DISTRIBUTING COORDINATED MOTOR OUTPUTS TO SEVERAL BODY SEGMENTS - ESCAPE MOVEMENTS IN THE COCKROACH

In the escape behavior of the cockroach, all six legs begin to make di rected movements nearly simultaneously. The sensory stimulus that evok es these leg movements is a wind puff. Posterior wind receptors excite giant interneurons that carry a multi-cellular code for stimulus dire ction - and thus for turn direction - to the three thoracic ganglia, w hich innervate the three pairs of legs. We have attemptd to discrimina te among various possible ways that the directional information in the giant interneurons could be distributed to each leg's motor circuit. Do the giant interneurons, for instance, inform separately each thorac ic ganglion of wind direction? Or is there one readout system that con veys this information to all three ganglia, and if so, might the ident ified thoracic interneurons, which are postsynaptic to the giant inter neurons, subserve this function? We made mid-sagittal lesions in one o r two thoracic ganglia, thus severing the initial segments of all the known thoracic interneurons in these ganglia, and thus causing their p rojection axons to the other thoracic ganglia to degenerate. This lesi on did not sever the giant interneurons, however (Fig. 5). Following s uch lesions, the legs innervated by the intact thoracic ganglia made n ormally directed leg movements (Figs. 4, 6, 7). Thus, the projection a xons of the thoracic interneurons are not necessary for normal leg mov ements. Rather, the giant interneurons appear to specify to each thora cic ganglion in which direction to move the pair of legs it innervates .