Sensory Plasticity and Learning: The Magnocellular Medial Geniculate Nucleus of the Auditory System

Summary

The magnocellular medial genículate nucleus (MGm) is a nonlemniscal component of the thalamo-cortical auditory system. It develops discharge plasticity rapidly during behavioral conditioning, in contrast to the ventral medial geniculate, the lemniscal and non-plastic component. Continual recordings from single cells during the acquisition of the pupillary conditioned response reveals an exceptionally high proportion of plastic neurons, the most plastic of which have a pronounced onset discharge to initial presentation of acoustic stimuli. Facilitation of monosynaptic field potentials in MGm lasts for several hours following brief high-frequency stimulation of its major afferent, with respect both to increased amplitude and decreased latency. Responses of single units are also facilitated for hours, as indexed by increased probability of discharges and decreased latency and latency variability. Together, these findings suggest a functional relationship between conditioning and long-lasting facilitation. Moreover, they underscore the capacity of the auditory system to express physiological plasticity under a variety of circumstances.