Synergistic effects of noisy galvanic vestibular stimulation and oral L-dopa in improving manual tracking performance in Parkinson’s disease

s / Brain Stimulation 8 (2015) 360e377 368 cognitive deficits in working memory and sustained attention are associated with worse outcomes. A single session of transcranial direct current stimulation (tDCS) when given to the left dorsolateral prefrontal cortex (LDLPFC) has been shown to enhance working memory in healthy and clinical populations. We examined whether a single session of tDCS can similarly enhance working memory or sustained attention in euthymic bipolar disorder patients. Fifteen euthymic bipolar disorder patients were randomized to receive a single session of sham tDCS, anodal tDCS to the LDLPFC with extracephalic cathode (F-EX tDCS) and anodal tDCS to the LDLPFC with cerebellar cathode (F-CE tDCS), in a counterbalanced order. Participants completed a 3-back letter working memory task and an auditory continuous performance test ‘online’ during active or sham tDCS at each session. Active tDCS was administered for 30 minutes at 2 mA. No effect of either active F-EX or F-CE tDCS on working memory or sustained attention was found for the entire group. However, exploratory cluster analyses conducted on performance outcomes for both active conditions relative to sham tDCS revealed 2-cluster solutions for both abilities, suggesting improvement in some individuals but not others. Specifically, working memory improved in 4/15 with F-EX, and 5/15 patients with F-CE tDCS, respectively. Improved sustained attention performance was also found in 4/15 patients with F-CE tDCS, however, no improvement was found with F-EX tDCS. Cognitive enhancing effects of active F-EX and F-CE tDCS were evident only in a minority of participants. The considerable interindividual variability in outcomes observed with active tDCS is consistent with known variability in the motor cortex. This study provides preliminary evidence in support of F-CE tDCS for improving working memory and sustained attention in euthymic bipolar disorder patients.