Unconscious Influences on "Free Will" Movement Initiation: Slow-wave Brain Stimulation and the Readiness Potential.

A central objective in the study of volition has been to identify how changes in neural activity relate to voluntary-"free will"-movement. The readiness potential (RP) is observed in the EEG as a slow-building signal that precedes action onset. Many consider the RP as a marker of an underlying preparatory process for initiating voluntary movement. However, the RP may emerge from ongoing slow-wave brain oscillations that influence the timing of movement initiation in a phase-dependent manner. Transcranial alternating current stimulation (tACS) enables brain oscillations to be entrained at the frequency of stimulation. We delivered tACS at a slow-wave frequency over frontocentral motor areas while participants (n = 30) performed a simple, self-paced button press task. During the active tACS condition, participants showed a tendency to initiate actions in the phase of the tACS cycle that corresponded to increased negative potentials across the frontocentral motor region. Comparisons of premovement EEG activity observed over frontocentral and central scalp electrodes showed earlier onset and increased amplitude of RPs from active stimulation compared with sham stimulation. This suggests that movement-related activity in the brain can be modulated by the delivery of weak, nonconsciously perceptible alternating currents over frontocentral motor regions. We present novel findings that support existing theories, which suggest the timing of voluntary movement is influenced by the phase of slow-changing oscillating brain states.

Bayesian population receptive field modeling in human somatosensory cortex.

Somatosensation is fundamental to our ability to sense our body and interact with the world. Our body is continuously sampling the environment using a variety of receptors tuned to different features, and this information is routed up to primary somatosensory cortex. Strikingly, the spatial organization of the peripheral receptors in the body are well maintained, with the resulting representation of the body in the brain being referred to as the somatosensory homunculus. Recent years have seen considerable advancements in the field of high-resolution fMRI, which have enabled an increasingly detailed examination of the organization and properties of this homunculus. Here we combined advanced imaging techniques at ultra-high field (7T) with a recently developed Bayesian population receptive field (pRF) modeling framework to examine pRF properties in primary somatosensory cortex. In each subject, vibrotactile stimulation of the fingertips (i.e., the peripheral mechanoreceptors) modulated the fMRI response along the post-central gyrus and these signals were used to estimate pRFs. We found the pRF center location estimates to be in accord with previous work as well as evidence of other properties in line with the underlying neurobiology. Specifically, as expected from the known properties of cortical magnification, we find a larger representation of the index finger compared to the other stimulated digits (middle, index, little). We also show evidence that the little finger is marked by the largest pRF sizes, and that pRF size increases from anterior to posterior regions of S1. The ability to estimate somatosensory pRFs in humans provides an unprecedented opportunity to examine the neural mechanisms underlying somatosensation and is critical for studying how the brain, body, and environment interact to inform perception and action.

Pushing attention to one side: Force field adaptation alters neural correlates of orienting and disengagement of spatial attention.

Sensorimotor adaptation to wedge prisms can alter the balance of attention between left and right space in healthy adults, and improve symptoms of spatial neglect after stroke. Here we asked whether the orienting of spatial attention to visual stimuli is affected by a different form of sensorimotor adaptation that involves physical perturbations of arm movement, rather than distortion of visual feedback. Healthy participants performed a cued discrimination task before and after they made reaching movements to a central target. A velocity-dependent force field pushed the hand aside during each reach, and required participants to apply compensatory forces toward the opposite side. We used event-related potentials (ERPs) to determine whether electroencephalography (EEG) responses reflecting orienting (cue-locked N1) and disengagement (target-locked P1) of spatial attention are affected by adaptation to force fields. After adaptation, the cue-locked N1 was relatively larger for stimuli presented in the hemispace corresponding to the direction of compensatory hand force. P1 amplitudes evoked by invalidly cued targets presented on the opposite side were reduced. This suggests that force field adaptation boosted attentional orienting responses toward the side of hand forces, and impeded attentional disengagement from that side, mimicking previously reported effects of prism adaptation. Thus, remapping between motor commands and intended movement direction is sufficient to bias ERPs, reflecting changes in the orienting of spatial attention in the absence of visuo-spatial distortion or visuo-proprioceptive mismatch. Findings are relevant to theories of how sensorimotor adaptation can modulate attention, and may open new avenues for treatment of spatial neglect.

Perceived freedom of choice is associated with neural encoding of option availability.

Freedom of choice has been defined as the opportunity to choose alternative plans of action. In this fMRI study, we investigated how the perceived freedom of choice and the underlying neural correlates are influenced by the availability of options. Participants made an initial free choice between left or right doors before beginning a virtual walk along a corridor. At the mid-point of the corridor, lock cues appeared to reveal whether one or both doors remained available, requiring participants either to select a particular door or allowing them to freely choose to stay or switch their choice. We found that participants rated trials as free when they were able to carry out their initial choice, but even more so when both doors remained available. Multi-voxel pattern analysis showed that upcoming choices could initially be decoded from visual cortices before the appearance of the lock cues, and additionally from the motor cortex after the lock cues had confirmed which doors were open. When participants were able to maintain the same choice that they originally selected, the availability of alternative options was represented in fine-grained patterns of activity in the dorsolateral prefrontal cortex. Further, decoding accuracy in this region correlated with the subjective level of freedom that participants reported. These results suggest that there is neural encoding of the availability of alternative options in the dorsolateral prefrontal cortex, and the degree of this encoding predicts an individual's perceived freedom of choice.

Serial correlations in single-subject fMRI with sub-second TR.

When performing statistical analysis of single-subject fMRI data, serial correlations need to be taken into account to allow for valid inference. Otherwise, the variability in the parameter estimates might be under-estimated resulting in increased false-positive rates. Serial correlations in fMRI data are commonly characterized in terms of a first-order autoregressive (AR) process and then removed via pre-whitening. The required noise model for the pre-whitening depends on a number of parameters, particularly the repetition time (TR). Here we investigate how the sub-second temporal resolution provided by simultaneous multislice (SMS) imaging changes the noise structure in fMRI time series. We fit a higher-order AR model and then estimate the optimal AR model order for a sequence with a TR of less than 600 ms providing whole brain coverage. We show that physiological noise modelling successfully reduces the required AR model order, but remaining serial correlations necessitate an advanced noise model. We conclude that commonly used noise models, such as the AR(1) model, are inadequate for modelling serial correlations in fMRI using sub-second TRs. Rather, physiological noise modelling in combination with advanced pre-whitening schemes enable valid inference in single-subject analysis using fast fMRI sequences.

Using multi-echo simultaneous multi-slice (SMS) EPI to improve functional MRI of the subcortical nuclei of the basal ganglia at ultra-high field (7T).

The nuclei of the basal ganglia pose a special problem for functional MRI, especially at ultra-high field, because T2* variations between different regions result in suboptimal BOLD sensitivity when using gradient-echo echo-planar imaging (EPI). Specifically, the iron-rich lentiform nucleus of the basal ganglia, including the putamen and globus pallidus, suffers from substantial signal loss when imaging is performed using conventional single-echo EPI with echo times optimized for the cortex. Multi-echo EPI acquires several echoes at different echo times for every imaging slice, allowing images to be reconstructed with a weighting of echo times that is optimized individually for each voxel according to the underlying tissue or T2* properties. Here we show that multi-echo simultaneous multi-slice (SMS) EPI can improve functional activation of iron-rich subcortical regions while maintaining sensitivity within cortical areas. Functional imaging during a motor task known to elicit strong activations in the cortex and the subcortex (basal ganglia) was performed to compare the performance of multi-echo SMS EPI to single-echo SMS EPI. Notably within both the caudate nucleus and putamen of the basal ganglia, multi-echo SMS EPI yielded higher tSNR (an average 84% increase) and CNR (an average 58% increase), an approximate 3-fold increase in supra-threshold voxels, and higher t-values (an average 39% increase). The degree of improvement in the group level t-statistics was negatively correlated to the underlying T2* of the voxels, such that the shorter the T2*, as in the iron-rich nuclei of the basal ganglia, the higher the improvement of t-values in the activated region.

Effect of mindfulness yoga programme MiYoga on attention, behaviour, and physical outcomes in cerebral palsy: a randomized controlled trial.

AIM: To investigate the efficacy of an embodied mindfulness-based movement programme (MiYoga), targeting attention in children with cerebral palsy (CP). METHOD: Total number of participants 42, with 24 boys (57.1%) and 18 girls (42.9%); mean age 9y 1mo, SD 3y; Gross Motor Function Classification System levels I=22, II=12, III=8) and their parents were randomized to either MiYoga (n=21) or waitlist comparison (n=21) groups. The primary outcome was attention postintervention measured by the Conners' Continuous Performance Test, Second Edition (CCPT). Secondary outcomes included parent and child mindfulness, child quality of life, parental well-being, child executive function, child behaviour, child physical measures, and the parent-child relationship. RESULTS: Children in the MiYoga group demonstrated significantly better attention postintervention than the waitlist comparison group, with lower inattention scores on the hit reaction time standard error (F1,33 =4.59, p=0.04, partial eta-squared [ηp2]=0.13) variable and fewer perseveration errors (F1,33 =4.60, p=0.04, ηp2=0.13) on the CCPT. Intention-to-treat analysis also revealed that sustained attention in the MiYoga group was significantly better than in the waitlist comparison group postintervention (F1,37 =5.97, p=0.02, ηp2=0.14). Parents in the MiYoga group demonstrated significantly decreased mindfulness (Mindfulness Attention Awareness Scale; F1,33 =10.130, p=0.003, ηp2=0.246). INTERPRETATION: MiYoga offers a lifestyle intervention that improves attention in children with CP. MiYoga can be considered as an additional option to standard rehabilitation to enhance attention for children with CP. WHAT THIS PAPER ADDS: MiYoga, an embodied mindfulness-based movement programme, can enhance attention (more attentive and consistent performance) in children with cerebral palsy. MiYoga had no significant effect on physical functioning.

Timing in Predictive Coding: The Roles of Task Relevance and Global Probability.

Predictive coding models of attention propose that attention and prediction operate synergistically to optimize perception, as reflected in interactive effects on early sensory neural responses. It is yet unclear whether attention and prediction based on the temporal attributes of expected events operate in a similar fashion. We investigated how attention and prediction based on timing interact by manipulating the task relevance and a priori probability of auditory stimulus onset timing within a go/no-go task while recording EEG. Preparatory activity, as indexed via the contingent negative variation, reflected temporally specific anticipation as a function of both attention and prediction. Higher stimulus probability led to significant predictive N1 suppression; however, we failed to find an effect of task relevance on N1 amplitude and an interaction of task relevance with prediction. We suggest the predictability of sensory timing is the predominant influence on early sensory responses where a priori probabilities allow for strong prior beliefs. When this is the case, we find that the effects of temporal prediction on early sensory responses are independent of the task relevance of sensory stimuli. Our findings contribute to the expansion of predictive coding frameworks to include the role of timing in sensory processing.

Measuring the effects of attention to individual fingertips in somatosensory cortex using ultra-high field (7T) fMRI.

Attention to sensory information has been shown to modulate the neuronal processing of that information. For example, visuospatial attention acts by modulating responses at retinotopically appropriate regions of visual cortex (Puckett and DeYoe, 2015; Tootell et al. 1998). Much less, however, is known about the neuronal processing associated with attending to other modalities of sensory information. One reason for this is that visual cortex is relatively large, and therefore easier to access non-invasively in humans using tools such as functional magnetic resonance imaging (fMRI). With high-resolution fMRI, however, it is now possible to access smaller cortical areas such as primary somatosensory cortex (Martuzzi et al., 2014; Sanchez-Panchuelo et al., 2010; Schweisfurth et al. 2014; Schweizer et al. 2008). Here, we combined a novel experimental design and high-resolution fMRI at ultra-high field (7T) to measure the effects of attention to tactile stimulation in primary somatosensory cortex, S1. We find that attention modulates somatotopically appropriate regions of S1, and importantly, that this modulation can be measured at the level of the cortical representation of individual fingertips.

Brain changes following four weeks of unimanual motor training: Evidence from fMRI-guided diffusion MRI tractography.

We have reported reliable changes in behavior, brain structure, and function in 24 healthy right-handed adults who practiced a finger-thumb opposition sequence task with their left hand for 10 min daily, over 4 weeks. Here, we extend these findings by using diffusion MRI to investigate white-matter changes in the corticospinal tract, basal-ganglia, and connections of the dorsolateral prefrontal cortex. Twenty-three participant datasets were available with pre-training and post-training scans. Task performance improved in all participants (mean: 52.8%, SD: 20.0%; group P < 0.01 FWE) and widespread microstructural changes were detected across the motor system of the "trained" hemisphere. Specifically, region-of-interest-based analyses of diffusion MRI (n = 22) revealed significantly increased fractional anisotropy (FA) in the right caudate nucleus (4.9%; P < 0.05 FWE), and decreased mean diffusivity in the left nucleus accumbens (-1.3%; P < 0.05 FWE). Diffusion MRI tractography (n = 22), seeded by sensorimotor cortex fMRI activation, also revealed increased FA in the right corticospinal tract (mean 3.28%; P < 0.05 FWE) predominantly reflecting decreased radial diffusivity. These changes were consistent throughout the entire length of the tract. The left corticospinal tract did not show any changes. FA also increased in white matter connections between the right middle frontal gyrus and both right caudate nucleus (17/22 participants; P < 0.05 FWE) and right supplementary motor area (18/22 participants; P < 0.05 FWE). Equivalent changes in FA were not seen in the left (non-trained) hemisphere. In combination with our functional and structural findings, this study provides detailed, multifocal evidence for widespread neuroplastic changes in the human brain resulting from motor training. Hum Brain Mapp 38:4302-4312, 2017. © 2017 Wiley Periodicals, Inc.

Feedforward compensation for novel dynamics depends on force field orientation but is similar for the left and right arms.

There are well-documented differences in the way that people typically perform identical motor tasks with their dominant and the nondominant arms. According to Yadav and Sainburg's (Neuroscience 196: 153-167, 2011) hybrid-control model, this is because the two arms rely to different degrees on impedance control versus predictive control processes. Here, we assessed whether differences in limb control mechanisms influence the rate of feedforward compensation to a novel dynamic environment. Seventy-five healthy, right-handed participants, divided into four subsamples depending on the arm (left, right) and direction of the force field (ipsilateral, contralateral), reached to central targets in velocity-dependent curl force fields. We assessed the rate at which participants developed predictive compensation for the force field using intermittent error-clamp trials and assessed both kinematic errors and initial aiming angles in the field trials. Participants who were exposed to fields that pushed the limb toward ipsilateral space reduced kinematic errors more slowly, built up less predictive field compensation, and relied more on strategic reaiming than those exposed to contralateral fields. However, there were no significant differences in predictive field compensation or kinematic errors between limbs, suggesting that participants using either the left or the right arm could adapt equally well to novel dynamics. It therefore appears that the distinct preferences in control mechanisms typically observed for the dominant and nondominant arms reflect a default mode that is based on habitual functional requirements rather than an absolute limit in capacity to access the controller specialized for the opposite limb.

Interpreting Intervention Induced Neuroplasticity with fMRI: The Case for Multimodal Imaging Strategies.

Direct measurement of recovery from brain injury is an important goal in neurorehabilitation, and requires reliable, objective, and interpretable measures of changes in brain function, referred to generally as "neuroplasticity." One popular imaging modality for measuring neuroplasticity is task-based functional magnetic resonance imaging (t-fMRI). In the field of neurorehabilitation, however, assessing neuroplasticity using t-fMRI presents a significant challenge. This commentary reviews t-fMRI changes commonly reported in patients with cerebral palsy or acquired brain injuries, with a focus on studies of motor rehabilitation, and discusses complexities surrounding their interpretations. Specifically, we discuss the difficulties in interpreting t-fMRI changes in terms of their underlying causes, that is, differentiating whether they reflect genuine reorganisation, neurological restoration, compensation, use of preexisting redundancies, changes in strategy, or maladaptive processes. Furthermore, we discuss the impact of heterogeneous disease states and essential t-fMRI processing steps on the interpretability of activation patterns. To better understand therapy-induced neuroplastic changes, we suggest that researchers utilising t-fMRI consider concurrently acquiring information from an additional modality, to quantify, for example, haemodynamic differences or microstructural changes. We outline a variety of such supplementary measures for investigating brain reorganisation and discuss situations in which they may prove beneficial to the interpretation of t-fMRI data.

Reciprocal interactions of the SMA and cingulate cortex sustain premovement activity for voluntary actions.

Voluntary action is one of the core functions of the human brain, and is accompanied by the well known readiness potential or Bereitschaftspotential. A network of cortical areas is responsible for the motor preparation process, including the anterior mid-cingulate cortex (aMCC) and the SMA. However, the relationship between activity in these regions during movement preparation and the readiness potential is poorly understood. We examined this relationship by integrating simultaneously acquired EEG and fMRI through computational modeling. We first observed that global field power of premovement neural activity showed a specific correlation with BOLD responses in the aMCC. We then used dynamic causal modeling to infer premovement interactions between these regions and their relationship to the premovement neural activity underlying the readiness potential. These analyses suggest that SMA and aMCC have strong reciprocal connections that act to sustain each other's activity, and that this interaction is mediated during movement preparation according to the readiness potential amplitude, as reflected in global cortical field power. Our study suggests that the reciprocal connections between SMA and aMCC are important to maintain the sustained activity of the readiness potential before movement and lead to a weak system instability at movement onset. We suggest that the effective connectivity of this network underlies its functional role in the preparation of self-generated actions.

Implicit agency in observed actions: evidence for N1 suppression of tones caused by self-made and observed actions.

Every day we make attributions about how our actions and the actions of others cause consequences in the world around us. It is unknown whether we use the same implicit process in attributing causality when observing others' actions as we do when making our own. The aim of this research was to investigate the neural processes involved in the implicit sense of agency we form between actions and effects, for both our own actions and when watching others' actions. Using an interval estimation paradigm to elicit intentional binding in self-made and observed actions, we measured the EEG responses indicative of anticipatory processes before an action and the ERPs in response to the sensory consequence. We replicated our previous findings that we form a sense of implicit agency over our own and others' actions. Crucially, EEG results showed that tones caused by either self-made or observed actions both resulted in suppression of the N1 component of the sensory ERP, with no difference in suppression between consequences caused by observed actions compared with self-made actions. Furthermore, this N1 suppression was greatest for tones caused by observed goal-directed actions rather than non-action or non-goal-related visual events. This suggests that top-down processes act upon the neural responses to sensory events caused by goal-directed actions in the same way for events caused by the self or those made by other agents.

Mitii™ ABI: study protocol of a randomised controlled trial of a web-based multi-modal training program for children and adolescents with an Acquired Brain Injury (ABI).

BACKGROUND: Acquired brain injury (ABI) refers to multiple disabilities arising from damage to the brain acquired after birth. Children with an ABI may experience physical, cognitive, social and emotional-behavioural impairments which can impact their ability to participate in activities of daily living (ADL). Recent developments in technology have led to the emergence of internet-delivered therapy programs. "Move it to improve it" (Mitii™) is a web-based multi-modal therapy that comprises upper limb (UL) and cognitive training within the context of meaningful physical activity. The proposed study aims to compare the efficacy of Mitii™ to usual care to improve ADL motor and processing skills, gross motor capacity, UL and executive functioning in a randomised waitlist controlled trial. METHODS/DESIGN: Sixty independently ambulant children (30 in each group) at least 12 months post ABI will be recruited to participate in this trial. Children will be matched in pairs at baseline and randomly allocated to receive either 20 weeks of Mitii™ training (30 min per day, six days a week, with a potential total dose of 60 h) immediately, or be waitlisted for 20 weeks. Outcomes will be assessed at baseline, immediately post-intervention and at 20 weeks post-intervention. The primary outcomes will be the Assessment of Motor and Process Skills and 30 s repetition maximum of functional strength exercises (sit-to-stand, step-ups and half kneel to stand). Measures of body structure and functions, activity, participation and quality of life will assess the efficacy of Mitii™ across all domains of the International Classification of Functioning, Disability and Health framework. A subset of children will undertake three tesla (3T) magnetic resonance imaging scans to evaluate functional neurovascular changes, structural imaging, diffusion imaging and resting state functional connectivity before and after intervention. DISCUSSION: Mitii™ provides an alternative approach to deliver intensive therapy for children with an ABI in the convenience of the home environment. If Mitii™ is found to be effective, it may offer an accessible and inexpensive intervention option to increase therapy dose. TRIAL REGISTRATION: ANZCTR12613000403730.

Reliance on visual attention during visuomotor adaptation: an SSVEP study.

Visuomotor adaptation involves the learning of a new mapping between a spatial goal and well-learned movements. In order to learn a new visuomotor transformation, visual attention is needed to monitor movements and their visual consequences. Once a transformation is learnt, it can be executed automatically without attentional control. Using steady-state visual evoked potentials (SSVEPs) measured from EEG activity, we examined how visual attention changes during the early phase of visuomotor adaptation. SSVEPs were elicited by a green disc flickering at 15 Hz which was either the movement target or the cursor that participants controlled. Participants performed an adapted continuous visuomotor adaptation task with either 60° or 120° screen cursor rotation, and changes in 15-Hz SSVEP power were examined. Participants' performance improved over time in all conditions, with the rate of learning significantly influenced by the degree of rotation. SSVEPs at 15 Hz showed a significant change over time with adaptation for 60° rotations, but not for 120° rotations, such that SSVEPs elicited by the stimuli were significantly lower for 60° compared with 120° rotation conditions over the last adaptation blocks. This suggests that visual attention to the movement target and feedback reduces over time as performance improves during visuomotor adaptation for easier rotations, but must be maintained throughout the task for more difficult 120° rotations that might require more strategic control.

The superior temporal sulcus and the N170 during face processing: single trial analysis of concurrent EEG-fMRI.

Face-selective neural signals have been reliably identified using both EEG and fMRI studies. These consist of the N170 component, a neural response peaking approximately 170ms after a face is presented, and face-selective activations in the fusiform face area (FFA), the occipital face area (OFA), and the superior temporal sulcus (STS). As most neuroimaging studies examine these face-selective processes separately, the relationship between the N170 neural response and activation in the fusiform gyrus is still debated. In this study, we concurrently measured EEG and fMRI responses to upright faces, inverted faces, and objects to examine this association. We introduce a method for single-trial estimation of N170 amplitudes and correlation of the trial-by-trial variation in N170 neural responses with fMRI BOLD responses. For upright faces, BOLD responses in the right STS were negatively correlated with N170 amplitudes, showing greater activation on trials in which N170 amplitudes were larger (more negative). For inverted faces, a medial region of the fusiform gyrus (mFG) was positively correlated with N170 amplitudes, showing greater activation on trials in which N170 amplitudes were smaller (less negative). This result points to the STS as a crucial region for generating the N170 associated with face perception, and suggests that the mFG is additionally recruited for processing inverted faces, particularly on trials in which N170 is small. Despite the different time resolution of fMRI and EEG signals, our single-trial estimation and EEG-fMRI correlation method can reveal associations between activation in face-selective brain regions and neural processes at 170ms associated with face perception.

Fusing concurrent EEG-fMRI with dynamic causal modeling: application to effective connectivity during face perception.

Despite the wealth of research on face perception, the interactions between core regions in the face-sensitive network of the visual cortex are not well understood. In particular, the link between neural activity in face-sensitive brain regions measured by fMRI and EEG markers of face-selective processing in the N170 component is not well established. In this study, we used dynamic causal modeling (DCM) as a data fusion approach to integrate concurrently acquired EEG and fMRI data during the perception of upright compared with inverted faces. Data features derived from single-trial EEG variability were used as contextual modulators on fMRI-derived estimates of effective connectivity between key regions of the face perception network. The overall construction of our model space was highly constrained by the effects of task and ERP parameters on our fMRI data. Bayesian model selection suggested that the occipital face area (OFA) acted as a central gatekeeper directing visual information to the superior temporal sulcus (STS), the fusiform face area (FFA), and to a medial region of the fusiform gyrus (mFG). The connection from the OFA to the STS was strengthened on trials in which N170 amplitudes to upright faces were large. In contrast, the connection from the OFA to the mFG, an area known to be involved in object processing, was enhanced for inverted faces particularly on trials in which N170 amplitudes were small. Our results suggest that trial-by-trial variation in neural activity at around 170 ms, reflected in the N170 component, reflects the relative engagement of the OFA to STS/FFA network over the OFA to mFG object processing network for face perception. Importantly, the DCMs predicted the observed data significantly better by including the modulators derived from the N170, highlighting the value of incorporating EEG-derived information to explain interactions between regions as a multi-modal data fusion method for combined EEG-fMRI.

Visual-motor interactions during action observation are shaped by cognitive context.

Interactions between the visual system and the motor system during action observation are important for functions such as imitation and action understanding. Here, we asked whether such processes might be influenced by the cognitive context in which actions are performed. We recorded ERPs in a delayed go/no-go task known to induce bidirectional interference between the motor system and the visual system (visuomotor interference). Static images of hand gestures were presented as go stimuli after participants had planned either a matching (congruent) or nonmatching (incongruent) action. Participants performed the identical task in two different cognitive contexts: In one, they focused on the visual image of the hand gesture shown as the go stimulus (image context), whereas in the other, they focused on the hand gesture they performed (action context). We analyzed the N170 elicited by the go stimulus to test the influence of action plans on action observation (motor-to-visual priming). We also analyzed movement-related activity following the go stimulus to examine the influence of action observation on action planning (visual-to-motor priming). Strikingly, the context manipulation reversed the direction of the priming effects: We found stronger motor-to-visual priming in the action context compared with the image context and stronger visual-to-motor priming in the image context compared with the action context. Taken together, our findings indicate that neural interactions between motor and visual processes for executed and observed actions can change depending on task demands and are sensitive to top-down control according to the context.

Seeing is believing: neural mechanisms of action-perception are biased by team membership.

Group identification can lead to a biased view of the world in favor of "in-group" members. Studying the brain processes that underlie such in-group biases is important for a wider understanding of the potential influence of social factors on basic perceptual processes. In this study, we used functional magnetic resonance imaging (fMRI) to investigate how people perceive the actions of in-group and out-group members, and how their biased view in favor of own team members manifests itself in the brain. We divided participants into two teams and had them judge the relative speeds of hand actions performed by an in-group and an out-group member in a competitive situation. Participants judged hand actions performed by in-group members as being faster than those of out-group members, even when the two actions were performed at physically identical speeds. In an additional fMRI experiment, we showed that, contrary to common belief, such skewed impressions arise from a subtle bias in perception and associated brain activity rather than decision-making processes, and that this bias develops rapidly and involuntarily as a consequence of group affiliation. Our findings suggest that the neural mechanisms that underlie human perception are shaped by social context.