Impaired illness awareness or insight into illness (IIA) is a common feature of schizophrenia that contributes to medication nonadherence and poor clinical outcomes. Neuroimaging studies suggest IIA may arise from interhemispheric imbalance in frontoparietal regions, particularly in the posterior parietal area (PPA) and the dorsolateral prefrontal cortex (dlPFC). In this pilot study, we examined the effects of transcranial direct current stimulation (tDCS) on brain regions implicated in IIA.

Eleven patients with schizophrenia with IIA (≥3 PANSS G12) and 10 healthy controls were included. A crossover design was employed where all participants received single-session bi-frontal, bi-parietal, and sham stimulation in random order. For each condition, we measured (i) blood oxygen level-dependent (BOLD) response to an illness awareness task pre- and post-stimulation, (ii) regional cerebral blood-flow (rCBF) prior to and during stimulation, and (iii) changes in illness awareness.

At baseline, patients with schizophrenia showed higher BOLD-response to an illness awareness task in the left-PPA compared to healthy controls. Bi-parietal stimulation reduced the interhemispheric imbalance in the PPA compared to sham stimulation. Relatedly, bi-parietal stimulation increased rCBF beneath the anode (21% increase in the right-PPA), but not beneath the cathode (5.6% increase in the left-PPA). Bi-frontal stimulation did not induce changes in rCBF. We found no changes in illness awareness.

Although single-session tDCS did not improve illness awareness, this pilot study provides mechanistic justification for future investigations to determine if multi-session bi-parietal tDCS can induce sustained changes in brain activity in the PPA in association with improved illness awareness.

Schizophrenia and bipolar disorder are associated with impairments in insight, leading to a poorer clinical outcome and functioning. Earlier studies comparing the two disorders on the basis of insight included inpatients or patients who were clinically symptomatic. The current study therefore assessed patients in remission of affective symptoms and positive symptoms of schizophrenia.

Schizophrenia and bipolar disorder patients (n = 32, n = 34; respectively) underwent clinical and functional evaluations. Insight was assessed using the Scale to assess Unawareness of Mental Disorder (SUMD) and the Positive and Negative Syndrome Scale (PANSS). Attention was assessed using a continuous performance task (CANTAB's Rapid Visual Information Processing).

Schizophrenia patients displayed poorer insight into having a mental disorder and into the social consequences thereof compared to the bipolar disorder patients. They were also less aware of their anhedonia-asociality. Age, however, was significantly correlated with insight and differences in insight between the patient groups became nonsignificant when age was used as a covariate in the statistical analyses. Age was not a moderating variable of the relationship between diagnosis and insight.

Significant differences in insight held by the two patient groups might be related to age disparities between patient groups. Earlier studies did not adequately address these age differences, their cause and their potential effects on findings. These issues are explored with regard to the findings of the current study, as well as earlier studies, emphasizing the need for further research of the relationship between age and insight.