Cathodal Transcranial Direct Current Stimulation of the Prefrontal Cortex Abolished Socio-emotional Influences over Instrumental Behaviour
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Emotional responses to environmental or internal stimuli have been proven to influence human instrumental decision making. Literature suggests that this emotional biasing reflects the influence of an affective controller of behavior that regulates automatic, evolutionary preprogrammed responses on a system that controls instrumental action selection. In many circumstances these two controllers interact with each other, thus biasing our behavior. When this interaction conflicts with current instrumental goals, the prefrontal cortex (PFC) is recruited to override the effect of such affective responses. This finding suggested the hypothesis that enhanced activity of the PFC would decrease the emotional bias on instrumental behavior. To test this hypothesis directly, we investigated the effects of anodal, cathodal, and sham transcranial direct current stimulation (tDCS, a brain stimulation technique able to increase/decrease the excitability of cortical neurons) in 120 women performing a task assessing affective influences on instrumental action. This task combines an emotional decision making game with a force platform, which is able to detect subjects’ movements. On the platform, participants first learned whole body approach/avoidance actions based on monetary feedback. Stimulation was then applied and they were tasked to repeat the learned instrumental actions while being primed by emotional faces (happy/angry) during extinction. A previous study implementing a very similar task found that angry faces (versus happy) slowed instrumental approach (as compared to avoidance). We predicted that anodal tDCS (found to increase the excitability of cortical neurons) of the PFC would decrease this emotional bias, while cathodal stimulation (found to decrease the excitability of cortical neurons) would either increase it or leave it unaltered. Contrary to our expectations, we found that it was cathodal tDCS that abolished the emotional bias. We speculated that this finding might reflect differential effects of tDCS on the evaluation/integration of affective and instrumental values abolished the emotional bias. We speculated that this finding might reflect differential effects of tDCS on the evaluation/integration of affective and instrumental values.
Faculteit der Sociale Wetenschappen