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Dissociable neural mechanisms of cognitive enhancement through transcranial stimulation and behavioral training.

Hayam A Alrasheed·Muhammad Ilyas·Zafar Ali Shah·Khlood M AlDossary·Ijaz Habib
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Abstract

BACKGROUND: Transcranial direct current stimulation (tDCS) and adaptive working memory (WM) training are promising cognitive enhancement approaches; however, their neural mechanisms and potential synergies remain poorly understood. OBJECTIVE: We directly compared how tDCS and WM training modulate neural oscillations during WM performance and examined whether combining both interventions produces additive effects. METHODS: We randomized 112 healthy adults into four groups: control (sham tDCS&#xa0;+&#xa0;non-adaptive 1-back), tDCS-only (active tDCS&#xa0;+&#xa0;non-adaptive 1-back), training-only (sham tDCS&#xa0;+&#xa0;adaptive n-back training), or combined (active tDCS&#xa0;+&#xa0;adaptive training). Participants underwent five daily intervention sessions. We recorded high-density EEG during transfer n-back tasks at baseline, post-intervention, and one-week follow-up. RESULTS: All active interventions improved WM performance relative to the control group, with the combined group showing the largest gains (n-back accuracy: +15.6% vs.&#xa0;+&#xa0;10.1% tDCS-only, +9.7% training-only, +0.7% control; all p&#xa0;<&#xa0;0.001). Critically, tDCS selectively increased gamma-band (30-50&#xa0;Hz) power in the frontal and parietal regions (cluster p&#xa0;=&#xa0;0.018, d&#xa0;>&#xa0;1.0), whereas WM training enhanced frontal theta-band (4-8&#xa0;Hz) power and theta-gamma phase-amplitude coupling (both cluster p&#xa0;<&#xa0;0.012, d&#xa0;>&#xa0;0.85). The combined group exhibited both neural signatures. Brain-behavior correlations revealed dissociable relationships: gamma increases predicted n-back accuracy improvements (r&#xa0;=&#xa0;0.61, p&#xa0;<&#xa0;0.001), whereas theta enhancements correlated with operation span gains (r&#xa0;=&#xa0;0.58, p&#xa0;=&#xa0;0.002). CONCLUSIONS: tDCS and WM training enhance cognition through distinct yet complementary neural mechanisms: tDCS via gamma-mediated cortical excitability and WM training via theta-mediated cognitive control. These findings provide neurophysiological evidence for multimodal enhancement strategies that target parallel pathways within WM networks.

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HumansTranscranial Direct Current StimulationCognitive EnhancementMaleMemory, Short-TermFemaleAdultElectroencephalographyYoung AdultCognitive TrainingCognitionBrainCognitive enhancementEEGNeural oscillationsPrefrontal cortexTranscranial direct current stimulationWorking memory trainingJournal ArticleRandomized Controlled Trial

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Hayam A Alrasheed, Muhammad Ilyas, Zafar Ali Shah, Khlood M AlDossary, Ijaz Habib. 2026-08-12. Dissociable neural mechanisms of cognitive enhancement through transcranial stimulation and behavioral training.. https://doi.org/10.1016/j.brainres.2026.150505

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Journal Article; Randomized Controlled Trial resourceAdult subjectBrain subjectCognition subjectCognitive Enhancement subjectCognitive Training subjectEEG subjectElectroencephalography subjectFemale subjectHumans subjectJournal Article subjectMale subjectRandomized controlled trials study

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