Learning and memory in the cricket Gryllus bimaculatus

For insects living in an environment where food supplies constantly change, the ability to learn and to memorize the association of a specific cue with food is indispensable. The advantages of using insects for studies on learning and memory have been of great help to uncover a reliable capability of associative learning in various insect species. However, regarding neuronal and molecular mechanisms underlying learning and memory, reports are largely confined to a few insect species: the fruit fly, honey bee, and field cricket. In this review, I will introduce summarized results obtained from our studies on learning and memory in crickets. First, associative conditioning paradigms, which have been our main experimental procedures, will be described. Second, I will introduce the roles of octopamine and dopamine in conveying signals about appetitive stimuli and aversive stimuli, respectively, in learning and in memory retrieval. Third, short-term memory and long-term memory, two distinct memory phases of associative memory in crickets, will be introduced with details of signalling pathways involved in long-term memory formation. Fourth, the high capability of learning and memory and characteristics of complex memory will be described. Lastly, I will summarize the results of studies on age-related memory impairment in crickets. Crickets have the potential to be suitable model insects for studying neuromolecular mechanisms underlying learning and memory, following fruit flies and honey bees. Extensive studies on learning and memory in crickets will contribute to the elucidation of diversities in the neuromolecular mechanisms of learning and memory acquired through evolution in insects.