Topographic relationship between anteromedial thalamic nucleus neurons and their cortical terminal fields in the rat

The present study has examined the topographic relationship between cells in the anteromedial thalamic nucleus (AM) and their cortical terminal fields, with retrograde transport of Fluoro Gold in the rat. Projections to the frontal area 2 originate from the ventrolateral part of the AM and the entire interanteromedial nucleus (IAM). Projections to the anterior cingulate area originate from the peripheral part of the rostral AM and the entire IAM. Fibers to the rostral retrosplenial area arise from the caudodorsal part of the AM, whereas those to the caudal retrosplenial area arise from the rostralmost and the rostrodorsomedial parts. Fibers to the rostral area 29D originate from the rostrocentral part of the AM, whereas those to the caudal area 29D originate from the rostroventrolateral and the ventromedial parts. Projections to the medial half of the entorhinal area originate from the rostrodorsomedial part of the AM. In contrast, projections to the lateral half of the entorhinal area originate from the IAM and the central part of the AM. The results show a complex topographic relationship between cells of origin of the AM and their cortical terminal fields, suggesting complex functional roles played by the AM in learning behavior such as discriminative avoidance behavior.