Topical versus diffuse organization of the corticospinal tract in the cat

1. The organization of the corticospinal system has been studies, in the cat, using electrophysiological techniques (stimulation of the lateral corticospinal tract at different spinal levels, recording in the contralateral cortex by means of transcortical bipolar electrodes) and anatomical techniques (HRP injection localized in the grey matter of a chosen spinal level). These two approaches give complementary results. Different cortical zones can be defined according to their spinal projections. 2. Some restricted cortical zones are at the origin of only contralateral corticospinal projections specific to a given spinal enlargement, cervical or lumbar. 3. Other larger cortical zones are at the origin of bilateral spinal projections specific to a given spinal enlargement, at least in the case of the cervical one. 4. Finally, a cortical zone is at the origin of bilateral cortical projections both to the cervical and lumbar enlargements. The question of multiple branching of individual cortisospinal neurons is considered, but cannot be answered using out techniques.