Neural control of hatching: fate of the pattern generator for the leg movements of hatching in post-hatching chicks.

Chicks from 0 to 61 days post-hatching were gently folded into the hatching position and placed in artificial glass eggs. Within 0 to 2 min they began to produce a behavior that qualitatively resembled normal hatching. Furthermore, quantitative analysis of electromyographic records showed that under these conditions the intralimb and interlimb leg motor output patterns produced during each hatching episode (the episode motor program) were those typical of normal hatching. The only major change associated with increasing post-hatching age was a gradual increase in inter-episode interval. Therefore, we conclude that the neural pattern-generating circuitry which produces the motor program for the leg movements of hatching remains functional in post-hatching chicks despite the fact that, under normal conditions, hatching behavior is never used again.