The aim of the study is to explore the effect of transcranial direct current stimulation (tDCS) on either the right tempo-parietal junction (rTPJ) or the dorsomedial prefrontal cortex (dmPFC) in healthy older adults (replication in a different sample of a study by Martin et al., 2020).

Humans are fundamentally social animals. The ability to operate within large social networks requires considerable cognitive capacity, often referred to as social cognition. One social cognitive process thought to involve embodied and nonembodied processes is perspective-taking. Recently, the right temporoparietal junction (rTPJ) has been suggested as a key hub for embodied processing relevant to social cognition. A study of Martin et al. (2020) could further provide causal evidence that the right temporoparietal junction is involved specifically in the embodied component of perspective-taking. Specifically, HD-tDCS (high-definition transcranial direct current stimulation) to the right temporoparietal junction, but not another hub of the social brain (dorsomedial PFC), increased the effect of body position during perspective-taking, but not tracking. As social cognition is affected by the aging process and decline of socio-cognitive abilities is a key feature of neurological diseases such as Alzheimer's or Parkinson's disease, the aim of the present study is to replicate the findings of Martin et al., (2020) in a sample of healthy older adults to better understand the modulation of socio-cognitive processes in older age.

The aim of the study is to explore the effect of transcranial direct current stimulation (tDCS) on either the right tempo-parietal junction (rTPJ) or the dorsomedial prefrontal cortex (dmPFC) in healthy older adults (replication in a different sample of a study by Martin et al., 2020). 60 healthy older adults and 30 younger participants (serving as a control group) will be tested in a Reading the Eyes in the Mind Task (RMET) and a Task of Visual Perspective Taking (VPT) , while stimulation either the rTPJ or the dmPFC with either active or sham tDCS (stimulation only in the group of older participants). In the RMET the expectation is that older participants have higher reaction times after correct answers under rTPJ tDCS. No stimulation effects of the dmPFC are expected. In the VPT older participants are expected to have a selective effect on body position (similar to the results of Martin et al., 2020) under rTPJ stimulation, but not dmPFC stimulation.

A further focus of the study is how functional and structural connectivity of the brain and individual differences measured with an MRI assessment influence with the success of the RMET and VPT paradigms in an explorative research question.

Inclusion Criteria:

• healthy older (60 - 80 years) and younger (18 - 30 years) participants
• German as their main language or sufficient german skills to understand the experiment and the task

Exclusion Criteria:

• participants with neuropsychological or psychiatric disease that affect cognition.
• standard MRI exclusion criteria (e.g. pregnancy, metal implants)
• standard tDCS exclusion criteria (e.g. metal implants in the head)

Participants were asked to name the gender with which they identify.

Participants will receive either an active or a sham tDCS stimulation. Sham stimulation will use a ramp-up, so that participants are not able to tell whether they are stimulated or not, if they are tDCS naive.

Sham or active tDCS is applied via codes. Principal Investigators are blinded for these codes.