Processing of spectral localization-informative changes in sound signals by neurons of inferior colliculus and auditory cortex of the house mouse Mus musculus

Comparative analysis was performed of sensitivity of three populations of neurons of the inferior colliculus central nucleus and of neurons of the auditory cortex A1 and AAF fields of the house mouse Mus musculus to series of signals of wideband noise with spectral notch shifting along the frequency axis and to series of the band noise signals with shifting band. Sensitivity to spectral notches in noise was estimated from a change of impulse activity depending on notch location on the frequency axis (modulation coefficients were determined as the normalized difference between the maximal and minimal spike number in neuronal responses to all noises with notch exposed in the series). It was shown that the highest modulation coefficient values and accordingly the highest frequency-dependent sensitivity to spectral notches in the noise were peculiar to inhibition-dependent inferior colliculus neurons. Statistical analysis confirmed that distribution of modulation coefficients for the group of the inhibition-dependent neurons differed statistically significantly from the distribution for groups of primary-like and V-shaped inferior colliculus neurons as well as of cortical neurons (U-test, p < 0.0001). The lowest sensitivity to spectral notches was revealed in the V-shaped inferior colliculus neurons and cortical neurons; in these groups, distribution of modulation coefficients did not differed statistically significantly (p > 0.3). Thus, although a part of cortical neurons does have the frequency-dependent selectivity to spectral localizationally informative changes in sound signals, its formation needs participation of the inferior colliculus and its inhibition-dependent neurons. Selectivity to direction of the shift of spectral changes in noise signals in neurons of the inferior colliculus and auditory cortex was similar and was manifested mainly as shift along the frequency axis of dependences of the spike number in the neuronal responses and latent periods on central frequency of notch in noise (the noise band).