PRODUCING DIRECTED BEHAVIOR - MUSCLE-ACTIVITY PATTERNS OF THE COCKROACH ESCAPE RESPONSE

The cockroach responds to wind from the front left by making an escape turn to the right, and vice versa. So far, no interneurones in the es cape system are known that respond only to wind from the left or only to wind from the right. In this study, we used electromyographic recor dings to determine whether motor neurones respond in this direction-se lective manner during escape behaviour. In the mesothoracic coral-femo ral joint, whose movement direction is diagnostic for escape direction , the fast motor neurones of one muscle respond selectively to one win d direction, and those of the antagonistic muscle respond selectively to wind from the other direction, resulting in an appropriate turning response. This rules out an alternative hypothesis, a co-activation me chanism of specifying turn direction, These results suggest that it wo uld be fruitful to search among the interneurones of the escape system for additional cells and circuit properties that could give rise to t his sharp directional discrimination.