Activity of neurons in the mouse inferior colliculus in relation to the position and direction of displacement of spectral contrast.

The variability of the responses of neurons in the inferior colliculus of the mouse (Mus musculus) to sequences of signals of noise bands and wide-band noise with spectral notches with regular changes (by 1/12 octave) in the central band frequency or notch frequency was studied. When the width of spectral changes was 1/3 octave, neurons with strong inhibitory influences in the excitatory zone of the response ("inhibition-dependent" neurons) showed low levels of spike activity if the noise band completely covered the excitatory part of the response. The most effective stimuli for these neurons were spectral contrasts passing through the center of the excitatory part of the response (through or close to the characteristic frequency). The responses of neurons to spectral contrasts created by noise bands and noises with notches were identical. It is suggested that approximation of the inhibitory and excitatory inputs sharpens the frequency tuning of neurons to the position of the spectral contrasts, as occurs in the visual system. The selectivity of neurons to the direction of moving spectral contrasts is manifest as a difference in responses when they move from the excitatory area of the response to the inhibitory and vice versa. The functional significance of the contrast mechanism for the analysis of sound source movement based on direction-dependent spectral features associated with the transfer characteristics of the external ear is discussed.