Light Enables Long-Term Memory Maintenance in Fruit Flies

S. Inami et al., “Environmental light is required for maintenance of long-term memory in Drosophila,” J Neurosci, 40:1427–39, 2020.

by Diana Kwon

As Earth rotates around its axis, the organisms that inhabit its surface are exposed to daily cycles of darkness and light. In animals, light has a powerful influence on sleep, hormone release, and metabolism. Work by Takaomi Sakai, a neuroscientist at Tokyo Metropolitan University, and his team suggests that light may also be crucial for forming and maintaining long-term memories.

The puzzle of how memories persist in the brain has long been of interest to Sakai. Researchers had previously demonstrated, in both rodents and flies, that the production of new proteins is necessary for maintaining long-term memories, but Sakai wondered how this process persisted over several days given cells’ molecular turnover. Maybe, he thought, an environmental stimulus, such as the light-dark cycles, periodically triggered protein production to enable memory formation and storage.

Sakai and his colleagues conducted a series of experiments to see how constant darkness would affect the ability of Drosophila melanogaster to form long-term memories. Male flies exposed to light after interacting with an unreceptive female showed reduced courtship behaviors toward new female mates several days later, indicating they had remembered the initial rejection. Flies kept in constant darkness, however, continued their attempts to copulate.

The team then probed the molecular mechanisms of these behaviors and discovered a pathway by which light activates cAMP response element-binding protein (CREB)—a transcription factor previously identified as important for forming long-term memories—within certain neurons found in the mushroom bodies, the memory center in fly brains.

“The fact that light is essential for long-term memory maintenance is fundamentally interesting,” says Seth Tomchick, a neuroscientist at the Scripps Research Institute in Florida who wasn’t involved in the study. However, he adds, “more work will be necessary” to fully characterize the molecular mechanisms underlying these effects.