Receptive Field Dynamics in Adult Primary Visual Cortex

Charles D. Gilbert & Torsten N. Wiesel

Psych 3FA3E

Neurobiology of Learning and Memory

Dr. Hong-jin Sun

Tuesday, October 7 2008

Abdullah Mayo

Barbara Fenesi

Charles Schandl

Charmaine Silveira Da Graca Costa

Margaret Cronyn

Sarah Babcock

Barbara

GROUP B3:

Schedule Aims

Key Terms Methods

Initial Preparation Experimental Procedures

Results Cortical Sites (Short-term and Long-term effects) LGN

Conclusions Horizontal Connections

Related Studies

Barbara

Aims In spite of a Scotoma,

the cortical representations of damaged cells in the visual cortex form new connections

Scotoma: An area of loss or impairment of visual acuity surrounded by a field of normal or

relatively well-preserved vision

Barbara

Aims Primary visual

cortex is capable of cortical topographic reorganization

Topographic Mapping: Mapping of the organization of the cells in the visual cortex corresponds to the organization in the spatial field

Barbara

Aims Horizontal

connections increase plasticity, and improve cortical input

Horizontal connections – pyramidal cells that link columns with shared orientation preference;allow cells to integrate visual information from outside their receptive

fields

Barbara

Aims Topographical

reorganization occurs within superficial layers of the visual cortex and not in earlier visual pathway structures such as the LGN

LGN (Lateral Geniculate Nucleus) - Located in the thalamus; receives information from the retina and sends projections directly to the primary visual cortex

Barbara

Aims Receptive field structure changes may occur

continuously during normal vision well past adulthood

Receptive Field - A small restricted spatial region of the sensory

field

Barbara

Methods

Initial Preparation Electrophysiology

and lesions were carried out on retina of anesthetized, paralyzed cats and monkeys

Receptive Field Map - show ‘minimum response’ fields for cells in the superficial layers

Abdullah

Methods

Procedure The lesions were

made in the parafoveal retina

Destroyed outer retinal cells

Positions of receptive fields relative to the lesions were determined

Initial lesions followed by lesions after 2 months

Parafoveal Vision

Abdullah

Methods Receptive field maps generated by mapping electrode

activity in Cortex and LGN Horseley-Clarke coordinates to map LGN Retrograde tracers in the cortex on either side of the

cortical scotoma Cortex and LGN compared

Horseley-Clarke - Apparatus helps make 3-D map of brain in Cartesian coordinates (x, y, and z)

Abdullah

Results Cortex

Short-term greater

expansion of receptive fields originally located near the boundary of the

lesion shift in receptive

field position

Charles

Results Long-term

for 2 month results after lesion

Receptive field size was not as great when compared to receptive field size immediately after lesion

Large shifts in field position Receptive fields of cells

shifted from the lesioned part of the retina to positions immediately

surrounding it

Charles

Results

Additional characteristics of recovered cortex - overrepresentation of perilesion retina, enlarged fields at the edge of the scotoma, bipartite fields

Charles

Results

Lateral Geniculate Nucleus (LGN) 1mm silent area

remained after 2 months

None of the characteristics of recovered cortex observed

Charles

Conclusions

Horizontal Connections Transmission of visual information

(immediate and long term) may be mediated by the long-range horizontal connections

Extent of long-range horizontal connections approximated that of the area of reorganization

Overall orientation map stays the same

Charles

Related Studies A quantitative measure for short-term cortical plasticity

in human vision (MK Kapadia, CD Gilbert, and G Westheimer) 1994 Dynamics of vision studied in humans, using artificial

scotoma Similar conclusions about horizontal connections

Future implications Plasticity of neuronal mechanisms Progress in Visual degenerative disorders

Abdullah

The End

Questions or Comments?

Abdullah

References Gilbert C.D. and Wiesel T.N. (1992). Receptive field

dynamics in adult primary visual cortex. Nature 356: 150– 52. Retrived from: http://dx.doi.org/10.1038/356150a0

Kapadia, M.K., Gilbert, C.D., and Westheimer, G. (1994). A quantitative measure for short-term cortical plasticity in human vision. J. Neurosci. 14, 451-457. Retrieved from: http://www.jneurosci.org/cgi/reprint/14/1/451