Neural correlates of different behavioral response to transcranial direct current stimulation between patients in the unresponsive wakefulness syndrome and minimally conscious state.

In this study, we used event-related potential (ERP) and 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) to study the neural correlates of different behavioral response to transcranial direct current stimulation (tDCS) between patients in unresponsive wakefulness syndrome (UWS) and minimally conscious state (MCS). Thirteen patients (eight in UWS and five in MCS) underwent 20 anodal tDCS sessions of the left dorsolateral prefrontal cortex (DLPFC). Before tDCS, all the patients and six age-matched healthy subjects underwent a cerebral FDG-PET scan and ERP test. The coma recovery scale-revised (CRS-R) results revealed that after tDCS, a significant improvement was observed only in the MCS group. The ERP results supported that MCS patients preserved more high-order cortical information processing capacities. The residual brain metabolism in the left DLPFC in MCS patients supported that a residual brain activity in the stimulated area was necessary for a behavioral response to tDCS. Our study also demonstrated that the cerebral metabolic rates of glucose (CMRgl) ratios in intrinsic network were correlated significantly with CRS-R in MCS patients. In addition, the right prefrontal region might be another potential therapeutic target for MCS patients.