Abstract
Every night, the human brain produces thousands of downstates and spindles during non-REM sleep. Previous studies indicate that spindles originate thalamically and downstates cortically, loosely grouping spindle occurrence. However, the mechanisms whereby the thalamus and cortex interact in generating these sleep phenomena remain poorly understood. Using bipolar depth recordings, we report here a sequence wherein: (1) convergent cortical downstates lead thalamic downstates; (2) thalamic downstates hyperpolarize thalamic cells, thus triggering spindles; and (3) thalamic spindles are focally projected back to cortex, arriving during the down-to-upstate transition when the cortex replays memories. Thalamic intrinsic currents, therefore, may not be continuously available during non-REM sleep, permitting the cortex to control thalamic spindling by inducing downstates. This archetypical cortico-thalamo-cortical sequence could provide the global physiological context for memory consolidation during non-REM sleep.
Highlights
IntroductionThe human brain produces thousands of downstates and spindles during nonREM sleep
Every night, the human brain produces thousands of downstates and spindles during nonREM sleep
This grouping of spindles by slow waves may hierarchically organize memory replay originating in the hippocampus: firing patterns encoding memories are replayed during hippocampal sharp waves and ripples, which are associated with cortical spindles and down-to-upstate transitions in rats[13,14,15,16]
Summary
The human brain produces thousands of downstates and spindles during nonREM sleep. Earlier studies described the grouping of spindles by slow waves in the anaesthetized cat cortex and thalamus[10], in encephalography (EEG) recordings[11], and in medial depth recordings in humans[12]. This grouping of spindles by slow waves may hierarchically organize memory replay originating in the hippocampus: firing patterns encoding memories are replayed during hippocampal sharp waves and ripples, which are associated with cortical spindles and down-to-upstate transitions in rats[13,14,15,16]. Our findings suggest strong functional interactions, enabling a structured neurophysiological environment to emerge during memory replay in humans
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