Figure 1.

Schematic illustrations of CST development in cat model during normal conditions and after activity manipulations. Each illustration is a semi-schematic representation of the CST cervical projection pattern. (A) Immature projection. Contralateral and ipsilateral are with respect to the motor cortex of origin of the pathway. The immature pattern is bilateral. (B) Normal development results in a predominantly contralateral projection, with multiple sites of high projection density (e.g., intermediate zone). (C) CSMS unilateral inactivation results in a greatly contracted termination space (left). The non-inactivated side develops aberrant ipsilateral misprojections. (D) Electrical stimulation of the corticospinal motor system (CSMS) results in maintenance of many of the extensive terminations observed in early development, as shown for the stimulated side (left). The non-stimulated side (right) develops fewer ventral projections (arrow).