Visual discrimination transfer and modulation by biogenic amines in honeybees

For more than a century, visual learning and memory has been studied in the honeybee Apis mellifera using operant appetitive conditioning. Although honeybees show impressive visual learning capacities in this well-established protocol, operant training of free-flying animals can hardly be combined with invasive protocols for studying the neurobiological basis of visual learning. In view of that, different efforts have been made to develop new classical conditioning protocols for studying visual learning in harnessed honeybees, though learning performances remain considerably poorer than those obtained in free-flying animals. Here we investigated the ability of honeybees to use visual information acquired during classical conditioning in a new operant context. We performed differential visual conditioning of the proboscis extension reflex (PER) followed by visual orientation tests in Y-maze. Classical conditioning and Y-maze retention tests were performed using a same pair of perceptually isoluminant monochromatic stimuli, to avoid the influence of phototaxis during free-flying orientation. Visual discrimination transfer was clearly observed, with pre-trained honeybees significantly orienting their flights towards the former positive conditioned stimulus (CS+). We thus show that visual memories acquired by honeybees are resistant to context changes between conditioning and retention test. We combined this visual discrimination approach with selective pharmacological injections to evaluate the effect of dopamine and octopamine in appetitive visual learning. Both octopaminergic and dopaminergic antagonists impaired visual discrimination performances, suggesting that both these biogenic amines modulate appetitive visual learning in honeybees. Our study brings new insights into cognitive and neurobiological mechanisms underlying visual learning in honeybees.