Interactions of acoustic and somatosensory evoked potentials were studied in the anterior suprasylvian gyrus of the cat. Two kinds of interaction could be observed: occlusion or facilitation. In most cases occlusion was observed. The interactions showed dynamic changes and were susceptible to different kinds of influences. After having determined the control values of interaction over a period of several minutes, reversible enhancement of occlusion was observed after synchronous activation of the acoustic and somatosensory inputs with 2 Hz frequency. The same effect could be observed during stimulation of the mesencephalic reticular formation with 200 Hz frequency. The interactions could also be influenced by amphetamine and γ-glutamyltaurine, known as drugs capable of influencing the arousal level of the brain. During treatment with amphetamine the interaction was shifted in the facilitatory direction. The antagonists of amphetamine (haloperidol and reserpine) prevented this effect. The authors suggest that the interactions of acoustic and somatosensory responses are mediated by interneurons (inhibitory and/or excitatory) and particular stimulus situations and drugs are able to modify the equilibrium between excitatory and inhibitory subsystems.
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