Cortical responses to amplitude modulation in guinea pigs and the effects of general anesthesia by pentobarbital

Test of amplitude modulation detection threshold against modulation frequency (Mf) is one of the major measures in behavior studies for exploring temporal acuity of the auditory system. In this experiment, we recorded cortical responses from implanted electrodes in guinea pigs to generate temporal modulation transfer functions (TMTFs) by calculating the response amplitude changes across a range of Mfs in order to evaluate the temporal resolution in different frequency regions. A -3dB cutoff frequency was measured from each TMTFs and was used as a single-value index for temporal resolution. We found that the temporal resolution, as represented by this index, did not change significantly with the carrier frequency. This result suggested that the temporal resolution of the auditory system is not simply determined by the bandwidth of peripheral auditory channels. We further evaluated the effects of the general anesthesia by pentobarbital on temporal acuity and found that, in addition to the suppressions of response amplitude, this anesthesia significantly decreases the -3dB cutoff frequencies of TMTF.