Amygdalar efferents initiate auditory thalamic discriminative training-induced neuronal activity

It is well known that neurons of the medial geniculate (MG) nucleus of the thalamus send axonal projections to the amygdala. It has been proposed that these projections supply information that supports amygdalar associative p rocesses underlying acquisition of acoustically cued conditioning and learn ing. Here we demonstrate the reverse direction of influence. Temporary inac tivation of the amygdala using the GABA(A) receptor agonist muscimol just b efore the onset of discriminative avoidance conditioning permanently blocke d the development of training-induced discriminative neuronal activity in t he MG nucleus of rabbits. No discriminative activity developed when the amy gdala was inactivated or during later training to criterion without muscimo l. Thus, amygdalar processing at the outset of training is necessary for th e development of training-induced discriminative activity of neurons in the MG nucleus.