Whole-brain haemodynamic after-effects of 1-Hz magnetic stimulation of the posterior superior temporal cortex during action observation

Specific tractography differences in autism compared to developmental coordination disorder

About 85% of children with autism spectrum disorder (ASD) experience comorbid motor impairments, making it unclear whether white matter abnormalities previously found in ASD are related to social communication deficits, the hallmark of ASD, or instead related to comorbid motor impairment. Here we aim to understand specific white matter signatures of ASD beyond those related to comorbid motor impairment by comparing youth (aged 8-18) with ASD (n = 22), developmental coordination disorder (DCD; n = 16), and typically developing youth (TD; n = 22). Diffusion weighted imaging was collected and quantitative anisotropy, radial diffusivity, mean diffusivity, and axial diffusivity were compared between the three groups and correlated with social and motor measures. Compared to DCD and TD groups, diffusivity differences were found in the ASD group in the mid-cingulum longitudinal and u-fibers, the corpus callosum forceps minor/anterior commissure, and the left middle cerebellar peduncle. Compared to the TD group, the ASD group had diffusivity differences in the right inferior frontal occipital/extreme capsule and genu of the corpus callosum. These diffusion differences correlated with emotional deficits and/or autism severity. By contrast, children with DCD showed unique abnormality in the left cortico-spinal and cortico-pontine tracts.Trial Registration All data are available on the National Institute of Mental Health Data Archive: https://nda.nih.gov/edit_collection.html?id=2254 .

Sensorimotor Expectations Bias Motor Resonance during Observation of Object Lifting: The Causal Role of pSTS

Transcranial magnetic stimulation studies have highlighted that corticospinal excitability is increased during observation of object lifting, an effect termed "motor resonance." This facilitation is driven by movement features indicative of object weight, such as object size or observed movement kinematics. Here, we investigated in 35 humans (23 females) how motor resonance is altered when the observer's weight expectations, based on visual information, do not match the actual object weight as revealed by the observed movement kinematics. Our results highlight that motor resonance is not robustly driven by object weight but easily masked by a suppressive mechanism reflecting the correctness of weight expectations. Subsequently, we investigated in 24 humans (14 females) whether this suppressive mechanism was driven by higher-order cortical areas. For this, we induced "virtual lesions" to either the posterior superior temporal sulcus (pSTS) or dorsolateral prefrontal cortex (DLPFC) before having participants perform the task. Importantly, virtual lesion of pSTS eradicated this suppressive mechanism and restored object weight-driven motor resonance. In addition, DLPFC virtual lesion eradicated any modulation of motor resonance. This indicates that motor resonance is heavily mediated by top-down inputs from both pSTS and DLPFC. Together, these findings shed new light on the theorized cortical network driving motor resonance. That is, our findings highlight that motor resonance is not only driven by the putative human mirror neuron network consisting of the primary motor and premotor cortices as well as the anterior intraparietal sulcus, but also by top-down input from pSTS and DLPFC.SIGNIFICANCE STATEMENT Observation of object lifting activates the observer's motor system in a weight-specific fashion: Corticospinal excitability is larger when observing lifts of heavy objects compared with light ones. Interestingly, here we demonstrate that this weight-driven modulation of corticospinal excitability is easily suppressed by the observer's expectations about object weight and that this suppression is mediated by the posterior superior temporal sulcus. Thus, our findings show that modulation of corticospinal excitability during observed object lifting is not robust but easily altered by top-down cognitive processes. Finally, our results also indicate how cortical inputs, originating remotely from motor pathways and processing action observation, overlap with bottom-up motor resonance effects.

Pregenual or subgenual anterior cingulate cortex as potential effective region for brain stimulation of depression

BACKGROUND

The dorsolateral prefrontal cortex (DLPFC) is the standard stimulation target for the repetitive transcranial magnetic stimulation (rTMS) treatment of major depression disorder (MDD). A retrospective study by Fox and colleagues found that a more negative resting-state functional magnetic resonance imaging (RS-fMRI) functional connectivity (FC) between left DLPFC and the subgenual anterior cingulate cortex (sgACC) in a large group of healthy participants is associated with a better curative effects of rTMS in MDD, suggesting that the sgACC may be an effective region. However, a recent meta-analysis on RS-fMRI studies found that the pregenual ACC (pgACC), rather than the sgACC, of MDD patients showed increased local activity.

METHODS

We used the stimulation coordinates in the left DLPFC analyzed by Fox et al. to perform RS-fMRI FC between the stimulation targets obtained from previous rTMS MDD studies and the potential effective regions (sgACC and pgACC, respectively) on the RS-fMRI data from 88 heathy participants.

RESULTS

(a) Both the pgACC and the sgACC were negatively connected to the left DLPFC; (b) both FCs of sgACC-DLPFC and pgACC-DLPFC were more negative in responders than in nonresponders; and (c) the associations between DLPFC-sgACC functional connectivity and clinical efficacy were clustered around the midline sgACC.

CONCLUSIONS

Both the pgACC and the sgACC may be potential effective regions for rTMS on the left DLPFC for treatment of MDD. However, individualized ACC-DLPFC FC-based rTMS on depression should be performed in the future to test the pgACC or the sgACC as effective regions.

Neural Processing and Production of Gesture in Children and Adolescents With Autism Spectrum Disorder

Individuals with autism spectrum disorder (ASD) demonstrate impairments in non-verbal communication, including gesturing and imitation deficits. Reduced sensitivity to biological motion (BM) in ASD may impair processing of dynamic social cues like gestures, which in turn may impede encoding and subsequent performance of these actions. Using both an fMRI task involving observation of action gestures and a charade style paradigm assessing gesture performance, this study examined the brain-behavior relationships between neural activity during gesture processing, gesturing abilities and social symptomology in a group of children and adolescents with and without ASD. Compared to typically developing (TD) controls, participants with ASD showed atypical sensitivity to movement in right posterior superior temporal sulcus (pSTS), a region implicated in action processing, and had poorer overall gesture performance with specific deficits in hand posture. The TD group showed associations between neural activity, gesture performance and social skills, that were weak or non-significant in the ASD group. These findings suggest that those with ASD demonstrate abnormalities in both processing and production of gestures and may reflect dysfunction in the mechanism underlying perception-action coupling resulting in atypical development of social and communicative skills.

Interactor's body shape does not affect visuo-motor interference effects during motor coordination

The biological-tuning of the Action Observation Network is highly debated. A current open question relates to whether the morphological appearance (body shape) and/or the biological motion of the observed agent triggers action simulation processes. Motor simulation of the partner's action is critical for motor interactions, where two partners coordinate their actions in space and time. It supports interpersonal alignment and facilitates online coordination. However, motor simulation also leads to visuo-motor interference effects when people are required to coordinate with complementary actions, i.e. incongruent movements as compared to the observed ones. Movement kinematics of interactive partners allows us to capture their automatic tendency to simulate and imitate the partner's complementary movements. In an online reach-to-grasp task, we investigated whether visuo-motor interference effects, visible in the kinematics of complementary movements, are modulated by the visual presence of the interactor's body shape. We asked participants to interact with 1) a humanoid agent with a human-like body shape and with real human, biological, movement kinematics, or 2) a non-humanoid agent, which did not resemble the human body-shape but moved with the same real kinematics. Through the combination of inferential and Bayesian statistics, the results show no effect of interactor's body shape on visuo-motor interference in reaching and grasping kinematics during online motor coordination. We discuss the results and propose that the kinematics of the observed movements, during motor interactions, might be the key factor for visuo-motor interference to take place independently from the morphological appearance of the partner. This is particularly relevant in a technological society that constantly asks humans to interact with artificial agents.

Modulating Mimetic Preference with Theta Burst Stimulation of the Inferior Parietal Cortex

We like an object more when we see someone else reaching for it. To what extent is action observation causally linked to object valuation? In this study, we set out to answer to this question by applying continuous theta burst stimulation (cTBS) over the left inferior parietal lobule (IPL). Previous studies pointed to this region as critical in the representation of others' actions and in tool manipulation. However, it is unclear to what extent IPL's involvement simply reflects action observation, rather than a casual role in objects' valuation. To clarify this issue, we measured cTBS-dependent modulations of participants' “mimetic preference ratings”, i.e., the difference between the ratings of pairs of familiar objects that were (vs. were not) reached out for by other individuals. Our result shows that cTBS increased mimetic preference ratings for tools, when compared to a control condition without stimulation. This effect was selective for items that were reached for or manipulated by another individual, whilst it was not detected in non-tool objects. Although preliminary, this finding suggests that the automatic and covert simulation of an observed action, even when there is no intention to act on an object, influences explicit affective judgments for objects. This work supports embodied cognition theories by substantiating that our subjective preference is grounded in action.

Contribution of transcranial magnetic stimulation to assessment of brain connectivity and networks

The goal of this review is to show how transcranial magnetic stimulation (TMS) techniques can make a contribution to the study of brain networks. Brain networks are fundamental in understanding how the brain operates. Effects on remote areas can be directly observed or identified after a period of stimulation, and each section of this review will discuss one method. EEG analyzed following TMS is called TMS-evoked potentials (TEPs). A conditioning TMS can influence the effect of a test TMS given over the motor cortex. A disynaptic connection can be tested also by assessing the effect of a pre-conditioning stimulus on the conditioning-test pair. Basal ganglia-cortical relationships can be assessed using electrodes placed in the process of deep brain stimulation therapy. Cerebellar-cortical relationships can be determined using TMS over the cerebellum. Remote effects of TMS on the brain can be found as well using neuroimaging, including both positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). The methods complement each other since they give different views of brain networks, and it is often valuable to use more than one technique to achieve converging evidence. The final product of this type of work is to show how information is processed and transmitted in the brain.

State-Dependent TMS Reveals Representation of Affective Body Movements in the Anterior Intraparietal Cortex

In humans, recognition of others' actions involves a cortical network that comprises, among other cortical regions, the posterior superior temporal sulcus (pSTS), where biological motion is coded and the anterior intraparietal sulcus (aIPS), where movement information is elaborated in terms of meaningful goal-directed actions. This action observation system (AOS) is thought to encode neutral voluntary actions, and possibly some aspects of affective motor repertoire, but the role of the AOS' areas in processing affective kinematic information has never been examined. Here we investigated whether the AOS plays a role in representing dynamic emotional bodily expressions. In the first experiment, we assessed behavioral adaptation effects of observed affective movements. Participants watched series of happy or fearful whole-body point-light displays (PLDs) as adapters and were then asked to perform an explicit categorization of the emotion expressed in test PLDs. Participants were slower when categorizing any of the two emotions as long as it was congruent with the emotion in the adapter sequence. We interpreted this effect as adaptation to the emotional content of PLDs. In the second experiment, we combined this paradigm with TMS applied over either the right aIPS, pSTS, and the right half of the occipital pole (corresponding to Brodmann's area 17 and serving as control) to examine the neural locus of the adaptation effect. TMS over the aIPS (but not over the other sites) reversed the behavioral cost of adaptation, specifically for fearful contents. This demonstrates that aIPS contains an explicit representation of affective body movements.SIGNIFICANCE STATEMENT In humans, a network of areas, the action observation system, encodes voluntary actions. However, the role of these brain regions in processing affective kinematic information has not been investigated. Here we demonstrate that the aIPS contains a representation of affective body movements. First, in a behavioral experiment, we found an adaptation after-effect for emotional PLDs, indicating the existence of a neural representation selective for affective information in biological motion. To examine the neural locus of this effect, we then combined the adaptation paradigm with TMS. Stimulation of the aIPS (but not over pSTS and control site) reversed the behavioral cost of adaptation, specifically for fearful contents, demonstrating that aIPS contains a representation of affective body movements.

The Impact of Single Session Intermittent Theta-Burst Stimulation over the Dorsolateral Prefrontal Cortex and Posterior Superior Temporal Sulcus on Adults with Autism Spectrum Disorder

Intermittent theta burst stimulation (iTBS), a patterned repetitive transcranial magnetic stimulation, was applied over the posterior superior temporal sulcus (pSTS) or dorsolateral prefrontal cortex (DLPFC) to explore its impact in adults with autism spectrum disorder (ASD). Among 25 adults with ASD, 19 (mean age: 20.8 years) completed the randomized, sham-controlled, crossover trial. Every participant received iTBS over the bilateral DLPFC, bilateral pSTS and inion (as a sham control stimulation) in a randomized order with a 1-week interval. Neuropsychological functions were assessed using the Conners' Continuous Performance Test (CCPT) and the Wisconsin Card Sorting Test (WCST). Behavioral outcomes were measured using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) and the Social Responsiveness Scale (SRS). In comparison to that in the sham stimulation, the reaction time in the CCPT significantly decreased following single DLPFC session (p = 0.04, effect size = 0.71) while there were no significant differences in the CCPT and WCST following single pSTS session. Besides, the results in behavioral outcomes were inconsistent and had discrepancy between reports of parents and patients. In conclusion, a single session of iTBS over the bilateral DLPFC may alter the neuropsychological function in adults with ASD. The impacts of multiple-sessions iTBS over the DLPFC or pSTS deserve further investigations.

Primary somatosensory contribution to action observation brain activity-combining fMRI and cTBS

Traditionally the mirror neuron system (MNS) only includes premotor and posterior parietal cortices. However, somatosensory cortices, BA1/2 in particular, are also activated during action execution and observation. Here, we examine whether BA1/2 and the parietofrontal MNS integrate information by using functional magnetic resonance imaging (fMRI)-guided continuous theta-burst stimulation (cTBS) to perturb BA1/2. Measuring brain activity using fMRI while participants are under the influence of cTBS shows local cTBS effects in BA1/2 varied, with some participants showing decreases and others increases in the BOLD response to viewing actions vs control stimuli. We show how measuring cTBS effects using fMRI can harness this variance using a whole-brain regression. This analysis identifies brain regions exchanging action-specific information with BA1/2 by mapping voxels away from the coil with cTBS-induced, action-observation-specific BOLD contrast changes that mirror those under the coil. This reveals BA1/2 exchanges action-specific information with premotor, posterior parietal and temporal nodes of the MNS during action observation. Although anatomical connections between BA1/2 and these regions are well known, this is the first demonstration that these connections carry action-specific signals during observation and hence, that BA1/2 plays a causal role in the human MNS.

Effects of Transcranial Direct Current Stimulation on the Recognition of Bodily Emotions from Point-Light Displays

Perceiving human motion, recognizing actions, and interpreting emotional body language are tasks we perform daily and which are supported by a network of brain areas including the human posterior superior temporal sulcus (pSTS). Here, we applied transcranial direct current stimulation (tDCS) with anodal (excitatory) or cathodal (inhibitory) electrodes mounted over right pSTS (target) and orbito-frontal cortex (reference) while healthy participants performed a bodily emotion recognition task using biological motion point-light displays (PLDs). Performance (accuracy and reaction times) was also assessed on a control task which was matched to the emotion recognition task in terms of cognitive and motor demands. Each subject participated in two experimental sessions, receiving either anodal or cathodal stimulation, which were separated by one week to avoid residual effects of previous stimulations. Overall, tDCS brain stimulation did not affect the recognition of emotional states from PLDs. However, when emotions with a negative or positive-neutral emotional valence were analyzed separately, effects of stimulation were shown for recognizing emotions with a negative emotional valence (sadness and anger), indicating increased recognition performance when receiving anodal (excitatory) stimulation compared to cathodal (inhibitory) stimulation over pSTS. No stimulation effects were shown for the recognition of emotions with positive-neutral emotional valences. These findings extend previous studies showing structure-function relationships between STS and biological motion processing from PLDs and provide indications that stimulation effects may be modulated by the emotional valence of the stimuli.

Virtual lesion of right posterior superior temporal sulcus modulates conscious visual perception of fearful expressions in faces and bodies

The posterior Superior Temporal Suclus (pSTS) represents a central hub in the complex cerebral network for person perception and emotion recognition as also suggested by its heavy connections with face- and body-specific cortical (e.g., the fusiform face area, FFA and the extrastriate body area, EBA) and subcortical structures (e.g., amygdala). Information on whether pSTS is causatively involved in sustaining conscious visual perception of emotions expressed by faces and bodies is lacking. We explored this issue by combining a binocular rivalry procedure (where emotional and neutral face and body postures rivaled with house images) with off-line, 1-Hz repetitive transcranial magnetic stimulation (rTMS). We found that temporary inhibition of the right pSTS reduced perceptual dominance of fearful faces and increased perceptual dominance of fearful bodies, while leaving unaffected the perception of neutral face and body images. Inhibition of the vertex had no effect on conscious visual perception of neutral or emotional face or body stimuli. Thus, the right pSTS plays a causal role in shortening conscious vision of fearful faces and in prolonging conscious vision of fearful bodies. These results suggest that pSTS selectively modulates the activity of segregated networks involved in the conscious visual perception of emotional faces or bodies. We speculate that the opposite role of the right pSTS for conscious perception of fearful face and body may be explained by the different connections that this region entertains with face- and body-selective visual areas as well as with amygdalae and premotor regions.

Visual and Sensorimotor Contributions to the Esthetic Appraisal of Body Form, Motion, and Emotion

Recent neuroscience studies indicate that the visual processing of human bodies relies on a cortical network comprising different sensorimotor regions (extrastriate body area [EBA], superior temporal sulcus [STS], parietal cortex [PC], and premotor cortex [PM]). These regions seem to be specifically involved in the processing of morphological (form) and dynamic (movement) cues of the body. Importantly, the integrated activity within the network dedicated to body processing seems to underpin the unified perception of the body and its movements via simulation-like mechanisms (“cold embodiment”). Studies also suggest that regions within the body-related network are involved in the esthetic appreciation of human bodies together with a variety of cortical and subcortical regions associated to the emotional reward coding of stimuli (e.g., the amygdala for fear/disgust and the nucleus accumbens, the insula, and the cingulate cortex for pleasure reward), which may drive a form of “hot embodiment.” Thus, the esthetic evaluation of human bodies may rely upon a large cortico-subcortical network. Here we review evidence concerning the role of specific sensorimotor cortical and subcortical regions in the perception of beauty and attractiveness of the body. We conclude that exploring the way in which visual, sensorimotor, affective, and multisensory information in art and ecological life in general perturb our body representations is crucial for understanding the neural foundations of esthetic body appreciation.

Neuroanatomical substrates of action perception and understanding: an anatomic likelihood estimation meta-analysis of lesion-symptom mapping studies in brain injured patients

Several neurophysiologic and neuroimaging studies suggested that motor and perceptual systems are tightly linked along a continuum rather than providing segregated mechanisms supporting different functions. Using correlational approaches, these studies demonstrated that action observation activates not only visual but also motor brain regions. On the other hand, brain stimulation and brain lesion evidence allows tackling the critical question of whether our action representations are necessary to perceive and understand others’ actions. In particular, recent neuropsychological studies have shown that patients with temporal, parietal, and frontal lesions exhibit a number of possible deficits in the visual perception and the understanding of others’ actions. The specific anatomical substrates of such neuropsychological deficits however, are still a matter of debate. Here we review the existing literature on this issue and perform an anatomic likelihood estimation meta-analysis of studies using lesion-symptom mapping methods on the causal relation between brain lesions and non-linguistic action perception and understanding deficits. The meta-analysis encompassed data from 361 patients tested in 11 studies and identified regions in the inferior frontal cortex, the inferior parietal cortex and the middle/superior temporal cortex, whose damage is consistently associated with poor performance in action perception and understanding tasks across studies. Interestingly, these areas correspond to the three nodes of the action observation network that are strongly activated in response to visual action perception in neuroimaging research and that have been targeted in previous brain stimulation studies. Thus, brain lesion mapping research provides converging causal evidence that premotor, parietal and temporal regions play a crucial role in action recognition and understanding.

Cortical Mechanisms Underlying the Organization of Goal-Directed Actions and Mirror Neuron-Based Action Understanding

Our understanding of the functions of motor system evolved remarkably in the last 20 years. This is the consequence not only of an increase in the amount of data on this system but especially of a paradigm shift in our conceptualization of it. Motor system is not considered anymore just a “producer” of movements, as it was in the past, but a system crucially involved in cognitive functions. In the present study we review the data on the cortical organization underlying goal-directed actions and action understanding. Our review is subdivided into two major parts. In the first part, we review the anatomical and functional organization of the premotor and parietal areas of monkeys and humans. We show that the parietal and frontal areas form circuits devoted to specific motor functions. We discuss, in particular, the visuo-motor transformation necessary for reaching and for grasping. In the second part we show how a specific neural mechanism, the mirror mechanism, is involved in understanding the action and intention of others. This mechanism is located in the same parieto-frontal circuits that mediate goal-directed actions. We conclude by indicating future directions for studies on the mirror mechanism and suggest some major topics for forthcoming research.

Perturbing the action observation network during perception and categorization of actions' goals and grips: state-dependency and virtual lesion TMS effects

Watching others grasping and using objects activates an action observation network (AON), including inferior frontal (IFC), anterior intraparietal (AIP), and somatosensory cortices (S1). Yet, causal evidence of the differential involvement of such AON sensorimotor nodes in representing high- and low-level action components (i.e., end-goals and grip type) is meager. To address this issue, we used transcranial magnetic stimulation-adaptation (TMS-A) during 2 novel action perception tasks. Participants were shown adapting movies displaying a demonstrator performing goal-directed actions with a tool, using either power or precision grips. They were then asked to match the end-goal (Goal-recognition task) or the grip (Grip-recognition task) of actions shown in test pictures to the adapting movies. TMS was administered over IFC, AIP, or S1 during presentation of test pictures. Virtual lesion-like effects were found in the Grip-recognition task where IFC stimulation induced a general performance decrease, suggesting a critical role of IFC in perceiving grips. In the Goal-recognition task, IFC and S1 stimulation differently affected the processing of "adapted" and "nonadapted" goals. These "state-dependent" effects suggest that the overall goal of seen actions is encoded into functionally distinct and spatially overlapping neural populations in IFC-S1 and such encoding is critical for recognizing and understanding end-goals.

Vicarious motor activation during action perception: beyond correlational evidence

Neurophysiological and imaging studies have shown that seeing the actions of other individuals brings about the vicarious activation of motor regions involved in performing the same actions. While this suggests a simulative mechanism mediating the perception of others' actions, one cannot use such evidence to make inferences about the functional significance of vicarious activations. Indeed, a central aim in social neuroscience is to comprehend how vicarious activations allow the understanding of other people's behavior, and this requires to use stimulation or lesion methods to establish causal links from brain activity to cognitive functions. In the present work, we review studies investigating the effects of transient manipulations of brain activity or stable lesions in the motor system on individuals' ability to perceive and understand the actions of others. We conclude there is now compelling evidence that neural activity in the motor system is critical for such cognitive ability. More research using causal methods, however, is needed in order to disclose the limits and the conditions under which vicarious activations are required to perceive and understand actions of others as well as their emotions and somatic feelings.