ABSTRACT
BACKGROUND: Several recent studies indicated that transcranial direct current stimulation (tDCS) of the left dorsolateral prefrontal cortex (DLPFC) showed promising results in patients in a minimally conscious state (MCS). However, the neurological characteristics of patients in MCS considered to be tDCS responders have not been firmly established. OBJECTIVES: In the current study, we aimed to explore a reliable electrophysiological biomarker of tDCS response before the patients' inclusion in a tDCS protocol. METHOD: A hierarchical auditory event-related potential (ERP) pattern was applied to thirty-one MCS patients who subsequently received 20 anodal tDCS sessions of the left DLPFC over 10 consecutive working days. The patients were divided into responders and non-responders according to the Coma Recovery Scale-Revised (CRS-R) behavioral evaluation, and the differences in cortical information processing were compared using the P300 component in the ERP pattern. RESULTS: For the Tone-SON (TO) paradigm, CRS-R score (OR = 2.229, 95% CI: 1.241-4.005, P = 0.007) at admission was independently associated with tDCS response, while in the SDN-SON (DO) paradigm, CRS-R score at admission (OR = 2.369, 95% CI: 1.143-4.908, P = 0.020) and P300 (OR = 22.795, 95% CI: 1.823-285.038, P = 0.015) were independently associated with tDCS response in MCS patients. CONCLUSION: Our findings showed that higher total CRS-R score and presence of P300 in the hierarchical auditory ERP pattern, especially P300 in the DO paradigm, are associated with tDCS response in MCS patients. We speculate that P300 in the DO paradigm indicates patients with more preserved semantic processing abilities, and a priority to recover. The results provide important information for guidelines on the use of tDCS in MCS patients.
