A horseradish peroxidase study of parallel thalamocortical projections responsible for the generation of mid-latency auditory-evoked potentials.

Mid-latency auditory-evoked potentials (MAEP) were recorded from the parietotemporal region of the rat using a high spatial resolution epicortical multielectrode array. Horseradish peroxidase was injected into regions of primary and secondary auditory cortex which generate spatially and temporally distinct components of the MAEP complex to retrogradely label their thalamocortical projections. These data provide anatomical evidence for three parallel thalamocortical projection systems, originating in the ventral, dorsal and medial subdivisions of the medial geniculate nucleus, which may be responsible for the asynchronous activation of three distinct subpopulations of cortical neurons giving rise to components of the MAEP complex. Specific and non-specific characteristics of the thalamocortical projections are discussed.