No evidence for mirror system dysfunction in schizophrenia from a multimodal TMS/EEG study

Motor cognition in schizophrenia: Control of automatic imitation and mapping of action context are reduced

The ability to imitate is considered impaired in schizophrenia patients. This assumption, however, is based on heterogeneous studies mostly targeting voluntary imitation, e.g., pantomime. Studies on automatic imitation, however, and on underlying mechanisms of top-down inhibition of automatic imitation and contextual modulation in schizophrenia are highly limited. We employed two sensorimotor paradigms to examine imitation-inhibition and action context mapping in 37 schizophrenia patients and 36 matched controls. In the first experiment, participants performed finger lifts while observing a hand executing compatible or incompatible finger lifts from the third-person perspective. The compatibility or incompatibility of these finger lifts affected participants' reaction times (RTs). The comparison of between-condition RT differences shows a larger movement compatibility effect in schizophrenia than in controls. The second experiment involved finger lifts while watching a still hand, from the first-person perspective, with constrained fingers that either corresponded or did not correspond to the participants' response fingers. Here, schizophrenia patients showed a diminished RT slowing in corresponding constraint trials. While the former results provide evidence for an impaired control of imitation in patients with schizophrenia, the latter results indicate a reduced encoding of action context. In conclusion, this study provides the first evidence for deficits of top-down control of imitation and motor context processing in the same sample of schizophrenia patients.

The mirror mechanism in schizophrenia: A systematic review and qualitative meta-analysis

BACKGROUND

Mirror neuron system (MNS) consists of visuomotor neurons that are responsible for the mirror neuron activity (MNA), meaning that each time an individual observes another individual performing an action, these neurons encode that action, and are activated in the observer's cortical motor system. Previous studies report its malfunction in autism, opening doors to investigate the underlying pathophysiology of the disorder in a more elaborate way and coming up with new rehabilitation methods. The study of MNA function in schizophrenia patients has not been as frequent and conclusive as in autism. In this research, we aimed to evaluate the functional integrity of MNA and the microstructural integrity of MNS in schizophrenia patients.

METHODS

We included case-control studies that have evaluated MNA in schizophrenia patients compared to healthy controls using a variety of objective assessment tools. In August 2022, we searched Embase, PubMed, and Web of Science for eligible studies. We used an adapted version of the NIH Quality Assessment of Case-Control Studies tool to assess the quality of the included studies. Evidence was analyzed using vote counting methods of the direction of the effect and was tested statistically using the Sign test. Certainty of evidence was assessed using CERQual.

RESULTS

We included 32 studies for the analysis. Statistical tests revealed decreased MNA (p = 0.002) in schizophrenia patients. The certainty of the evidence was judged to be moderate. Investigations of heterogeneity revealed a possible relationship between the age and the positive symptoms of participants in the included studies and the direction of the observed effect.

DISCUSSION

This finding contributes to gaining a better understanding of the underlying pathophysiology of the disorder by revealing its possible relation to some of the symptoms in schizophrenia patients, while also highlighting a new commonality with autism.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO identifier: CRD42021236453.

TMS-EEG Research to Elucidate the Pathophysiological Neural Bases in Patients with Schizophrenia: A Systematic Review

Schizophrenia (SCZ) is a serious mental disorder, and its pathogenesis is complex. Recently, the glutamate hypothesis and the excitatory/inhibitory (E/I) imbalance hypothesis have been proposed as new pathological hypotheses for SCZ. Combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) is a non-invasive novel method that enables us to investigate the cortical activity in humans, and this modality is a suitable approach to evaluate these hypotheses. In this study, we systematically reviewed TMS-EEG studies that investigated the cortical dysfunction of SCZ to examine the emerging hypotheses for SCZ. The following search terms were set in this systematic review: (TMS or ‘transcranial magnetic stimulation’) and (EEG or electroencephalog*) and (schizophrenia). We inspected the articles written in English that examined humans and were published by March 2020 via MEDLINE, Embase, PsycINFO, and PubMed. The initial search generated 379 studies, and 14 articles were finally identified. The current review noted that patients with SCZ demonstrated the E/I deficits in the prefrontal cortex, whose dysfunctions were also associated with cognitive impairment and clinical severity. Moreover, TMS-induced gamma activity in the prefrontal cortex was related to positive symptoms, while theta/delta band activities were associated with negative symptoms in SCZ. Thus, this systematic review discusses aspects of the pathophysiological neural basis of SCZ that are not explained by the traditional dopamine hypothesis exclusively, based on the findings of previous TMS-EEG research, mainly in terms of the E/I imbalance hypothesis. In conclusion, TMS-EEG neurophysiology can be applied to establish objective biomarkers for better diagnosis as well as to develop new therapeutic strategies for patients with SCZ.

Association of visual motor processing and social cognition in schizophrenia

Patients with schizophrenia have difficulties in social cognitive domains including emotion recognition and mentalization, and in sensorimotor processing and learning. The relationship between social cognitive deficits and sensorimotor function in patients with schizophrenia remains largely unexplored. With the hypothesis that impaired visual motor processing may decelerate information processing and subsequently affects various domains of social cognition, we examined the association of nonverbal emotion recognition, mentalization, and visual motor processing in schizophrenia. The study examined mentalization using the verbal subset of the Chinese version of Theory of Mind (CToM) Task, an equivalent task of the Faux Pas Test; emotion recognition using the Diagnostic Analysis of Nonverbal Accuracy 2-Taiwan version (DANVA-2-TW), and visual motor processing using a joystick tracking task controlled for basic motor function in 34 individuals with chronic schizophrenia in the community and 42 healthy controls. Patients with schizophrenia had significantly worse performance than healthy controls in social cognition, including facial, prosodic emotion recognition, and mentalization. Visual motor processing was also significantly worse in patients with schizophrenia. Only in patients with schizophrenia, both emotion recognition (mainly in prosodic modality, happy, and sad emotions) and mentalization were positively associated with their learning capacity of visual motor processing. These findings suggest a prospective role of sensorimotor function in their social cognitive deficits. Despite that the underlying neural mechanism needs further research, our findings may provide a new direction for restoration of social cognitive function in schizophrenia by enhancing visual motor processing ability.

Enhanced mirroring upon mutual gaze: multimodal evidence from TMS-assessed corticospinal excitability and the EEG mu rhythm

Previous research has demonstrated that eye contact between actor and observer specifically enhances the 'mirroring' of others' actions, as measured by transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs). However, it remains unknown whether other markers of mirror system activation, such as suppression of the EEG mu rhythm (8-13 Hz) over the sensorimotor strip, are also susceptible to perceived eye contact. Here, both TMS-induced MEPs and EEG mu suppression indices were assessed (in separate sessions) while 32 participants (mean age: 24y; 8m) observed a simple hand movement combined with direct or averted gaze from the actor. Both measures were significantly modulated by perceived eye gaze during action observation; showing an increase in MEP amplitude and an attenuation of the mu rhythm during direct vs. averted gaze. Importantly, while absolute MEP and mu suppression scores were not related, a significant association was identified between gaze-related changes in MEPs and mu suppression, indicating that both measures are similarly affected by the modulatory impact of gaze cues. Our results suggest that although the neural substrates underlying TMS-induced MEPs and the EEG mu rhythm may differ, both are sensitive to the social relevance of the observed actions, which might reflect a similar neural gating mechanism.

Is the Putative Mirror Neuron System Associated with Empathy? A Systematic Review and Meta-Analysis

Theoretical perspectives suggest that the mirror neuron system (MNS) is an important neurobiological contributor to empathy, yet empirical support is mixed. Here, we adopt a summary model for empathy, consisting of motor, emotional, and cognitive components of empathy. This review provides an overview of existing empirical studies investigating the relationship between putative MNS activity and empathy in healthy populations. 52 studies were identified that investigated the association between the MNS and at least one domain of empathy, representing data from 1044 participants. Our results suggest that emotional and cognitive empathy are moderately correlated with MNS activity, however, these domains were mixed and varied across techniques used to acquire MNS activity (TMS, EEG, and fMRI). Few studies investigated motor empathy, and of those, no significant relationships were revealed. Overall, results provide preliminary evidence for a relationship between MNS activity and empathy. However, our findings highlight methodological variability in study design as an important factor in understanding this relationship. We discuss limitations regarding these methodological variations and important implications for clinical and community translations, as well as suggestions for future research.

Social Cognition and Schizophrenia: Unresolved Issues and New Challenges in a Maturing Field of Research

Social cognition has become a topic of widespread interest in experimental and treatment research in schizophrenia over the past 15 years. This explosion of interest largely reflects the robust evidence that social cognition is among the strongest known correlates of poor community functioning throughout the course of schizophrenia. While progress has been impressive, we consider several fundamental questions about the scope, structure, and optimal measurement of social cognition that remain unanswered and point to the need for continued method development. We also consider more recently emerging questions about individual differences, ecological and cross-cultural validity, and intervention approaches, as well as broader technological changes that impact how we understand and use social cognition at a societal level. Continued efforts to creatively grapple with the complexities and challenges the field now faces hold great promise for helping us understand and more effectively treat a major source of functional disability in schizophrenia.

Investigational and Therapeutic Applications of Transcranial Magnetic Stimulation in Schizophrenia

PURPOSE OF REVIEW

This current review summarizes the investigational and therapeutic applications of transcranial magnetic stimulation (TMS) in schizophrenia.

RECENT FINDINGS

Fairly consistent findings of an impaired cortical excitation-inhibition balance, cortical plasticity, and motor resonance have been reported in schizophrenia. Cortical connectivity impairments have also been demonstrated in motor and prefrontal brain regions. In terms of treatment, the best support is for 1-Hz TMS to the left temporoparietal cortex for the short-term treatment of persistent auditory hallucinations. High-frequency TMS to the left prefrontal cortex improves negative and cognitive symptoms, but with inconsistent and small effects. TMS combined with diverse brain mapping techniques and clinical evaluation can unravel critical brain-behavior relationships relevant to schizophrenia. These provide critical support to the conceptualization of schizophrenia as a connectopathy with anomalous cortical plasticity. Adaptive modulation of these aberrant brain networks in a neuroscience-informed manner drives short-term therapeutic gains in difficult-to-treat symptoms of schizophrenia.

Diminished modulation of motor cortical reactivity during context-based action observation in schizophrenia

BACKGROUND

Deficient mirror neuron system (MNS)-activity is associated with social cognition deficits in schizophrenia. However, it is not known how socio-emotional contexts modulate the MNS-response. In a Transcranial Magnetic Stimulation (TMS)-experiment, we aimed to compare putative MNS-responses to action observation stimuli with and without a context, in patients with schizophrenia and healthy subjects.

METHOD

TMS-evoked motor cortical reactivity was measured by single and paired [short interval intracortical inhibition (SICI) and facilitation (ICF)] pulse-paradigms in schizophrenia patients (n = 39) and healthy subjects (n = 28) while they observed three experimental-blocks: a static image, a neutral hand action (NA) and a context-based hand action (CA). The degree of cortical reactivity facilitation with the two action observation blocks, relative to the static block provided indirect measures of premotor MNS-activity. A subset of patients (n = 31) also underwent comprehensive social cognition assessments.

RESULTS

RMANOVA demonstrated significantly higher cortical reactivity during the CA-block in both groups (all TMS-paradigms); albeit significantly less pronounced in patients (SICI and ICF paradigms). MNS-activity during the CA-block was significantly higher compared to that during the NA-block in both groups (all TMS-paradigms), but significantly less pronounced in patients (SICI and single-pulse paradigms). MNS-activity during the CA-block measured by the ICF paradigm was positively correlated with social cognition performance.

CONCLUSION

Providing a context to the action modulates MNS-activity. This modulation is diminished in schizophrenia patients, suggestive of a diminished sensorimotor associative learning process. This novel, ecologically valid paradigm to tap into the MNS may serve as a neuro-marker of social cognition performance in schizophrenia.

Enhanced Automatic Action Imitation and Intact Imitation-Inhibition in Schizophrenia

Imitation plays a key role in social learning and in facilitating social interactions and likely constitutes a basic building block of social cognition that supports higher-level social abilities. Recent findings suggest that patients with schizophrenia have imitation impairments that could contribute to the social impairments associated with the disorder. However, extant studies have specifically assessed voluntary imitation or automatic imitation of emotional stimuli without controlling for potential confounders. The imitation impairments seen might therefore be secondary to other cognitive, motoric, or emotional deficits associated with the disorder. To overcome this issue, we used an automatic imitation paradigm with nonemotional stimuli to assess automatic imitation and the top-down modulation of imitation where participants were required to lift one of 2 fingers according to a number shown on the screen while observing the same or the other finger movement. In addition, we used a control task with a visual cue in place of a moving finger, to isolate the effect of observing finger movement from other visual cueing effects. Data from 33 patients (31 medicated) and 40 matched healthy controls were analyzed. Patients displayed enhanced imitation and intact top-down modulation of imitation. The enhanced imitation seen in patients may have been medication induced as larger effects were seen in patients receiving higher antipsychotic doses. In sum, we did not find an imitation impairment in schizophrenia. The results suggest that previous findings of impaired imitation in schizophrenia might have been due to other cognitive, motoric, and/or emotional deficits.

Investigating Mirror System (MS) Activity in Adults with ASD When Inferring Others' Intentions Using Both TMS and EEG

ASD is associated with mentalizing deficits that may correspond with atypical mirror system (MS) activation. We investigated MS activity in adults with and without ASD when inferring others' intentions using TMS-induced motor evoked potentials (MEPs) and mu suppression measured by EEG. Autistic traits were measured for all participants. Our EEG data show, high levels of autistic traits predicted reduced right mu (8-10 Hz) suppression when mentalizing. Higher left mu (8-10 Hz) suppression was associated with superior mentalizing performances. Eye-tracking and TMS data showed no differences associated with autistic traits. Our data suggest ASD is associated with reduced right MS activity when mentalizing, TMS-induced MEPs and mu suppression measure different aspects of MS functioning and the MS is directly involved in inferring intentions.

Impairments of spontaneous and deliberative mentalizing co-occur, yet dissociate, in schizophrenia

OBJECTIVES

Evidence of impairment in explicit mentalizing in people with schizophrenia has inspired interventions to improve awareness of others' mental states in these individuals. Less is known of implicit mentalizing in schizophrenia, with current findings mixed. We sought to resolve previous inconsistencies using Heider & Simmel's (H&S) classic animation to elicit spontaneous mentalizing and examined relations between spontaneous and deliberative mentalizing.

METHODS

Forty-five schizophrenia outpatients and 27 general-community controls completed two explicit theory-of-mind (TOM) tasks and then described the H&S animation (to elicit spontaneous social attributions about emotionally driven, as well as goal-driven, behaviours), before and after an instruction to think of the shapes as people. Accuracy of basic and social facts and frequencies of personification and different mental-state terms were recorded.

RESULTS

Explicit TOM performance was impaired in patients. Patients also generated fewer social (but not basic) facts than controls to describe the H&S animation, and used less mental-state language, before, and even more so, after the 'people' instruction, despite that both groups had used more personification terms after the 'people' instruction. Measures of explicit and spontaneous mentalizing contributed independently to discriminating between groups.

CONCLUSIONS

Patients respond less to the bottom-up signals of agency that ought normally to elicit spontaneous social attributions, even when cued to think of the stimuli as people, and the stimuli depict emotionally driven, as well as goal-driven, behaviour. That impairments of spontaneous and deliberative mentalizing dissociate in schizophrenia suggests that training deliberative mentalizing may not be enough; interventions to improve spontaneous mentalizing are also needed.

PRACTITIONER POINTS

Findings People with schizophrenia were less likely than controls to spontaneously attribute causal mental states when viewing dynamic signals of emotionally driven and goal-driven behaviours. These impairments were even more pronounced when participants were instructed to think of the stimuli as people, suggesting that perceiving others in social roles does not prompt people with schizophrenia to anthropomorphize about others as agents motivated by their own inner worlds. Impairments of spontaneous mentalizing were found to co-occur independently with explicit mentalizing deficits in schizophrenia, consistent with the claim that humans can access two distinct systems for understanding others' minds. Findings suggest that interventions to improve conscious deliberative mentalizing in schizophrenia may not be enough; we also need to target implicit mentalizing processes. Limitations The patient sample was chronic and only mildly symptomatic. As such, findings cannot be generalized to other stages and phases of the illness. All patients were also medicated, allowing for the possibility that automatic responses to socially salient stimuli may have been pharmacologically attenuated. Future research may examine whether unmedicated young people at ultra-high risk of psychosis show a similar profile of mentalizing impairment. Future work may also examine whether impairments of deliberative and spontaneous mentalizing associate differentially with social functioning and different cognitive domains in schizophrenia.

Sources of mu activity and their functional connectivity in perceiving complexities in reciprocal social interactive motion: An exploratory study using the 'Namaste' task

Cognitive processes underlying reciprocal social interactions are understood by the mechanism of embodiment, which is closely related to the mirror neuron system. Electroencephalographic (EEG) mu activity is a neural marker of the mirror neuron system. This study investigated the mu activity, localization of its sources and functional connectivity, which was induced while watching reciprocal social interactive motion across various degrees of complexity. Eighteen healthy participants underwent high-resolution EEG recording using 256-channels while they watched a specifically designed, culture specific, video task that showed two persons interacting socially using body gestures. Task complexity was determined by (1) whether there was an identical gestural response or a non-identical one; (2) whether the participant watched two persons interacting or was virtually involved in the interaction. Source localization and functional connectivity analysis was conducted for mu activity across various tasks. We also correlated mu activity and functional connectivity measures with serum BDNF. We found that spectral densities in various brain sources of mu activity and their increased functional connectivity distinguished identical and non-identical reciprocal expression observations, while mu suppression alone did not discriminate various degrees of complexities. These findings might have important implications in the understanding of mechanisms underlying mirror neuron dysfunction in various psychiatric disorders.