The Association of Sleep Spindle and Slow Wave Phase-Amplitude Cross Frequency Coupling during NREM with Executive Function in a Sleep Clinic Population

There is evidence that the onset of cognitive impairments associated with dementia and normal ageing are related to sleep disturbances. The present study investigated the link between sleep microarchitecture in NREM and cognitive performance in patients referred to a sleep clinic (N =60). A cognitive battery assessing verbal episodic memory (RAVLT) and executive function (Stroop, Trails) was administered prior to a full polysomnography. Sleep spindles and slow waves in NREM sleep were the sleep microarchitecture aspects of interest. There were no significant correlations between these individual characteristics and any measure of cognition. However, the results of a phase-amplitude cross frequency coupling analysis showed that preferred phase, a measure of sleep spindle and slow wave coupling, was correlated with both measures of executive function. The other measures of coupling, the modulation index, did not show this correlation. There was no association between either of the coupling characteristics and verbal episodic memory in either frontal or central brain regions. The fact that both measures of executive function, but not the measure of verbal episodic memory, were significantly correlated with preferred phase in the frontal electrodes strongly implicates the role of coupling in executive functions. Further, while executive function appears to be more trait-dependent and does not rely on variations in brain activity night-to-night, it seems as though verbal episodic memory is more influenced by neural communication as described by the sleep-dependent memory consolidation theory. More research is required to determine whether both pre- and post- memory testing is required to assess the effects of coupling on memory, as well as to investigate the utility of coupling as a more sensitive predictor of cognition, as well as it’s functional role in neural communication