RELATIONSHIP BETWEEN SPONTANEOUS AND EVOKED UNIT ACTIVITY IN THE INFERIOR COLLICULUS OF RATS

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Abstract
Responses of 128 neurons of the inferior colliculus to 1-sec. acoustic stimuli were examined in curarized rats with the poststimulation histogram technique. The spontaneous activity was changed by polarization and/or electrophoretic application of glutamate through the recording microelectrode. Over a wide range of background frequencies reactions of the majority of collicular neurons (90%) displayed either additive reactions (the sound-induced change of firing rate [DELTA]F remained constant in spite of considerable variations of the background activity F) or multiplicative reactions (the acoustic response [DELTA] F changed proportionally to the spontaneous activity F so that the ratio [DELTA]F/F remained constant). Relative incidence of both these types of reactions is approximately equal. In a group of 32 neurons which did not react to the sound under control conditions, acoustic responses could be elicited in about 50% of units when current was applied to the microelectrode.