Stimulation of the Social Brain Improves Perspective Selection in Older Adults: A HD-tDCS Study.

There is evidence for dissociable, causal roles for two key social brain regions in young adults. Specifically, the right temporoparietal junction (rTPJ) is associated with embodied perspective taking, whereas the dorsomedial prefrontal cortex (dmPFC) is associated with the integration of social information. However, it is unknown whether these causal brain-behaviour associations are evident in older adults. Fifty-two healthy older adults were stratified to receive either rTPJ or dmPFC anodal high-definition transcranial direct current stimulation in a sham-controlled, double-blinded, repeated-measures design. Self-other processing was assessed across implicit and explicit level one (line-of-sight) and level two (embodied rotation) visual perspective taking (VPT) tasks, and self-other encoding effects on episodic memory. Both rTPJ and dmPFC stimulation reduced the influence of the alternate perspective during level one VPT, indexed by a reduced congruency effect (difference between congruent and incongruent perspectives). There were no stimulation effects on level two perspective taking nor self-other encoding effects on episodic memory. Stimulation to the rTPJ and dmPFC improved perspective selection during level one perspective taking. However, dissociable effects on self-other processing, previously observed in young adults, were not identified in older adults. The results provide causal evidence for age-related changes in social brain function that requires further scrutinization.

Improving Cross-cultural "Mind-reading" with Electrical Brain Stimulation.

A cross-cultural disadvantage exists when inferring the mental state of others, which may be detrimental for individuals acting in an increasingly globalized world. The dorsomedial prefrontal cortex (dmPFC) is a key hub of the social brain involved in ToM. We explored whether facilitation of dmPFC function by focal high-definition tDCS can improve cross-cultural mind-reading. 52 (26 F/M) Singaporeans performed the Caucasian version of the Reading the Mind in the Eyes Test (RMET) and received HD-tDCS to either the dmPFC or a control site (right temporoparietal junction, rTPJ) in sham-controlled, double-blinded, crossover studies. Contact with Caucasians was determined for the Singaporean cohort as a potential mediator of RMET performance and HD-tDCS response. 52 Caucasians completed the RMET during sham-tDCS and served as a comparison group. A cross-cultural disadvantage on the RMET was confirmed in the Singaporean cohort and this disadvantage was more pronounced in those participants who had less contact with Caucasians. Importantly, HD-tDCS to the dmPFC improved RMET performance in those with less contact. No effect was identified for rTPJ HD-tDCS or for the age/sex control task demonstrating task and site specificity of the stimulation effects. Electrical stimulation of the dmPFC selectively improves the rate of cross-cultural ToM inference from facial cues, effectively removing cross-cultural disadvantage that was found in individuals with lower cross-cultural exposure.

A causal role for the right angular gyrus in self-location mediated perspective taking.

Recent theories suggest that self-consciousness, in its most elementary form, is functionally disconnected from the phenomenal body. Patients with psychosis frequently misattribute their thoughts and actions to external sources; and in certain out-of-body experiences, lucid states, and dreams body-ownership is absent but self-identification is preserved. To explain these unusual experiences, we hypothesized that self-identification depends on inferring self-location at the right angular gyrus (i.e., perspective-taking). This process relates to the discrimination of self-produced signals (endogenous attention) from environmental stimulation (exogenous attention). Therefore, when this mechanism fails, this causes altered sensations and perceptions. We combined a Full-body Illusion paradigm with brain stimulation (HD-tDCS) and found a clear causal association between right angular gyrus activation and alterations in self-location (perspective-taking). Anodal versus sham HD-tDCS resulted in: a more profound out-of-body shift (with reduced sense of agency); and a weakened ability to discriminate self from other perspectives. We conclude that self-identification is mediated in the brain by inferring self-location (i.e., perspective-taking). Self-identification can be decoupled from the bodily self, explaining phenomena associated with disembodiment. These findings present novel insights into the relationship between mind and body, and may offer important future directions for treating psychosis symptoms and rehabilitation programs to aid in the recovery from a nervous system injury. The brain's ability to locate itself might be the key mechanism for self-identification and distinguishing self from other signals (i.e., perspective-taking).

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

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 (VPT)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 (SRE) in episodic memory 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.

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

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.

Sex Mediates the Effects of High-Definition Transcranial Direct Current Stimulation on "Mind-Reading".

Sex differences in social cognitive ability are well established, including measures of Theory of Mind (ToM). The aim of this study was to investigate if sex mediates the effects of high-definition transcranial direct current stimulation (HD-tDCS) administered to a key hub of the social brain (i.e., the dorsomedial prefrontal cortex, dmPFC) on the Reading the Mind in the Eyes Test (RMET). Forty healthy young adults (18-35 years) were randomly allocated to receive either anodal or cathodal HD-tDCS in sham HD-tDCS controlled, double blind designs. In each of the two sessions, subjects completed the RMET. Anodal stimulation to the dmPFC increased accuracy on the RMET in females only. To assure regional specificity we performed a follow-up study stimulating the right temporoparietal junction and found no effect in either sex. The current study is the first to show improved performance on the RMET after tDCS to the dmPFC in females only. The polarity-specific effects and use of focal HD-tDCS provide evidence for sex-dependent differences in dmPFC function in relation to the RMET. Future studies using tDCS to study or improve ToM, need to consider sex.

Neural correlates of unihemispheric and bihemispheric motor cortex stimulation in healthy young adults.

Bihemispheric non-invasive motor cortex stimulation has shown promise for facilitating motor learning and recovery after stroke. However, previous studies yielded mixed results that can primarily be attributed to inter-individual variability in response. We therefore aimed at investigating neural correlates of bihemispheric transcranial direct current stimulation (tDCS) effects using multimodal magnetic resonance imaging (MRI). Twenty-four young healthy adults underwent diffusion tensor imaging (DTI), resting state and task-related functional MRI in a randomized sham-controlled, double-blind study using a triple cross-over design. We compared two active stimulation conditions-bihemispheric (or "dual") and unihemispheric anodal tDCS-with sham tDCS. The anode was placed over the left primary motor cortex in all conditions, and subgroups of responders were defined according to task-related activity in this area while subjects pressed a response button with their right index fingers during a choice reaction time task. Compared to sham, "dual responders" and "anodal responders" were characterized by mean beta value increases of 86±55% and 126±55%, respectively. In line with electrophysiological studies, tDCS effects on motor cortex activation appeared to be highly variable across the group. At rest, dual tDCS caused widespread bihemispheric alterations of functional connectivity, possibly mediating its most striking effect, which consisted of bilateral motor cortex disinhibition during the task-related functional MRI. In contrast, unihemispheric anodal tDCS was characterized by more local modulations of functional motor networks. As in aging and after stroke, the impact of dual tDCS on the motor system in young adults seems to depend on the microstructural status of transcallosal motor tracts as well. In sum, these results shed light on the neural correlates of dual and anodal tDCS effects in young adults and help in explaining the great inter-individual variability in response.

Electromagnetic brain activity in higher frequency bands during automatic word processing indicates recovery of function in aphasia.

AIM: Little is known about how treatment affects the neural substrate of language function in stroke sufferers. In the present study authors investigated neuronal correlates of treatment induced recovery of language functions in patients with chronic aphasia. METHODS: In 10 chronic aphasia patients and 10 age- and gender-matched control participants, evoked high-frequency activity (HFA, >20 Hz) was determined from the magnetoencephalogram in an automatic word recognition task, in which content, function, and pseudowords were visually presented at fast rate (350-ms). Recording was repeated after 2 weeks, in aphasics after intensive language training to evaluate training effects, in controls to establish HFA stability. RESULTS: In the first recording, bilateral HFA distribution in controls contrasted right-hemispheric predominance in the patients. After training, this right>left asymmetry in aphasics was reduced to a bilateral pattern similar to controls. While word class did not substantially affect HFA patterns in the two groups, enhanced right-hemispheric HFA in the patients varied with better language function (test performance) prior to training, while after training, left-temporal function- and pseudoword evoked HFA varied with performance in tests of written language. CONCLUSION: Results suggest that HFA might serve as a measure in the evaluation of rehabilitation efforts in chronic aphasia: enhanced right-hemispheric HFA might indicate compensatory activation of contralateral language areas, which tends towards patterns comparable to normal subjects after effective language training.

[Intense language training for aphasia. Contribution of cognitive factors]. / Intensives Sprachtraining bei Aphasie. Einfluss kognitiver Faktoren.

The best predictor of successful language therapy after stroke is a high intensity of treatment (with 5-10 h training per week). However, the necessity of several hours of language exercises each day draws considerably on attentional and cognitive resources of the patients. Thus, not all aphasic patients may be equally suited for intense training approaches. In the present review non-verbal cognitive deficits that often accompany a stroke-induced aphasia are described. Furthermore, initial empirical data on cognitive functions, which predict the success of therapy (intense) after stroke, are summarized. Patients in the acute stage benefit most from intense aphasia treatment, when long-term memory consolidation is relatively preserved. For the chronic stage, indirect evidence suggests that premorbid intelligence as well as attentional functions have positive effects on the success of intense therapy. An empirically based allocation of patients to intense aphasia treatment awaits the results of multicenter trials with sufficiently large sample sizes.

Recovery from aphasia as a function of language therapy in an early bilingual patient demonstrated by fMRI.

Knowledge about the recovery of language functions in bilingual aphasic patients who suffer from left-hemispheric stroke is scarce. Here, we present the case of an early bilingual patient (German/French) with chronic aphasia. Functional magnetic resonance imaging (fMRI) was used to investigate neural correlates of language performance during an overt picture naming task in German and French (a) 32 months after stroke to assess differential recovery of both languages as a function of the preceding language therapy that was provided exclusively in German and (b) after additional short-term intensive (German) language training. At the first investigation behavioral performance confirmed selective recovery of German naming ability which was associated with increased functional brain activation compared to the French naming condition. Changes in behavioral performance and brain activation pattern as disclosed by fMRI after an additional experimental treatment were confined to the trained (German) language and indicate bilateral neuroplastic reorganization. No generalization to the untrained (French) language was observed. The present case results demonstrate use and/or training-dependent differential recovery of expressive language functions and an enhanced pattern of brain activation as a function of the rehabilitation efforts that were focussed exclusively on the patient's German language abilities.

[New developments in stroke rehabilitation based on behavioral and neuroscientific principles: constraint-induced therapy]. / Die Fortentwicklung der Neurorehabilitation auf verhaltensneurowissenschaftlicher Grundlage. Beispiel Constraint-induced-Therapie.

Recent discoveries about the central nervous system's response to injury and how patients reacquire behavioral capabilities by training have yielded promising new therapies for neurorehabilitation. This family of interventions is termed constraint-induced (CI) therapy and is essentially behavioral in nature. Constraining movement of the arm which is less affected by the stroke and training (by shaping) the more affected arm for many hours a day for two consecutive weeks proved effective in the treatment of hemiplegia in many studies. Successful applications other than for stroke have been for traumatic brain injury, cerebral palsy, spinal cord injury, fractured hip, and focal hand dystonia. Extending the principles to other consequences of stroke such as aphasia is examined. Constraint-induced therapy is shown to produce large changes in the organization and function of the brain,which emphasizes the significance of cortical reorganization and learning for neurorehabilitation.