Anatomical substrates for functional columns in macaque monkey primary visual cortex
In this review we re-examine the concept of a cortical column in macaque primary visual cortex, and consider to what extent a functionally defined column reflects any sort of anatomical entity that subdivides cortical territory. Functional studies have shown that columns relating to different response properties are mapped in cortex at different spatial scales. We suggest that these properties first emerge in mid-layer 4C through a combination of thalamic afferent inputs and local intracortical circuitry, and are then transferred to other layers in a columnar fashion, via interlaminar relays, where additional processing occurs. However, several properties are not strictly columnar since they do not appear in all cortical layers. In contrast to the functional column, an anatomically-based cortical column is defined most clearly in terms of the reciprocal connections it makes, both via intra-areal lateral connections and inter-areal feed-back/ feed-forward pathways. The column boundaries are reinforced by interplay between lateral inhibition spreading beyond the column boundary and dis-inhibition within the column. The anatomical column acts as a functionally tuned unit and point of information collation from laterally offset regions and feed-back pathways. Thalamic inputs provide the high-contrast receptive field sizes of the columnšs neurons, intra-areal lateral connections provide their low contrast summation field sizes, and feed-back pathways provide surround modulation of receptive fields responses.
University of Utah
| Department of Mathematics
|
bressloff@math.utah.edu
Aug 2001.