Divergent effects of high-frequency rTMS on cognitive performance in sleep-deprived nurses: An EEG brain network...

Sleep deprivation (SD) is a common occupational hazard, particularly for shift workers like nurses, leading to significant impairments in cognitive functions such as sustained attention and working memory. High-frequency repetitive transcranial magnetic stimulation (rTMS) is a promising neuromodulation technique for cognitive enhancement, but its effects in sleep-deprived individuals and the underlying neural mechanisms remain poorly understood. This study aimed to investigate the efficacy of high-frequency rTMS over the left dorsolateral prefrontal cortex (DLPFC) in modulating sustained attention and working memory after a night shift and to explore the associated changes in brain network topology.

In a within-subject design, 28 healthy female night-shift nurses participated in two experimental sessions after a night of work: one with real 5 Hz rTMS and one with sham rTMS applied to the left DLPFC. Following stimulation, participants performed a psychomotor vigilance task (PVT) and a 2-back task while their electroencephalography (EEG) data were recorded. Behavioral performance (reaction time and accuracy) and subjective fatigue were assessed. Graph theory analysis was applied to the EEG data to evaluate changes in functional brain network topology at both global and nodal levels.

Real rTMS significantly reduced subjective mental fatigue compared to sham stimulation. However, the behavioral effects were task-dependent. For the 2-back task, real rTMS led to a significant impairment in performance, characterized by slower reaction times and lower accuracy. For the PVT, there was a non-significant trend towards improved performance. These behavioral outcomes were mirrored by distinct patterns of network reorganization. During the PVT, real rTMS induced decreased functional segregation (lower clustering coefficient and local efficiency) in the alpha band. Conversely, during the 2-back task, it resulted in increased functional segregation and small-worldness in the theta band.

High-frequency rTMS over the left DLPFC exerts differential, task-specific effects on cognitive function in a sleep-deprived state. The impairment in working memory, despite a network configuration theoretically supportive of local processing, likely results from an inverted-U effect, where the rTMS pushed an already strained and compensating brain system past its optimal level of cortical excitability. The findings highlight the critical role of both baseline brain state and specific cognitive demands in determining the outcomes of neuromodulation, providing crucial insights for the targeted application of rTMS to mitigate cognitive deficits from sleep deprivation.