Introduction HD-tDCS of the dorsolateral prefrontal cortex A: Electrode position B: Simulated electrical field Stimulation The effect of transcranial direct current stimulation on the interplay between executive control, behavioral variability and mind wandering: A registered report - Mind wandering (MW) is a mental phenomenon we humans experience on a daily basis - High-Definition transcranial direct current stimulation (HD-tDCS) can modulate neuronal excitability and potentially lead to changes in cognition - This study aimed to replicate a previous finding of reduced mind wandering using HD-tDCS over the dorsolateral prefrontal cortex (DLPFC) in adult humans (Boayue et al., 2020) - Additionally we investigated if we could find neurophysiological markers of MW, and whether they were influenced by HD-tDCS, by recording electroencephalogram (EEG) and pupil size (pupillometry) Andreas Alexandersen aal077@uit.no +4791854015 Cognitive task and measured variables Finger-tapping random sequence generator task (FT-RSGT) - Press two buttons in a random order - Match every button press to a rhythmic tone - The tone is presented for 75ms, with an interval of 750ms - Behavioral variabiliy Standard deviation of inter-tap intervals - Approximate entropy Randomness of tapping pattern - Self reported mind wandering score Sampled by thought probes Where was your thoughts focused right before this question appeared? 1 2 3 4 Clearly on-task Clearly off-task Results Andreas Alexandersen1, Gábor Csifcsák1, Josephine Groot1, Matthias Mittner1 Registered hypotheses 1. Expected propensity to mind-wander to be reduced in the real relative to the sham stimulation group. 2. We expect behavioural variability (BV) to be increased prior to mind wandering when compared to on-task periods. 3. We expect the utilisation of executive resources (AE) to be reduced prior to mind wandering. 4. We expect an interaction effect of BV and AE such that the BV-MW effect is more pronounced during periods of high AE. Statistical model Bayesian hierarchical ordered-probit regression model Dependent variable: Thought-Probe responses Predictors: Behavioral variability (BV), Approximate entropy (AE), BV x AE, Trial (probe number), Group (sham vs real stimulation), Block (baseline vs stimulation) and Group x Block - Block nested in subject - Posterior mean and high density intervals of the regression coefficient as well as evidence ratios Methods 1Institute for Psychology, The Artic University of Norway (UiT) Baseline Stimulation Sham Offline Instructions and preparing equipment Training, miniquiz and baseline Stimulation or sham protocol Offline protocol Questionnaires and removing equipment Approximately 90 minutes total 10 minutes, 10 probes EEG & Pupillometry 800 trials N=100 10 minutes, 10 probes EEG and Pupillometry 800 trials (~70 oddballs) N=100 20 minutes, 20 probes HD-tDCS and Pupillometry 1600 trials N=50 20 minutes 20 minutes 20 minutes 10 minutes 10 minutes N=50 20 minutes, 20 probes HD-tDCS and Pupillometry 1600 trials Design Apparatus EEG A) Mismatch negativity waveforms for sham and real HD-tDCS groups B) Occipital alpha power spectra for the sham and real HD-tDCS groups C) Individual mismatch negativity amplitudes D) Posterior occipital alpha power values for sham and real HD-tDCS groups Pupillometry Predictors and coefficientsfrom the two Bayesian hierarchical linear regression models with tonic (left) and phasic (right) pupil responses as dependent variables C) Frequency (Hz) Time (ms) Power (µV²) 10 5 0 -800 -400 400 -1200 -1 0 1 Fz 5100 5400 high low Power (µV²) A) Voltage (µV) Time (ms) -100 0 100 200 300 400 0 1 2 3 4 -1 Difference waveform (Fz) Standard (Fz) Oddball (Fz) Difference waveform (POz) Difference waveform (Oz) B) Frequency (Hz) Power (µV²) 0 2 4 6 8 10 12 14 16 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Difference waveform On-task Mind wandering POz/Oz 3.6 4.8 MW OT Power (µV²) A) Mismatch negativy in the expected time window B) Increased occipital alp