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Interactions between inhibitory and excitatory circuits in the human motor cortex

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Abstract

Cortical activity depends on the balance between excitatory and inhibitory influences. Several different excitatory and inhibitory systems in the human motor cortex can be tested by transcranial magnetic stimulation (TMS). While considerable information is known about these different inhibitory and excitatory phenomena individually, how they are related to each other and how they interact is not well understood. Several recent studies have investigated the interactions between some of these circuits by applying them together. It has been found that short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI) are mediated by different circuits. LICI appears to inhibit SICI, which may occur through presynaptic GABAB receptors. Interhemispheric inhibition elicited by stimulation of the contralateral motor cortex also inhibits SICI and may share inhibitory mechanisms with LICI. Long-interval afferent inhibition induced by median nerve stimulation inhibits LICI but does not interact with SICI. Based on these results, a model of interactions between different inhibitory systems that can be tested and refined in the future is proposed. Further studies of the interaction between different cortical inhibitory and excitatory circuits should improve our understanding of the functional organization of the motor cortex and allow better interpretation of abnormal findings in disease states. It may also be developed into a new way of studying the pathophysiology of diseases and the effects of intervention.

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Acknowledgements

I thank Drs. Guillermo Paradiso, Jeff Daskalakis, and Ristuko Hanajima for their helpful comments on the manuscript. The author’s work was supported by the Canadian Institutes of Health Research, Canada Foundation for Innovation, Ontario Innovation Trust, and the University Health Network Krembil Family Chair in Neurology.

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  1. Division of Neurology and Krembil Neuroscience Centre, Toronto Western Research Institute, University Health Network, University of Toronto, Ontario, Canada

    Robert Chen

  2. Toronto Western Hospital, 5W-445, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada

    Robert Chen

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Chen, R. Interactions between inhibitory and excitatory circuits in the human motor cortex. Exp Brain Res 154, 1–10 (2004). https://doi.org/10.1007/s00221-003-1684-1

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