P120 Asymmetric function of the right and left inferior parietal lobule in mind wandering – A tDCS and fMRI study

Abstract

Recent researches have shown that inappropriate self-generated thought, namely mind wandering (MW), is decreased by transcranial direct current stimulation (tDCS) of the right inferior parietal lobule (IPL) through altering information flow within the default mode network (DMN). However, it remains unknown whether this effect is specific to the “right” IPL. We explored the difference of right and left IPL involvement in MW using tDCS and fMRI. As the right IPL has been indicated to regulate other core regions of the DMN, any reduction in MW resulting from tDCS should be observed only by right IPL stimulation. Twenty-seven non-clinical subjects were allocated to either a right- or left-tDCS group and completed two experiments with different tDCS conditions (real and sham) over an interval of more than a week (the experiment order was counterbalanced). On both days subjects underwent resting-state fMRI before and after tDCS. After the second scan they completed an attention task containing thought probes measuring their attentional state (on-/off-task). The ratio of off-task thoughts was defined as MW propensity. In the real tDCS condition, direct current (density: 0.043 mA/cm2) was applied through anodal electrodes placed on either the right or left IPL (reference: contralateral cheek) for 20 min. At the behavioral level, only stimulation of the right IPL decreased MW propensity compared to the sham condition. In parallel, directed connection strengths within the DMN core regions (calculated by spectral dynamic causal modeling) significantly changed only by stimulation to the right IPL. As anodal tDCS is thought to enhance original connectivity/function, this supports the possibility that the right but not the left IPL regulate other DMN regions. Mediation analysis further revealed that the changes to the recurrent connections of the posterior cingulate cortex and its afferent connections from other core regions of the DMN partially mediated the decrease in MW. Interestingly, in contrast with the inhibitory function of the right IPL connections, the left IPL connections were associated with increasing MW. In conclusion, the present study is the first to demonstrate the neural asymmetry of right and left IPL function in MW. Download : Download high-res image (281KB) Download : Download full-size image Download : Download high-res image (356KB) Download : Download full-size image