Elsevier

Neurocomputing

Volumes 65–66, June 2005, Pages 697-707
Neurocomputing

A network model with pyramidal cells and GABAergic non-FS cells in the cerebral cortex

https://doi.org/10.1016/j.neucom.2004.10.100Get rights and content

Abstract

Recent experiments revealed that there exist electrophysiologically, anatomically, and functionally distinct two classes of GABAergic interneurons in the cerebral cortex, fast spiking (FS) cells, and non-FS cells. We propose a network model of cortical local circuits including dendritic inhibition, which is the anatomical hallmark of the non-FS cells. While conventional lateral inhibition models always converge to winner-take-all states if the self-excitation is strong, our model does so only for appropriate inputs, but otherwise converges to another states, in which all the neurons have little activities, even if the self-excitation is strong enough to keep the winner's activity after the extinction of the inputs.

Introduction

There are a wide variety of GABAergic interneurons in the cerebral cortex. Recent experiments using intracellular dual recordings revealed that these GABAergic neurons are divided into mainly two classes, fast spiking (FS) cells and non-FS cells including low threshold spiking (LTS) cells, according to their electrophysiological features. Additionally, this physiological grouping largely accords with the anatomical grouping based on the difference in the locations where they make the synapses on the target pyramidal cells; while FS cells tend to make their synapses at the somata or proximal regions of the dendrites, non-FS cells are apt to target the distal sites of the dendrites [2], [3], [4], [21]. Therefore, as for non-FS cells, localized interaction between the excitatory synaptic inputs and inhibitory ones on each dendritic branch could occur, raising the possibility of the local computation, proposed by Koch et al. as “dendritic gate” [10], such that inhibitory inputs on a certain dendritic branch effectively shunt excitatory inputs on the same branch but do not have effects on other branches. Increasing evidences indicate that the non-FS GABAergic system is functionally different in many situations from the FS system [2], [3], [26], and so it seems to be important to analyze the interaction between pyramidal cells and non-FS cells not only in the single cell level but also in the network level. In this paper, we propose a firing rate-based neural network model of cortical local circuits consisting of pyramidal cells and non-FS GABAergic cells, in which we include location-restricted effects of dendritic inhibitions mediated by non-FS cells. We examine the dynamical properties of the model, showing that this nonlinearity of single neurons changes the network behavior from those of conventional lateral inhibition networks.

Section snippets

The model

We propose a neural network model that corresponds to relatively small regions of the cerebral cortex, possibly cortical columns [22], [23], including excitatory pyramidal cells and inhibitory GABAergic interneurons of such types as LTS or other non-FS cells that make synapses on to the distal dendrites of the target pyramidal cells (Fig. 1). We consider four types of connections: (1) excitatory feedforward connections from input sources such as thalamus, other subcortical regions, or other

Simulation results

In both the conventional model (Eq. (2)) and our new model (Eq. (1)), there are two regimes about the strength of the self-excitation (α). If α<1, whenever the input is absent, all the neurons are quiet because the decay term (−x) exceeds the self-excitation term (+αx). If α>1, on the other hand, the self-excitation term exceeds the decay term so that activities of some neurons persist even after the input is turned off. In this paper, we concentrate on the latter case, namely α>1, in which the

Discussion

We discuss here the possibility that our simplified network model is related to the real neocortical neuronal networks. At first, consider the problem that though our model includes only non-FS type of GABAergic cells, actually there coexist both types, non-FS and FS, of GABAergic cells in the cerebral cortex. In general, it goes without saying that models including both types of GABAergic cells should be constructed. Nevertheless, the network model with only the non-FS cells, as those proposed

Acknowledgements

This study is partially supported by a Grant-in-Aid No. 15016023 on priority areas (C) Advanced Brain Science Project from the Ministry of Education, Sports, Science, and Technology, the Japanese Government. K.M. is supported by JSPS Research Fellowships for Young Scientists (10834).

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