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Abstract:
Anhedonia is a core symptom in many mental disorders such as schizophrenia and major depression. It is generally defined as the 'inability to experience pleasure' but recent
debates push for a conceptual revision emphasizing an understanding of anhedonia as a motivational deficit to work for reward. In this study we aimed to clarify on the interplay of 'wanting' and 'liking' when physical effort is required in order to gain a reward. We used transcutaneous vagus nerve stimulation (tVNS) at the left ear to manipulate
metabolic signaling and the perceived availability of energy in the body. In a randomized crossover design, tVNS/sham stimulation was applied to N=20 healthy subjects. They completed 2 sessions of an adapted version of the effort allocation task and had to press a button until reaching a certain proportion of their maximum frequency in order to gain rewards. Preliminary results in 13 participants indicate that the task tracks important aspects of costs and benefits of action as expected. This is reflected in significant effects of reward levels (F(1,12)=9.67, p = .009) and an interaction of reward level and task diffculty
(F(1,12)=8.12, p = .015) on the motivation to expend effort across reward domains (money and food). Moreover, our preliminary results point to improvements in response vigor after tVNS, particularly in session 2, but more data is needed to substantiate the hypothesized effect. The findings confirm the suitability of the effort allocation task to study effort based decision making over time. Motivational vigor and subjective assessment of effort might be increased by tVNS. It therefore may be a promising approach to study motivational deficits related with anhedonia.
