Abstract
The ability to learn sequential contingencies of actions for predicting future outcomes is indispensable for flexible behavior in many daily decision-making contexts. It remains open whether such ability may be enhanced by transcranial direct current stimulation (tDCS). The present study combined tDCS with functional near-infrared spectroscopy (fNIRS) to investigate potential tDCS-induced effects on sequential decision-making and the neural mechanisms underlying such modulations. Offline tDCS and sham stimulation were applied over the left and right dorsolateral prefrontal cortex (dlPFC) in young male adults (N = 29, mean age = 23.4 years, SD = 3.2) in a double-blind between-subject design using a three-state Markov decision task. The results showed (i) an enhanced dlPFC hemodynamic response during the acquisition of sequential state transitions that is consistent with the findings from a previous functional magnetic resonance imaging (fMRI) study; (ii) a tDCS-induced increase of the hemodynamic response in the dlPFC, but without accompanying performance-enhancing effects at the behavioral level; and (iii) a greater tDCS-induced upregulation of hemodynamic responses in the delayed reward condition that seems to be associated with faster decision speed. Taken together, these findings provide empirical evidence for fNIRS as a suitable method for investigating hemodynamic correlates of sequential decision-making as well as functional brain correlates underlying tDCS-induced modulation. Future research with larger sample sizes for carrying out subgroup analysis is necessary in order to decipher interindividual differences in tDCS-induced effects on sequential decision-making process at the behavioral and brain levels.
Highlights
Everyday decision-making often involves considerations about short- or long-term goals that entail learning from immediate or delayed action–outcome associations for updating one’s behavior
We provide empirical evidence that functional near-infrared spectroscopy (fNIRS) is a suitable method for measuring hemodynamic correlates of sequential decision-making
The results showed that the acquisition of sequential state transitions to predict future rewards is accompanied by enhanced dorsolateral prefrontal cortex (PFC) (dlPFC) activation in younger adults
Summary
Everyday decision-making often involves considerations about short- or long-term goals that entail learning from immediate or delayed action–outcome associations for updating one’s behavior. Reaching long-term goals often presupposes transitioning between different decision states, involving complex valuebased learning or adaptive assignment of values to sequential actions based on the outcome (Puterman, 1990; Beroggi, 2013; Preuschoff et al, 2013) These abilities and their underlying neural mechanisms have previously been investigated (see Badre and D’Esposito, 2009 for a review; Tanaka et al, 2004; Smittenaar et al, 2013; Eppinger et al, 2015; Wittkuhn et al, 2018).
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