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

Action adaptation during natural unfolding social scenes influences action recognition and inferences made about actor beliefs

When observing another individual's actions, we can both recognize their actions and infer their beliefs concerning the physical and social environment. The extent to which visual adaptation influences action recognition and conceptually later stages of processing involved in deriving the belief state of the actor remains unknown. To explore this we used virtual reality (life-size photorealistic actors presented in stereoscopic three dimensions) to see how visual adaptation influences the perception of individuals in naturally unfolding social scenes at increasingly higher levels of action understanding. We presented scenes in which one actor picked up boxes (of varying number and weight), after which a second actor picked up a single box. Adaptation to the first actor's behavior systematically changed perception of the second actor. Aftereffects increased with the duration of the first actor's behavior, declined exponentially over time, and were independent of view direction. Inferences about the second actor's expectation of box weight were also distorted by adaptation to the first actor. Distortions in action recognition and actor expectations did not, however, extend across different actions, indicating that adaptation is not acting at an action-independent abstract level but rather at an action-dependent level. We conclude that although adaptation influences more complex inferences about belief states of individuals, this is likely to be a result of adaptation at an earlier action recognition stage rather than adaptation operating at a higher, more abstract level in mentalizing or simulation systems

Reduced connectivity between mentalizing and mirror systems in autism spectrum condition

The mentalizing system and mirror system are thought to play important roles in inferring the internal mental states of others – a process known as mentalizing. Autism spectrum condition (ASC) is associated with difficulties in mentalizing. The aim of this study was to determine whether the behavioural difficulties in mentalizing associated with ASC can be explained by changes in functional connectivity between the mentalizing and mirror system. We recruited 40 adult participants (20 with ASC and 20 typically-developing). Brain activity was monitored using functional magnetic resonance imaging while participants watched videos in which actors performed hand actions. The videos were shown in separate mentalizing and non-mentalizing blocks. During mentalizing blocks, participants were asked to indicate whether hand actions were clumsy or spiteful (i.e. to judge the intent of the action). During non-mentalizing blocks, participants indicated whether the actions were successful or unsuccessful (i.e. to judge the outcome of the action). Higher activity during the mentalizing blocks compared to non-mentalizing blocks was found in regions associated with the mentalizing system: the dorsal medial prefrontal cortex (dmPFC) and the temporo-parietal junction (TPJ), as well as in regions typically associated with the mirror system: the inferior frontal gyrus (IFG) and the inferior parietal lobe (IPL). Next, functional connectivity between regions was evaluated as a function of task. During mentalizing blocks, there was increased functional connectivity between the dmPFC and the mirror system in typically developing participants. In contrast, there was no increase in functional connectivity between these regions in ASC participants. Connectivity between the dmPFC and IFG was negatively correlated with autistic traits. The reduced connectivity in ASC participants was consistent with behavioural performance on the mentalizing task, which was also negatively correlated with the level of autistic traits. Together, these data emphasise the importance of functional connectivity between the mentalizing and mirror systems when inferring social intentions and show that reduced connectivity between these systems may explain some of the behavioural difficulties experienced by adults with ASC

Visual adaptation to goal-directed hand actions

Prolonged exposure to visual stimuli, or adaptation, often results in an adaptation “aftereffect” which can profoundly distort our perception of subsequent visual stimuli. This technique has been commonly used to investigate mechanisms underlying our perception of simple visual stimuli, and more recently, of static faces. We tested whether humans would adapt to movies of hands grasping and placing different weight objects. After adapting to hands grasping light or heavy objects, subsequently perceived objects appeared relatively heavier, or lighter, respectively. The aftereffects increased logarithmically with adaptation action repetition and decayed logarithmically with time. Adaptation aftereffects also indicated that perception of actions relies predominantly on view-dependent mechanisms. Adapting to one action significantly influenced the perception of the opposite action. These aftereffects can only be explained by adaptation of mechanisms that take into account the presence/absence of the object in the hand. We tested if evidence on action processing mechanisms obtained using visual adaptation techniques confirms underlying neural processing. We recorded monkey superior temporal sulcus (STS) single-cell responses to hand actions. Cells sensitive to grasping or placing typically responded well to the opposite action; cells also responded during different phases of the actions. Cell responses were sensitive to the view of the action and were dependent upon the presence of the object in the scene. We show here that action processing mechanisms established using visual adaptation parallel the neural mechanisms revealed during recording from monkey STS. Visual adaptation techniques can thus be usefully employed to investigate brain mechanisms underlying action perception.Publisher PDFPeer reviewe

Timing of mirror system activation when inferring the intentions of others

Neuroimaging studies have shown mirror system (MS) activation when participants infer internal states e.g. emotions, intentions or beliefs (known as ‘mentalizing’) from others’ actions. However, the exact role of the MS in mentalizing tasks is unknown. Dysfunctional MS activation may underlie mentalizing deficits experienced by adults with autism spectrum disorder (ASD). This study investigated the timing of MS activity when inferring intentions in order to delineate between existing models of MS involvement. Single-pulse transcranial magnetic stimulation (TMS) was applied to the primary motor cortex at different time points during the observation of hand actions whilst participants inferred intentions (mentalizing task) and performed a non-mentalizing task. Electromyographic activity in the contralateral hand was used as an indirect measure of MS activity. Greater corticospinal activity was found during the mentalizing task than the non-mentalizing task, but only at the end of observed actions, suggesting late MS involvement in processing intentions. Enhanced corticospinal activity was not related to autistic traits or behavioural performance suggesting the MS has a more automatic role in processing others’ intentions, irrespective of mentalizing ability. Our results extend current knowledge of MS activation when mentalizing, allowing initial delineation between different models of MS involvement in mentalizing

Interactions between conscious and subconscious signals: Selective attention under feature-based competition increases neural selectivity during brain adaptation

functional magnetic resonance imaging study of the interaction between neural adaptation and attention signal

The sensitivity of primate STS neurons to walking sequences and to the degree of articulation in static images

We readily use the form of human figures to determine if they are moving. Human figures that have arms and legs outstretched (articulated) appear to be moving more than figures where the arms and legs are near the body (standing). We tested whether neurons in the macaque monkey superior temporal sulcus (STS), a region known to be involved in processing social stimuli, were sensitive to the degree of articulation of a static human figure. Additionally, we tested sensitivity to the same stimuli within forward and backward walking sequences. We found that 57% of cells that responded to the static image of a human figure was also sensitive to the degree of articulation of the figure. Some cells displayed selective responses for articulated postures, while others (in equal numbers) displayed selective responses for standing postures. Cells selective for static images of articulated figures were more likely to respond to movies of walking forwards than walking backwards. Cells selective for static images of standing figures were more likely to respond to movies of walking backwards than forwards. An association between form sensitivity and walking sensitivity could be consistent with an interpretation that cell responses to articulated figures act as an implied motion signal.</p

The sensitivity of primate STS neurons to walking sequences and to the degree of articulation in static images

We readily use the form of human figures to determine if they are moving. Human figures that have arms and legs outstretched (articulated) appear to be moving more than figures where the arms and legs are near the body (standing). We tested whether neurons in the macaque monkey superior temporal sulcus (STS), a region known to be involved in processing social stimuli, were sensitive to the degree of articulation of a static human figure. Additionally, we tested sensitivity to the same stimuli within forward and backward walking sequences. We found that 57% of cells that responded to the static image of a human figure was also sensitive to the degree of articulation of the figure. Some cells displayed selective responses for articulated postures, while others (in equal numbers) displayed selective responses for standing postures. Cells selective for static images of articulated figures were more likely to respond to movies of walking forwards than walking backwards. Cells selective for static images of standing figures were more likely to respond to movies of walking backwards than forwards. An association between form sensitivity and walking sensitivity could be consistent with an interpretation that cell responses to articulated figures act as an implied motion signal.</p