Encoding of alternating acoustical signals in the medial geniculate body of guinea pigs.

In unanaesthetized guinea pigs 102 single units of the medial geniculate body were recorded under acoustical stimulation with alternating noise and tone impulses. The temporal parameters of the signals were chosen in close relation to psychoacoustical pulsation-threshold measurements. Most units showed a strong interaction between the responses of the non-simultaneously presented signal components (temporal suppression). The phasic part of each impulse-evoked response was more affected by the suppression than the tonic part. Thus, two regions of responsiveness could be verified: a region of pure tonic discharge and a region of tonic and phasic discharge. The borderline between both regions was defined as 'on-threshold'. The temporal suppression effect of the discharge rate did depend on impulse duration, impulse shape, gap duration, and the levels of the signal components. The overall unit-response characteristic-especially the lac of temporal onset information--suggested a close relation between psychoacoustical pulsation threshold and physiological 'on-threshold'.