Corticothalamic feedback for sound-specific plasticity of auditory thalamic neurons elicited by tones paired with basal forebrain stimulation.

Recent studies have revealed that the auditory cortex (AC) plays a crucial role in the plastic changes in the physiological properties of subcortical auditory neurons through corticofugal projections. In this study with the C57 mouse, we investigated the receptive field plasticity of the ventral division of the medial geniculate body (MGBv) of the thalamus and the impact of the primary AC using the electrical stimulation of the cholinergic basal forebrain, the nucleus basalies, paired with a tone (tone-ES(NB)). We found that tone-ES(NB) evoked significant changes in MGBv receptive fields; the best frequencies (BFs) of MGBv neurons shifted toward the frequency of the paired tone. The BF shifts of MGBv neurons were maximal when the difference between the BFs of MGBv neurons and the frequency of the paired tone was 7 kHz. In addition to the BF shifts, the minimum threshold was decreased and the spike number was increased in response to the paired tone. Importantly, these plastic changes of MGBv neurons were completely abolished when the AC was inactivated with a cortical application of muscimol, a gamma-aminobutyric acid receptor subtype A receptor agonist. Our data indicate that the corticofugal system is an essential neural substrate for the sound-specific plasticity in the auditory thalamus.