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Previous research has demonstrated that sleep spindles (11-17 Hz), which are known to be important for memory consolidation, and occipital alpha rhythms (8 – 11 Hz), which are suggested to play a role in inhibiting visual processing, are modulated by the thalamus; however, it is unclear how the relationship between the thalamus and these oscillations differs between wake and sleep. We recruited nine human subjects to undergo simultaneous EEG-fMRI data collection at 3T to investigate the dynamics of thalamo-cortical circuits. EEG data was scored to identify epochs of wake, stage 1, and stage 2 sleep, and pulvinar and mediodorsal nuclei were manually labeled in each subject. For each sleep stage, we calculated the temporal correlation between occipital alpha power and BOLD signals from the primary visual area (V1) as well as the pulvinar and mediodorsal nuclei; additionally, we measured the correlation between frontal spindle power and BOLD signals from the pulvinar and mediodorsal nuclei. Although we did not find any significant changes regarding spindle power, we found that the correlation between occipital alpha power and V1 BOLD activity was significantly negative in wake, and became significantly less negative during stage 2 sleep compared to wake. Furthermore, we found that the correlation between occipital alpha power and BOLD activity in the pulvinar nucleus became more positive in stage 2 sleep compared to both wake and stage 1 sleep, and was significantly positive during stage 2 sleep. Finally, we found that the correlations between occipital alpha power and BOLD signals from the mediodorsal vs. pulvinar nuclei were significantly different during wake. Therefore, our study is the first to identify focal thalamic circuit activity in the human brain associated with cortical rhythms during sleep. In addition, our results suggest that the neural circuits that regulate visual processing during wake become altered during sleep. Future studies should further investigate how the dynamics of other thalamic nuclei may also differ during wake vs. sleep.
Available for download on Sunday, April 26, 2020