Effects of non-invasive brain stimulation on visual perspective taking: A meta-analytic study

Brain stimulation over dorsomedial prefrontal cortex causally affects metacognitive bias but not mentalising

Despite the importance of metacognition for everyday decision-making, its neural substrates are far from understood. Recent neuroimaging studies linked metacognitive processes to dorsomedial prefrontal cortex (dmPFC), a region known to be involved in monitoring task difficulty. dmPFC is also thought to be involved in mentalising, consistent with theoretical accounts of metacognition as a self-directed subform of mentalising. However, it is unclear whether, and if so how, dmPFC causally affects metacognitive judgements, and whether this can be explained by a more general role of dmPFC for mentalising. To test this, participants performed two tasks targeting metacognition in perceptual decisions and mentalising whilst undergoing excitatory anodal versus sham dmPFC tDCS. dmPFC tDCS significantly decreased subjective confidence reports while leaving first-level performance in accuracy and reaction times unaffected, suggesting a causal contribution of dmPFC to representing metacognitive bias. Furthermore, we found no effect of dmPFC tDCS on neither metacognitive sensitivity and efficiency nor on mentalising, providing no evidence for an overlap between perceptual metacognition and mentalising in the dmPFC. Together, our findings highlight the dmPFC's causal role in metacognition by representing subjective confidence during evaluations of cognitive performance.

Intact embodiment during perspective-taking in older adults is not affected by focal tDCS

Embodied processing is crucial for visual perspective taking (VPT), with evidence from non-invasive transcranial direct current stimulation (tDCS) suggesting a causal role of the right temporoparietal junction (rTPJ). However, it is not known whether such embodied factors are maintained in older adults or whether rTPJ-tDCS has comparable effects in advanced age. We employed a balanced and sham-tDCS controlled, double-blinded, cross-over design, including two randomized experimental groups of healthy older adults, receiving focal tDCS over either the rTPJ (n = 30), or a control region in the dorsomedial prefrontal cortex (dmPFC, n = 30). A healthy young control group (n = 30, not receiving tDCS) was included to investigate potential changes in embodied processing in older adults. All groups completed neuropsychological baseline testing and an experimental VPT paradigm, in which perspective-taking (requiring embodied rotation) and perspective-tracking (line-of-sight judgements) were assessed. Structural magnetic resonance imaging data were acquired to conduct individualized current flow simulations, aimed at identifying potential changes in neurophysiological effects of tDCS in older adults. Older adults responded slower across perspective tracking and perspective taking tasks but showed comparable embodied effects of body posture and angle of rotation during perspective taking. Contrary to previous results in younger adults that demonstrated regionally and task-specific effects of focal rTPJ-tDCS, no stimulation effects on embodied processing were found in older adults. Electrical field simulations suggested focal current delivery in both age-groups but also significantly reduced current strength in the target regions for tDCS in older adults. Older adults are as embodied as young adults during perspective taking. However, tDCS administered to the rTPJ or dmPFC had no effect, which may be explained by reduced current delivery to the target regions due to age-associated changes in skull and brain anatomy and/or functional brain reorganization. Our results are in line with previous studies suggesting that tDCS effects obtained in young participants may not translate directly to advanced age. Future studies could address this by using individualized modelling approaches aimed at adjusting current dose for (older) study participants and pre-stimulation functional imaging involving VPT tasks-of-interest, to identify optimized target regions for tDCS.Registration: ClinicalTrials.gov Identifier: NCT04633499.

Tipping the balance between fairness and efficiency through temporoparietal stimulation

Maximizing the welfare of society requires distributing goods between groups of people with different preferences. Such decisions are difficult because different moral principles impose irreconcilable solutions. For example, utilitarian efficiency (maximize overall outcome across individuals) may need trade-off against Rawlsian fairness norms (maximize the outcome for the worst-off individual). We identify a brain mechanism enabling decision-makers to solve such trade-offs between efficiency and fairness using separate neuroimaging and sham-controlled brain stimulation experiments. As activity in the temporoparietal junction (TPJ) increases, people are more likely to implement the Rawlsian fairness criterion rather than efficiency or inequality concerns. Strikingly, reducing TPJ excitability with brain stimulation reduces the concern for fairness in fairness-efficiency trade-offs. Moreover, the reduced fairness concerns statistically relate to stimulation-induced reductions in perspective-taking skills as measured in a separate task. Together, our findings not only reveal the neural underpinning of efficiency-fairness trade-offs but also recast the role of TPJ in social decision-making by showing that its perspective-taking function serves to promote fairness for the worst-off rather than efficiency or equality.

The brain dynamics of visuospatial perspective-taking captured by intracranial EEG

Visuospatial perspective-taking (VPT) is the ability to imagine a scene from a position different from the one used in self-perspective judgments (SPJ). We typically use VPT to understand how others see the environment. VPT requires overcoming the self-perspective, and impairments in this process are implicated in various brain disorders, such as schizophrenia and autism. However, the underlying brain areas of VPT are not well distinguished from SPJ-related ones and from domain-general responses to both perspectives. In addition, hierarchical processing theory suggests that domain-specific processes emerge over time from domain-general ones. It mainly focuses on the sensory system, but outside of it, support for this hypothesis is lacking. Therefore, we aimed to spatiotemporally distinguish brain responses domain-specific to VPT from the specific ones to self-perspective, and domain-general responses to both perspectives. In particular, we intended to test whether VPT- and SPJ specific responses begin later than the general ones. We recorded intracranial EEG data from 30 patients with epilepsy who performed a task requiring laterality judgments during VPT and SPJ, and analyzed the spatiotemporal features of responses in the broad gamma band (50-150 Hz). We found VPT-specific processing in a more extensive brain network than SPJ-specific processing. Their dynamics were similar, but both differed from the general responses, which began earlier and lasted longer. Our results anatomically distinguish VPT-specific from SPJ-specific processing. Furthermore, we temporally differentiate between domain-specific and domain-general processes both inside and outside the sensory system, which serves as a novel example of hierarchical processing.

Seeing in my way or your way: impact of intelligence, attention, and empathy on brain reactivity

Previous studies showed that neurotypical adults are able to engage in unconscious analyses of others' mental states in the context of automatic perspective taking and experience systematic difficulties when judging the conflicts between their own (Self) and another's (Other) perspective. Several functional MRI (fMRI) studies reported widespread activation of mentalizing, salience, and executive networks when adopting the Other compared to Self perspective. This study aims to explore whether cognitive and emotional parameters impact on brain reactivity in dot perspective task (dPT). We provide here an fMRI analysis based on individual z-scores in eighty-two healthy adults who underwent the Samson's dPT after detailed assessment of fluid intelligence, attention, levels of alexithymia and social cognition abilities. Univariate regression models were used to explore the association between brain activation patterns and psychological variables. There was a strong positive association between Wechsler Adult Intelligence Scale (WAIS) and fMRI z-scores in Self perspective. When the Other perspective is taken, Continuous Performance Test (CPT)-II parameters were negatively associated with fMRI z-scores. Individuals with higher Toronto Alexithymia scale (TAS) score and lower scores in mini-Social cognition and Emotional Assessment (SEA) displayed significantly higher egocentric interference-related fMRI z-scores. Our data demonstrate that brain activation when focusing on our own perspective depends on the levels of fluid intelligence. Decreased attentional recruitment and decreased inhibitory control affects the brain efforts to adopt the Other perspective. Egocentric interference-associated brain fMRI activation was less marked in cases with better empathy abilities but the opposite was true for persons who experience increased difficulties in the recognition of emotions.

Perspectives on Rehabilitation Using Non-invasive Brain Stimulation Based on Second-Person Neuroscience of Teaching-Learning Interactions

Recent advances in second-person neuroscience have allowed the underlying neural mechanisms involved in teaching-learning interactions to be better understood. Teaching is not merely a one-way transfer of information from teacher to student; it is a complex interaction that requires metacognitive and mentalizing skills to understand others’ intentions and integrate information regarding oneself and others. Physiotherapy involving therapists instructing patients on how to improve their motor skills is a clinical field in which teaching-learning interactions play a central role. Accumulating evidence suggests that non-invasive brain stimulation (NIBS) modulates cognitive functions; however, NIBS approaches to teaching-learning interactions are yet to be utilized in rehabilitation. In this review, I evaluate the present research into NIBS and its role in enhancing metacognitive and mentalizing abilities; I then review hyperscanning studies of teaching-learning interactions and explore the potential clinical applications of NIBS in rehabilitation. Dual-brain stimulation using NIBS has been developed based on findings of brain-to-brain synchrony in hyperscanning studies, and it is delivered simultaneously to two individuals to increase inter-brain synchronized oscillations at the stimulated frequency. Artificial induction of brain-to-brain synchrony has the potential to promote instruction-based learning. The brain-to-brain interface, which induces inter-brain synchronization by adjusting the patient’s brain activity, using NIBS, to the therapist’s brain activity, could have a positive effect on both therapist-patient interactions and rehabilitation outcomes. NIBS based on second-person neuroscience has the potential to serve as a useful addition to the current neuroscientific methods used in complementary interventions for rehabilitation.