Protocerebral circadian pacemakers in crayfish: evidence for mutually coupled pacemakers

Similar to intact crayfish, animals with an isolated protocerebrum-eyestalk complex, exhibit competent circadian rhythms in the electroretinogram (ERG). The ERG rhythms of the two eyes remain in phase after isolation of the protocerebrum but can be desynchronized after surgical bisection of the protocerebrum. The desynchrony of the two ERG rhythms reveals the existence of at least two circadian pacemakers in the eyestalk-protocerebrum complex. In addition, the fact that desynchrony of the ERG rhythms only occurs in bisected preparations suggests that pathways between the protocerebral lobes normally couple the two pacemakers.