P172 Frequency modulation of reward and punishment feedback processing during frontal cathodal transcranial direct current stimulation

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Introduction Evidence from electroencephalographam (EEG) studies indicates that reward and punishment-related feedback signals during decision making are associated with delta (1–3 Hz) and theta (4–7 Hz) oscillatory activity. Cathodal transcranial direct current stimulation (tDCS) to the frontal cortex has shown to impair decision making in healthy volunteers. Whether this impairment of cathodal tDCS involves the modulation of delta and theta activity to reward and punishment feedback is not known. Objective To test the hypothesis that cathodal tDCS attenuates reward and punishment related feedback activity in the delta and theta frequency range. Methods In a within-subjects, cross-over, double-blind, sham-controlled design, thirty healthy adult volunteers received cathodal over the frontal cortex (cathodal position: FPz, 5 × 7 cm, reference position: Cz, 10 × 10 cm) at an intensity of 1 mA for a maximum of twelve minutes. During tDCS administration, volunteers performed a decision making task in which reward and punishment feedback was delivered in a random fashion. Event-related EEG feedback signals to reward and punishment were recorded from thirteen sensors near the stimulation electrodes. A complex Morlet wavelets analysis was performed to extract delta and theta activity following reward and punishment feedback. The study protocol was approved by the Committee on Research Involving Human Subjects of the Radboud University Medical Centre. Results Artifact free EEG signals were analyzed in twenty-three participants from the posterior midline electrode. Cathodal compared to sham tDCS significantly decreased theta oscillatory activity between 210 and 500 ms to reward feedback. No effects were observed in the delta frequency range. Furthermore, no differences were observed during punishment-related feedback processing. Conclusion Our findings provide evidence for frequency-specific modulatory effects of cathodal tDCS. The reduction in theta oscillations during reward-related feedback processing may indicate reduced cortical responsiveness to reward signals.