The interactions between acoustic and somatosensory evoked potentials were examined in the anterior suprasylvian gyrus of the cat. Under conditions of barbiturate anaesthesia, occlusion was the dominant form of interaction. γ-Aminobutyrate in local and intravenous application, and baclofen and diazepam in intravenous application significantly deepened the occlusion. γ-Aminobutyrate antagonists, picrotoxin and bicuculline, in subconvulsive doses decreased occlusion or turned it into facilitation. γ-Aminobutyrate agonists and γ-aminobutyrate depressed and γ-aminobutyrate antagonists enhanced the amplitude of the evoked potentials but the interactions by themselves proved independent from the absolute amplitudes. The interactions between evoked potentials of different modalities in the association cortex of the cat can be regarded as an expression of the actual equilibrium between excitatory and inhibitory interneuronal systems.
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