Effects of repetitive transcranial magnetic stimulation on cognition through sleep slow-wave activity in older adults.

Abstract

Background: Increases in slow-wave activity (SWA) during sleep are associated with improvements in overnight memory retention and cognitive performance in young adults. Links between SWA and overnight improvements in cognition among older populations, however, are poorly understood. This proof-of-concept pilot study used a single session of excitatory repetitive transcranial magnetic stimulation (rTMS) during wakefulness to increase SWA during subsequent sleep in older adults with subjective cognitive decline. We examined whether this single night increase in SWA led to improvements in overnight memory retention, executive function, and vigilant attention.

Methods: Participants (mean age = 70 years, SD = 5.2) with subjective reports of cognitive decline participated in a 40-min session of active (n = 11) or Sham (n = 9) high frequency (10 Hz) rTMS applied to the left dorsolateral prefrontal cortex. Participants spent two nights in a sleep lab pre- and post-rTMS with high-density EEG to assess changes in SWA. A behavioral task battery examining overnight memory retention (Word Pair Task, Face-Profession, Object Recognition), executive control (Stroop, Sternberg, task-switching) and vigilant attention (Psychomotor Vigilance Task) were also assessed pre- and post-rTMS.

Results: Overall reaction time (RT) on the Stroop task, across task conditions, improved between sessions with rTMS, but not with Sham. There was no evidence of improved performance on other cognitive domains with rTMS. Increased fronto-parietal SWA in the first NREM period was associated with the improvement in overall Stroop RT. Stroop congruent and neutral trial RT, Stroop neutral trial accuracy, and Sternberg working memory RT were also associated with increased whole night and first NREM period SWA.

Conclusions: These preliminary results suggest that acute increases in SWA are associated with improved processing speed in older adults at risk for cognitive decline, as evidenced by an improvement in overall Stroop RT as opposed to improvements on specific task conditions. Multi-session rTMS studies and randomized controlled trials are needed to fully assess the effect of enhanced SWA through rTMS on improvements in overnight memory retention and executive function.