ENCODING OF SOUND DURATION BY NEURONS IN THE AUDITORY-CORTEX OF THE LITTLE BROWN BAT, MYOTIS-LUCIFUGUS

Responses of 117 single- or multi-units in the auditory cortex (AC) of bats (Myotis lucifugus) to tone bursts of different stimulus duration s (1-400 ms) were studied over a wide range of stimulus intensities to determine how stimulus duration is represented in the AC. 36% of AC n eurons responded more strongly to short stimulus durations showing sho rt-pass duration response functions, 31% responded equally to all puls e durations (i.e., all-pass), 18% responded preferentially to stimuli having longer durations (i.e., long-pass), and 15% responded to a narr ow range of stimulus durations (i.e., band-pass). Neurons showing long -pass and short-pass duration response functions were narrowly distrib uted within two horizontal slabs of the cortex, over the rostrocaudal extent of the AC. The effects of stimulus level on duration selectivit y were evaluated for 17 AC neurons. For 65% of these units, an increas e in stimulus intensity resulted in a progressive decrease in the best duration. In light of the unusual intensity-dependent duration respon ses of AC neurons, we hypothesized that the response selectivities of AC neurons is different from that in the brainstem. This hypothesis wa s validated by results of study of the duration response characteristi cs of single neurons in the inferior colliculus.