Interconnections between the subthalamic nucleus and the cerebral cortex of the cat

The corticosubthalamic and subthalamocortical projections were examined in the cat by anterograde and retrograde axonal transport of horseradish peroxidase (HRP). Injections of HRP into the gyrus proreus, gyrus sigmoideus anterior and the part lateral to the sulcus cruciatus gave rise to anterogradely labelled terminals in all parts of the ipsilateral subthalamic nucleus in a topographical manner. Injections of HRP into these cerebral cortices as well as the gyrus sigmoideus posterior, the posterior part of the gyrus coronalis and the middle part of the gyrus ectosylvius produced retrogradely labelled neurons in the medial half of the ipsilateral subthalamic nucleus in a topographical manner. These findings suggest that the subthalamic nucleus acts as a link not only in the pallido-subthalamo-pallidal loop but also in the corticosubthalamo-cortical pathways.