Structure of internal interneuronal connections in field 17 of the cat cerebral cortex.

The spatial distribution of horizontal internal connections in field 17 of the cat cortex was studied after microiontophoretic application of horseradish peroxidase to individual cortical columns. Cluster analysis of the distribution of labeled cells in the superficial layers in the tangential plane of the cortex was performed. Field 17 included 7 +/- 1 clusters of up to five cells. Clusters were distributed into two layers, separated by 1.2 +/- 0.3 mm. The distance between the centers of the clusters forming rows was 0.8 +/- 0.3 mm. The spatial characteristics of the grouping of cells sending axons into the cortical column were compared with published data based on optical visualization of the activity of neurons in orientational and eye-dominant columns of the visual cortex. It is suggested that columns in field 17 are associated with 6-8 hypercolumns, though only with a single type of neuron within these hypercolumns, in terms of eye dominance and orientational preference.