Neuronal composition of processing modules in human V1: laminar density for neuronal and non-neuronal populations and a comparison with macaque

Abstract

The neuronal composition of homologous brain regions in different primates is important for understanding their processing capacities. Primary visual cortex (V1) has been widely studied in different members of the catarrhines. Neuronal density is considered to be central in defining the structure–function relationship. In human, there are large variations in the reported neuronal density from prior studies. We found the neuronal density in human V1 was 79,000 neurons/mm3, which is 35% of the neuronal density previously determined in macaque V1. Laminar density was proportionally similar between human and macaque. In V1, the ocular dominance column (ODC) contains the circuits for the emergence of orientation preference and spatial processing of a point image in many mammalian species. Analysis of the total neurons in an ODC and of the full number of neurons in macular vision (the central 15°) indicates that humans have 1.3× more neurons than macaques even though the density of neurons in macaque is 3× the density in human V1. We propose that the number of neurons in a functional processing unit rather than the number of neurons under a mm2 of cortex is more appropriate for cortical comparisons across species.

Human V4 size predicts crowding distance

“…A fixed neural count implies a fixed area, which we estimate at A / λ =2 mm 2 of cortex. This is analogous to a V1 hypercolumn analyzing local scale and orientation, with an area of 1.5 mm 2 in human 16 . In seeking a link between behavior and brain measures, we emphasized anatomy (map size) rather than physiology (neural response properties).…”

“…This area contains about a quarter million neurons 39 . This proposed V4 computational unit isolating an object is analogous to a V1 hypercolumn analyzing local scale and orientation 40 , about 1.5 mm 2 in human (and 0.6 mm 2 in macaque) 41 .…”