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

Abstract

Total words: 5105Culture and social brain stimulation effects ABSTRACT Cultural background influences social cognition, however no study has examined brain stimulation differences attributable to cultural background. 104 young adults [52 South-East Asian Singaporeans (SEA); 52 Caucasian Australians (CA)] received anodal high-definition transcranial direct current stimulation (HD-tDCS) to the dorsomedial prefrontal cortex (dmPFC) or the right temporoparietal junction (rTPJ). Participants completed tasks with varying demands on self-other processing including visual perspective taking and episodic memory with self and other encoding. At baseline, SEA showed greater self-other integration than CA in the level one (line-of-sight) VPT task as indexed by greater interference from the alternate perspective. Anodal HD-tDCS to the dmPFC resulted in the CA performing closer to the SEA during egocentric perspective judgements. Baseline performance on level two (embodied rotation) VPT task and the self-reference effect in memory (SRE) was comparable between the two groups. In the combined sample, HD-tDCS to the rTPJ decreased the interference from the egocentric perspective during level two VPT and dmPFC HD-tDCS removed the SRE in episodic memory. Stimulation effects were comparable when baseline performance was comparable. When baseline performance differed, stimulation differences were identified. Therefore, social cognitive differences due to cultural background are an important consideration in social brain stimulation studies.

The right temporoparietal junction is causally associated with embodied perspective taking

“…At the same time rTPJ was desynchronising with the ventral visual stream, suggesting that rTPJ might control the switch from external events to internal states and information manipulation such as embodied mental simulations (see also Bzdok et al, 2013; Wu et al, 2015). The division of labour between TPJ and executive and social processing areas in the prefrontal cortex during embodied perspective taking has now further been corroborated by the current results, as well as by our previous anodal HD-tDCS stimulation studies (Martin et al, 2018; Martin et al, 2019). Using anodal HD-tDCS Martin et al (2017a) were able to characterise the role of dmPFC as crucial to suppressing the egocentric perspective.…”

“…Moreover, it provides site- and task-specific evidence for the efficacy of HD-tDCS to modulate specific embodied cognitive processes relevant to social functioning. The results therefore support the theory that the rTPJ is causally involved in embodied processes relevant for social cognition (Arzy et al, 2006; Wang et al, 2016; Martin et al, 2018; Martin et al, 2019). Anodal HD-tDCS to the rTPJ increased the effect of body posture on perspective taking corroborating previous evidence using TMS, which found reduced embodied processing after inhibiting the rTPJ (Wang et al, 2016), yet, faster perspective taking and enhanced embodied facilitation after entraining rTPJ at theta frequency in contrast to alpha frequency (Gooding-Williams et al, 2017).…”

“…Moreover, older adults may use less embodied strategies (Costello and Bloesch, 2017) coupled with reduced social cognitive performance (Moran et al, 2012). Recently, non-invasive brain stimulation has shown considerable promise as a method for enhancing embodied processes (Wang et al, 2016; Lira et al, 2018; Martin et al, 2018; Hornburger et al, 2019; Martin et al, 2019) and our present and previous results across several social cognitive tasks (Martin et al, 2017a; Martin et al, 2017b, 2018; Martin et al, 2019), suggest that HD-tDCS offers an exciting new technique for improving specific social cognitive processes across a range of cohorts, especially when based on modelling of electric current flow (Martin et al, 2017b, 2018). Therefore, future research investigating the efficacy of HD-tDCS to improve embodied social cognitive processes in clinical groups is warranted.…”

“…Safety has also been demonstrated (Gbadeyan et al, 2016). Electrodes were held in place with electroconductive gel (Weaver Ten20 conductive paste) and an EEG cap to ensure consistent adhesion to the skin (for details see Martin et al, 2019) of tDCS setup. The dmPFC was located 65% of the distance from FZ towards the FPz using the 10-20 EEG system.…”

“…In comparison, perspective-tracking, or understanding what another person can see, simply requires a line-of-sight judgement that does not rely on embodied processes to the same extent (Michelon and Zacks, 2006; Kessler and Rutherford, 2010). Recently, the right temporoparietal junction (rTPJ) has been suggested as a key hub for embodied processing relevant to social cognition (Wang et al, 2016; Martin et al, 2018; Martin et al, 2019). In the present study, we aimed to provide causal evidence that the rTPJ is involved in a site- and task-specific manner in embodied perspective taking.…”