[Characteristics of borderline modulation frequencies in the differentiation of tonal and amplitude-modulated stimuli following the removal of the inferior colliculus in rats].

Elaboration of differentiation between sound stimuli was carried out in 15 laboratory rats. After bilateral ablations of auditory inferior colliculi the border frequency of stimulus amplitude modulation was determined for all rats when they still could differentiate between tonal and amplitude-modulated stimuli. Decrease in frequency of modulation by 2 Hz and more from the border frequency caused a complete loss of ability to differentiate. In all rats bilateral inferior colliculi ablations completely disturbed differentiation between tonal and amplitude-modulated signals with modulation frequency below 183-191 Hz (the range of border frequencies). The surgery however did not affect differentiation between tonal and amplitude-modulated signals with the modulation frequencies above 183-191 Hz. The data suggest that the functions of completion of coding of amplitude-modulated stimuli in the auditory system is strictly linked with definite structures.