WANING OF CRAYFISH ESCAPE RESPONSE AS A RESULT OF REPEATED STIMULATION

1. 1. The tail-flip escape reflex of the crayfish is very difficult to elicit reliably. The most reliable stimulus we could find was a brief lateral compression of the abdomen. 2. 2. About 36 per cent of the crayfish tested would not respond at all when tested with this stimulus (under moderate restraint), whereas about 2 per cent responded to each of 10 stimuli delivered at 4-min intervals. Individual differences in escape reflex excitability were consistent over several weeks of testing. 3. 3. Repetition of the stimulus at 5-min intervals caused failure of the reflex within ten trials in most animals. 4. 4. During rest after repetitive stimulation, recovery of reflex excitability occurred gradually. Only a small amount of recovery had occurred after two hr, and excitability was probably still subnormal after more than six hr. 5. 5. When stimuli leading to reflex failure were confined to one abdominal segment, the excitability of other segments became depressed but not to the same degree as did that of the stimulated segment. 6. 6. The failure of the reflex is not efferent to the giant axons which mediate the tail-flip response and is unlikely to be due to sensory accommodation. 7. 7. The above properties are typical of the habituation processes which can be demonstrated in most escape and startle reflexes. They are of special interest, however, because the crayfish escape reflex is unusually amenable to detailed electrophysiological analysis. © 1969.