Enhancement of cognitive insight and higher-order neurocognitive function by fronto-temporal transcranial direct current stimulation (tDCS) in patients with schizophrenia

Abstract No studies have examined the effects of fronto-temporal transcranial direct current stimulation (tDCS) on cognitive insight and neurocognitive function in schizophrenia patients and the dynamic interplay between tDCS-induced changes in these two outcomes. In this double-blind, randomized, sham-controlled study, we investigated the effects of fronto-temporal tDCS [anode corresponding to left dorsolateral prefrontal cortex and cathode to left temporo-parietal junction; 2-mA, twice-daily sessions for 5 days] on illness severity, psychosocial functioning, cognitive insight and neurocognitive function in schizophrenia patients (N = 60). The authors observed significant trends that tDCS ameliorated the severity of total and general psychopathology as measured by the Positive and Negative Syndrome Scale. No significant effects were observed for other psychopathological symptoms and psychosocial functioning. Cognitive insight as measured by the Beck Cognitive Insight Scale (BCIS) was rapidly enhanced by 10-session tDCS (F = 10.80, Cohen's d = 0.44, p = 0.002) but the beneficial effect became borderline significant 1 month after stimulation. A trend-level improvement with tDCS of planning ability (F = 6.40, Cohen's d = 0.339, p = 0.014) as measured by the accuracy in Tower of London task was also observed. In the active tDCS group, the change in cognitive insight from baseline to immediately after tDCS assessment was positively correlated with that in planning ability (r = 0.46, p = 0.015), which was independent of the corresponding change in illness severity. The promising results regarding the fast-acting beneficial effects of tDCS on cognitive insight and planning ability in schizophrenia require confirmation in future replication studies.