FIGURE 1.

Corticospinal tracts in the intact rodent and after unilateral pyramidotomy. (A) The corticospinal tracts originating in each hemisphere are shown, together with their callosal interconnections. The corticospinal tract axons descend in the dorsal, lateral, and ventral columns; most descend in the dorsal columns. Note that each hemisphere gives rise to dense contralateral and sparse ipsilateral spinal terminations. (B) Unilateral pyramidal tract lesion (pyramidotomy) eliminates all corticospinal tract axons from one hemisphere. What remains on the affected side are sparse terminations from the ipsilateral motor cortex.