Gc. Deangelis et al., Functional micro-organization of primary visual cortex: Receptive field analysis of nearby neurons, J NEUROSC, 19(10), 1999, pp. 4046-4064
It is well established that multiple stimulus dimensions (e.g., orientation
and spatial frequency) are mapped onto the surface of striate cortex. Howe
ver, the detailed organization of neurons within a local region of striate
cortex remains unclear. Within a vertical column, do all neurons have the s
ame response selectivities? And if not, how do they most commonly differ an
d why? To address these questions, we recorded from nearby pairs of simple
cells and made detailed spatiotemporal maps of their receptive fields. From
these maps, we extracted and analyzed a variety of response metrics. Our r
esults provide new insights into the local organization of striate cortex.
First, we show that nearby neurons seldom have very similar receptive field
s, when these fields are characterized in space and time. Thus, there may b
e less redundancy within a column than previously thought. Moreover, we sho
w that correlated discharge increases with receptive field similarity; thus
, the local dissimilarity between neurons may allow for noise reduction by
response pooling. Second, we show that several response variables are clust
ered within striate cortex, including some that have not received much atte
ntion such as response latency and temporal frequency. We also demonstrate
that other parameters are not clustered, including the spatial phase (or sy
mmetry) of the receptive field. Third, we show that spatial phase is the si
ngle parameter that accounts for most of the difference between receptive f
ields of nearby neurons. We consider the implications of this local diversi
ty of spatial phase for population coding and construction of higher-order
receptive fields.