Abstract
The use of transcranial electrical stimulation (TES) as a method to augment neural activity has increased in popularity in the last decade and a half. The specific application of TES to the left prefrontal cortex has been shown to produce broad cognitive effects; however, the neural mechanisms underlying these effects remain unknown. In this work, we evaluated the effect of repetitive TES on cerebral perfusion. Stimulation was applied to the left prefrontal cortex on three consecutive days, and resting cerebral perfusion was quantified before and after stimulation using arterial spin labeling. Perfusion was found to decrease significantly more in a matched sham stimulation group than in a group receiving active stimulation across many areas of the brain. These changes were found to originate in the locus coeruleus and were broadly distributed in the neocortex. The changes in the neocortex may be a direct result of the stimulation or an indirect result via the changes in the noradrenergic system produced from the altered activity of the locus coeruleus. These findings indicate that anodal left prefrontal stimulation alters the activity of the locus coeruleus, and this altered activity may excite the noradrenergic system producing the broad behavioral effects that have been reported.
Highlights
The use of transcranial electrical stimulation (TES) as a method to augment neural activity has increased in popularity in the last decade and a half
The changes in the neocortex may be a direct result of the stimulation or an indirect result via the changes in the noradrenergic system produced from the altered activity of the locus coeruleus
The specific application of transcranial direct current stimulation (tDCS) with the anode placed over the left prefrontal cortex has been routinely applied in the literature with demonstrable behavioral effects in combating performance decrements associated with vigilance [8], decreasing the effect of fatigue on cognitive performance [9, 10], accelerating learning processes [2, 3, 11, 12], enhancing multitasking performance [13], and improving procedural memory [14]
Summary
The use of transcranial electrical stimulation (TES) as a method to augment neural activity has increased in popularity in the last decade and a half. Using a cohort of 30 participants (10 placebo gum, 10 caffeine gum with sham tDCS, and 10 2 mA anodal left prefrontal tDCS with placebo gum), McIntire et al [9] performed psychomotor vigilance tasks, delayed matching-to-sample working memory tasks, and the Mackworth clock test throughout 30 hours of continuous wakefulness They reported improved latencies in working memory tasks and faster reaction times in psychomotor tasks in the groups receiving active tDCS and caffeine gum compared to placebo throughout the sleep deprivation period. These findings provide evidence for the central role of the prefrontal cortex in vigilance, accelerated learning, fatigue, and multitasking performance but indicate that tDCS may be utilized to maintain performance levels in environments requiring little to no rest or settings required sustained attentional focus. Recent evidence suggests that the neuroplastic effects of tDCS have some dependence on synaptic activity during stimulation [7]
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