Effect of Contrast on Visual Spatial Summation in Different Cell Categories in Cat Primary Visual Cortex.

Ke Chen,Ai-Min Ding,Ling Wang,Li-Peng Zhang,Xiao-Hua Liang,Xue-Mei Song,Hisao Nishijo

doi:10.1371/journal.pone.0144403

Abstract

Multiple cell classes have been found in the primary visual cortex, but the relationship between cell types and spatial summation has seldom been studied. Parvalbumin-expressing inhibitory interneurons can be distinguished from pyramidal neurons based on their briefer action potential durations. In this study, we classified V1 cells into fast-spiking units (FSUs) and regular-spiking units (RSUs) and then examined spatial summation at high and low contrast. Our results revealed that the excitatory classical receptive field and the suppressive non-classical receptive field expanded at low contrast for both FSUs and RSUs, but the expansion was more marked for the RSUs than for the FSUs. For most V1 neurons, surround suppression varied as the contrast changed from high to low. However, FSUs exhibited no significant difference in the strength of suppression between high and low contrast, although the overall suppression decreased significantly at low contrast for the RSUs. Our results suggest that the modulation of spatial summation by stimulus contrast differs across populations of neurons in the cat primary visual cortex.

Highlights

Most neocortical neurons are excitatory pyramidal neurons (70%-80% neoneurons), and the GABAergic ‘local circuit neurons’, which account for only 20–30% of cortical neurons, but show a rich morphological and electrophysiological diversity [1, 2]
Our results showed that both fast-spiking units (FSUs) and regular-spiking units (RSUs) exhibited significant enlargement in classical receptive field (CRF) and non-classical receptive filed (nCRF) size at low contrast, but the expansion was more marked for the RSUs than for the FSUs
Our results show that neurons in cat V1 can be divided into FSUs and RSUs based on their action potentials waveform

Summary

Introduction

Most neocortical neurons are excitatory pyramidal neurons (70%-80% neoneurons), and the GABAergic ‘local circuit neurons’, which account for only 20–30% of cortical neurons, but show a rich morphological and electrophysiological diversity [1, 2]. Studies of neocortical circuits have shown that the connection patterns and functional properties of both neuron types have marked difference: excitatory pyramidal neurons can have both long-range and short-range connections, whereas inhibitory interneurons display more local connection patterns [1, 12]. Compared to excitatory pyramidal cells, inhibitory interneurons showed much broader tuning and tend to respond more strongly to sensory stimuli [13,14]. Recent studies have used the features of extracellular action potentials to characterize two PLOS ONE | DOI:10.1371/journal.pone.0144403 December 4, 2015

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