Brain Function II: Evidence from Neuroanatomy and Perception

1. Brain, Mind, and Belief: The Quest for Truth Brain Function II: Evidence fromNeuroanatomy and Perception “Our neural pathways establish reruns of what has gone on before. Like the three-year-old who insists on watching The Little Mermaid over and over again, we cling to our warped illusions with a tenacious grip. Get your bloody hands off my illusion! Even though it makes us miserable, we prefer to place our faith in the disaster we have made.” Pam Grout

2. Where we have been • Figuring out how the brain works • Methods in general use • Lesion studies • Functional brain imaging • Guiding principles in current use • Tool-driven inquiry • Functional brain imaging • Misapplied metaphor • The brain is a computer • A better way • Think harder • Use evidence from linguistics

3. REVIEW Thinking harder • Avoid metaphorical thinking • The brain is not a computer • Not like a human being with paper & pencil & books • In fact it is not like anything else • It is itself: the brain

4. Where we are • The mind is a relational network system • As revealed by evidence from linguistics • We can study relational networks at different levels of precision • Abstract network notation • Narrow network notation • Hypothesis: • Relational networks are implemented in neural structures

5. Levels of precision • Abstract relational network notation • Narrow relational network notation • Neural structures • A node of narrow RN notation is implemented physically as a bundle of neurons

6. Where we are headed • Consider further evidence • Neuroanatomy • Perceptual neuroscience • Examine further findings on perception

7. “[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.” Functional bundles of neurons:Cortical columns Vernon Mountcastle, Perceptual Neuroscience (1998), p. 192

8. Compare: atom and molecule :: neuron and column of neurons The cortical (mini)column Cortical Column: a bundle of neurons that function together as a unit Molecule: a bundle of atoms that function together as a unit

9. Gray matter and white matter Gray matter White matter

10. Coronal section magnified From top to bottom, About 3 mm Has 6 layers

11. Microscopic views Different stains show different features

12. The node of narrow RN notationvis-à-vis neural structures • The node corresponds not to a single neuron but to a bundle of neurons • The cortical column • A column consists of 70-100 neurons stacked on top of one another • All neurons within a column act together • When a column is activated, all of its neurons are activated

13. Large-scale cortical anatomy • The cortex in each hemisphere • Appears to be a three-dimensional structure • But it is actually very thin and very broad • The grooves – sulci – are there because the cortex is “crumpled” in order to fit inside the skull

14. Topologically, the cortex of each hemisphere (not including white matter) is.. • Like a thick napkin, with • Area of about 1300 square centimeters • 200 sq. in. • 2600 sq cm for whole cortex • Thickness varying from 3 to 5 mm • Subdivided into six layers • Just looks 3-dimensional because it is “crumpled” in order to fit inside the skull

15. Topological essence of cortical structure • Each column represents a node • The network is thus a large two-dimensional array of nodes • Third dimension for • Internal structure of the nodes (columns) • Cortico-cortical connections (white matter)

16. Neurons, Columns, Cortex • At the small scale.. • Each column contains around 80 neurons • At a larger scale.. • Each column acts as a node of the cortical network • The cerebral cortex as an array* of columns: • Grey matter — columns of neurons • White matter — inter-column connections *Array: two dimensional (a lot simpler than 3-dimensional)

17. Composition of a typical minicolumn • Contains about 80 neurons • Range: 70 to 110 • Mostly pyramidal neurons • Cell bodies of these neurons are “stacked” vertically • (i.e., in a column – hence the name) • Fibers extending from the cell bodies • Many are vertical (especially those of pyramidal cells) • Some are horizontal • They connect to neighboring columns

18. Evidence for columns • Microelectrode penetrations of cortex • Electrode is small enough to detect activation in a single neuron • If perpendicular to cortical surface • Neurons all of same response properties • If not perpendicular • Neurons of different response properties

19. Column in a cat’s cortex fora point on the cat’s paw

20. Columns as functional units:Orientation of lines (visual cortex) Microelectrode penetrations K. Obermayer & G.G. Blasdell, 1993

21. Bundles of columns • Minicolumn – 30-50 microns diameter • Maxicolumn – a contiguous bundle of minicolumns (typically around 100) • 300-500 microns diameter • Dimensions vary from one part of cortex to another • In some areas at least, they are roughly hexagonal • (There are also larger bundles)

22. Columns of different sizes Minicolumn Larger column View: looking downward from top of column. So each circle represents a column

23. Cortical minicolumns: Quantities • Diameter of minicolumn: 30 microns • Neurons per minicolumn: 70-110 (avg. 75-80) • Minicolumns/mm2 of cortical surface: 1460 • Minicolumns/cm2 of cortical surface: 146,000 • Neurons under 1 sq mm of cortical surface: 110,000 • Approximate number of minicolumns in Wernicke’s area: 2,920,000 (at 20 sq cm for Wernicke’s area) • (Wernicke’s area is devoted to speech recognition) Cf. Mountcastle 1998: 96

24. Cortical column operation • The linguistic system operates as a network whose nodes are cortical columns • Columns do not store symbols • Their basic function: receive and send activation • 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

25. Integration and Broadcasting Now I’ll tell my friends! Broadcasting Integration Wow, I got activated!

26. Operations in neurocognitive networks • Activation moves along lines and through nodes • (along the pathways of the brain) • Integration • Broadcasting • Connection strengths are variable • A connection becomes stronger with repeated successful use • A stronger connection can carry greater activation

27. Basic answer to the what/how question:What goes on in those nodes of the network? Integration and Broadcasting • Broadcasting • To multiple locations • In parallel • Integration

28. Part of the network for FORK Each node in this diagram represents a cortical column C T M C — conceptual M — motor T — tactile V — visual V

29. Part of the network for FORK Each node in this diagram connects to a supporting subnet. For example, C T M Let’s zoom in on this one V

30. Zooming in on the “V” Node.. A network of visual features V FORK The cardinal node of this subnet Etc. etc. (many layers)

31. Some nodes of the cortical net for fork T Ar – Articulation Au – Auditory C – Conceptual M – Motor P – Phonological T – Tactile V – Visual M C Ar P V Au

32. Some nodes of the cortical net for fork T M C PP P V PA

33. Perception: the basic process • A bottom-up process • From primary perceptual area upwards • E.g. primary auditory, for auditory perception • Multiple steps of integration and broadcasting • Takes place in a perceptual area of cortex • E.g. auditory cortex for auditory perception • Works by integrating inputs to the associated sense organ • E.g. auditory input for auditory perception • Multiple steps of integration • From very simple • To more complex

34. Perception: Multiple steps of integration and broadcasting V DOG From lower levels up to higher levels

35. These are cortical (network) structures that have to be learned • Experiment by David Hubel and Torsten Wiesel • Kittens kept in dark room during critical period for developing vision • Exposed to vertical lines but not horizontal lines • Later, bumped into strings stretched horizontally in their path • Couldn’t see them • Their eyes received the information • But their brains couldn’t integrate it

36. Hints of what goes on in visual perception(multiple steps of integration and broadcasting)I: Shapes recognized by different low level columns

37. Hints of what goes on in visual perception(multiple steps of integration and broadcasting)II. Relatively higher level (but still quite low)

38. Hints of what goes on in visual perception(multiple steps of integration and broadcasting)III. At a somewhat higher level

39. Hints of what goes on in visual perception(multiple steps of integration and broadcasting)IV. Somewhat higher level Elementary shapes like these..

40. Hints of what goes on in visual perception(multiple steps of integration and broadcasting)IV. Somewhat higher level ..can be integrated into more complex formations

41. We see only the past • Perception is a bottom-up process • From primary perceptual area upwards • Step by step through multiple levels • Using network connections that have been established • These connections have been built step by step • From lower levels to higher levels • As a result of previous experience • The whole perceptual structure is built through experience • Therefore, it is based upon the past • Hence, we see nothing as it is now

42. Returning to work after 30 years http://www.youtube.com/watch?v=mFCCFS_lhA8 Play video

43. Perception: Refining the starting (simple) view • The simple (starting) view: • A single perceptual modality • Auditory perception in auditory cortex • using auditory information • Step by step from bottom up • Complications/Refinements • It is not confined to a single perceptual modality • Not just bottom-up • Not even confined to posterior cortex

44. The McGurk Effect http://www.youtube.com/watch?v=aFPtc8BVdJk • Acoustic syllable [ba] presented to subjects • with visual presentation of articulatory gestures for [ga] • Subjects typically heard [da] or [ga] • “Evidence has accumulated that visual speech modifies activity in the auditory cortex, even in the primary auditory cortex.” Mikko Sams (2006) • How does it work? • Visual input • Top-down processing

45. Refining the starting (simple-minded) view: I • It is not confined to a single perceptual modality • Example: The McGurk effect • Auditory perception affected by visual input • i.e., top-down processing from visual to auditory • Conceptual structure affects auditory perception • The influence of context on speech perception • She cooked it in the frying an • I’ll help you if I an

46. An important finding from neuroanatomy: Reciprocal connections An established fact of neuroanatomy: A connection from point A to point B in the cortex is generally accompanied by a connection from point B to point A Separate fibers (axons): (1) A to B, (2) B to A In short, cortico-cortical connections are generally bidirectional Hence, Bidirectional Processing A B

47. Bidirectional processing: reciprocal links excitatory inhibitory

48. Perception – Refining a simple-minded view: II • Not confined to a single perceptual modality • Example: The McGurk effect • Visual input affects auditory perception • Conceptual structure affects auditory perception • Not just bottom-up • Top-down processing fills in unsensed details • Not even confined to posterior cortex

49. Perception: All these lines represent bi-directional connections V DOG Etc. etc. (many layers)

50. A terminological problem • We need to distinguish • Perception narrowly conceived • The basic process of recognition • Single perceptual modality • Bottom-up processing • No motor involvement • Perception broadly conceived • Two different terms needed • Recognition (a.k.a. ‘microperception’) • Bottom-up process in a single perceptual modality • Perception (the broad conception) (a.k.a. ‘macroperception’)