Meeting Abstract
A cockroach may be easy to spot on your kitchen floor, but their quickness makes them hard to catch. In contrast, a stick insect will not easily escape once detected. Locomotion of these insects has long been compared due to their divergent adaptations of speed range and morphology. Both have homologous muscles, motor units, sensors, and nervous centers that they use to control their six legs. However, strategies of control are likely different. Specifically, spike rate codes of motor neurons have limited information bandwidth for fast behaviors, and a spike timing code may be necessary. Here we investigate how the encoding of muscle activity differs between the two. In both animals, we compared activity from similar muscles in the coxa that extend the trochanter joint to the kinematic output of the leg. At their preferred speeds, the stride frequency of cockroaches is about five to ten times faster than that of stick insects. Therefore, this motor unit spikes less often per stride in the cockroach than the stick insect. Even though this discrepancy means the stick insect motor unit has higher potential information capacity, similar amounts of mutual information are shared between the motor unit and leg movement in the cockroach and stick insect. Moreover, when timing of motor unit activity is taken into account, encoded information triples in the cockroach and only doubles in the stick insect. This comparison indicates that during fast locomotion, the timing of muscle activity becomes more important for control compared to slow locomotion, although both strategies are important in each case.
