Poster No:
751
Submission Type:
Abstract Submission
Authors:
Tara Rasmussen1, Paul Dux1, Hannah Filmer1
Institutions:
1The University of Queensland, Brisbane, Queensland
First Author:
Co-Author(s):
Introduction:
The impact of mind wandering on our daily lives ranges from diminishing productivity, to facilitating creativity and problem solving. There is evidence that distinct internal thought types can be modulated by transcranial direct current stimulation (tDCS; Boayue et al., 2021; Filmer et al., 2019; Rasmussen et al., 2024), although little is known about optimal stimulation parameters or the mechanisms behind such effects. In addition, recent findings suggest changes in dopamine availability may alter the effect tDCS on neural and behavioural outcomes (Borwick et al., 2020; Leow et al., 2023, 2024). Dopaminergic functioning has also been implicated in executive processes anticorrelated with mind wandering such as attention and working memory (Cools & D'Esposito, 2011; D'Ardenne et al., 2012), however the neurochemical mechanisms involved in internal thoughts are largely unknown. Thus, this registered report aimed to investigate the role of dopamine, and tDCS, on internal thought processes.
Methods:
Using an executive control task, we tested whether dopamine availability (levodopa or placebo) mediated the effects of online high definition tDCS (HD-tDCS; 2mA, or sham). We recruited a final sample of 231 participants, who were pseudo-randomly allocated between four conditions: (1) sham HD-tDCS and placebo; (2) sham HD-tDCS and levodopa; (3) 2mA anodal HD-tDCS and placebo; (4) 2mA anodal HD-tDCS and levodopa. Participants completed a 10-minute baseline block and 30-minute online stimulation block, consisting of 2mA active or sham HD-tDCS over the left prefrontal cortex. After completing the baseline block participants also received either a levodopa or placebo tablet from an alternative experimenter (to preserve the double blinding) and there was a 40-minute wait before then completing the stimulation block. During each block participants completed the finger-tapping random-sequence generation task, where they were required to generate random sequences in time to an ongoing metronome tone and they were periodically presented with four thought probes throughout, which were designed to assess the contents of participants thoughts.
Results:
This study primarily employed hierarchical order probit modelling to investigate the effects of HD-tDCS and dopamine on the dynamic thought types (Alexandersen et al., 2022; Boayue et al., 2021; Rasmussen et al., 2024). This analysis technique treated the thought probe responses as ordinal data, which allowed for investigation into time on task effects and individual's response variability across the duration of the task. There was no evidence for our hypothesised effect of left prefrontal cortex HD-tDCS reducing task unrelated thought, nor freely moving thought from both the probit modelling and the Bayesian independent samples t-test (BF01 = 10.12 and 2.60, respectively). This failure to replicate previous HD-tDCS findings emphasises the importance of employing robust methodological practices within this field to improve confidence in the findings. However, we did find that levodopa reduced freely moving thought, relative to placebo, via a negative main effect of levodopa in the winning probit model (b = -.41, 95% CI [-.74, -.10]). We also found preliminary evidence that dopamine availability may moderate the relationship between stimulation and behavioural variability performance during periods of task unrelated thought. Specifically, the winning probit models found active stimulation alone resulted in worse performance, relative to sham stimulation (b = .65, 95% CI [.21, 1.09]). However, levodopa and active stimulation combined improved performance during periods of task unrelated thought (b = -.54, 95% CI [-.96, -.14]).
Conclusions:
Overall, these findings suggest that stimulation does not affect dynamic internal thought, however there is initial evidence for the potential effectiveness of targeting the dopaminergic system to reduce spontaneous internal thoughts and improve behavioural performance.
Brain Stimulation:
Non-invasive Electrical/tDCS/tACS/tRNS 2
TDCS
Higher Cognitive Functions:
Executive Function, Cognitive Control and Decision Making 1
Modeling and Analysis Methods:
Bayesian Modeling
Physiology, Metabolism and Neurotransmission:
Pharmacology and Neurotransmission
Keywords:
Dopamine
Other - Mind wandering, dynamic thought, levodopa, tDCS, task unrelated thought, prefrontal cortex
1|2Indicates the priority used for review
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Please indicate below if your study was a "resting state" or "task-activation” study.
Other
Healthy subjects only or patients (note that patient studies may also involve healthy subjects):
Healthy subjects
Was this research conducted in the United States?
No
Were any human subjects research approved by the relevant Institutional Review Board or ethics panel?
NOTE: Any human subjects studies without IRB approval will be automatically rejected.
Yes
Were any animal research approved by the relevant IACUC or other animal research panel?
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Please indicate which methods were used in your research:
Behavior
Other, Please specify
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tDCS, pharmacological manipulation
Provide references using APA citation style.
Alexandersen, A., Csifcsák, G., Groot, J., & Mittner, M. (2022). The effect of transcranial direct current stimulation on the interplay between executive control, behavioral variability and mind wandering: A registered report. Neuroimage: Reports, 2(3), 100109. https://doi.org/10.1016/J.YNIRP.2022.100109
Boayue, N. M., Csifcsák, G., Kreis, I. V., Schmidt, C., Finn, I., Hovde Vollsund, A. E., & Mittner, M. (2021). The interplay between executive control, behavioural variability and mind wandering: Insights from a high-definition transcranial direct-current stimulation study. European Journal of Neuroscience, 53(5), 1498–1516. https://doi.org/10.1111/EJN.15049
Borwick, C., Lal, R., Lim, L. W., Stagg, C. J., & Aquili, L. (2020). Dopamine depletion effects on cognitive flexibility as modulated by tDCS of the dlPFC. Brain Stimulation, 13(1), 105–108. https://doi.org/10.1016/J.BRS.2019.08.016
Cools, R., & D’Esposito, M. (2011). Inverted-U–Shaped Dopamine Actions on Human Working Memory and Cognitive Control. Biological Psychiatry, 69(12), e113–e125. https://doi.org/10.1016/J.BIOPSYCH.2011.03.028
D’Ardenne, K., Eshel, N., Luka, J., Lenartowicz, A., Nystrom, L. E., & Cohen, J. D. (2012). Role of prefrontal cortex and the midbrain dopamine system in working memory updating. Proceedings of the National Academy of Sciences of the United States of America, 109(49), 19900–19909. https://doi.org/10.1073/PNAS.1116727109/SUPPL_FILE/PNAS.201116727SI.PDF
Filmer, H. L., Griffin, A., & Dux, P. E. (2019). For a minute there, I lost myself … dosage dependent increases in mind wandering via prefrontal tDCS. Neuropsychologia, 129, 379–384. https://doi.org/10.1016/J.NEUROPSYCHOLOGIA.2019.04.013
Leow, L.-A., Jiang, J., Bowers, S., Zhang, Y., Dux, P. E., & Filmer, H. L. (2024). Intensity-dependent effects of tDCS on motor learning are related to dopamine. Brain Stimulation, 17(3), 553–560. https://doi.org/https://doi.org/10.1016/j.brs.2024.03.015
Leow, L.-A., Marcos, A., Nielsen, E., Sewell, D. K., Ballard, T., Dux, P. E., & Filmer, H. L. (2023). Dopamine alters the effect of brain stimulation on decision-making. BioRxiv, 2023.06.05.543812. https://doi.org/10.1101/2023.06.05.543812
Rasmussen, T., Filmer, H. L., & Dux, P. E. (2024). On the role of prefrontal and parietal cortices in mind wandering and dynamic thought. Cortex, 178, 249–268. https://doi.org/10.1016/J.CORTEX.2024.06.017
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