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Peter H. Schiller, Edward J. Tehovnik; The role of cortical inhibitory circuits in target selection with saccadic eye movements. Journal of Vision 2002;2(7):577. doi: 10.1167/2.7.577.
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In work reported last year at this meeting we had shown that subthreshold microstimulation in V1, V2, LIP, FEF and MEF of monkeys can variously produce facilitation, interference, and delays in saccade initiation, thereby identifying some of the essential neural computations carried out in the process of target selection with saccadic eye movements. We now report the effects of local administration of the GABA antagonist bicuculline and the GABA agonist muscimol on this process. Following fixation, monkeys had the free choice of selecting one of two identical targets presented with various temporal asynchronies, with one placed into the receptive or motor field of the neurons treated with the pharmacological agents. Also tested were the brightness, color and shape discrimination abilities at intact and affected sites. Bicuculline produced a high level of facilitation in the choice of the target appearing in the receptive and motor fields of the neurons in the FEF but yielded major interference in V1. Bicuculline also produced deficits in brightness, color and shape discrimination at the injected sites in V1 but not in LIP and the FEF. Muscimol in V1 produced dramatic interference in target selection as well as in visual discrimination whereas in the FEF it produced only moderate interference. Our results suggest that (1) GABAergic inhibitory circuits in V1 play a central role in the analysis of visual stimuli, (2) Signals for the generation of eye movements in V1 appear to be produced not by disinhibition but predominantly by excitation, (3) in the FEF disinhibition is a central process for initiating eye movements and (4) inhibitory circuits in the FEF do not appear to be central for visual analysis.
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