A new perspective for evaluating the efficacy of tACS and tDCS in improving executive functions: A combined tES and fNIRS study

Abstract

BackgroundExecutive function enhancement is considered necessary for improving the quality of life of patients with neurological or psychiatric disorders, such as attention‐deficit/hyperactivity disorder, obsessive‐compulsive disorder and Alzheimer's disease. Transcranial electrical stimulation (tES) has been shown to have some beneficial effects on executive functioning, but the quantification of these improvements remains controversial. We aimed to explore the potential beneficial effects on executive functioning induced by the use of transcranial alternating current stimulation (tACS)/transcranial direct current stimulation (tDCS) on the right inferior frontal gyrus (IFG) and the accompanying brain function variations in the resting state.MethodsWe recruited 229 healthy adults to participate in Experiments 1 (105 participants) and 2 (124 participants). The participants in each experiment were randomly divided into tACS, tDCS, and sham groups. The participants completed cognitive tasks to assess behavior related to three core components of executive functions. Functional near‐infrared spectroscopy (fNIRS) was used to monitor the hemodynamic changes in crucial cortical regions in the resting state.ResultsInhibition and cognitive flexibility (excluding working memory) were significantly increased after tACS/tDCS, but there were no significant behavioral differences between the tACS and tDCS groups. fNIRS revealed that tDCS induced decreases in the functional connectivity (increased neural efficiency) of the relevant cortices.ConclusionsEnhancement of executive function was observed after tES, and the beneficial effects of tACS/tDCS may need to be precisely evaluated via brain imaging indicators at rest. tDCS revealed better neural benefits than tACS during the stimulation phase. These findings might provide new insights for selecting intervention methods in future studies and for evaluating the clinical efficacy of tES.

Does tDCS Selectively Modulate the Pre-frontal Cortex Hemodynamics? An Immediate Effect-Controlled Trial on Depressed and Healthy People

“…Functional near-infrared spectroscopy (fNIRS) is a noninvasive optical imaging technique that relies on the difference in the absorption of NIR light between oxyhemoglobin (HbO) and deoxyhemoglobin (HbR) [13]. The technique quantifies the hemoglobin concentration changes using variations in the absorbed light intensity measured by emitting continuous wave light through the skull into the brain [11,14].…”

“…The technique quantifies the hemoglobin concentration changes using variations in the absorbed light intensity measured by emitting continuous wave light through the skull into the brain [11,14]. The fNIRS has been proposed as a less expensive alternative over the fMRI to assess brain blood flow [13]. However, the fNIRS has been usually used in combination to cognitive or motor tasks in order to activate specific cortical regions of interest, not isolating the tDCS effect itself.…”