Cell and neuron densities in the primary motor cortex of primates

Nicole A. Young,Christine E. Collins,Jon H. Kaas

doi:10.3389/fncir.2013.00030

Abstract

Cell and neuron densities vary across the cortical sheet in a predictable manner across different primate species (Collins et al., 2010b). Primary motor cortex, M1, is characterized by lower neuron densities relative to other cortical areas. M1 contains a motor representation map of contralateral body parts from tail to tongue in a mediolateral sequence. Different functional movement representations within M1 likely require specialized microcircuitry for control of different body parts, and these differences in circuitry may be reflected by variation in cell and neuron densities. Here we determined cell and neuron densities for multiple sub-regions of M1 in six primate species, using the semi-automated flow fractionator method. The results verify previous reports of lower overall neuron densities in M1 compared to other parts of cortex in the six primate species examined. The most lateral regions of M1 that correspond to face and hand movement representations, are more neuron dense relative to medial locations in M1, which suggests differences in cortical circuitry within movement zones.

Highlights

The cerebral cortex is a heterogeneous structure that contains multiple sensory and motor information-processing systems (e.g., Van Essen et al, 2011)
The features of the typical primate pattern of cell and neuron distribution and number are (1) the highest cell and neuron densities are found in primary visual cortex, V1; (2) extrastriate cortical areas have relatively high cell and neuron densities; (3) primary auditory and somatosensory areas have relatively high cell and neuron densities compared to surrounding areas; and (4) motor cortex, M1, appears to have low neuron densities compared to other areas of cortex
Despite the comprehensive evaluation of cortical cell and neuron number and distribution in the study by Collins and colleagues, the number of species examined in detail was limited and the dissection techniques used in that study had not been refined to allow evaluation of variation in cell and neuron density in different parts of topographically organized cortical areas, and in cases where functional areas were dissected from the cortex, areal boundaries were estimated from surface landmarks and sulcal patterns

Summary

Introduction

The cerebral cortex is a heterogeneous structure that contains multiple sensory and motor information-processing systems (e.g., Van Essen et al, 2011). The features of the typical primate pattern of cell and neuron distribution and number are (1) the highest cell and neuron densities are found in primary visual cortex, V1; (2) extrastriate cortical areas have relatively high cell and neuron densities; (3) primary auditory and somatosensory areas have relatively high cell and neuron densities compared to surrounding areas; and (4) motor cortex, M1, appears to have low neuron densities compared to other areas of cortex These results are consistent with the earlier findings of Beaulieu and Colonnier (1989) who determined neuron number in the cortex below 1 mm of cortical surface in four visual areas, somatosensory area 3b, and two motor areas (4 gamma, 6a alpha) of the cortex of cats, and found that motor areas have the smallest number of neurons per column, while sensory areas contain more neurons, with the greatest number found in the binocular region of visual area 17. Despite the comprehensive evaluation of cortical cell and neuron number and distribution in the study by Collins and colleagues, the number of species examined in detail was limited and the dissection techniques used in that study had not been refined to allow evaluation of variation in cell and neuron density in different parts of topographically organized cortical areas, and in cases where functional areas were dissected from the cortex, areal boundaries were estimated from surface landmarks and sulcal patterns

Methods

Results

Conclusion