Columnar Functions: Neural Basis of Perceptual Systems

1. Ling 411 – 13 Words in the Brain:Functional Webs

2. REVIEW Findings relating to columns(Mountcastle, Perceptual Neuroscience, 1998) • The column is the fundamental module of perceptual systems • probably also of motor systems • Perceptual functions are very highly localized • Each column has a very specific local function • This columnar structure is found in all mammals that have been investigated • The theory is confirmed by detailed studies of visual, auditory, and somatosensory perception in living cat and monkey brains

3. REVIEW Quote from Mountcastle “[T]he effective unit of operation…is not the single neuron and its axon, but bundles or groups of cells and their axons with similar functional properties and anatomical connections.” Vernon Mountcastle, Perceptual Neuroscience (1998), p. 192

4. Quote from Hjelmslev REVIEW The postulation of objects as something different from the terms of relationships is a superfluous axiom and consequently a metaphysical hypothesis from which linguistic science will have to be freed. Louis Hjelmslev Prolegomena to a Theory of Language (1943: 61)

5. Columnar Functions: Integration and Broadcasting Integration: A column is activated if it receives enough activation from Other columns Thalamus Can be activated to varying degrees Can keep activation alive for a period of time Broadcasting: An activated column transmits activation to other columns Exitatory Inhibitory Learning: adjustment of connection strengths and thresholds REVIEW

6. What matters is not ‘what’ but ‘where’ What distinguishes one kind of information from another is what it is connected to Lines and nodes are approximately the same all over Hence, uniformity of cortical structure Same kinds of columnar structure Same kinds of neurons Same kinds of connections Different areas have different functions because of what they are connected to REVIEW

7. REVIEW Operations in relational networks • Activation moves along lines and through nodes • Integration • Broadcasting • Connection strengths are variable • A connection becomes stronger with repeated successful use • A stronger connection can carry greater activation

8. REVIEW Operation of the Network • The linguistic system operates as distributed processing of multiple individual components – cortical columns • Columnar Functions • Integration: A column is activated if it receives enough activation from other columns • Can be activated to varying degrees • Can keep activation alive for a period of time • Broadcasting: An activated column transmits activation to other columns • Excitatory – contribution to higher level • Inhibitory – dampens competition at same level • Columns do not store symbols

9. Functional webs as neural basis of cognition • Earlier proposals (Pulvermüller 2002: p. 23) • Individual neurons (Barlow 1972) • Individual neurons too noisy and unreliable • Would require more information processing capacity than one neuron has • Mass activity and interference patterns in the entire cortex (Lashley 1950) • Better alternative: • Functional webs of neurons (Pulvermüller) • Even better • Functional webs of cortical columns • (not mentioned by Pulvermüller)

10. Pulvermüller’s functional webs • A large set of neurons that • Are strongly connected to each other • Are distributed over a set of cortical areas • Work together as a functional unit • Are functionally interdependent so that each is necessary for the optimal functioning of the web (2002: 24)

11. Deductions from findings about cortical columns • If linguistic structure is purely relational, then the properties of cortical structure identified earlier also apply to language • So they also apply to functional webs • A functional web is a subnetwork of the linguistic network • Consisting of nodes and their interconnections • Property I: Intra-column uniformity of function • Property II: Cortical topography • Property III: Nodal specificity • Property IV: Adjacency • Property V: Extension of II-IV to larger columns • Property VI: Competition

12. Deductions from findings about cortical columns • If linguistic structure is purely relational, then the properties of cortical structure identified earlier also apply to language • So they also apply to functional webs • Property I: Intra-column uniformity of function • Therefore, the nodes of functional webs are (implemented as) cortical columns

13. Deductions: Properties of Functional Webs • If linguistic structure is purely relational, as seems likely, then the properties of cortical structure identified earlier also apply to language • So they also apply to functional webs • Property I: Intra-column uniformity of function • Therefore, the nodes of functional webs are (implemented as) cortical columns • Property II: Cortical topography • Linguistic structure as a two-dimensional array of nodes • Therefore, every functional web is a two-dimensional array of columns

14. Deductions: Properties of Functional Webs • Properties of cortical structure applied to language: • Property I: Intra-column uniformity of function • Property II: Cortical topography • Property III: Nodal specificity • Every linguistic node has a specific function • So every node of a functional web has a specific function • This point represents a disagreement with Pulvermüller’s view • Property IV: Adjacency • Property V: Extension of II-IV to larger columns • Property VI: Competition

15. Support for Nodal Specificity: the paw area of a cat’s cortex REVIEW Column (node) represents specific location on paw

16. Pulvermüller’s functional webs • For example, a web for the word ‘cat’ • Pulvermüller: • A significant portion of the web’sneurons are active whenever the cat concept is being processed • The function of the web depends on the intactness of its member neurons • If neurons in the functional web are strongly linked, they should show similar response properties in neurophysiological experiments (2002:26)

17. A Memory Experiment (Pulverműller 2002: 26-27) • Performed with macaque monkeys • Delayed matching – monkey must remember • Monkey must keep in mind the shape or color of an object and perform a matching response after delay of several seconds • Neural activity detected in frontal and temporal lobes • Temporary lesion of frontal or temporal area leads to impaired stimulus specificity in other area • Supports the hypothesis of a functional web including sites in frontal and temporal areas

18. Pulvermüller’s line of reasoning • “If neurons in the functional web are strongly linked, they should show similar response properties in neurophysiological experiments. • “If the neurons of the functional web are necessary for the optimal processing of the represented entity, lesion of a significant portion of the network neurons must impair the processing of this entity. This should be largely independent of where in the network the lesion occurs. • “Therefore, if the functional web is distributed over distant cortical areas, for instance, certain frontal and temporal areas, neurons in both areas should (i) share specific response features and (ii) show these response features only if the respective other area is intact.” (2002: 26, see also 27)

19. Reasoning from memory experiment • Temporary lesion of frontal or temporal area leads to impaired stimulus specificity in other area • “Together, these data provide evidence that neurons in both temporal and frontal areas (a) showed the same specific response features and (b) showed these response features if and only if the respective other area was intact…” • Compares language impairment vis-à-vis Wernicke’s and Broca’s areas (2002: 28) Not so fast! … the same specific response features?

20. Elsewhere he writes “similar” “If neurons in the functional web are strongly linked, they should show similar response properties in neurophysiological experiments.” (2002:26) N.B.: similar – not same! • Similar: • Sharing some features • There may be differences with respect to other features

21. Pulvermüller’s reasoning (cont’d) “These results obtained in memory experiments with macaque monkeys are reminiscent of well-known facts from … investigation into acquired language disorders … . These … studies … showed that prefrontal and temporal areas are most crucial for language processing. They also showed that lesions in either area can lead to aphasia, which in the majority of cases include deficits in both language production … and perception … .” (2002: 28)

22. Pulvermüller on Wernicke’s aphasia “… patients with Wernicke’s aphasia have difficulty speaking…. These deficits are typical…and cannot be easily explained by assuming a selective lesion to a center devoted to language comprehension.” (2002: 36-37)

23. Pulvermüller’s hypothesis on phonological word forms “The functional webs realizing phonological word forms may be distributed over the perisylvian area of the dominant left hemishpere. Circles represent local neuron clusters and lines represent reciprocal connections between them.” Friedemann Pulvermüller, The Neuroscience of Language, 2002: 52

24. REVIEW Basic and complex functions • Phonological recognition is a basic function • Located in Wernicke’s area • Speaking is a complex function • A cooperative effort of several areas, including Broca’s area and Wernicke’s area • Phonological recognition is a necessary component of speaking Wernicke: “Primary functions alone can be referred to specific areas…. All processes which exceed these primary functions…are dependent on the fiber bundles, that is, association.” Aphasia Symptom Complex (1874)

25. REVIEW Wernicke’s Area and Speaking • Phonological images guide speech production • Phonological recognition monitors production • Compare.. • Painting without visual perception • Playing a piano without auditory perception • Conclusion: Of course phonological recognition (i.e. Wernicke’s area) plays a role in speech production

26. REVIEW Paraphrasing Pulvermüller …patients with Wernicke’s aphasia have difficulty speaking…. These deficits are typical…and cannot be easily explained by assuming a selective lesion to a center devoted to language comprehension. The Neuroscience of Language (2002) Altered quote: …patients with damage to the occipital lobe have difficulty drawing pictures…. These deficits are typical…and cannot be easily explained by assuming a selective lesion to a center devoted to visual perception.

27. Re-examining the monkey memory experiment(and revising Pulvermüller’s conclusion) • Compare short-term verbal memory • Hypothesis: reverberating activation between Broca’s area and Wernicke’s area • If one of those areas is impaired, the reverberating activity is disrupted, leading to diminished activity in the other area • Same principle could apply in memory test in macaque monkey • Reverberation between temporal lobe (recognition zone) and frontal lobe (action zone) • Does not require that the two areas share “same specific response features”

28. Conclusion:The components of a functional web are diverse • The phonological representation of a word may be seen as a functional web in the perisylvian area • But each component of the web has its own specific local function within that representation • For example, phonological recognition in Wernicke’s area • If they are all the same, why have many of them, spread out over different areas? Compare Property III: Nodal specificity

29. Deductions: Properties of Functional Webs • Properties of cortical structure applied to language: • Property I: Intra-column uniformity of function • Property II: Cortical topography • Property III: Nodal specificity • Every linguistic node has a specific function • So every node of a functional web has a specific function • This point represents a disagreement with Pulvermüller’s view • Property IV: Adjacency • Property V: Extension of II-IV to larger columns • Property VI: Competition

30. Elsewhere, Pulvermüller gets it right “…activation of the web, so to speak, completes itself as a result of the strong web-internal links. If the web of neurons is considered a memory representation of an object and each neuron to represent one particular feature of this object memory, the full ignition would be the neuronal correlate of the activation of the stored object representation. Such full activation of the object memory could occur if only a fraction of the features of the object are present in the actual input.” (2002: 29)

31. Why do the nodes in a web appear to have similar response features? • Not because each node has – on its own – response features similar to those of other nodes in the web • Simply because all the nodes are “tied together” in the web • Therefore, all respond when the whole web is ignited • Actually they have, individually, very different response features • E.g. in Wernicke’s area and in Broca’s area

32. Localizing components of Functional Webs • A functional web is spread over a wide area of cortex • Includes perceptual information • Relating to the meaning • Visual: occipital and temporal • Auditory: temporal • Somatosensory: parietal • As well as phonological information • Temporal, parietal, frontal • As well as specifically conceptual information • For nominal concepts, mainly in • Angular gyrus and/or middle temporal gyrus and/or BA 37 • (?) Maybe also supramarginal gyrus

33. Deductions: Properties of Functional Webs • Properties of cortical structure applied to language: • Property I: Intra-column uniformity of function • Property II: Cortical topography • Property III: Nodal specificity • Property IV: Adjacency • Adjacent linguistic nodes have similar linguistic functions • Therefore, in functional webs, nodes of related function are in adjacent locations • And, more closely related function, more closely adjacent

34. Property IV(b): A deduction from the adjacency property The nodes in each area of a functional web Constitute a subweb Their function fits the portion of cortex in which they are located For example, Phonological recognition in Wernicke’s area Visual subweb in occipital and lower temporal lobe Tactile subweb in parietal lobe Nodal specificity: Each node of a subweb also has a specific function within that of the subweb

35. Property IV(c): Functional specificity of subwebs • The nodes in each area of a functional web • Constitute a subweb • Each node of a subweb has a specific function within that of the subweb (Property III) • Each subweb has specific function within the web • Fits its location in the cortex • For example, • Visual subweb in occipital and lower temporal lobe • Tactile subweb in parietal lobe

36. Example: The meaning of dog • We know what a dog looks like • Visual information, in occipital lobe • We know what its bark sounds like • Auditory information, in temporal lobe • We know what its fur feels like • Somatosensory information, in parietal lobe • All of the above.. • constitute perceptual information • are subwebs with many nodes each • have to be interconnected into a larger web • along with further web structure for conceptual information

37. A phonological subweb: /bil/ Cardinal node for bill Subweb for bill bil bi- -il

38. A functional web showing two subwebs T C PP PR PA V M Control of articulation Visual features

39. Deductions: Properties of Functional Webs • If linguistic structure is purely relational, as seems likely, then the properties of cortical structure identified earlier also apply to language: • Property I: Intra-column uniformity of function • Property II: Cortical topography • Property III: Nodal specificity • Property IV: Adjacency • Property V: Competition • Contiguous linguistic nodes are in competition • E.g. , stop consonants • Property VI: Extension of II-IV to larger columns

40. Deductions: Properties of Functional Webs • If linguistic structure is purely relational, as seems likely, then the properties of cortical structure identified earlier also apply to language: • Property I: Intra-column uniformity of function • Property II: Cortical topography • Property III: Nodal specificity • Property IV: Adjacency • Property V: Competition • Property VI: Extension of II-IV to larger columns • Linguistic categories in neighboring cortical areas • (to be considered later)

41. Three more properties • Property VII: Hierarchy in functional webs • Property VIII: Cardinal nodes • Property IX: Reverberation

42. Property VII: Hierarchy in functional webs A functional web is hierarchically organized Bottom levels in primary areas Lower levels closer to primary areas Higher (more abstract) levels in Associative areas – e.g., angular gyrus Executive areas – prefrontal These higher areas are much larger in humans than in other mammals Property VII(a): Each subweb is likewise hierarchically organized

43. Hierarchy in a visual subweb A network of visual features V FORK Etc. etc. (many layers)

44. Properties of Hierarchy • Relates to general hierarchy in the cortex • Each level has fewer nodes than lower levels, more than higher levels • Compare • The organization of management of a corporation • Ranks in an army or navy

45. Property VIII: Cardinal nodes Every functional web has a cardinal node At the top of the entire functional web Unique to that concept For example, C/cat/ at “top” of the web for CAT Property VIII(a): Each subweb likewise has a cardinal node At the top level of the subweb Unique to that subweb For example, V/cat/ At the top of the visual subweb

46. (Part of) the functional web for the concept CAT The cardinal node for the entire functional web T C P A V M Cardinal nodes of subwebs

47. The Wernicke-Lichtheim concept node (1885) Where?

48. The “C” Node • Not just in one place • Conceptual information for a single word is widely distributed • Conceptual information is in different areas for different kinds of concepts • The second of these points and probably also the first were already recognized by Wernicke • But.. • There may be a single “C” node anyway as cardinal node of a distributed network

49. “C” node as cardinal node of a web For example, FORK Labels for Properties: C – Conceptual M – Motor T – Tactile V - Visual C T M V Each node in this diagram represents the cardinal node of a subweb of properties

50. Some connections of the “C” node for FORK Each node in this diagram represents the cardinal node of a subweb of properties For example, C T M Let’s zoom in on this one V