Accelerated rTMS for Enhancing Intact Cognition: An Examination of Dose Effects on Electrocortical Indicators of Attention and Working Memory
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BACKGROUND AND AIMS
Improvements in cognition (e.g., attention, working memory) are common after repetitive trans-cranial magnetic stimulation (rTMS) treatment and have also been observed in non-clinical samples. This study investigated whether rTMS can enhance cognitive resilience in individuals who perform in high-stress environments using cognitive measures and electroencephalography (EEG) to explore potential neural mechanisms of rTMS-induced cognitive change.
METHODS
40 college-educated adults not reporting cognitive or psychiatric concerns underwent a 5-day accelerated (10 sessions/ day) rTMS treatment and pre-post cognitive assessment. Participants were assigned to 1 of 10 doses defined as number of active vs. sham stimulation sessions/ day (total active pulses = 3,000 – 30,000). To assess cognitive effects, standard batteries (NIH Toolbox, Spaceflight Cognitive Assessment Tool for Windows [WinSCAT]) were administered – and a subset (n=21) also did an N-Back working memory task with EEG measurement – before, immediately after, and 1 month after rTMS. For all indices, linear and quadratic correlations of pre-to-post-rTMS change with dose were examined to test if an optimal dose was achieved.
RESULTS
From pre- to post-rTMS, participants improved in fluid cognition (working memory, processing speed) as measured by NIH toolbox, t (39)=8.4, p <.001, d =1.3, and WinSCAT, t (39)=4.1, p <.001, d =.65; and, improvement in the latter related linearly to rTMS dose, r (39)=.40, p =.01. Regarding EEG, subjects who received high (6+ active sessions/day) also showed increased amplitudes of an event-related marker of stimulus-directed attention (P300) whether it was elicited by simple task targets, t (10)=3.1, p =.01, d =.95, or task-unrelated noise stimuli played during the task as probes of peripheral attention, t (10)=3.6, p =.005, d =1.1. Additionally, there were linear relationships between change magnitude and rTMS dose for simple task target-related, r (20)=.45, p =.04, and peripheral noise-related, r (20)=.54, p =.009, P300s.
CONCLUSIONS
rTMS improved fluid reasoning abilities and also changed how dynamic attention is deployed during high-demand challenges as a potential mediator of fluid cognition improvements. While linear dose-response relationships support that changes were rTMS-elicited, absence of a response curve asymptote also suggests that still-higher doses could be warranted to achieve maximal effects in non-clinical samples.
