PATTERNS OF MUSCLE-ACTIVITY DURING DIFFERENT BEHAVIORS IN CHICKS - IMPLICATIONS FOR NEURAL CONTROL

The large behavioral repertoire that spans the embryonic and postembry onic stages of development make chicks an ideal system for identifying patterns of muscle activity that are common to different behaviors an d those that are behavior-specific. The main goal of this work was to identify the similar and dissimilar aspects of the recruitment pattern s and the regulation of muscle activity during three distinct postembr yonic behaviors: walking, swimming and airstepping. We. identified two synergies that were common to each of these behaviors. The synergies were not disrupted by the absence of FT1 activity in airstepping. With in each synergy the recruitment time, recruitment order and duration o f activity were not rigid, but varied according to the context-specifi c resistance that the leg encountered. Unlike the other muscles, FT2 a ctivity was not recruited as part of the same synergy in each behavior . When weight-bearing contact with the substrate did not occur, as in swimming and airstepping, as well as in walking in chicks with deaffer ented legs, FT2 activity was not recruited as part of either synergy, but was recruited during the time between them. Although not identical , embryonic motility and hatching motor pattern both show the two syne rgies described for the postembryonic behaviors. Like the latter behav iors, the synergies tolerated the absence of activity from specific mu scles. Thus, we suggest that the CNS produces different behaviors usin g many of the same muscles by organizing the patterned activity around two common synergies while permitting the different muscles that part icipate in a synergy to be modified in tandem or on an individual basi s. Furthermore, the common synergies are established early during pren atal development in chicks.