Cathodal tDCS evidence on how perceived body weight similarity and weight stigma can modulate the understanding of observed familiar actions.

Previous experimental evidence has shown that motor resonance (i.e. the mapping of others’ actions onto one’s own motor repertoire) can be influenced by individual differences in personality traits. However, no evidence has been reported so far of the effects of physical appearance and negative attitudes toward obesity to the mechanism of MR. In the present study, normal-weight and overweight participants performed an implicit task, in which they were observing amateur actors reaching and grasping a light or heavy cube with or without deception (true vs. fake actions). Physical similarity between observers and actors was manipulated by presenting videos of slim or overweight actors. Before the task, all participants received cathodal or sham transcranial direct current stimulation (tDCS) over the left motor cortex, previously shown to decrease excitability of the aforementioned cortical area. At the end of each video-clip participants were instructed to indicate the correct cube size (light or heavy). Fat phobic attitudes and automatic preference for thin than fat people were also examined. Signal detection analysis (d’) on the currently acquired accuracy data (N=15) has indicated a significant 3-way interaction between type of stimulation (cathodal, sham), type of action (true, fake) and model weight. Overall, both normal and overweight participants were able to better simulate the actions performed by the slim as compared to overweight actors. However, this effect was diminished after cathodal stimulation of the left hemisphere motor area. Hence, we provide experimental evidence of action simulation and understanding being modulated by an implicit preference towards slim bodies.