MICROELECTRODE STUDIES ON MEDIAL GENICULATE BODY OF CAT: II. RESPONSE TO CLICKS

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Abstract
The electrical response aroused in the medial geniculate body by clicks consists of a slow-wave sequence, and spikes that represent the discharge of single neural units. Each unit discharges at a relatively fixed time interval (latency) after delivery of the stimulus. Different units vary widely in latency, with the extremes at 6 msec, and 125 msec. A considerable variability is displayed by most units when responding to a succession of identical clicks. This variability occurs in latency, in whether or not the unit discharges, and (when the unit does fire) in the number of discharges evoked by each click. The neural correlates for stimulus intensity are complex. In general, the more intense clicks evoke unit responses more often and earlier in time. Some units, however, behave in exactly the opposite manner. Spontaneous activity, steady or cyclical, in single units is often observed. A single click may set up cyclical activity that resembles the spontaneous variety. Cyclical activity of both types is recordable with the homolateral auditory cortex intact or extirpated. The capacity of each ear to arouse response at a given microelectrode position was tested. Different units in the same animal may respond to clicks applied to either ear, to the contralateral ear alone, and to the ipsilateral ear alone. However, a bias in favor of the contralateral ear appears to exist.