Role of the geniculate body in performing conditioned reflexes to amplitude-modulated stimuli in the rat

In 13 laboratory rats with bilateral auditory cortex ablation, the border frequency of amplitude-modulation still allowing differentiation between tonal and amplitude-modulated stimuli, did not change after bilateral section of the brachii of the posterior colliculi. Bilateral auditory cortex ablation and section of the brachii drastically disturbed this differentiation when the modulation frequencies were higher than 27-31 Hz. The data suggest that the completion of coding of amplitude-modulated stimuli does not take place at the level of the medial geniculate body, and that border frequencies defined after auditory cortex ablation are linked with the frontier posterior colliculi--thalamo-cortical system.