Transcript PSYCHOLOGY 506b Cognitive Neuroscience Core Course …

Netherlands Graduate School of Linguistics
LOT Summer School 2006
Issues in the biology and evolution of
language
Massimo Piattelli-Palmarini
University of Arizona
Session 1 (June 12)
The birth of a paradigm:
Innatism versus selectivism
Plan of this course
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Today (Monday): The birth of selectivism and
the idea of parameters
Tuesday: Towards a genetics of language
Wednesday: Loss of speech
Thursday: The return of the laws of form
Friday: Contemporary biology and the
minimalist program
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Little guide to the readings
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General position papers on biolinguistics:
 Chomsky’s
Three factors
 My paper with Cedric Boeckx
 Freidin and Vergnaud
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Tutorials
 Boeckx
Chapter 5 on minimalism
 My handout on the Hauser, Chomsky and Fitch
versus Pinker and Jackendoff on evolution
 Christiansen and Kirby on language evolution
 NEW Simon Fisher The tangled web in Cognition
June 6, 06
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Little guide to the readings (2)
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“Representative” pieces
 Turing on morphogenesis
 Davidson and Erwin on Gene Networks
 Hill and Walsh on brain evolution
 Marcus and Fisher (on FOXP2)
 Gibbs on epigenetics
Punctual papers
 Somerville et al. on Williams syndrome
 Fisher on genes and language
 Scharf and White on Foxp2 in birds
 Uriagereka and me on the immune syntax
(unreadable)
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Some caveats
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The biology of language is a huge field
750 papers just on brain imaging and language
About 150 references (papers and books) on
the evolution of language, just in the last 10
years or so
About 25 genes (tentatively) identified already
as being language-related
Many other fields are relevant (molecular
genetics, evo-devo, neuroscience of cognition,
various pathologies, comparative cognitive
ethology etc.)
Not to mention, of course, linguistics, language
acquisition and psycholinguistics
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Some caveats
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Our strategy here:
Explore with a critical eye the “possibility” of a
biology of language
Its “logic” and its possible import
Privileging what we know (rather than what we
would like to know, but we don’t)
Concentrating on the strong points
Singling out the best cases (breakthroughs)
And plausible avenues of future development
With (yes!) some “fine” details that may, at first
blush, seem of scant interest to linguists
But they are not (I hope I will persuade you that
they are really very interesting)
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Three factors in language design
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(1) genetic endowment, which sets limits on the
attainable languages, thereby making language
acquisition possible;
(2) external data, converted to the experience that
selects one or another language within a narrow
range;
(3) principles not specific to FL.
Some of the third factor principles have the flavor of
the constraints that enter into all facets of growth
and evolution, and that are now being explored
intensively in the “evo-devo” revolution.
There are other third factor elements as well, among
them properties of the human brain that determine
what cognitive systems can exist. It also might turn
out that general cognitive principles that enter into
language acquisition pose conditions on FL design.
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Two varieties of pessimism
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Max Planck: A new scientific truth does not
triumph by convincing its opponents and
making them see the light, but rather because
its opponents eventually die, and a new
generation grow up that is familiar with it.
Noam Chomsky: New ideas circulate only
because, eventually, professors are
embarrassed by their students for confessing
they do not know about them.
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The innatist-selectivist explanatory
strategy:
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Enters linguistics via the Poverty of the
Stimulus (POS)
Explicit references (in earlier work by Chomsky)
to Luria and Delbruck, to Hubel and Wiesel and
to Monod and Jacob.
In continuity with the powerfully emerging trend
in molecular biology
Later reinforced by Fodor’s modularity
By data on language acquisition
And by the principles-and-parameters
framework
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Charles Darwin
(1809 -1882)
selection
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Jean-Baptiste de Lamarck
(1744 - 1829)
instruction
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A long-standing debate
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Instructive versus selective change and
adaptation
Revamped in immunology (around 1890)
Revamped in microbiology (Pasteur and Koch,
from 1880 onwards)
Koch’s postulate: one disease = one microbial
agent (cholera, typhus, tuberculosis etc.)
Doubts that bacteria could “have a genetics”
until about 1935
Frederick Griffith (1928): the “transforming
agent” of pneumococcus from harmless to
pathogenic
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A long-standing debate (continued)
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Avery, McLeod and McCarty (1944): the
transforming agent is DNA
Quite a shock to everyone (Nobel Prize 1983)
Further revamped by the discovery of the
healing power of antibiotics in the late Thirties
and Forties (penicillin, streptomycin,
chloramphenicol)
In particular, by the appearance of resistant
microbial strains
A debate about what?
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Two positions: The first
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The “inductivists” (Felix D’Hérelle et al.):
Adaptive mutations are induced by the external
agent (temperature, antibiotics, viruses,
metabolites etc.)
There are “directed adaptive heritable changes”
(induced adaptations)
The reference conceptual model: spontaneous
radioactive decay
(The probability of decaying is constant across
all atoms of a given isotope of that element)
And catalysis (the dominant conceptual model)
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Two positions: The second
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The “selectivists” (A. Gratia, F. M. Burnet et al.):
Mutations are spontaneous, with a stable fixed
average probability of occurrence (about 10-8
per locus per generation)
BUT
They occur independently of, in the absence of,
and prior to, any exposure to the environmental
factor.
No “directionality”.
At the 3rd Congress of Microbiology in New York,
in 1939, Andre’ Gratia declared: "Adaptation by
passive selection of pre-existing variants is the only
fact to be proven beyond any doubt" (GRATIA 1939)
Selection acts post hoc and “adaptation” is a
result of it
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Why do we care?
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Reference to these phenomena, and to
selectivist explanations, is ubiquitous in
Chomsky’s work (see his debate with Piaget)
Luria and Chomsky and Eric Lenneberg at MIT
created a bio-linguistics group meeting
regularly
The 1974 meeting at Endicott House
Fodor’s innatism and the pre-existence of all
concepts
Principles and parameters (ever since the late
Seventies)
Parameter-based language acquisition
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No learning:
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Rather the fixation of a handful of linguistic
parameters
Each having only two possible values
+ or A “cascade” of switches
One language?
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Mark Baker 2001, 2003
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A simple “knockdown” experiment
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Salvador E. Luria and Max Delbrück (1943)
“Mutation of bacteria from virus sensitivity to
virus resistance”, Genetics, Vol. 28, pp 491-511
Nobel Prize in 1969 with Alfred D. Hershey
Hall of fame of elegant experiments in biology
Inspiration from a slot-machine in a Country
Club in Bloomington Indiana
The very idea: Grow different cultures of
bacteria sensitive to a virus (a phage)
Make successive dilutions of samples from the
various cultures (successive generations)
Add the virus, then see how many resistant
colonies you obtain
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A simple “knockdown” experiment
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If the inductivists are right, then
You get an average constant percentage of
resistant mutants at each generation
If and only if, they have been exposed to the
virus.
If the selectivists are right, you get “a
distribution with an abnormally high variance”
All (or most) of the descendants of a mutant are
resistant
All (or most) of the descendants of a sensitive
wild type are wiped out
The presence of the virus allows us to make a
selection, but it is not the “inducing agent”
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A technical challenge:
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In order to ascertain the existence of resistant
mutants
You have to add the virus to the culture
But then it’s hard to decide whether the mutants
pre-existed or are “induced” by the virus
Luria’s and Delbrück’s solution
Fluctuations across generations.
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The Luria-Delbrück dilution experiment
Bacteria sensitive to the virus (a bacteriophage) in black.
Resistant mutants in red. Culture 1 harbors a 3rd generation mutant.
Culture 3 harbors a 1st generation mutant. The probability of
observing mutants varies very strongly. In fact, it is 1 or 0, depending
on whether the ancestor is or is not a mutant.
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The Luria-Delbrück dilution experiment
Had the mutation been “induced” by the exposure, we would
Expect a uniform probability of finding mutant colonies
(an average constant fraction of all later cultures would be mutants)
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Conclusion:
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“We consider the above results as proof that in
our case the resistance to virus is due to a
heritable change of the bacterial cell which
occurs independently of the action of the
virus.” (emphasis added)
Do we need successive dilutions?
Not necessarily
Same results with a different technique: Replica
Plating
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Replica plating (Joshua and Esther Lederberg 1952)
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“The procedure at no time exposes the indirectly
selected populations to the specific agent
[streptomycin]. These observations, therefore, are
cited as confirmation of previous evidence for the
participation of spontaneous mutation and
population selection in the heritable adaptation of
bacteria to new agents.” (emphasis added)
Joshua and Esther Lederberg (then at Madison Wisconsin)
Journal of Bacteriology, 1952
Joshua Lederberg, Nobel Prize 1959 “for studies on genetic
recombination and organization of the genetic material in
bacteria”
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1st important lesson:
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The selective agent does not induce the
mutation
It selects pre-existing mutants
Specific mutants pre-exist, regardless of all
encounters with the selective agent
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Next classic experiment
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Preceded, over many years, by a puzzle
(enzymatic adaptation)
Something you expected to happen but doesn’t.
Imagine the following cases:
(1) A new kind of combustion engine
Outputs 200 HPs when burning fuel A
Outputs 300 HPs when burning fuel B
What do you expect with a mixture of the two
fuels?
(2) Most patients recover in 30 days under
treatment with antibiotic A
Most patients recover in 60 days under
treatment with antibiotic B
What do you expect with a mixed treatment?
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Jacques Monod and the “double growth” (diauxia) (1940)
Log n
Log n
2
Glucose
1
Xylose
1
t
Log n
t
Glucose + Xylose
Expected
t
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Jacques Monod and the “double growth” (diauxia) (1940)
Log n
Log n
2
Glucose
1
Xylose
1
t
t
Log n
Glucose + Xylose
Actually observed
t
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Monod’s original (non-logarithmic) graphs
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In Monod’s doctoral dissertation (1940)
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“Microbiology will not make much progress until
we have solved this puzzle”.
It took 20 years to solve it:
Genetic regulation as a switching process
(not a “catalytic” one)
There are DNA sequences (genes) whose
exclusive function is the activation-inactivation
of adjacent genes.
Nobel Prize with François Jacob and André
Lwoff in 1965
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Monod’s and Jacob’s explanation
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The regulating mechanism and the final result
have been associated and fine-tuned by natural
selection
(the “inductor” is the very metabolite that the
enzyme - expressed by the activated gene “digests”)
But the process is totally “mechanical”
The regulator and “its” gene can be separately
disassembled and re-assembled at leisure
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QuickTime™ and a
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In the absence of lactose repressor blocks promoter
QuickTime™ and a
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In the presence of lactose repressor cannot bind
QuickTime™ and a
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Central points:
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Seeing clearly that a puzzle in a class of
phenomena stonewalls the discipline as a
whole
Even in the absence of the faintest idea on how
to solve the puzzle
Seeing clearly that the extant
conceptualizations (catalysis) cannot begin to
solve the puzzle
An educated guess that the solution of the
puzzle will reverberate much beyond that class
of phenomena
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The case of antibodies
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Selectivism, then 50 years of instructivism
Then, finally, selectivism
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How everything began: Paul Ehrlich
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The hypothesis Ehrlich
developed to explain
immunological phenomena was
the side-chain theory, which
described how antibodies - the
protective proteins produced
by the immune system - are
formed and how they react
with other substances.
This theory was based on an
understanding of the way in
which a cell was thought to
absorb and assimilate
nutrients.
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Ehrlich’s side-chain theory of
antibody production
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Each cell has on its surface a series of side
chains, or receptors, that function by
attaching to certain food molecules.
While each side chain interacts with a
specific nutrient - in the same manner as a
key fits into a lock - it can also interact with
disease-causing toxins produced by an
infectious agent.
When a toxin binds to a side chain, the
interaction is irreversible and blocks
subsequent binding and uptake of nutrients.
The body then tries to overwhelm the
obstruction by producing a great number of
replacement side chains — so many that they
cannot fit on the surface of the cell and
instead are secreted into the circulation.
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Ehrlich’s side-chain theory of
antibody production
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According to Ehrlich's theory, the
circulating side chains are the
antibodies, which are all gauged
to and able to neutralize the
disease-causing toxin and then
remain in the circulation, thus
immunizing the individual against
subsequent invasions by the
infectious agent.
Antibodies pre-exist.
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Karl Landsteiner and the dawn of biochemistry
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Small organic molecules of simple
structure, such as phenyl arsonates
and nitrophenyls, are not natural
danger signals, and do not provoke
antibodies when injected by
themselves.
However, antibodies can be raised
against them if the molecule is
attached covalently, by simple
chemical reactions, to a protein
carrier.
Such small molecules were termed
haptens (from the Greek haptein, to
fasten) by the immunologist Karl
Landsteiner, who first studied them
in the early 1900s.
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Karl Landsteiner and the dawn of
biochemistry
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Landsteiner found that animals
immunized with a hapten-carrier
conjugate respond by producing
distinct sets of antibodies.
No lock-and-key, but a more or less
good fit.
Antibodies drape themselves over
the charge outline of their target
antigen (instructivist model).
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Felix Haurowitz and the Template
Theory of Antibody Formation.
Selectivism is unvorstellbar
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Haurowitz and Landsteiner
collaborated to define the chemical
nature of antibodies.
"I concluded that the antibody must
be serum globulin and suggested
therefore that the antigen interferes
with the process of globulin
biosynthesis in such a way that
globulins complementarily adjusted
to the antigen are formed."
Antibody formation takes place by the
assembly of the antibody molecule on
the antigen (instructivist model).
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The 1984 Nobel Prize in Physiology or
Medicine: Niels Jerne
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Niels Jerne’s natural selection
theory for the immune system
was published in 1955 (!).
Lederberg and Nossall: one
lymphocyte clone = one antibody
Jerne proposed that the capacity
of the immune system to
recognize millions of foreign
molecules was predetermined,
already existing in the body
when the very first contact with
a foreign structure was made.
What then happened was merely
a selection amongst the naturally
occurring antibody population
resulting in an increase in
production of exactly those
antibodies which happened to
have a good fit for the structure.
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The 1984 Nobel Prize in Physiology or
Medicine: Niels Jerne
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Jerne's theory stood in great
contrast to prevailing theories at
that time (the unimaginable
wastefulness of selection), but
was rapidly confirmed and
extended.
Natural selection applies to the
cells of the immune system.
Those cells which happen to
have received the property to
produce a wanted antibody type
will upon vaccination be
rewarded with proliferative
capacity and survival.
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The adaptive immune response
The molecules of adaptive immunity (e.g., antibodies):
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Are generated by random DNA rearrangements
Pre-exist to the encounter with danger signals
(innate)
Are selected by specific stimuli
Repertoire is virtually unlimited (3D recognition of
molecular shapes)
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Grammar is a science that is more than 2000 years old,
whereas immunology has become a respectable part of
biology only during the past hundred years. Though both
sciences still face exasperating problems, this lecture attempts
to establish an analogy between linguistics and immunology,
between the descriptions of language and of the immune
system.
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An immunologist quotes a linguist
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At this point, I (Jerne) shall make a quotation
from Noam Chomsky concerning linguistics:
“The central fact to which any significant
linguistic theory must address itself is this: a
mature speaker can produce a new sentence of
his language on the appropriate occasion, and
other speakers can understand it immediately,
though it is equally new to them … Grammar is
a device that specifies the infinite set of wellformed sentences and assigns to each of these
one or more structural descriptions. Perhaps
we should call such a device a generative
grammar … which should, ideally, contain a
central syntactic component…, a phonological
component and a semantic component.”
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Jerne’s conclusion
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The inheritable “deep” structure of the immune
system is now known: certain chromosomes of
all vertebrate animals contain DNA segments
which encode the variable regions of antibody
polypeptides. Furthermore, experiments in
recent years have demonstrated the generative
capacities of this innate system.
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A remarkable insight:
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“It seems a miracle that young children easily
learn the language of any environment into
which they were born. The generative approach
to grammar, pioneered by Chomsky, argues
that this is only explicable if certain deep,
universal features of this competence are
innate characteristics of the human brain.
Biologically speaking, this hypothesis of an
inheritable capability to learn any language
means that it must somehow be encoded in the
DNA of our chromosomes. Should this
hypothesis one day be verified, then
linguistics would become a branch of
biology”. (emphasis added)
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Chomsky’s “Review of Skinner’s
‘Verbal Behavior’” (1959)
“The magnitude of the failure of this [the
behaviorist’s] attempt to account for
verbal behavior serves as a kind of
measure of the importance of the factors
omitted from consideration, and an
indication of how little is really known
about this remarkably complex
phenomenon”.
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A Review of Skinner’s “Verbal
Behavior” (1959)
“Study of the actual observed ability of a speaker
to distinguish sentences from non-sentences,
detect ambiguities, etc., apparently forces us to
the conclusion that this grammar is of an
extremely complex and abstract character, and
that the young child has succeeded in carrying
out what from the formal point of view, at least,
seems to be a remarkable type of theory
construction. Furthermore, this task is
accomplished in an astonishingly short time, to
a large extent independently of intelligence, and
in a comparable way by all children. Any
theory of learning must cope with these
facts.” (my emphasis)
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Jerry Fodor in the debate with
Piaget (1976)
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“…there must be some notion of learning that is
so incredibly different from the one we have
imagined that we don’t even know what it would
be like, as things now stand.”
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Another window of opportunity:
Selective visual deprivation
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Extreme specificity of the sensitivity of
individual neurons;
Modularity of the organization of the primary
visual cortex
Strong innate components
The “selective” (not instructive) nature of the
visual inputs
The effects of selective deprivation (shift of
allegiance)
The crucial importance of critical periods.
The crucial importance of competitive
mechanisms
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In essence: a whole new paradigm
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The specificity and fine-graininess of the innate
endowment
(pre-wired selective sensitivity to shapes,
modes of motion, edges, contrasts, etc.)
Strong modularity
The role of specific data (from experience) as
selectors (activators / suppressors)
The crucial role of critical periods
The crucial role of competition mechanisms
(winner-take-all)
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Our two protagonists
David Hubel
Torsten Wiesel
At Johns Hopkins and then at Harvard 1959-1962
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Our two protagonists
David Hubel
Torsten Wiesel
Nobel Prize in 1981
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The role of experience
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From their Nobel lectures
“Innate mechanisms endow the visual system with
highly specific connections, but visual experience
early in life is necessary for their maintenance and
full development.”
“Deprivation experiments demonstrate that neural
connections can be modulated by environmental
influences during a critical period of postnatal
development.”
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The role of experience (continuation)
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“Such sensitivity of the nervous system to the
effects of experience may represent the
fundamental mechanism by which the
organism adapts to its environment during the
period of growth and development.”
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A central reflection, an afterthought
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“Visual experience seems to have the power of
validating or vetoing not only the outcomes of
the process of differentiation but the process
itself”. (my emphasis)
Wiesel, T.N. 1982 Postnatal development of the
visual cortex and the influence of environment.
Nature, 299, 583-591.
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Blakemore, C., and Cooper, G. F. (1970). Development of the
brain depends on the visual environment. Nature , 228:477-478.
The result is that the “vertical”
cells multiply, while the
“horizontal” cells shrink and
degenerate.
Neither eye was ever closed.
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Optic nerve
Optic chasm
Optic tract
Lateral geniculate
body
Primary visual cortex
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(Drawing by Jeff Stripling)
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Area V1
Striate cortex
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QuickTime™ and a
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Area 17
http://webvision.med.utah.edu/imageswv/capas-cortex.jpg
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Quic kTime™ and a
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QuickTime™ and a
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QuickTime™ and a
TIFF (Uncompressed) decompressor
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The columnar organization of the
cortex
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In the years 1955-1959 Vernon B. Mountcastle
(at Johns Hopkins University) discovered the
columnar organization of the cortex
Basically, this means that, as we proceed
“vertically”, from the outside inwards,
we encounter groups of cells (of about 100 cells
each) that are very similar in their specialization
(they are sensitive to the same stimuli)
If, instead, we proceed “horizontally” (parallel to
the surface of the cortex), we encounter groups
of cells that have different specializations.
With “abrupt transitions in functional properties
which separate one column from the next”.
See http://cercor.oupjournals.org/cgi/content/full/13/1/2
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The “meaning” of a column
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In Hubel’s words:
A column = “a little machine that takes care of
contours in a certain orientation in a certain part
of the visual field”.
If the cells of one set are to be interconnected,
and to some extent isolated from neighboring
sets, it makes obvious sense to gather them
together.
The function of the visual cortex is the
transformation of information from circularly
symmetric form to orientation-specific form, and
the stepwise increase in complexity.
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Binocular cells
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A high proportion of cells in the primary
visual (striate) cortex receive inputs from
both eyes.
BUT
In the lateral geniculate body, cells
receive input from one eye only.
Hubel and Wiesel discovered that there is
a striking similarity of the corresponding
cells’ receptive fields in the two eyes, in
size, complexity, orientation and
position.
Presumably this forms the basis of the
fusion of the images in the two eyes.
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A wonderful online treatise on eye
and vision, with great images:

http://webvision.med.utah.edu/index.html
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The first “processing” station:
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The retinal ganglion cells are the “output” of the
retina
They act largely independently one from the
other to encode information
see Niremberg S. et al (2001) Nature Vol. 411,
pp. 698-701
They gather and integrate impulses from
several cells in the retina
Haldan Keffer Hartline (Nobel with Ragnar
Granit and George Wald in 1967) discovered in
1935 that there are basically three kinds of
such cells: The ON, the OFF and the ON-OFF
ganglion cells
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A subtle concept: The receptive field
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http://psych.hanover.edu/Krantz/receptive/
The region of the retina within which a local
change of brightness would cause the ganglion
cell to discharge (Hartline, 1935-38)
The interactive “annulus” (center and ring) that
causes a ganglion cell to discharge (Kuffler,
1953)
Includes the structure of the effective stimulus
(Hubel and Wiesel, 1956)
area of the visual field in which stimulation
leads to response of a particular sensory
neuron (Levine and Shefner, 1991)
Notice: The definition went from the retina to
the “outside world”
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See David Hubel’s online book Eye, Brain and Vision
http://neuro.med.harvard.edu/site/dh/bcontex.htm
No stimulus
On-center retinal ganglion cell
No stimulus
Off-center retinal ganglion cell
Stephen Kuffler (Johns Hopkins, ever since 1952)
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
This cell not only responds exclusively to a moving slit in an eleven
o'clock orientation but also responds to movement right and up, but hardly
at all to movement left and down.
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Responses to a long, narrow slit of light
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Orientation is crucial
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How narrow is the optimum angle?
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Typically it’s 10-20 degrees
Notice that the degree between two successive
hours on a clock dial is 30 degrees
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A typical
“vertical” cell
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A typical (vertically) directionally sensitive complex cell,
more sensitive to the top-down than to the bottom-up
displacement
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A remarkable fact (Pasko Rakic 1972)
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By the 26th gestational week the human
neocortex is already composed of a large
number of minicolumns in parallel vertical
arrays.
This remarkable regularity is revealed in
histological sections closely aligned with the
vertical axes of minicolumns.
At least at the level of the cortex, “modularity” is
quite precocious.
Columns vary between 300 and 500 µm in
transverse diameter, and do not differ
significantly in size between brains that vary in
size over three orders of magnitude (Bugbee
and Goldman-Rakic, 1983)
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Species-specificity of the critical
period
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The length of the critical period varies between
species.
In cats it is 3 to 4 months
And from clinical observations in humans (in
ophthalmology clinics) it may extend up to 5 10 years,
though the susceptibility to deprivation appears
to be most pronounced during the first year and
declines with age.
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The organization
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Cells of different complexities, whose receptive
fields are in the same part of the visual field and
which have the same optimal orientation, are
likely to be interconnected, whereas cells with
different optimal orientations are far less likely
to be interconnected.
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
S. M. Kosslyn, A. Pascual-Leone, et al Science Vol 284,
pp. 167-170,1999
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References
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Pathways of the Brain, chapters 16-17 and
Vernon Mountcastle Perceptual Neuroscience:
The Cerebral Cortex, Harvard University Press,
1998. See also Yves Burnod, An Adaptive
Neural Nework: The Cerebral Cortex (1990)
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The forming of maps and associations
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Cortical columns in sensory areas (auditory,
visual, somatosensory) form maps.
Regions of cortex adjacent to these maps are
associative, with the associations becoming
progressively higher level and more abstract
with greater distance from the sensory map.
For instance, the intensities of different
frequencies of sound waves are mapped on the
planum temporale,
while cortical areas in more inferior areas of the
temporal lobe process higher level information,
starting with sounds and moving to word
concepts.
http://www.ruf.rice.edu/~lngbrain/Farh/cc.html
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The famous deprivation experiments
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“In an animal that has undergone monocular
deprivation, the geniculate terminals with input
from the non-deprived eye take over much of
the space that would normally have been
occupied by terminals from the deprived eye”.
“The deprived eye input has shrunken down to
occupy the small strips lying between the
terminals of the non-deprived eye input”.
“Tangential electrode penetrations through
cortical layers reveal long expanses of cells
driven by the non-deprived eye interrupted by
small patches of cells that are either
unresponsive or driven by the deprived eye.”
From the Nobel lectures (emphasis added)
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Shift of allegiance, not un-responsiveness
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“Cells at later stages have shifted their
allegiance from the deprived to the nondeprived eye, rather than becoming
unresponsive”. (my - MPP - emphasis)
“This conclusion is supported by the
physiological findings that the large majority of
cells in superficial and deep layers respond
only to the stimulation of the normal eye”.
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Innateness
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It still seems remarkable that a cell should not
only be wired with the precision necessary to
produce complex or hyper-complex properties,
but should have a duplicate set of such
connections, one from each eye.
That this is hard wired at birth forms some of
the material of Torsten Wiesel’s lecture.
In vertical penetrations the preference remains
the same all the way through the cortex.
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Projections from one eye only (the ipsilateral one) in the adult
macaque’s striate cortex
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From Wiesel’s Nobel Lecture
Monocularly deprived
at 2 weeks for 18 months
1,256 cells
100 cells
ipsilateral
Ocular dominance histograms (Rhesus macaque)
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Ocular dominance histograms
Right eye closed at 2 weeks
for 18 months
At 1 year
for 1 year
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for 4 months
At 6 years
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The sooner, the worse, and no recovery
20-day-old monkey whose
right eye had been closed
since 8 days of age.
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right eye had been closed
from 21 to 30 days of age.
Tested after 4 years of normal
vision
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A more recent validation
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“Innate mechanisms endow the visual system
with highly specific connections, although the
specificity is initially blurred by a high degree of
exuberant growth”.
Pascal D. Zufferey, Fuzi Jin, Hiroyuki Nakamura,
Laurent Tettoni and Giorgio M. Innocenti European
Journal of Neuroscience Volume 1, Page 2669 August 1999
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A later generalization:
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The connective organization of an evolving
neuronal network is related to the effects of the
environment on this organization
by stabilization or degeneration of labile
synapses associated with functioning.
Learning, or the acquisition of an associative
property, is related to a characteristic variability
of the connective organization:
the interaction of the environment with the
genetic program is printed as a particular
pattern of such organization through neuronal
functioning.
A Theory of the Epigenesis of Neuronal Networks by Selective
Stabilization of Synapses, by Jean-Pierre Changeux, Philippe Courrege
and Antoine Danchin PNAS (1973) vol. 70; pp 2974-2978
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Another Nobel Prizewinner
(but for a very different kind of work)
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The theory of neuronal group selection (Neural
Darwinism) by Gerald Edelman (Basic Books,
1987)
Focus on perceptual categorization as it relates
to memory and learning.
He proposes that these functions could be
understood in terms of "neural Darwinism" —
the idea that higher brain functions are
mediated by developmental and somatic
selection upon anatomical and functional
variance occurring in each individual animal.
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“Overflow” of the paradigm onto
linguistics
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Essentially, detailed in my 1989 Cognition
paper “Evolution, selection and cognition: From
“learning” to parameter-setting in biology and in
the study of language”
In two parts, for electronic viability
Downloadable in pdf from my web-page
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