Location of rabbit auditory cortex and description of single unit activity

The following data were obtained from microelectrode exploration of rabbit auditory cortex (AC). (1) Location of AC--Major portions of the rabbit's right hemisphere were stereotaxically mapped for auditory responsive and non-responsive regions. Auditory responsive regions were found to lie behind the rhinal sulcus, extending from its midpoint to its inferior border. (2) Frequency selectivity--Characteristic frequencies (CFs) ranged from 0.4 to 33 kHz. Sharp, multipeaked and broad tuning curves were described. (3) Response patterns--A variety of post-stimulus-time (PST) histogram shapes were obtained in response to tonal stimuli. The response of a given neuron often varied with changes in stimulus frequency or intensity. (4) Latency--Neural response latencies ranged from 10 to 100 msec following stimulus onset. (5) Spontaneous rate--In the absence of acoustic stimulation, spike discharges ranged from less than 1 spike/sec to 48 spikes/sec. Spontaneous rates of less than 5 spikes/sec were measured in 42% of the neurons. Rates in excess of 15 spikes/sec occurred in fewer than 18% of the cells examined. (6) Response variability--Stimulus-evoked activity was seen to vary over time. Changes consisted of an overall increase or attenuation of discharge rate, as well as modifications of selected portions of the response pattern (PST histogram shape). The characteristics of single unit activity in rabbit auditory cortex are consistent with findings reported in other species.