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#3131 Stimulation of the ventrolateral prefrontal cortex speeds up evidence accumulation in conflictual-uncertain environments
  1. Alekhya Mandali,
  2. Natalie Valle Guzman,
  3. Valerie Voon
  1. Department of Psychiatry, University of Cambridge, UK


Introduction Evaluation of the available choices, an integral step in decision-making, leads to the selection of the optimal and most rewarding one. This process of choice selection depends on its features such as value and reward-likelihood, which form the basis for constructs such as Conflict- easy or difficult (difference between reward probabilities of the stimuli-pairs) and Uncertainty- low, medium, or high (inverse U-shaped probability-uncertainty function).The ventrolateral prefrontal cortex (vlPFC) has been implicated in various processes ranging from uncertainty processing to washing behaviours in Obsessive-compulsive disorder (OCD). Here, we target the vlPFC using trans-cranial stimulation, to modulate decision-making behaviours in the context of conflict and uncertainty.

Methods Using a single-blinded design, we tested 60 healthy controls (30 per group) randomly allocated to either active (continuous theta burst protocol c-TBS) or sham group. The c-TBS protocol used the standard three-pulse burst design repeated every 200ms, with a total of 600 pulses delivered at stimulation intensity set at 80% of the participants Active Motor Threshold. The sham stimulation was delivered with the coil positioned at a 90 angle to the target. Post-stimulation (active or sham), the participants completed 134 trials of the sequential learning paradigm, which consisted of 2 stages. We focused on the second stage of the task, specifically on Conflict and Uncertainty which were used as model dependents of a hierarchical drift-diffusion model(HDDM) to extract the parameters (a- amount of evidence accumulated before making a decision) and the drift rates (v- information processing speed).

Results Using the choice and reaction time information as inputs to the HDDM model, we extracted the threshold and drift rates for all conflict and uncertainty conditions. A Bayesian repeated-measures ANOVA on threshold showed a very strong evidence for the main effect of conflict-uncertainty condition (BF10 = 5.2 x 1010) and stimulation by condition interaction (BF10 = 6.4 x 103) but no main effect of stimulation (BF10 = 0.46). A Bayesian Independent samples t-test showed strong evidence (BF10 = 77.54) for stimulation to speed up the decision-making process, by decreasing the amount of evidence accumulated (threshold)whilst selecting a choice in a difficult uncertain scenario.

Conclusions By applying an inhibitory based stimulation protocol tovlPFC, we show a modulation in behaviour specific to context, where the choices are similar in value but their reward likelihood being uncertain. This finding has key implications to the design of novel interventions for OCD.

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