An Analysis of Field Potentials During Different Tailflip Behaviours in Crayfish

Abstract

Crayfish tailflips have been intensively studied to reveal the decision-making processes and neural organisation underlying a stereotyped escape behaviour. Three behaviours mediated by different neural pathways have been well described: medial giant, lateral giant and non-giant tailflips. It has proved difficult to distinguish between the three without invasive or restrictive experimental manipulation. We report unambiguous differences between the signals generated by the crayfish Cherax destructor during the three types of tailflip when recorded by bath electrodes placed in the holding aquarium. Using our ability to distinguish between the different behaviours in freely moving animals we examined the relationship between the type of tailflip evoked by stimulation to different parts of the body. The transition zone between medial and lateral giant tailflips is the thoracic-abdominal border but it is not absolute and some stimuli produce responses that cannot be unambiguously assigned to either behavioural category. We examined the latency between stimulation at different points down the length of the body and the appearance of the electrical signal accompanying escape for both medial and lateral tailflips. We used two methods to estimate the proportion of the latency accounted for by giant fibre conduction velocity. The results support current views of the differences between the activation sites of the two giant fibre systems and suggest why stimulation in the transition zone results in ambiguous outcomes.