Advancing Transcranial Electrical Stimulation for Personalised Cognitive Enhancement

Transcranial electrical stimulation (tES) demonstrates potential for cognitive enhancement, including improvements in vigilant attention. However, its efficacy across the population is limited by numerous challenges, including inter-individual variability in the electric fields induced by tES and brain-state dependent responses to stimulation.
This thesis first presents a comprehensive literature review critically analysing challenges in non-invasive brain stimulation (NIBS) research, encompassing the principal brain stimulation modalities and sources of variability. Recommendations are presented, including accounting for inter-individual variability, inclusive research practices, improving spatial precision, and the use of multimodal and multi-site stimulation, among others.
Following the literature review, this thesis addresses the challenge of accessible, participant-specific tES dose control through a novel MRI-free approach developed using the largest electric field modelling simulation of its kind. This scalable approach, which utilises readily available demographic and morphological data, significantly reduces peak electric field strength variability across participants compared to fixed-dose stimulation.
Commercial and academic trends within NIBS and tES are analysed to assess the market readiness for the proposed MRI-free tES dosing approach. This includes a systematic search of academic publications across NIBS modalities and of clinical trials utilizing tES. In addition, the current state of the commercial usage of tES and intellectual property challenges are discussed.
This thesis then explores the electrophysiological correlates of vigilant attention during a continuous random-dot motion task, known to measure spatial attention performance. Electroencephalography features associated with arousal, active attentional suppression and off-task thought are identified. Potentially enabling the future development of brain-state dependent stimulation.
Subsequently, a within-subject sham-controlled electroencephalography and transcranial direct current stimulation experiment investigates the effects of transcranial direct current stimulation applied to the right dorsolateral prefrontal cortex on vigilant attention. While no significant effects were observed, the methodological insights of this work are discussed.
Together, the advances presented in this thesis contribute to a multifaceted approach to addressing key challenges in NIBS research. This thesis proposes a scalable approach to personalized tES dosing, insights into the electrophysiological underpinnings of vigilant attention and offers broader NIBS recommendations. Ultimately, these contributions aim to advance translational, accessible, and individualized cognitive enhancement.