Enhancement of synchronization between hippocampal 1 and amygdala theta waves associated with pontine wave 2 density 3 4 Running head : Hippocampal and amygdala theta synchronization

30 Theta waves in the amygdala are known to be synchronized with theta waves 31 in the hippocampus. Synchronization between amygdala and hippocampal theta waves 32 is considered important for neuronal communication between these regions during the 33 memory-retrieval process. These theta waves are also observed during rapid eye 34 movement (REM) sleep. However, few studies have examined the mechanisms and 35 functions of theta waves during REM sleep. This study examined correlations between 36 the dynamics of hippocampal and amygdala theta waves and pontine (P) waves in the 37 subcoeruleus region, which activates many brain areas including the hippocampus and 38 amygdala, during REM sleep in rats. We confirmed that the frequency of hippocampal 39 theta waves increased in association with P wave density, as demonstrated in our 40 previous study. The frequency of amygdala theta waves also increased with in 41 associated with P wave density. In addition, we confirmed synchronization between 42 hippocampal and amygdala theta waves during REM sleep in terms of the 43 cross-correlation function and found that this synchronization was enhanced in 44 association with increased P wave density. We further studied theta wave 45 synchronization associated with P wave density by lesioning the pontine subcoeruleus 46 region. This lesion not only decreased hippocampal and amygdala theta frequency, but 47