Modulating mental state recognition by anodal tDCS over the cerebellum

Abstract

Increasing evidence from neuroimaging and clinical studies has demonstrated cerebellar involvement in social cognition components, including the mentalizing process. The aim of this study was to apply transcranial direct current stimulation (tDCS) to modulate cerebellar excitability to investigate the role the cerebellum plays in mental state recognition. Forty-eight healthy subjects were randomly assigned to different groups in which anodal, cathodal, or sham tDCS (2 mA for 20 min) was delivered centering the electrode on the vermis to stimulate the posterior portion of the cerebellum. The ability to attribute mental states to others was tested before and after tDCS using a digital version of the 'Reading the Mind in the Eyes test', which includes visual perceptive and motor stimuli as control conditions. Correct response and reaction times (RTs) were recorded. The results revealed a significant reduction in RTs between the baseline and post-stimulation sessions after cerebellar anodal tDCS only for mental state stimuli (Wilcoxon test p = 0.00055), whereas no significant effect was found in the cathodal or sham conditions or for visual perceptive and motor stimuli. Overall, our study suggests that cerebellar anodal tDCS might selectively improve mental state recognition and constitute an effective strategy to positively modulate the mentalizing process.

Figure 1

Reading the Mind in the Eyes Test results. Graphs show the mean reaction times (in milliseconds) (a) and the number of correct responses (b) for each group and stimuli type before and after tDCS stimulation. Standard Error is reported (a, b). *p value < 0.005. Regarding the mental state stimuli, the results for each group are plotted as median before (in red) and after stimulation (in green) (c). Box: 25–75%; Whisker: non-outlier range.

Figure 2

Time course of the tDCS real vs sham stimulation. Schematic depiction of the time course of the real cerebellar tDCS conditions (a) and time course of the sham tDCS condition (b).

Figure 3

Schematic depiction of the experimental procedure. (a) Example of tDCS extracephalic montage in which the anode (red) is centered 2 cm below the inion and the cathode (blue) is placed over the right deltoid. (b) Time course of the experimental phases: the behavioral task was administered, before and 35 min after the end of the stimulation session, using a PC with Presentation software, and the correct response and reaction time were recorded; the tDCS session lasted 20 min. (c) Stimuli examples of the digital RMET: in the computerized version of the RMET the original photos (MS stimuli) were randomly administered together with two kinds of control stimuli to evaluate visual perception (V-P) (trials = 36) and visual motor (V-M) (trials = 36) factors. The stimuli were administered with an intertrial interval of 6 s and were preannounced by a cross appearing in the middle of the screen for 500 ms. MS = Mental State stimuli; V-P = visual perception; V-M = visual motor. Affinity Photo 1.10 was used to optimize images (https://affinity.serif.com), and Microsoft Office 365 PowerPoint was used to layout the figure.