Straube, B., van Kemenade, B.M., Kircher, T. & Schülke, R. (2020). Transcranial Direct Current Stimulation Improves Action-Outcome Monitoring in Schizophrenia Spectrum Disorder. Submitted to Brain Communications https://academic.oup.com/braincomms/advance-article/doi/10.1093/braincomms/fcaa151/5907908
Background: Patients with schizophrenia spectrum disorder (SSD) often demonstrate impairments in action-outcome monitoring. Passivity phenomena and hallucinations, in particular, have been related to impairments of efference copy-based predictions which are relevant for the monitoring of outcomes produced by voluntary action. Frontal transcranial direct current stimulation (tDCS) has been shown to improve action-outcome monitoring in healthy subjects. However, whether tDCS can improve action monitoring in patients with SSD remains unknown.
Objective: We investigated whether tDCS can improve the detection of temporal action-outcome discrepancies in patients with SSD.
Methods: On 4 separate days, we applied sham or left cathodal/right anodal tDCS in a randomised order to frontal (F3/F4), parietal (CP3/CP4) and frontoparietal (F3/CP4) areas of 19 patients with SSD and 26 healthy control (HC) subjects. Action-outcome monitoring was assessed subsequent to 10 min of sham/tDCS (1.5 mA). After a self-generated (active) or externally generated (passive) key press, subjects were presented with a visual outcome (a dot on the screen), which was presented after various delays (0–417 ms). Participants had to detect delays between the key press and the visual consequence. Symptom subgroups were explored based on the presence or absence of symptoms related to a paranoid-hallucinatory syndrome (SSD phs+/phs-).
Results: In general, delay-detection performance was impaired in the SSD compared to the HC group. Interaction analyses showed group-specific (SSD vs HC) and symptom-specific (SSD phs+ vs SSD phs-) tDCS effects. Post-hoc tests revealed that frontal tDCS improved the detection of long delays in active conditions and reduced the proportion of false alarms in undelayed trials of the passive condition in patients. The SSD phs- group benefited especially from frontal tDCS in active conditions, while improvement in the SSD phs+ group was predominantly reflected in reduced false alarm rates in passive conditions.
Conclusion: These data provide some first evidence for the potential utility of tDCS in improving efference copy mechanisms and action-outcome monitoring in SSD. Current data indicate that improving efference copy-related processes can be especially effective in patients with no or few positive symptoms, while intersensory matching (i.e. task-relevant in passive conditions) could be more susceptible to improvement in patients with paranoid-hallucinatory symptoms.
Keywords: transcranial direct current stimulation; action-perception; action feedback; delay detection; schizophrenia.