Objective: To determine the causal role of pre-supplementary motor area in risk-taking behavior during sequential decision making.

Background: A recent functional magnetic resonance (fMRI) study in healthy individuals demonstrated an involvement of the pre-supplementary motor area (pre-SMA) in sequential risk taking. Activity in pre-SMA scaled positively with increasing risk when subjects continued with sequential gambling by pressing a button (1). Here we used inhibitory (1 Hz) repetitive transcranial magnetic stimulation (rTMS) to assess the causal development of pre-SMA in sequential gambling.

Methods: Nineteen healthy volunteers participated in this study (nine males, mean age: 29.15, range: 20-52). On two separate days, participants received real (100 % of M1 resting motor threshold, rMT, in the first dorsal interosseous (FDI) muscle) or sham (30 % rMT) 1Hz rTMS applied to right pre-SMA. After 30 minutes of rTMS, participants performed a sequential gambling task while we acquired whole-brain fMRI to assess neural activity. In the gambling task, participants accumulate points as they repeatedly roll a die until they decide to bank the winnings and start a new round, or until rolling a “1” resulting in the loss of all points in that round. Participants regularly switched be-tween blocks in which participants (1) had to press a button to continue gambling and not to press in order to end a gambling round (i.e., active gambling) or (2) participants remaining completely passive during the gam-bling trials where the die was rolled automatically until participants ended the round by pressing a button (i.e., passive gambling).

Results: Compared to sham rTMS, real rTMS of preSMA increased the tendency to continue with active gambling relative to passive gambling. However, this was only present in those individuals in whom real TMS was given in the first gambling session shown by a significant interaction effect between TMS and the order of the real and sham session (linear mixed model, p = 0.046).

Conclusions: These results indicate an involvement of pre-SMA in active gambling, when the gambling task was novel to the subjects. Inhibition the pre-SMA might facilitate habitual repetitive button presses and hereby, rendering indi-viduals more risk seeking. The findings are relevant for disorders of impulse control in, e.g., pathological gambling and impulse control disorder in Parkinson disease, a condition in which preSMA activity has been reported to be low.

References: 1. D. Meder, B. N. Haagensen et al., Tuning the Brake While Raising the Stake: Network Dynamics during Se-quential Decision-Making. J. Neurosci 36 5417-5426 (2016).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/pre-supplementary-motor-area-contributes-to-motor-aspects-of-sequential-risk-taking/