To examine the involvement of subetween G65 and G95. Since spinal cord transection praspinal inputs in the maturation of motor activity patterns in the developing fetal lamb, we recorded leads to the motor behavior of the G65 fetus reverting spontaneous electromyographic activity from spinally to the cyclic pattern characteristic of the G45 fetus, innervated muscles at approximately 45, 65, and 95
we conclude that supraspinal inputs begin to modulate days gestation (G45, G65, and G95; term Γ
147 days).
the output of the spinal pattern generators at some At G45, fetal activity occurred in synchronized activstage between G45 and G65. The observation that spiity-inactivity cycles of approximately 2 min duration, nally transected fetuses generate identical behavior at with the activity phase lasting 22.2 { 4.8 s and the G65 and G95, both in terms of its cyclic character inactivity phase lasting 95.4 { 13.3 s (mean { stanand the duration of cycles, suggests that spinal circuits dard error of the mean, n Γ
5). At G65 and G95, the undergo little autonomous development overthis peorganization of activity was clearly different from that riod; that is, the altered behavior observed in the deat G45 in that it was no longer cyclic, nor was the veloping intact fetus reflects the influence of supradischarge of different muscles synchronized. By conspinal inputs on the motor circuits of the spinal cord. trast, after spinal cord transection at G62, synchro-