Disruption of neurotransmission in Drosophila mushroom body blocks retrieval but not acquisition of memory

Surgical, pharmacological and genetic lesion studies have revealed distinct anatomical sites involved with different forms of learning. Studies of pat ients with localized brain damage and work in rodent model systems, for exa mple, have shown that the hippocampal formation participates in acquisition of declarative tasks but is not the site of their long-term storage(1,2). Such lesions are usually irreversible, however, which has limited their use for dissecting the temporal processes of acquisition, storage and retrieva l of memories(3,4). Studies in bees and flies have similarly revealed a dis tinct anatomical region of the insect brain, the mushroom body, that is inv olved specifically in olfactory associative learning(5,6). We have used a t emperature-sensitive dynamin transgene, which disrupts synaptic transmissio n reversibly and on the time-scale of minutes(7), to investigate the tempor al requirements for ongoing neural activity during memory formation. Here w e show that synaptic transmission from mushroom body neurons is required du ring memory retrieval but not during acquisition or storage. We propose tha t the hebbian processes underlying olfactory associative learning reside in mushroom body dendrites or upstream of the mushroom body and that the resu lting alterations in synaptic strength modulate mushroom body output during memory retrieval.