Sleep in honeybees: its role in learning and memory

Sleep-like behavior has been studied in honeybees before but the possibility of sleep related memory processes had not been explored. We here describe a new technique which allowed us to not only investigate sleep parameters but also to manipulate bees to perform learning tasks. Restrained bees were placed under a web camera and their antennal activities, which we used as indicators of sleep, were monitored. We found that bees sleep more during dark cycle and less during the light cycle. We observed two distinct patterns of antennal activities. The symmetrical activities were more prominent during night and asymmetrical activities were more common during the day. In next set of experiments we subjected the bees to various conditioning stimuli and observed their sleep thereafter. We showed that bees subjected to odor and reward, using classical conditioning of the proboscis extension response (PER) showed lowered sleep compared to bees that were subjected to odor alone, reward alone or air alone. Sleep depriving with light interference after conditioning did not affect duration of sleep and learning was similar to the non-deprived group. Also, sleep deprivation with shaking did not have any effect on acquisition memory. In another set of experiments, we tried to block the extinction memory by subjecting the bees to acquisition learning on day-1, two extinction trials on day-2 followed by sleep deprivation with shaking and extinction memory retrieval on day-3. Sleep deprivation after two extinction trials showed reduced extinction memory compared to non-deprived group on day-3 retrieval tests. This showed that sleep deprivation does not affect all forms of learning.