Dissociable Roles Within the Social Brain for Self–Other Processing: A HD-tDCS Study

Abstract

Theories of right temporoparietal junction (rTPJ) function in social cognition include self–other distinction, self-inhibition, or embodied rotation, whereas the dorsomedial prefrontal cortex (dmPFC) is associated with integrating social information. However, no study has provided causal evidence for dissociable roles of the rTPJ and dmPFC in social cognition. A total of 52 healthy young adults were stratified to receive either dmPFC or rTPJ anodal high-definition transcranial direct current stimulation (HD-tDCS) in a sham-controlled, double-blinded, repeated measures design. Self–other processing was assessed across implicit and explicit level 1 (line-of-sight) and level 2 (mental rotation) visual perspective taking (VPT) tasks, and self–other effects on memory. DmPFC stimulation selectively increased the influence of the allocentric perspective during egocentric perspective taking, indexed by an increase in congruency effect across explicit VPT tasks. Moreover, dmPFC stimulation removed the self-reference effect in episodic memory by increasing the recognition of other and decreasing the recognition of self-encoded words. Stimulation of the rTPJ resulted in improved inhibition of the egocentric-perspective during level 2 VPT only, indexed by a reduction of the congruency effect when taking the allocentric perspective. This research supports theories suggesting that the rTPJ facilitates embodied mental rotation of the self into an alternate perspective, whereas the dmPFC integrates social information relevant to self-directed processes.

Common and unique effects of HD-tDCS to the social brain across cultural groups

“…A power analysis was computed using G*Power 3.1 indicating a sample size of 96 as adequate power Culture and social brain stimulation effects (0.8) with alpha set at 0.05. A sample of 104 was used to guard against dropout and maintain identical sample sizes with a previous study in Caucasian Australians only (Martin, Huang, et al, 2018). All participants were tDCS-naïve and had no history of psychiatric or neurological disorder and reported no psychoactive substance or medication use.…”

“…The return electrode was 9.2/11.5 cm inner/outer in diameter for the dmPFC site, whereas a smaller electrode of 7.5/9.8 cm was used for the rTPJ site, due to the position of the right ear. Current modelling and safety information for these montages are presented in detail in previous studies (Gbadeyan et al, 2016;Martin, Huang, Hunold, & Meinzer, 2017;Martin, Huang, et al, 2018).…”

“…The visual perspective taking (VPT) task has been described in detail previously (Martin, Dzafic, et al, 2017;Martin, Huang, et al, 2018;Martin et al, 2019). In brief, three separate tests were administered measuring implicit, explicit level one and explicit level two.…”

“…The main outcome of interest was the congruency effect (incongruentcongruent) for both egocentric and allocentric conditions. The avatar and traffic light factor was only of interest in the implicit VPT task and was collapsed across for the explicit tasks, similar to previous studies (Martin, Dzafic, et al, 2017;Martin, Huang, et al, 2018;Martin et al, 2019;Santiesteban, Catmur, Hopkins, Bird, & Heyes, 2014).…”

“…2016). Recently, we have demonstrated that high-definition transcranial direct current stimulation (HD-tDCS) to the dmPFC and rTPJ, can produce regional and task specific effects on self-other processes (Martin, Dzafic, Ramdave, & Meinzer, 2017;Martin, Huang, Hunold, & Meinzer, 2018). Excitatory stimulation to the dmPFC increased the integration of the other (allocentric) perspective into the self (egocentric) perspective across explicit VPT tasks and removed the SRE in episodic memory.…”