[Electrophysiological and Pharmacological Research on Neural Activity in the Neocortex and Hippocampus During Sleep]

Sleep is fundamental for living animals. Although they are not conscious during sleep, their brains are continuously working. This neural activity during sleep can be reflected by neural oscillations closely related to cognitive function. While the relationship between neural activity in sleep and cognition has been extensively investigated, it is not fully understood how neural activity in sleep and relevant memory are modulated by specific receptors. In particular, I focused on melatonin receptors and their agonist, ramelteon. While the effects of ramelteon on sleep have been widely documented, it is still poorly understood how ramelteon affects learning and memory as well as neural activity in sleep. To address this question, I first recorded neural oscillations in the neocortex of rats treated with ramelteon and found that ramelteon promoted non-rapid eye movement (NREM) sleep and increased fast gamma power in the primary motor cortex during NREM sleep. I then evaluated the behavioral performance of ramelteon-treated mice using the novel object recognition task and the spontaneous alternation task, demonstrating that ramelteon enhanced object recognition memory and spatial working memory. These results shed light on new aspects of the functions of melatonin receptors.