Relationships among unit discharge rate, pattern, and phasic arousal in the medical geniculate nucleus of the waking cat.

The present experiment was designed to investigate some of the labile discharge characteristics of single units in the medial geniculate body (MGB) of the locally anesthetized, paralyzed cat. In particular, the following problems were addressed : To what extent do MGB cells exhibit stationary discharge rates; what are the effects of phasic arousal (produced by infrequent shock to the paw) upon the discharge rate of units; and how does the pattern of unit discharge relate to its rate? Only 4 out of 20 units showed stationary discharge rates throughout the entire time they were studied. Furthermore approximately 50% of the cells showed changes in discharge rate prior to the occurrence of paw shock indicating that nonstationary discharge rate cannot be attributed entirely to shock. When discharge rates preceding shock xvere compared with discharge rates following shock, a change in rate was seen in about 50% of the units of which the majority showed increases in rate. The discharge rates of single units in this preparation may apparently change both spontaneously and in response to paw shock. W-hen the poststimulus time histograms (PSTH) were analyzed with respect to the over-all discharge rate of the cell, several striking features became apparent. If the rate was stationary, the PSTH generally showed no systematic variations in shape. If the rate was nonstationary, however, the PSTH systematically displayed certain properties. The initial short latency peak (< 20 msec) showed no changes corresponding to changes in rate. In contrast to the first peak, the longer latency peaks (SO-300 msec) varied systematically with the discharge rate. These observations were verified statistically. The results are discussed with reference to the role of sensory systems in hehavioral plasticity.