Closed-Loop Transcranial Electrical Neurostimulation for Sustained Attention Enhancement: Towards Personalized Intervention Strategies

Sustained attention is a critical aspect of daily life. It is essential for effectively accomplishing tasks and engaging with the surrounding world. Whether it's studying, working on assignments, or driving, maintaining focus and concentration for extended periods is crucial, since sustained attention enables to stay on track, resist distractions, and achieve heightened levels of productivity and performance. This study aims to investigate the effectiveness of adaptive transcranial direct current stimulation (tDCS) in enhancing sustained attention. A sample of 10 healthy university students aged between 20 and 27 years old is used during the execution of a specific cognitive task, namely the Continuous Performance Task-AX (CPT-AX). By applying weak electrical currents (0.1 mA-2 mA) to specific regions of the scalp, this non-invasive technique modulates the underlying brain activity associated with sustained attention. The study consists of three distinct phases. Firstly, an initial electroencephalography (EEG) assessment is conducted to identify reliable metrics for evaluating attention levels. The analysis reveals that entropy measures effectively capture brain signals' complexity and information content, providing discriminative features to differentiate between states of attention and relaxation. Subsequently, an experiment is carried out using a fixed 1 mA current intensity to evaluate the impact of tDCS on attentional performance under controlled conditions. Lastly, a final experiment is conducted with continuous monitoring of the relevant metrics. This real-time assessment enables the dynamic personalized optimization of the current amplitude and stimulation site, tailored specifically to each participant. In particular, the current amplitude can range between 0.5 mA and 2 mA, while the stimulation site can be either frontal (anode: F3, cathode: Fp2) or parietal (anode: P3, cathode: P4). The findings demonstrate improvements in accurate rates, reduced reaction times, and enhanced entropy metrics during the adaptive tDCS intervention compared to the fixed current amplitude experiment. The results highlight the potential of adaptive tDCS as a personalized intervention for enhancing sustained attention in healthy individuals. Future investigations are needed to explore long-term effects, optimize stimulation protocols, and generalize the outcomes to other populations and cognitive tasks.