Transcranial Direct Current Stimulation and Decision-Making: The Neuromodulation of Cognitive Reflection

The ability to make judgements and decisions is crucial to our lives. The dual-process framework of judgement and decision-making (e.g. Stanovich, 2009) proposes that decisions are usually made using mental processes relying on automatic processes (called Type 1 processing) or on more controlled processes (called Type 2 processing). According to this theory, when we make a decision without conscious effort we rely on the autonomous processes of Type 1 intuitive thinking, which is prone towards errorful decision-making. Alternatively, if we use Type 2 thinking by committing cognitive resources (e.g., working memory) we engage analytic thinking by at least partly inhibiting Type 1 processing. The primary goal for this thesis is to test whether Type 1 versus Type 2 processes in decision-making can be linked to different neural substrates. Transcranial direct current stimulation (tDCS), a non-invasive method for enhancing or decreasing cortical excitability was used. Participants completed decision-making tasks (e.g., Cognitive Reflection Test (CRT), syllogistic reasoning) to capture performance indicating Type 1 or Type 2 processing, and executive function tasks to assess the basis of Type 1 and Type 2 processing. First, a meta-analysis was performed on a variety of experiments using tDCS, finding evidence for the involvement of frontal structures in judgement and decision-making. In subsequent experiments stimulation of the right but not left dorsolateral prefrontal cortex (DLPFC) with anodal tDCS increased performance compared to sham in the CRT and solving vignettes measuring heuristic thinking. In experiment three there was a cumulative effect of neuromodulation on Type 2 processing, with an increase in reflective thinking performance following each of two stimulation sessions. Individual differences in thinking dispositions and cognitive ability could not explain the results, and there were no performance-enhancing effects of stimulation on syllogisms or executive functions. These experiments provide evidence for the involvement of the right DLPFC in decision-making which relies on the inhibition of pre-potent responses (e.g., the CRT).