抄録
Multi-tonotopic fields have been implicated in the temporal cortex of the rat. To reveal anatomical framework for corticofugal modulations by multi-tonotopic fields including the primary auditory area that largely corresponds to area Te1, we examined corticothalamic projections by making small injections of biocytin in the cortex. Best frequency (BF) was determined by epicortical recording of field potentials evoked by pure tones under anesthesia. The rostral portion of area Te1 and the cortical region (area Te2d) dorsal to the caudal end of area Te1, which both exhibited high BF, projected to the ventral zone of the ventral division of the medial geniculate body (MGV). On the other hand, the caudal portion of area Te1 and the rostroventral margin of area Te1 (area Te1v), which both exhibited low BF, projected to the dorsal zone of the MGV. The results suggest that tonotopically comparable subfields in the primary and secondary auditory areas in the cortex exert synergistic modulations on thalamic information processing through topographic projections that converge to a specific part of the MGV. By contrast, collateral projections to the thalamic reticular nucleus (TRN) terminated in different zones of the TRN in each pair of the cortical regions. Putative corticofugal inhibition via the TRN may operate in different parts of the MGV unlike putative corticofugal excitation through the converging direct projections to the MGV. [Jpn J Physiol 54 Suppl:S167 (2004)]
