1 / 36

PSY303: Topographic maps and their development 1 of 4 Tom Stafford t.staffordshef.ac.uk handouts are available from:

Main Theme. Maps are ubiquitous in neural organisationCan we understand how they develop? Using computational modellingAlthough taking our examples from the visual system, approach speaks to themes of plasticity, development and innateness. Outline. What are topographic maps?Some examplesstructural featuresgeneral definitionHow do they develop?activity mediated plasticity involved.so, how could they develop in principle?

nizana
Download Presentation

PSY303: Topographic maps and their development 1 of 4 Tom Stafford t.staffordshef.ac.uk handouts are available from:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. PSY303: Topographic maps and their development 1 of 4 Tom Stafford t.stafford@shef.ac.uk *handouts are available from: http://tomstafford.staff.shef.ac.uk/teaching/psy303

    2. Main Theme Maps are ubiquitous in neural organisation Can we understand how they develop? Using computational modelling Although taking our examples from the visual system, approach speaks to themes of plasticity, development and innateness

    3. Outline What are topographic maps? Some examples structural features general definition How do they develop? activity mediated plasticity involved. so, how could they develop in principle?…. models Hebb rule locally connected neighbourhoods in cortex models and biology compared

    4. Retinotopic maps

    5. Ocular dominance stripes

    6. Orientation tuning

    7. Ocular dominance stripes

    8. Bearing a remarkable similarity to...

    9. …and...

    10. …and also maybe...

    11. A kettle from Dublin

    12. Orientation maps: Artificially colour rendered images

    13. Alternative views

    14. Optically imaged orientation maps

    16. Orientation tuning - monochrome maps

    17. Cooperativity of separate maps Orientation tuning and ocular dominance

    19. Topographic map - general definition

    20. How do maps form? Activity mediated plasticity global properties of macroscopic maps (e.g. retinotopy) determined by chemical gradients All maps: substantial refinement by ongoing neural activity spontaneous driven by external stimuli Neonatal plastic or critical period

    21. Evidence for activity mediated plasticity

    22. Ocular dominance in cats 1 Biased selectivity (Wiesel and Hubel,1963) suture one eyelid for period 1wk - 2.5mth postnatal. Record from randomly chosen cells in visual cortex. RESULT - almost all cells selective for normal (unsutured) eye. ‘Territorial encroachment’ (Hubel and Wiesel 1977) the area that might have been used by the sutured is not dormant - it is used by the normal eye

    23. 23.4 Effect of early closure of one eye on the distribution of cortical neurons. (Part 1) neuro3e-fig-23-04-1.jpg neuro3e-fig-23-04-1.jpg

    24. 23.5 The consequences of a short period of monocular deprivation at the critical period in the cat. neuro3e-fig-23-05-0.jpg neuro3e-fig-23-05-0.jpg

    25. 23.4 Effect of early closure of one eye on the distribution of cortical neurons. (Part 2) neuro3e-fig-23-04-2.jpg neuro3e-fig-23-04-2.jpg

    26. Ocular dominance in cats 2 Induced strabismus (‘squint’) decreases stereoscopic sensitivity (Hubel and Wiesel 1977) decrease in number of stereoscopically sensitive cells Confirmation of activity dependant effect (Stryker 1986) Possible that eye-suturing works in some obscure way not related to activity Stryker et al. blocked neural activity in visual cortex (using TTX) No ocular-dominance columns

    27. 23.9 Ocular dominance histograms obtained by electrophysiological recordings in cats. neuro3e-fig-23-09-0.jpg neuro3e-fig-23-09-0.jpg

    28. Orientation selectivity in ferrets (Chapman and Stryker 1993) Suturing leads to some (but not total) impairment of the development of orientation selectivity Infusion of TTX (blocks action potentials (APs) ) leads to total impairment Difference explained by spontaneous activity?

    29. Driven versus spontaneous activity Some ocular dominance before birth Also some orientation selectivity under suture. Retinal ganglion cells produce spontaneous waves of activity - don’t need external stimulus Clarification by Crair et al (1998)…..

    30. Development of orientation selectivity in cats Crair et al 1998 Single electrode recording from: cats binocularly deprived (BD) soon after birth normal cats Cells divided into those that responded most strongly to stimulus via eye contralateral and ipselateral to the cell.

    31. BD and normal compared (Contralateral only)

    32. ‘Contralateral’ and ‘ipselateral’compared (normal only)

    33. ‘Contralateral’ and ‘ipselateral’compared (BD only)

    34. Contralateral connections ‘coach’ ipselateral connections Compare to the recent experience of Scott Adams (creator of Dilbert) : http://itre.cis.upenn.edu/~myl/languagelog/archives/003708.html

    35. Spontaneous versus stimulus driven activity - review There is an early period of development that may involve innate signals This is followed by a critical period that relies on patterned (stimulus driven) neural activity in order to maintain and consolidate the map structure. Also true for ocular dominance (see review by Crowley and Katz)

    36. What determines the length of the critical period? Normally, dark rearing can be used to delay critical period closure in the visual system… Bartoletti et al (2004). Nature Neuroscience, 7(3), 215-26

    37. Summary Should understand what a topographic map is good example is orientation tuning in visual cortex general definition abstracts main features Should know of evidence that suggest that maps are formed by activity driven processes. Should be curious if simple formal rules can be found which generate the interesting complexity of topographic maps (and zebra stripes etc?)

More Related