Papel do acoplamento hipocampo-pré-frontal para a formação de memória espacial durante o sono

Abstract

For declarative memory consolidation, recently encoded experiences become available for long-term memory evocation. In order for this to happen, information initially processed in the hippocampus seems to be transferred to associative cortical regions, such as the pre-frontal cortex (PFC). Scientific evidence indicates that sleep has a fundamental role in information transfer after codification in the hippocampus. More specifically, the different sleep phases’ neural rhythms generate synchronization patterns that act as opportunity windows for memory corticalization. An example is the theta oscillation (5-12Hz), whose disturbance during REM sleep is sufficient to impair spatial memory consolidation. A possible explanation for this pheno- menon is that theta oscillations would aid the communication between different brain regions, such as hippocampal CA1 and the medial prefrontal cortex (mPFC). Therefore, disruption of this hippocampal-cortical communication during REM sleep could be sufficient to impair spa- tial memory consolidation. However, this hypothesis has not been directly tested. As a first step in this direction, we investigated whether there is any significant association between oscilla- tory patterns during REM sleep and object location memory consolidation. For this, adult male Wistar rats were implanted with electrodes in the mPFC and CA1 of the hippocampus, in order to record their sleep and the dynamics between the regions. Simultaneously to the recordings, the animals were subjected to the object location test. We then evaluated several parameters, such as sleep architecture, local oscillatory patterns, and synchrony measurements between re- gions of interest before and after memory acquisition. Furthermore, we sought to correlate such measurements during sleep, especially REM sleep, with the animals’ performance in the test. Our results indicate a significant reduction in latency to REM in post-learning sleep (-54%, pai- red t-test, one-tailed, p=0.037). We also observed a significant correlation (Pearson correlation, p=0.04 and r=0.69) between hippocampal-cortical phase coherence in theta during REM and the animal’s performance in the object location memory task. Our findings are in line with pre- vious studies on the role of REM sleep in memory formation. We hope that our study motivates future investigations involving strategies for selectively manipulating the coordination between the hippocampus and mPFC during REM sleep.