Crayfish escape behavior: Neurobehavioral analysis of phasic extension reveals dual systems for motor control

Summary

• 1. Electromyograms (EMGs) from phasic abdominal muscles of unrestrained and variously restrained crayfish were used to study the involvement of sensory information in phasic abdominal extension during escape behavior.

• 2. Lateral giant neuron impulses (escape commands), elicited either with natural stimuli or via direct shocks, caused a flexion which was followed at short and near-constant latency by extension (Figs. 1 and 2).

• 3. Extension produced as above was termed ‘postgiant’ extension and had the following properties: it was labile (Figs. 3 and 4), it was eliminated when flexion was prevented, and it was reduced or eliminated if flexion was hampered (Fig. 5 and Table 1).

• 4. The above observations, which suggest sensory involvement in post-giant extension, are complemented by the observation that phasic extensor activity could be evoked without prior flexion by rapid water displacements over the abdomen or by taps to the abdomen (Fig. 7).

• 5. In addition to post-giant extension the extensors were active during many kinds of non-giant tailflips. During swimming, non-giant extensionpreceded flexion at short and constant latency (Fig. 9) and persisted after flexor root section (Fig. 10) or during restraint. Non-giant extension was not labile (Fig. 11), and it depended on the integrity of the rostral nervous system.

• 6. Animals frequently initiate escape with a giantmediated tailflip followed by non-giant swimming. When this occurred our most common observation was consistent with the interpretation that both postgiant and non-giant extension occurred between the first two flexions (Figs. 13 and 14).

• 7. We interpret our results to mean that extension occurs as a chained reflex following giant-mediated flexion, with subsequent control of the extensors passing to a central pattern generator.