Increase in EEG Alpha-to-theta Ratio After transcranial Direct Current Stimulation (tDCS) in Patients with Disorders of Consciousness: A Pilot Study

Background: Transcranial direct current stimulation (tDCS) has emerged as a potentially effective intervention for improving consciousness levels in patients with disorders of consciousness (DoC). Most studies demonstrating benefits have targeted the left dorsolateral prefrontal cortex (DLPFC). However, inconsistent results have been reported across studies, and the brain effects of the stimulation remain unclear. Objective: This work aimed to investigate the effects of a tDCS treatment on brain reactivity at rest in patients with DoC. Methods: A 10-session tDCS treatment was administered over the left DLPFC in a group of patients with DoC. The effect of this stimulation was tested by combining the conventional behavioral assessment, conducted with the Coma Recovery Scale-Revised (CRS-R), with a quantitative analysis of the resting-state electrical brain activity, measured by electroencephalography (EEG). Results: Following treatment, there was a slight improvement in CRS-R scores. More importantly, an increase in the ratio between alpha and theta power over posterior scalp regions was observed, even in patients who did not show changes in CRS-R scores. Conclusions: These findings suggest that adding a simple quantitative EEG analysis alongside conventional clinical assessment post-tDCS could enhance the detection of changes in brain reactivity.