Location of the auditory cortex in the Mongolian gerbil as determined by click stimulation

An investigation was made of the auditory projection area in the cerebral cortex of the Mongolian gerbil (Meriones unguiculatus) using clicks at a standard intensity to map the cerebral hemisphere by the evoked potential method. The major results can be summarized as follows: (1) As is typical for other mammals, click-evoked responses characterizing the gerbil auditory area were initially surface-positive potentials (amplitudes ranging between 0.1 and 1.7 mV) with peak latencies ranging between 13 and 32 msec. (2) Only one click-responsive field was found in the temporal area. However, the data suggest that this area may actually represent two separate projections to the cortex, since a small subarea characterized by longer response latencies was located posteriorally and laterally within the click field in the majority of animals investigated. (3) The size (5 mm long by 4 mm wide) and location (temporal neocortex below the middle cerebral artery) of the gerbil auditory cortex are consistent with mapping results obtained in other rodent species. (4) The validity of the surface maps was confirmed in four cases by demonstrating that the evoked response reversed polarity between the cortical surface and underlying white matter. The reversal was demonstrated by recording with a penetrating microelectrode at representative points "bordering" the auditory projection area.