Increasing propensity to mind-wander with transcranial direct current stimulation

Abstract

Humans mind-wander quite intensely. Mind wandering is markedly different from other cognitive behaviors because it is spontaneous, self-generated, and inwardly directed (inner thoughts). However, can such an internal and intimate mental function also be modulated externally by means of brain stimulation? Addressing this question could also help identify the neural correlates of mind wandering in a causal manner, in contrast to the correlational methods used previously (primarily functional MRI). In our study, participants performed a monotonous task while we periodically sampled their thoughts to assess mind wandering. Concurrently, we applied transcranial direct current stimulation (tDCS). We found that stimulation of the frontal lobes [anode electrode at the left dorsolateral prefrontal cortex (DLPFC), cathode electrode at the right supraorbital area], but not of the occipital cortex or sham stimulation, increased the propensity to mind-wander. These results demonstrate for the first time, to our knowledge, that mind wandering can be enhanced externally using brain stimulation, and that the frontal lobes play a causal role in mind-wandering behavior. These results also suggest that the executive control network associated with the DLPFC might be an integral part of mind-wandering neural machinery.

Keywords: brain stimulation; frontal lobes; mind wandering; spontaneous activity; tDCS.

Fig. 1.

Experimental paradigm. The SART paradigm that was used in the experiment is shown. Participants were asked to press a keyboard spacebar when a stimulus (digit) other than 3 appeared on a screen. For the digit 3, they had to restrain themselves from pressing the spacebar. The periodic thought probe consisted of a question regarding propensity to mind-wander (i.e., TUTs).

Fig. 2.

tDCS design. The stimulation started with the beginning of the experimental task. The first half of the experimental task was executed during the stimulation (20 min), and the second half of the experimental task was executed after the stimulation (20 min).

Fig. 3.

TUT results of experiments 1 and 2. (A) Results of experiment 1. The experiment using a within-subjects design included two conditions: prefrontal cortex stimulation and sham stimulation. (B) Results of experiment 2, The experiment using a between-subjects design included three conditions: prefrontal cortex stimulation, sham stimulation, and occipital cortex stimulation. A TUT rating scale ranging from 1 (minimal TUT) to 4 (maximal TUT) was used for both experiments. Analysis of the full experimental length (40 min) is shown. The asterisk denotes a significant difference (P = 0.021 in experiment 1 and P < 0.016 in experiment 2). The error bars denote the SEM.