1 2 Discharge Patterns in the Lateral Superior Olive of Decerebrate Cats

26 Anatomical and pharmacological studies have shown that the lateral superior olive (LSO) 27 receives inputs from a number of sources, and that LSO cells can alter the balance of their own 28 excitatory and inhibitory drive. It is thus likely that the ongoing sound-evoked responses of LSO 29 cells reflect a complex interplay of excitatory and inhibitory events, which may be affected by 30 anesthesia. The goal of this study was to characterize the temporal discharge patterns of single 31 units in the LSO of unanesthetized, decerebrate cats in response to long-duration ipsilateral best32 frequency tone bursts. A decision tree is presented to partition LSO units on the basis of post33 stimulus time histogram shape, adaptation of instantaneous firing rate as a function of time and 34 sustained discharge rate. The results suggest that LSO discharge patterns form a continuum with 35 four archetypes: sustained choppers that show two or more peaks of activity at stimulus onset 36 and little adaptation of rate throughout the response; transient choppers that undergo a decrease 37 in rate that eventually stabilizes with time; primary-like units that display an initial peak of 38 activity followed by a monotonic decline in rate to a steady-state value; and onset-sustained units 39 that exhibit an initial peak of activity at stimulus onset followed by a low sustained activity. 40 Compared to the chopper units, the non-chopper units tend to show longer first-spike latencies, 41 lower peak firing rates and more irregular sustained discharge patterns. Modeling studies show 42 that the full range of LSO response types can be obtained from an underlying sustained chopper 43 by varying the strength and latency of a sound-driven ipsilateral inhibition relative to that of 44 excitation. Taken together, these results suggest that inhibition plays a major role in shaping the 45 temporal discharge patterns of units in unanesthetized preparations. 46 47