psychological states
insofar as they are often triggered, in the words of James, "in
advance of, and often in direct opposition of our deliberate
reason concerning them" (2). Finally, and most importantly,
emotions are less encapsulated than other psychological states as
evident in their global effects on virtually all aspects of
cognition. This is exemplified in the fact that when we are sad
the world seems less bright, we struggle to concentrate, and we
become selective in what we recall. These latter aspects of
emotion and their influences on other psychological functions are
addressed here.

4) In summary: Emotion is central to the quality and range of
everyday human experience. The neurobiological substrates of
human emotion are now attracting increasing interest within the
neurosciences, motivated to a considerable extent by advances in
functional neuroimaging techniques. An emerging theme is the
question of how emotion interacts with and influences other
domains of cognition, in particular attention, memory, and
reasoning. The psychological consequences and mechanisms
underlying the emotional modulation of cognition provide the
focus of much new research.(3-5)

References (abridged):

1. K. J. Friston, et al., Neuroscience 59, 229 (1994)

2. W. James, The Principles of Psychology (Holt, New York, 1890)

3. A. Ohman, et al., J. Exp. Psychol. Gen. 130, 466 (2001)

4. J. L. Armony, et al., Neuropsychologia 40, 817 (2002)

5. K. Mogg, et al., Behav. Res. Ther. 35, 297 (1997)

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3. MEMORY AND THE MEMORY CONSOLIDATION HYPOTHESIS

The following points are made by James L. McGaugh (Science 2000
287:248):

1) A century has passed since Georg Mueller (1850-1934) and
Alfons Pilzecker proposed the perseveration-consolidation
hypothesis of memory (1). In pioneering studies with human
subjects, they found that memory of newly learned information was
disrupted by the learning of other information shortly after the
original learning and suggested that processes underlying new
memories initially persist in a fragile state and consolidate
over time. At the beginning of this new millennium, the
consolidation hypothesis still guides research investigating the
time-dependent involvement of neural systems and cellular
processes enabling lasting memory (2-4).

2) Clinical evidence that cerebral trauma induces loss of recent
memory was reported two decades before the publication of Mueller
and Pilzecker's monograph, and shortly after its publication it
was noted that the consolidation hypothesis provided an
explanation for such retrograde amnesia (5). Ignored for almost
half a century, the consolidation hypothesis was reinvigorated in
1949, when two papers reported that electroconvulsive shock
induced retrograde amnesia in rodents, triggering a burst of
studies of experimentally induced retrograde amnesia (2-4). That
same year, Donald O. Hebb (1904-1985) and Ralph W. Gerard (1900-
1974) proposed dual-trace theories of memory, suggesting that the
stabilization of reverberating neural activity underlying short-
term memory produces long-term memory.

3) The finding that protein synthesis inhibitors did not prevent
the learning of tasks but disrupted memory of the training
supports the view that there are (at least) two stages of memory
and indicates that protein synthesis is required only for
consolidation of long-term memory. The issue of whether short-
and long-term memory (and, perhaps, other memory stages) are
sequentially linked, as proposed by Hebb and Gerard, or act
independently in parallel (3) remains central to current inquiry.
The discovery that stimulant drugs administered within minutes or
hours after training enhance memory consolidation further
stimulated studies of memory consolidation (3). The use of
treatments administered shortly after training to impair or
enhance memory provides a highly effective and extensively used
method of influencing memory consolidation without affecting
either acquisition or memory retrieval.

4) In summary: The memory consolidation hypothesis proposed 100
years ago by Mueller and Pilzecker continues to guide memory
research. The hypothesis that new memories consolidate slowly
over time has stimulated studies revealing the hormonal and
neural influences regulating memory consolidation, as well as
molecular and cellular mechanisms.

References (abridged):

1. G. E. Müller and A. Pilzecker, Z. Psychol. 1, 1 (1900)

2. S. E. Glickman, Psychol. Bull. 58, 218 (1961) [ISI] ; J. L.
McGaugh and M. J. Herz, Memory Consolidation (Albion, San
Francisco, 1972); H. Weingartner and E. S. Parker, Eds., Memory
Consolidation (Erlbaum, Hillsdale, NJ, 1984); H. A. Lechner, L.
R. Squire, J. H. Byrne, Learn. Mem. 6, 77 (1999) [Free Full
Text]; M. R. Polster, L. Nadel, D. L. Schacter, J. Cogn.
Neurosci. 3, 95 (1991)

3. J. L. McGaugh, Science 153, 1351 (1966)

4. Y. Dudai, Neuron 17, 367 (1996)

5. T. Ribot, Diseases of Memory (Appleton, New York, 1882); W.
McDougall, Mind 10, 388 (1901) ; W. H. Burnham, Am. J. Psychol.
14, 382 (1903)

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4. CONSCIOUSNESS AND COMPLEXITY

The following points are made by Giulio Tononi and Gerald M.
Edelman (Science 1998 282:1846):

1) What is the neural substrate of conscious experience? While
William James (1842-1910) concluded that it was the entire brain
(1), recent approaches have attempted to narrow the focus: are
there neurons endowed with a special location or intrinsic
property that are necessary and sufficient for conscious
experience? Does primary visual cortex contribute to conscious
experience? Are brain areas that project directly to prefrontal
cortex more relevant than those that do not (2)? Although
heuristically useful, these approaches 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? Conferring this property on neurons seems to
constitute a category error, in the sense of ascribing to things
properties they cannot have (3).

2) The authors pursue a different approach. Instead of arguing
whether a particular brain area or group of neurons contributes
to consciousness or not, their strategy is to characterize the
kinds of neural processes that might account for key properties
of conscious experience. The authors emphasize two properties:
conscious experience is integrated (each conscious scene is
unified) and at the same time it is highly differentiated (within
a short time, one can experience any of a huge number of
different conscious states). Neurobiological data indicates that
neural processes associated with conscious experience are highly
integrated and highly differentiated.

3) Consciousness, as William James pointed out, is not a thing,
but a process or stream that is changing on a time scale of
fractions of seconds (1). As he emphasized, a fundamental aspect
of the stream of consciousness is that it is highly unified or
integrated. Integration is a property shared by every conscious
experience irrespective of its specific content: Each conscious
state comprises a single "scene" that cannot be decomposed into
independent components (5). Integration is best appreciated by
considering the impossibility of conceiving of a conscious scene
that is not integrated, that is, one which is not experienced
from a single point of view. A striking demonstration is given by
split-brain patients performing a spatial memory task in which
two independent sequences of visuospatial positions were
presented, one to the left and one to the right hemisphere. In
these patients, each hemisphere perceived a separate, simple
visual problem and the subjects were able to solve the double
task well. Normal subjects could not treat the two independent
visual sequences as independent, parallel tasks. Instead, they
combined the visual information into a single conscious scene and
into a single, large problem that was much more difficult to
solve.

4) In summary: Conventional approaches to understanding
consciousness are generally concerned with the contribution of
specific brain areas or groups of neurons. By contrast, the
authors consider what kinds of neural processes can account for
key properties of conscious experience. Applying measures of
neural integration and complexity, together with an analysis of
extensive neurological data, leads to a testable proposal -- the
dynamic core hypothesis -- about the properties of the neural
substrate of consciousness.(4)

References (abridged):

1. W. James, The Principles of Psychology (Holt, New York, 1890)

2. F. Crick and C. Koch, Cold Spring Harbor Symp. Quant. Biol.
55, 953 (1990) [Medline] ; Nature 375, 121 (1995); S. Zeki and A.
Bartels, Proc. R. Soc. London Ser. B 265, 1583 (1998)

3. G. Ryle, The Concept of Mind (Hutchinson, London, 1949)

4. G. M. Edelman, The Remembered Present (Basic Books, New York,
1989); ___ and G. Tononi, Consciousness: How Matter Becomes
Imagination (Basic Books, New York, in press); see also G. Tononi
and G. M. Edelman, in Consciousness, H. Jasper et al., Eds.
(Plenum, New York, 1998). pp. 245-280

5. In this context, a "conscious state" is an idealization,
exemplified by viewing a rapid succession of slides.

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5. NATURALIZING CONSCIOUSNESS: A THEORETICAL FRAMEWORK

The following points are made by Gerald M. Edelman (Proc. Nat.
Acad. Sci. 2003 100:5520):

1) Since Descartes' dualistic proposal (1), consciousness has
been considered by many to be outside the reach of physics (2),
or to require strange physics (3), or even to be beyond human
analysis (4). Over the last decade, however, there has been a
heightened interest in attacking the problem of consciousness
through scientific investigation (5). To succeed, such a program
must take account of what is special about consciousness while
rejecting any extraphysical assumptions. It must then construct a
theory to account for the properties of consciousness and provide
a framework for the design and interpretation of experiments.

2) Scientific understanding of consciousness in neural terms
requires the acceptance of a number of constraints. Any account
of consciousness must reject extraphysical tenets such as
dualism, and thus be physically based as well as evolutionarily
sound. Consciousness is not a thing but rather, as William James
(1842-1910) pointed out, a process that emerges from interactions
of the brain, the body, and the environment. It is a
multidimensional process with a rich variety of properties. Of
the properties, several stand out as particular challenges to any
theoretical effort. (i) The contrast between the diversity and
changeability of conscious states and the unitary appearance to
the conscious individual of each conscious state. This unity
requires the binding together of diverse sensory modalities that
show constructive features such as those seen in Gestalt
phenomena. (ii) The property of intentionality. This term refers
to the fact that consciousness is generally, but not always,
about objects or events. At the same time, consciousness is
modulated by attention and has wide access to memory and imagery.
(iii) Subjective feelings or qualia; the experiencing, for
example, of the redness of red, the warmness of warmth. This is
put pointedly by Nagel's phrase: "What is it like to be a bat?"
or, as he implies, any other conscious being.

3) Can we construct a neural framework to account for such a wide
range of properties? The author believes that present advances in
neuroscience permit us to do so, provided that we take into
account some constraints based on experimental observations.
These suggest that consciousness is not a property of a single
brain location or neuronal type, but rather is the result of
dynamic interactions among widely distributed groups of neurons.
A major system that is essential for conscious activity is the
thalamocortical system. The integrative dynamics of conscious
experience suggest that the thalamocortical system behaves as a
"functional cluster"; that is, it interacts mainly with itself.
Nevertheless, it also interacts with other brain systems. For
example, interactions between the basal ganglia and the
thalamocortical system are likely to influence the modulation of
consciousness by attention as well as the development of
automaticity through learning. The threshold of activity in these
neural structures is governed by diffuse ascending value systems,
such as the mesencephalic reticular activating system interacting
with the intralaminar nuclei of the thalamus, as well as
noradrenergic, serotonergic, cholinergic, and dopaminergic
nuclei.

4) In summary: Consciousness has a number of apparently disparate
properties, some of which seem to be highly complex and even
inaccessible to outside observation. To place these properties
within a biological framework requires a theory based on a set of
evolutionary and developmental principles. The author describes
such a theory, which aims to provide a unifying account of
conscious phenomena.

References (abridged):

1.  Descartes, R. (1975) in The Philosophical Works of Descartes,
eds. Haldane, E. & Ross, G. (Cambridge Univ. Press, Cambridge,
U.K.), Vol. 1 and 2

2.  Popper, K. & Eccles, J. F. (1977) The Self and Its Brain
(Springer, New York)

3.  Penrose, R. (1994) Shadows of the Mind: A Search for the
Missing Science of Consciousness (Oxford Univ. Press, New York)

4.  McGinn, C. (1991) The Problem of Consciousness: Essays Toward
a Resolution (Blackwell, Oxford)

5.  Metzinger, T., ed. (2000) Neural Correlates of Consciousness:
Empirical and Conceptual Questions (MIT Press, Cambridge, MA)

Proc. Nat. Acad. Sci. http://www.pnas.org

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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.

The following points are made by P. La Cerra and R. Bingham
(Proc. Nat. Acad. Sci. 1998 95:11290):

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.

7) 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".

Proc. Nat. Acad. Sci. http://www.pnas.org

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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.

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6. ORGANIZATION OF CELL ASSEMBLIES IN THE HIPPOCAMPUS

The following points are made by Kenneth D. Harris (Nature 2003
424:552):

1) Neurons can produce action potentials with high temporal
precision(1). A fundamental issue is whether, and how, this
capability is used in information processing. According to the
"cell assembly" hypothesis, transient synchrony of anatomically
distributed groups of neurons underlies processing of both
external sensory input and internal cognitive mechanisms(2-4).
Accordingly, neuron populations should be arranged into groups
whose synchrony exceeds that predicted by common modulation by
sensory input.

2) In sensory brain regions, the temporal pattern of spikes can
correlate precisely with the time course of an external stimulus.
In high-level structures, however, neural responses are often
more variable than is expected from sensory control. Is this
variability simply noise, or does it reflect the operation of
internal, non-sensory processes? In the hippocampus, the timing
of pyramidal cell spikes with respect to a clock ("theta") rhythm
is correlated with the animal's location in space(5). This timing
does not reflect the occurrence of external sensory events
precisely timed with respect to the theta rhythm, but rather must
arise because of dynamics internal to the brain, a conclusion
that is reinforced by the existence of similar phenomena during
non-spatial behaviors.

3) The authors that the spike times of hippocampal pyramidal
cells can be predicted more accurately by using the spike times
of simultaneously recorded neurons in addition to the animals
location in space. This improvement remained when the spatial
prediction was refined with a spatially dependent theta phase
modulation(5). The time window in which spike times are best
predicted from simultaneous peer activity is 10–30 ms, suggesting
that cell assemblies are synchronized at this timescale. Because
this temporal window matches the membrane time constant of
pyramidal neurons, the period of the hippocampal gamma
oscillation, and the time window for synaptic plasticity, the
authors propose that cooperative activity at this timescale is
optimal for information transmission and storage in cortical
circuits.

References (abridged):

1. Mainen, Z. F. & Sejnowski, T. J. Reliability of spike timing
in neocortical neurons. Science 268, 1503-1506 (1995)

2. Hebb, D. O. The Organization of Behavior (Wiley, New York,
1949)

3. Freiwald, W. A., Kreiter, A. K. & Singer, W. Synchronization
and assembly formation in the visual cortex. Prog. Brain Res.
130, 111-140 (2001)

4. Engel, A. K., Fries, P. & Singer, W. Dynamic predictions:
oscillations and synchrony in top-down processing. Nature Rev.
Neurosci. 2, 704-716 (2001)

5. O'Keefe, J. & Recce, M. L. Phase relationship between
hippocampal place units and the EEG theta rhythm. Hippocampus 3,
317-330 (1993)

Nature http://www.nature.com/nature

ScienceWeek http://www.scienceweek.com

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7. ON THE NEURONAL CODING OF NUMBER

The following points are made by Vincent Walsh (Current Biology
2003 13:R447):

1) We humans are fond of lauding our cognitive abilities and have
long sought to use them to distinguish man from other animals.
One of the first capacities identified as special to humans was
that of reason, and especially mathematical ability. This early
conceit is now a casualty of recent single unit recordings from
the prefrontal cortex of non-human primates, which show that the
representation of numerical quantity obeys the same
psychophysical constraints as other sensory and magnitude
systems. Studies of the single units, or "numerons", which
respond to numerical quantity suggest that the cognitive
representation of number may be closely linked to that of other
magnitudes, such as size and time.

2) Our ability to manipulate numbers or quantities may seem to be
one of the most complex of human achievements but, as with all
our other abilities, there are precedents or parallels in other
species. When it comes to counting or assessing whether an amount
of something is more than or less than some other amount, birds
do it (1), bees definitely do it (2) and, although I cannot
provide a reference, my money is also on educated fleas being
able to do it. Knowing how much food there is (estimated
quantity), how far away it is (distance), how long it will take
to get there (time) and how many competitors (specific quantity)
also want the food are all important factors that require
magnitude estimation of some sort (3).

3) Humans can of course carry out explicit computations that are
beyond the capabilities of other species, but behavioral studies
show that our basic quantity functions obey the same rules as
those of other animals. The best worked examples of this are in
the time domain: our ability to discriminate between two
intervals of time exhibits a Weber function (4), as does our
ability to discriminate between two numbers (5). This raises the
question of whether the neural instantiation of quantities -- of
whatever type, number, size or time -- shows the logarithmic
compression displayed in behavior, or whether some more abstract,
symbolic code is used to represent them. The answer to the
question has important consequences, because some theories of
cognitive processing are dependent on the existence of
propositional, symbolic representations which are independent of
the sensory qualities of the stimuli.

4) In summary: Whether the neuronal encoding of number is linear
or logarithmic divides cognitive neuroscientists working on
mathematical cognition. Recordings from the prefrontal cortex of
the monkey support the logarithmic hypothesis. Similarities
between number and the coding of other quantities are also
beginning to become apparent.

References (abridged):

1 Brannon, E.M., Wusthoff, C.J., Gallistel, C.R., and Gibbon, J.
(2001). Numerical subtraction in the pigeon: evidence for a
linear subjective number scale. Psychol. Sci. 12, 238-243

2 Renner, M. (1960). The contribution of the honey bee to the
study of the time sense. Cold Spring Harbour Symp. Quant Biol 25,
361-367

3 Galistel, C.R. and Gellman, R. (2000). Non-verbal numerical
cognition: from reals to integers. Trends Cogn. Neurosci. 4, 59-
65

4 Gibbon, J. (1977). Scalar expectancy theory and Weber's Law in
animal timing. Psychol. Rev. 84, 279-335

5 Dehaene, S. (1997). The Number Sense. (Penguin Books)

Current Biology http://www.current-biology.com

--------------------------------

COGNITIVE SCIENCE: NUMBERS AND COUNTING IN A CHIMPANZEE

In this context, let us define "animals" as all living multi-
cellular creatures other than humans that are not plants. In
recent decades it has become apparent that the cognitive skills
of many animals, especially non-human primates, are greater than
previously suspected. Part of the problem in research on
cognition in animals has been the intrinsic difficulty in
communicating with or testing animals, a difficulty that makes
the outcome of a cognitive experiment heavily dependent on the
ingenuity of the experimental approach. Another problem is that
when investigating the non-human primates, the animals whose
cognitive skills are closest to that of humans, one cannot do
experiments on large populations because such populations either
do not exist or are prohibitively expensive to maintain. The
result is that in the area of primate cognitive research reported
experiments are often "anecdotal", i.e., experiments involving
only a few or even a single animal subject. But anecdotal
evidence can often be of great significance and have startling
implications: a report, even in a single animal, of important
abstract abilities, numeric or conceptual, is worthy of
attention, if only because it may destroy old myths and point to
new directions in methodology. In 1985, T. Matsuzawa reported
experiments with a female chimpanzee that had learned to use
Arabic numerals to represent numbers of items. This animal (which
is still alive and whose name is "Ai") can count from 0 to 9
items, which she demonstrates by touching the appropriate number
on a touch-sensitive monitor. Ai can also order the numbers from
0 to 9 in sequence.

The following points are made by N. Kawai and T. Matsuzawa
(Nature 2000 403:39):

1) The author report an investigation of Ai's memory span by
testing her skill in numerical tasks. The authors point out that
humans can easily memorize strings of codes such as phone numbers
and postal codes if they consist of up to 7 items, but above this
number of items, humans find memorization more difficult. This
"magic number 7" effect, as it is known in human information
processing, represents an apparent limit for the number of items
that can be handled simultaneously by the human brain.

2) The authors report that the chimpanzee Ai can remember the
correct sequence of any 5 numbers selected from the range 0 to 9.

3) The authors relate that in one testing session, after choosing
the first correct number in a sequence (all other numbers still
masked), "a fight broke out among a group of chimpanzees outside
the room, accompanied by loud screaming. Ai abandoned her task
and paid attention to the fight for about 20 seconds, after which
she returned to the screen and completed the trial without
error."

4) The authors conclude: "Ai's performance shows that chimpanzees
can remember the sequence of at least 5 numbers, the same as (or
even more than) preschool children. Our study and others
demonstrate the rudimentary form of numerical competence in non-
human primates."

Nature http://www.nature.com/nature

ScienceWeek http://www.scienceweek.com

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8. TACTILE PERCEPTION, CORTICAL REPRESENTATION, AND THE BODILY
SELF

The following points are made by P. Haggard et al (Current
Biology 2003 13:R170):

1 The sensory information we receive from our own bodies is
unique, both from epistemological and neurological points of
view. Philosophers have noted the immediate, private quality of
bodily sensation. I can understand your visual percepts by
looking in the same direction as you, but understanding your
tactile sensation would require being in your skin! Rene
Descartes (1596-1650) took an additional step, arguing that
because bodily sensation is immediate, it is also reliable: “nor
was it without some reason that I believed that that body which,
by a special right, I call mine, belonged to me more properly and
closely than any other; for, in truth, I could never be separated
from it as from other bodies” (6th Meditation).

2) The reliability of bodily sensation implies accurate
transmission of peripheral information to the higher brain
centers of conscious perception. The authors argue that Descartes
was wrong, at least as regards the sense of touch: Higher
cortical regions which underlie tactile perception also provide
several top–down influences which modulate perception: so the
brain constructs our sense of the body, rather than passively
receiving it.

3) Bodily sensation is also unique in its neurophysiological
basis. The body has many different classes of sensory receptor,
each transducing a specific type of stimulus. Tactile perception
may have a special role in body representation, because the skin
forms the interface between the body and the outside world. Other
sensory systems, notably pain and body position sense, also
contribute to body representation. Nociception lacks the spatial
specificity of touch, and proprioceptive contributions to body
representation are difficult to dissociate from the tactile and
motor events normally correlated with them. So the brain's
processing of touch is perhaps the clearest way to study the
construction of our sense of our own body.

4) The structure and function of the peripheral and subcortical
somatosensory system is well known. Tactile information is
conveyed to the primary somatosensory cortex (SI) of the
contralateral hemisphere. Here, tactile perception and body
representation begin to converge. SI contains a somatotopic map
of the contralateral side of the body. Early studies emphasized
its role as a veridical, organized projection, faithfully
transmitting peripheral inputs. For example, intracranial
stimulation of sites in the SI map produces sensation on the
corresponding body part. More recent studies suggest that SI
processes may be modulated by context, in particular the general
perceptual experience of the body provided by other senses such
as vision.

References (abridged):

1 Baumeister, R.F. (1999). The self in social psychology.
(Philadelphia: Taylor & Francis)

2 Head, H. and Holmes, G. (1911). Sensory disturbances from
cerebral lesions. Brain 34, 102-254

3 Kennett, S., Taylor-Clarke, M., and Haggard, P. (2001).
Noninformative vision improves the spatial resolution of touch in
humans. Curr. Biol. 11, 1188-1191

4 Merzenich, M.M., Nelson, R.J., Stryker, M.P., Cynader, M.S.,
Schoppmann, A., and Zook, J.M. (1984). Somatosensory cortical map
changes following digit amputation in adult monkeys. J. Comp.
Neurol. 224, 591-605

5 Pavani, F., Spence, C., and Driver, J. (2000). Visual capture
of touch: Out-of-the-body experiences with rubber gloves.
Psychol. Sci. 11, 353-359

Current Biology http://www.current-biology.com

ScienceWeek http://www.scienceweek.com

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9. GRAMMAR VS. LANGUAGE IN NEUROLINGUISTICS

The following points are made by Massimo Piatelli-Palmarini
(Nature 2002 416:129):

1) Two styles of explaining the science of mind and behavior have
been competing for as long as anyone cares to remember:
empiricist, centering on habit formation, statistical learning,
imitation and association; and rationalist, focusing on the
projection of internally represented rules. Despite relentless
effort, the former has delivered rather meager results, whereas
the latter, with its pivotal concept of an internally represented
grammar, has produced the solid "conceptual cognitive
revolution".

2) For a rationalist cognitive scientist, a grammar is a finite
mental object, systematically assigning abstract structures to
all the well-formed expressions of a language -- that is, to each
member of a set that, for natural languages (such as Chinese or
Italian), is infinite and discrete. Infinite, because every
speaker of a language can produce and understand an unlimited
number of new grammatical sentences. Discrete, because continuous
modification of a sentence to change it into another is
impossible. No sentence could be halfway between "It's a good
car, but they don't sell it" and "It's a good car, but they don't
tell it."

3) A grammar capable of generating complex structures for all
well-formed sentences of a natural language must have recursive
rules, because phrasal constituents can contain other phrasal
constituents of the same or higher kinds ("The young doctor's
three beautiful sisters" is a noun phrase containing another noun
phrase; "The spy who came in from the cold" is a noun phrase
containing a sentence). Moreover, structural rules of sentence
formation can be applied recursively to embed relative clauses
embedding other relative clauses, without limit (as in "This is
the cat that killed the rat that ate the malt that lay in the
house that Jack built"). Because such grammars are finite,
whereas the languages they generate are infinite and contingently
shaped by use, it is advantageous, and methodologically cogent,
to consider the concept of grammar as primary, and that of
language as derived.

4) Since the mid-1950s, powerful formal criteria, derived from
analysis of the artificial languages of mathematics and computer
programming, have been applied to the study of natural languages
to determine principles by which a given class of grammars can
generate a given target language. A universal ('Chomsky')
hierarchy of grammars (automata) was established: the most
powerful class contains as a subclass the immediately less
powerful one, and so on. In tune with the dominant
empiricist–inductivist tradition of the 1950s, the first grammars
to be explored at the lowest level in the hierarchy were
probabilistic and finite-state. From a very large corpus of
ascertained utterances of the language, one can compute the
conditional probability that a word (or string of words) will
follow another.

Nature http://www.nature.com/nature

--------------------------------

A LANGUAGE IS MORE THAN WORDS

The following points are made by Geoffrey K. Pullum (Nature 2001
413:367):

1) In the popular view, a language is merely a fixed stock of
words. Purists worry about foreign loan-words; conservatives
decry slang; and groundless claims that there are hundreds of
Eskimo words for snow are constantly made in popular writing, as
if nothing matters about languages but their lexicons. But the
popular view cannot be right, because (as linguist Paul Postal
has observed) membership in the word stock of a natural language
is open.

2) Consider this example: "GM's new Zabundra makes even the
massive Ford Expedition look economical." If English had an
antecedently given set of words, then this expression would not
be an English sentence at all, because "Zabundra" is not a word
(we just invented it). Yet the sentence is not just grammatical
English, it is readily interpretable (it clearly implies that the
Zabundra is a large, fuel-hungry sports utility vehicle produced
by General Motors).

3) Similar points could be made regarding word borrowing,
personal names, scientific nomenclature, onomatopoeisis,
acronyms, loaned words, and so on; English is not a fixed set of
words. A more fundamental reason that a language cannot just be a
word stock is that expressions have syntactic structure. For
example, in most languages, the order of words can be
significant: "Mohammed will come to the mountain" contains the
same words as "The mountain will come to Mohammed", but the
expressions are very different.

Nature http://www.nature.com/nature

ScienceWeek http://www.scienceweek.com

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10. NEUROPSYCHIATRIC SYMPTOMS IN DEMENTIA AND COGNITIVE
IMPAIRMENT

The following points are made by C.G. Lyketsos et al (J. Am. Med.
Assoc. 2002 288:1475):

1) Dementia is a serious public health problem with an increasing
prevalence because of the aging of the population.(1) Dementia is
characterized by global cognitive decline sufficient to affect
functioning.(2) It is a chronic illness with seriously disabling
effects for patients, their families, and society.(2) Mild
cognitive impairment (MCI) describes cognitive impairment in
elderly persons not of sufficient severity to qualify for a
diagnosis of dementia.(3) Individuals with MCI have complaints of
impairment in memory or other areas of cognitive functioning
usually noticeable to those around them. In addition, their
performance on memory and cognitive tests is below that expected
for their age and education. However, their day-to-day
functioning is generally preserved. Several operational
definitions for MCI have been proposed.(3,4) Mild cognitive
impairment is a chronic condition and may be a precursor to
Alzheimer-type dementia.(4) Mild cognitive impairment is often
worrisome to patients and families, and is increasingly a
presenting complaint for care.

2) Neuropsychiatric symptoms are a common accompaniment of
dementia.(5) These include agitation, depression, apathy,
delusions, hallucinations, and sleep impairment. In some cases,
they cluster into syndromes, leading to the proposal of
operational criteria for specific dementia-associated psychotic
or mood disturbances. These symptoms have serious adverse
consequences for patients and caregivers, such as greater
impairment in activities of daily living, more rapid cognitive
decline, worse quality of life, earlier institutionalization, and
greater caregiver depression. Thus, the neuropsychiatric
accompaniments of dementia are serious conditions that are
increasingly becoming a focus of attention.

3) The authors report a population-based study to estimate the
prevalence of neuropsychiatric symptoms in dementia and MCI. A
total of 3608 participants were cognitively evaluated using data
collected longitudinally over 10 years and additional data
collected in 1999-2000 in 4 US counties. Dementia and MCI were
classified using clinical criteria and adjudicated by committee
review by expert neurologists and psychiatrists. A total of 824
individuals completed the Neuropsychiatric Inventory (NPI); 362
were classified as having dementia, 320 as having MCI; and 142
did not meet criteria for MCI or dementia. From their results,
the authors conclude: Neuropsychiatric symptoms occur in the
majority of persons with dementia over the course of the disease.
These are the first population-based estimates for
neuropsychiatric symptoms in MCI, indicating a high prevalence
associated with this condition as well. The authors suggest these
symptoms have serious adverse consequences and should be inquired
about and treated as necessary.

References (abridged):

1. Brookmeyer R, Gray S, Kawas C. Projections of Alzheimer's
disease in the United States and the public health impact of
delaying disease onset. Am J Public Health. 1998;88:1337-1342.

2. Rabins PV, Lyketsos CG, Steele C. Practical Dementia Care. New
York, NY: Oxford University Press; 1999.

3. Petersen RC, Stevens JC, Ganguli M, et al. Practice parameter:
Early detection of dementia: mild cognitive impairment (an
evidence-based review). Neurology. 2001;56:1133-1142.

4. Morris JC, Storandt M, Miller JP, et al. Mild cognitive
impairment represents early-stage Alzheimer disease. Arch Neurol.
2001;58:397-405.

5. Finkel SI, Costa e Silva J, Cohen G, et al. Behavioral and
psychological signs and symptoms of dementia. Int Psychogeriatr.
1996;8(suppl 3):497-500.

J. Am. Med. Assoc. http://www.jama.com

ScienceWeek http://www.scienceweek.com

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