Impact of neuromodulation on excessive daytime sleepiness: a narrative review.

Excessive daytime sleepiness (EDS), a global health issue, impairs daily functioning and increases the risk of accidents. Neuromodulation, which can adjust cortical excitability, has emerged as a promising EDS treatment. Although only a few studies have been conducted on this topic and sample sizes were consistently small, the available literature shows that anodal transcranial direct current stimulation or high frequency transcranial alternating current stimulation has been shown to reduce EDS caused by a variety of disorders. Moreover, high frequency repetitive transcranial magnetic stimulation (rTMS) over the left dorsolateral prefrontal cortex or low frequency rTMS targeting the right dorsolateral prefrontal cortex or posterior parietal cortex has demonstrated significant positive effects in the treatment of daytime sleepiness. Moreover, non-invasive neuromodulation has been found to provoke a net gain of cortical arousal, which is linked to the modulation of cortical activity by reducing slow-frequency (δ and θ) activity while enhancing faster frequencies (β1 and β2). Invasive neuromodulation, such as deep brain stimulation, has positive effects on sleep regulation in Parkinson's disease patients, which may contribute to an improvement in EDS. Similarly, vagus nerve stimulation has demonstrated potential benefits for patients with epilepsy, especially those experiencing EDS or co-morbid narcolepsy. Noninvasive neuromodulation for the treatment of EDS presents a promising horizon of opportunities to enhance current therapeutic modalities. However, further research is warranted to refine treatment protocols and validate outcomes through objective measures.