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Netherlands Graduate School of Linguistics LOT Summer School 2006 Issues in the biology and evolution of language Massimo Piattelli-Palmarini University.

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Presentation on theme: "Netherlands Graduate School of Linguistics LOT Summer School 2006 Issues in the biology and evolution of language Massimo Piattelli-Palmarini University."— Presentation transcript:

1 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

2 LOT Summer 2006Birth of a paradigm2 Plan of this course n Today (Monday): The birth of selectivism and the idea of parameters n Tuesday: Towards a genetics of language n Wednesday: Loss of speech n Thursday: The return of the laws of form n Friday: Contemporary biology and the minimalist program

3 LOT Summer 2006Birth of a paradigm3 Little guide to the readings n General position papers on biolinguistics: u Chomsky’s Three factors u My paper with Cedric Boeckx u Freidin and Vergnaud n Tutorials u Boeckx Chapter 5 on minimalism u My handout on the Hauser, Chomsky and Fitch versus Pinker and Jackendoff on evolution u Christiansen and Kirby on language evolution u NEW Simon Fisher The tangled web in Cognition June 6, 06

4 LOT Summer 2006Birth of a paradigm4 Little guide to the readings (2) n “Representative” pieces u Turing on morphogenesis u Davidson and Erwin on Gene Networks u Hill and Walsh on brain evolution u Marcus and Fisher (on FOXP2) u Gibbs on epigenetics Punctual papers u Somerville et al. on Williams syndrome u Fisher on genes and language u Scharf and White on Foxp2 in birds u Uriagereka and me on the immune syntax (unreadable)

5 LOT Summer 2006Birth of a paradigm5 Some caveats n The biology of language is a huge field n 750 papers just on brain imaging and language n About 150 references (papers and books) on the evolution of language, just in the last 10 years or so n About 25 genes (tentatively) identified already as being language-related n Many other fields are relevant (molecular genetics, evo-devo, neuroscience of cognition, various pathologies, comparative cognitive ethology etc.) n Not to mention, of course, linguistics, language acquisition and psycholinguistics

6 LOT Summer 2006Birth of a paradigm6 Some caveats n Our strategy here: n Explore with a critical eye the “possibility” of a biology of language n Its “logic” and its possible import n Privileging what we know (rather than what we would like to know, but we don’t) n Concentrating on the strong points n Singling out the best cases (breakthroughs) n And plausible avenues of future development n With (yes!) some “fine” details that may, at first blush, seem of scant interest to linguists n But they are not (I hope I will persuade you that they are really very interesting)

7 LOT Summer 2006Birth of a paradigm7 Three factors in language design n (1) genetic endowment, which sets limits on the attainable languages, thereby making language acquisition possible; n (2) external data, converted to the experience that selects one or another language within a narrow range; n (3) principles not specific to FL. n 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. n 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.

8 LOT Summer 2006Birth of a paradigm8 Two varieties of pessimism n 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. n Noam Chomsky: New ideas circulate only because, eventually, professors are embarrassed by their students for confessing they do not know about them.

9 LOT Summer 2006Birth of a paradigm9 The innatist-selectivist explanatory strategy: n Enters linguistics via the Poverty of the Stimulus (POS) n Explicit references (in earlier work by Chomsky) to Luria and Delbruck, to Hubel and Wiesel and to Monod and Jacob. n In continuity with the powerfully emerging trend in molecular biology n Later reinforced by Fodor’s modularity n By data on language acquisition n And by the principles-and-parameters framework

10 LOT Summer 2006Birth of a paradigm10 Charles Darwin Jean-Baptiste de Lamarck (1809 -1882) (1744 - 1829) selection instruction

11 LOT Summer 2006Birth of a paradigm11 A long-standing debate n Instructive versus selective change and adaptation n Revamped in immunology (around 1890) n Revamped in microbiology (Pasteur and Koch, from 1880 onwards) n Koch’s postulate: one disease = one microbial agent (cholera, typhus, tuberculosis etc.) n Doubts that bacteria could “have a genetics” until about 1935 n Frederick Griffith (1928): the “transforming agent” of pneumococcus from harmless to pathogenic

12 LOT Summer 2006Birth of a paradigm12 A long-standing debate (continued) n Avery, McLeod and McCarty (1944): the transforming agent is DNA n Quite a shock to everyone (Nobel Prize 1983) n Further revamped by the discovery of the healing power of antibiotics in the late Thirties and Forties (penicillin, streptomycin, chloramphenicol) n In particular, by the appearance of resistant microbial strains n A debate about what?

13 LOT Summer 2006Birth of a paradigm13 Two positions: The first n The “inductivists” (Felix D’Hérelle et al.): Adaptive mutations are induced by the external agent (temperature, antibiotics, viruses, metabolites etc.) n There are “directed adaptive heritable changes” (induced adaptations) n The reference conceptual model: spontaneous radioactive decay n (The probability of decaying is constant across all atoms of a given isotope of that element) n And catalysis (the dominant conceptual model)

14 LOT Summer 2006Birth of a paradigm14 Two positions: The second n 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) n BUT n They occur independently of, in the absence of, and prior to, any exposure to the environmental factor. n 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" (G RATIA 1939) n Selection acts post hoc and “adaptation” is a result of it

15 LOT Summer 2006Birth of a paradigm15 Why do we care? n Reference to these phenomena, and to selectivist explanations, is ubiquitous in Chomsky’s work (see his debate with Piaget) n Luria and Chomsky and Eric Lenneberg at MIT created a bio-linguistics group meeting regularly n The 1974 meeting at Endicott House n Fodor’s innatism and the pre-existence of all concepts n Principles and parameters (ever since the late Seventies) n Parameter-based language acquisition

16 LOT Summer 2006Birth of a paradigm16 No learning: n Rather the fixation of a handful of linguistic parameters n Each having only two possible values n + or - n A “cascade” of switches One language?

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19 LOT Summer 2006Birth of a paradigm19 Mark Baker 2001, 2003

20 LOT Summer 2006Birth of a paradigm20 A simple “knockdown” experiment 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

21 LOT Summer 2006Birth of a paradigm21 A simple “knockdown” experiment n If the inductivists are right, then n 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”

22 LOT Summer 2006Birth of a paradigm22 A technical challenge: n In order to ascertain the existence of resistant mutants n You have to add the virus to the culture n But then it’s hard to decide whether the mutants pre-existed or are “induced” by the virus n Luria’s and Delbrück’s solution n Fluctuations across generations.

23 LOT Summer 2006Birth of a paradigm23 The Luria-Delbr ü ck 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.

24 LOT Summer 2006Birth of a paradigm24 The Luria-Delbr ü ck 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)

25 LOT Summer 2006Birth of a paradigm25 Conclusion: n “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) n Do we need successive dilutions? n Not necessarily n Same results with a different technique: Replica Plating

26 LOT Summer 2006Birth of a paradigm26 Replica plating (Joshua and Esther Lederberg 1952)

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28 LOT Summer 2006Birth of a paradigm28 “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”

29 LOT Summer 2006Birth of a paradigm29 1st important lesson: n The selective agent does not induce the mutation n It selects pre-existing mutants n Specific mutants pre-exist, regardless of all encounters with the selective agent

30 LOT Summer 2006Birth of a paradigm30 Next classic experiment n Preceded, over many years, by a puzzle (enzymatic adaptation) n Something you expected to happen but doesn’t. n Imagine the following cases: n (1) A new kind of combustion engine n Outputs 200 HPs when burning fuel A n Outputs 300 HPs when burning fuel B n What do you expect with a mixture of the two fuels? n (2) Most patients recover in 30 days under treatment with antibiotic A n Most patients recover in 60 days under treatment with antibiotic B n What do you expect with a mixed treatment?

31 LOT Summer 2006Birth of a paradigm31 t Log n 1 2 1 Jacques Monod and the “double growth” (diauxia) (1940) t t Log n Xylose Glucose Glucose + Xylose Expected

32 LOT Summer 2006Birth of a paradigm32 t Log n 1 2 1 Jacques Monod and the “double growth” (diauxia) (1940) t t Log n Xylose Glucose Glucose + Xylose Actually observed

33 LOT Summer 2006Birth of a paradigm33 Monod’s original (non-logarithmic) graphs

34 LOT Summer 2006Birth of a paradigm34 In Monod’s doctoral dissertation (1940) n “Microbiology will not make much progress until we have solved this puzzle”. n It took 20 years to solve it: n Genetic regulation as a switching process n (not a “catalytic” one) n There are DNA sequences (genes) whose exclusive function is the activation-inactivation of adjacent genes. n Nobel Prize with François Jacob and André Lwoff in 1965

35 LOT Summer 2006Birth of a paradigm35 Monod’s and Jacob’s explanation n The regulating mechanism and the final result have been associated and fine-tuned by natural selection n (the “inductor” is the very metabolite that the enzyme - expressed by the activated gene - “digests”) n But the process is totally “mechanical” n The regulator and “its” gene can be separately disassembled and re-assembled at leisure

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37 LOT Summer 2006Birth of a paradigm37 In the absence of lactose repressor blocks promoter

38 LOT Summer 2006Birth of a paradigm38 In the presence of lactose repressor cannot bind

39 LOT Summer 2006Birth of a paradigm39 Central points: n Seeing clearly that a puzzle in a class of phenomena stonewalls the discipline as a whole n Even in the absence of the faintest idea on how to solve the puzzle n Seeing clearly that the extant conceptualizations (catalysis) cannot begin to solve the puzzle n An educated guess that the solution of the puzzle will reverberate much beyond that class of phenomena

40 LOT Summer 2006Birth of a paradigm40 The case of antibodies n Selectivism, then 50 years of instructivism n Then, finally, selectivism

41 LOT Summer 2006Birth of a paradigm41 How everything began: Paul Ehrlich n 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. n This theory was based on an understanding of the way in which a cell was thought to absorb and assimilate nutrients.

42 LOT Summer 2006Birth of a paradigm42 Ehrlich’s side-chain theory of antibody production n Each cell has on its surface a series of side chains, or receptors, that function by attaching to certain food molecules. n 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. n When a toxin binds to a side chain, the interaction is irreversible and blocks subsequent binding and uptake of nutrients. n 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.

43 LOT Summer 2006Birth of a paradigm43 Ehrlich’s side-chain theory of antibody production n 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. n Antibodies pre-exist.

44 LOT Summer 2006Birth of a paradigm44 Karl Landsteiner and the dawn of biochemistry n 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. n However, antibodies can be raised against them if the molecule is attached covalently, by simple chemical reactions, to a protein carrier. n 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.

45 LOT Summer 2006Birth of a paradigm45 Karl Landsteiner and the dawn of biochemistry n Landsteiner found that animals immunized with a hapten-carrier conjugate respond by producing distinct sets of antibodies. n No lock-and-key, but a more or less good fit. n Antibodies drape themselves over the charge outline of their target antigen (instructivist model).

46 LOT Summer 2006Birth of a paradigm46 Felix Haurowitz and the Template Theory of Antibody Formation. Selectivism is unvorstellbar n Haurowitz and Landsteiner collaborated to define the chemical nature of antibodies. n "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." n Antibody formation takes place by the assembly of the antibody molecule on the antigen (instructivist model).

47 LOT Summer 2006Birth of a paradigm47 The 1984 Nobel Prize in Physiology or Medicine: Niels Jerne n Niels Jerne’s natural selection theory for the immune system was published in 1955 (!). n Lederberg and Nossall: one lymphocyte clone = one antibody n 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.

48 LOT Summer 2006Birth of a paradigm48 The 1984 Nobel Prize in Physiology or Medicine: Niels Jerne n Jerne's theory stood in great contrast to prevailing theories at that time (the unimaginable wastefulness of selection), but was rapidly confirmed and extended. n 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.

49 LOT Summer 2006Birth of a paradigm49 The adaptive immune response The molecules of adaptive immunity (e.g., antibodies): n Are generated by random DNA rearrangements n Pre-exist to the encounter with danger signals (innate) n Are selected by specific stimuli n Repertoire is virtually unlimited (3D recognition of molecular shapes)

50 LOT Summer 2006Birth of a paradigm50 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.

51 LOT Summer 2006Birth of a paradigm51 An immunologist quotes a linguist n At this point, I (Jerne) shall make a quotation from Noam Chomsky concerning linguistics: n “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 well- formed 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.”

52 LOT Summer 2006Birth of a paradigm52 Jerne’s conclusion n 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.

53 LOT Summer 2006Birth of a paradigm53 A remarkable insight: n “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)

54 LOT Summer 2006Birth of a paradigm54 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”.

55 LOT Summer 2006Birth of a paradigm55 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)

56 LOT Summer 2006Birth of a paradigm56 Jerry Fodor in the debate with Piaget (1976) n “…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.”

57 LOT Summer 2006Birth of a paradigm57 Another window of opportunity: Selective visual deprivation n Extreme specificity of the sensitivity of individual neurons; n Modularity of the organization of the primary visual cortex n Strong innate components n The “selective” (not instructive) nature of the visual inputs n The effects of selective deprivation (shift of allegiance) n The crucial importance of critical periods. n The crucial importance of competitive mechanisms

58 LOT Summer 2006Birth of a paradigm58 In essence: a whole new paradigm n The specificity and fine-graininess of the innate endowment n (pre-wired selective sensitivity to shapes, modes of motion, edges, contrasts, etc.) n Strong modularity n The role of specific data (from experience) as selectors (activators / suppressors) n The crucial role of critical periods n The crucial role of competition mechanisms (winner-take-all)

59 LOT Summer 2006Birth of a paradigm59 David Hubel Torsten Wiesel Our two protagonists At Johns Hopkins and then at Harvard 1959-1962

60 LOT Summer 2006Birth of a paradigm60 David Hubel Torsten Wiesel Our two protagonists Nobel Prize in 1981

61 LOT Summer 2006Birth of a paradigm61 The role of experience 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.”

62 LOT Summer 2006Birth of a paradigm62 The role of experience (continuation) “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.”

63 LOT Summer 2006Birth of a paradigm63 A central reflection, an afterthought “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.

64 LOT Summer 2006Birth of a paradigm64 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.

65 LOT Summer 2006Birth of a paradigm65 Primary visual cortex Lateral geniculate body Optic chasm Optic nerve Optic tract

66 LOT Summer 2006Birth of a paradigm66 Area V1 Striate cortex Area 17 (Drawing by Jeff Stripling)

67 LOT Summer 2006Birth of a paradigm67 Area 17

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71 LOT Summer 2006Birth of a paradigm71 The columnar organization of the cortex n In the years 1955-1959 Vernon B. Mountcastle (at Johns Hopkins University) discovered the columnar organization of the cortex n Basically, this means that, as we proceed “vertically”, from the outside inwards, n we encounter groups of cells (of about 100 cells each) that are very similar in their specialization (they are sensitive to the same stimuli) n 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”. n See

72 LOT Summer 2006Birth of a paradigm72

73 LOT Summer 2006Birth of a paradigm73 The “meaning” of a column 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.

74 LOT Summer 2006Birth of a paradigm74 Binocular cells n A high proportion of cells in the primary visual (striate) cortex receive inputs from both eyes. n BUT n 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.

75 LOT Summer 2006Birth of a paradigm75 A wonderful online treatise on eye and vision, with great images: n

76 LOT Summer 2006Birth of a paradigm76 The first “processing” station: n The retinal ganglion cells are the “output” of the retina n They act largely independently one from the other to encode information n see Niremberg S. et al (2001) Nature Vol. 411, pp. 698-701 n They gather and integrate impulses from several cells in the retina n 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

77 LOT Summer 2006Birth of a paradigm77 A subtle concept: The receptive field 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”

78 LOT Summer 2006Birth of a paradigm78 On-center retinal ganglion cell Off-center retinal ganglion cell No stimulus Stephen Kuffler (Johns Hopkins, ever since 1952) See David Hubel’s online book Eye, Brain and Vision

79 LOT Summer 2006Birth of a paradigm79 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.

80 LOT Summer 2006Birth of a paradigm80 Responses to a long, narrow slit of light Orientation is crucial

81 LOT Summer 2006Birth of a paradigm81 How narrow is the optimum angle? n Typically it’s 10-20 degrees n Notice that the degree between two successive hours on a clock dial is 30 degrees

82 LOT Summer 2006Birth of a paradigm82 A typical “vertical” cell

83 LOT Summer 2006Birth of a paradigm83 A typical (vertically) directionally sensitive complex cell, more sensitive to the top-down than to the bottom-up displacement

84 LOT Summer 2006Birth of a paradigm84 A remarkable fact (Pasko Rakic 1972) 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)

85 LOT Summer 2006Birth of a paradigm85 Species-specificity of the critical period 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.

86 LOT Summer 2006Birth of a paradigm86 The organization 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.

87 LOT Summer 2006Birth of a paradigm87 S. M. Kosslyn, A. Pascual-Leone, et al Science Vol 284, pp. 167-170,1999

88 LOT Summer 2006Birth of a paradigm88 References 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)Yves Burnod, An Adaptive Neural Nework: The Cerebral Cortex

89 LOT Summer 2006Birth of a paradigm89 The forming of maps and associations 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. n

90 LOT Summer 2006Birth of a paradigm90 The famous deprivation experiments “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)

91 LOT Summer 2006Birth of a paradigm91 Shift of allegiance, not un-responsiveness “Cells at later stages have shifted their allegiance from the deprived to the non- deprived 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”.

92 LOT Summer 2006Birth of a paradigm92 Innateness 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.

93 LOT Summer 2006Birth of a paradigm93 Projections from one eye only (the ipsilateral one) in the adult macaque’s striate cortex

94 LOT Summer 2006Birth of a paradigm94 Ocular dominance histograms (Rhesus macaque) From Wiesel’s Nobel Lecture Monocularly deprived at 2 weeks for 18 months 1,256 cells 100 cells ipsilateral

95 LOT Summer 2006Birth of a paradigm95 Ocular dominance histograms Right eye closed at 2 weeks for 18 months At 10 weeks for 4 months At 1 year for 1 year At 6 years for 1and 1/2 years

96 LOT Summer 2006Birth of a paradigm96 20-day-old monkey whose right eye had been closed since 8 days of age. Adult monkey whose right eye had been closed from 21 to 30 days of age. Tested after 4 years of normal vision The sooner, the worse, and no recovery

97 LOT Summer 2006Birth of a paradigm97 A more recent validation “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

98 LOT Summer 2006Birth of a paradigm98 A later generalization: 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

99 LOT Summer 2006Birth of a paradigm99 Another Nobel Prizewinner (but for a very different kind of work) 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.

100 LOT Summer 2006Birth of a paradigm100 “Overflow” of the paradigm onto linguistics n Essentially, detailed in my 1989 Cognition paper “Evolution, selection and cognition: From “learning” to parameter-setting in biology and in the study of language” n In two parts, for electronic viability n Downloadable in pdf from my web-page

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