Surround Inhibition in the Basal Ganglia

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Abstract

This chapter is a review of existing evidence and current thinking in relation to the concept of surround inhibition in the basal ganglia. In the following sections, the possibility of inhibitory interactions among spiny projection neurons will be reconsidered in the light of recent evidence. Statistical considerations based on quantitative neuroanatomical fmdings suggest a low probability of synaptic connection between neighbouring neurons. Electrophysiological studies have failed to demonstrate inhibitory interactions between spiny projection neurons. Together these fmdings suggest that inhibitory interactions among spiny projection neurons are relatively sparse. This suggests that the collaterals of spiny projection neurons are not the major source of surround inhibition. Instead, feedforward inhibition by a network of GABA/parvalbumin containing intemeurons seems to explain surround inhibition at a macroscopic level. New models are needed to address the functional significance of powerful feedforward inhibition by GABA/parvalbumin containing intemeurons, and the function of sparse inhibitory interactions between spiny projection neurons.