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J+Vis
2015 ; 15
(16
): 3
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Multimap formation in visual cortex
#MMPMID26641946
Jain R
; Millin R
; Mel BW
J Vis
2015[]; 15
(16
): 3
PMID26641946
show ga
An extrastriate visual area such as V2 or V4 contains neurons selective for a
multitude of complex shapes, all sharing a common topographic organization.
Simultaneously developing multiple interdigitated maps--hereafter a
"multimap"--is challenging in that neurons must compete to generate a diversity
of response types locally, while cooperating with their dispersed same-type
neighbors to achieve uniform visual field coverage for their response type at all
orientations, scales, etc. Previously proposed map development schemes have
relied on smooth spatial interaction functions to establish both topography and
columnar organization, but by locally homogenizing cells' response properties,
local smoothing mechanisms effectively rule out multimap formation. We found in
computer simulations that the key requirements for multimap development are that
neurons are enabled for plasticity only within highly active regions of cortex
designated "learning eligibility regions" (LERs), but within an LER, each cell's
learning rate is determined only by its activity level with no dependence on
location. We show that a hybrid developmental rule that combines spatial and
activity-dependent learning criteria in this way successfully produces multimaps
when the input stream contains multiple distinct feature types, or in the
degenerate case of a single feature type, produces a V1-like map with
"salt-and-pepper" structure. Our results support the hypothesis that cortical
maps containing a fine mixture of different response types, whether in monkey
extrastriate cortex, mouse V1 or elsewhere in the cortex, rather than signaling a
breakdown of map formation mechanisms at the fine scale, are a product of a
generic cortical developmental scheme designed to map cells with a diversity of
response properties across a shared topographic space.
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