Representation of species-specific vocalizations in the medial geniculate body of the guinea pig.

Individual nuclei of the auditory pathway contribute in a specific way to the processing of complex acoustical signals. We investigated the responses of single neurons to typical guinea pig vocalizations (purr, chutter, chirp and whistle) in the ventral part of the medial geniculate body (MGB) of anesthetized guinea pigs. The neuronal and population peristimulus time histograms (PSTHs) reflected the repetition frequency of individual phrases in the calls. The patterns of PSTHs correlated well with the sound temporal envelope in calls with short phrases (purr, chirp). The dominant onset character of the neuronal responses resulted in a lower correlation between the sound envelope and the PSTH pattern in the case of longer calls (chutter and whistle). A time-reversed version of whistle elicited on average a 13% weaker response than did the natural whistle. The rate-characteristic frequency (CF) profile provided only a coarse representation of the sound frequency spectrum without detailed information about the individual spectral peaks and their relative magnitudes. In comparison with the inferior colliculus (Suta et al. in J Neurophysiol 90:3794-3808, 2003), the processing of species-specific vocalizations in the MGB differs in: (1) a less precise representation of the temporal envelope in the case of longer calls, but not in the case of calls consisting of one or more short phrases; (2) a less precise rate-CF representation of the spectral envelope in the case of low-frequency calls, but not in the case of broad-band calls; (3) a smaller difference between the responses to natural and time-reversed whistle.