A gravitational contribution to perceived body weight.

The weightlessness experienced by astronauts has fascinated scientists and the public. On Earth, body weight is given by Newton's laws as mass times gravitational acceleration. That is, an object's weight is determined by the pull of gravity on it. We hypothesised that perceived body weight is - like actual weight - dependent on the strength of gravity. If so, changes in the experienced strength of gravity should alter the experience of one's own body weight. We asked participants to estimate the weight of two body parts, their hand or their head, both in normal terrestrial gravity (1 g) and during exposure to experimentally altered gravitational fields, 0 g and +1.8 g during parabolic flight and +1 g using a short arm human centrifuge. For both body parts, there was an increase in perceived weight during the experience of hypergravity, and a decrease during the experience of microgravity. Our results show that experimental alterations of gravity produce rapid changes in the perceived weight of specific individual body parts. Traditionally, research has focused on the social factors for weight perception, as in the putative role of mass media in eating disorders. Our results, in contrast, emphasize that the perception of body weight is highly malleable, and shaped by immediate sensory signals.

I just lost it! Fear and anger reduce the sense of agency: a study using intentional binding.

Two recent studies have demonstrated that increases in arousal states lead to an increase people's sense of agency, i.e., the subjective experience of controlling one's own voluntary actions (Minohara et al. in Front Psychol 7:1165, 2016; Wen et al. in Conscious Cogn 36:87-95, 2015). We here extend these findings by showing that arousal states with negative emotional valence, such as fear and anger, decrease sense of agency. Anger and fear are negative emotional states. Anecdotally, they are often invoked as reasons for losing control, and neuroscientific evidence confirms important effects on the brain's action control systems. Surprisingly, the subjective experience of acting in anger or fear has scarcely been investigated experimentally. Thus, the legal notion that these intense emotions may undermine normal voluntary control over actions and outcomes (the 'Loss of Control', a partial defence for murder) lacks any clear evidence base. In three laboratory experiments, we measured sense of agency using an implicit measure based on time perception (the "intentional binding" paradigm). These actions occurred in either an emotionally neutral condition, or in a fearful (experiments 1 and 2) or angry state (experiment 3). In line with our hypotheses, fear or anger reduced the subjective sense of control over an action outcome, even though the objective causal link between action and outcome remained the same. This gap between the objective facts of agency, and a reduced subjective experience of agency under emotional conditions, has important implications for society and law.

High-precision voluntary movements are largely independent of preceding vertex potentials elicited by sudden sensory events.

KEY POINTS: Salient and sudden sensory events generate a remarkably large response in the human brain, the vertex wave (VW). The VW is coupled with a modulation of a voluntarily-applied isometric force. In the present study, we tested whether the VW is also related to executing high-precision movements. The execution of a voluntary high-precision movement remains relatively independent of the brain activity reflected by the preceding VW. The apparent relationship between the positive VW and movement onset time is explained by goal-related but stimulus-independent neural activities. These results highlight the need to consider such goal-related but stimulus-independent neural activities when attempting to relate event-related potential amplitude with perceptual and behavioural performance. ABSTRACT: Salient and fast-rising sensory events generate a large biphasic vertex wave (VW) in the human electroencephalogram (EEG). We recently reported that the VW is coupled with a modulation of concomitantly-applied isometric force. In the present study, in five experiments, we tested whether the VW is also related to high-precision visuomotor control. We obtained three results. First, the saliency-induced increase in VW amplitude was paralleled by a modulation in two of the five extracted movement parameters: a reduction in the onset time of the voluntary movement (P < 0.005) and an increase in movement accuracy (P < 0.005). Second, spontaneous trial-by-trial variability in vertex wave amplitude, for a given level of stimulus saliency, was positively correlated with movement onset time (P < 0.001 in four out of five experiments). Third, this latter trial-by-trial correlation was explained by a widespread EEG negativity independent of the occurrence of the positive VW, although overlapping in time with it. These results indicate that (i) the execution of a voluntary high-precision movement remains relatively independent of the neural processing reflected by the preceding VW, with (ii) the exception of movement onset time, for which saliency-based contextual effects are dissociated from trial-by-trial effects. These results also indicate that (iii) attentional effects can produce spurious correlations between event-related potentials (ERPs) and behavioural measures. Although sudden salient stimuli trigger characteristic EEG responses coupled with distinct reactive components within an ongoing isometric task, the results of the present study indicate that the execution of a subsequent voluntary movement appears largely protected from such saliency-based modulation, with the exception of movement onset time.

Ineffectiveness of tactile gating shows cortical basis of nociceptive signaling in the Thermal Grill Illusion.

Painful burning sensations can be elicited by a spatially-alternating pattern of warm and cold stimuli applied on the skin, the so called "Thermal Grill Illusion" (TGI). Here we investigated whether the TGI percept originates spinally or centrally. Since the inhibition of nociceptive input by concomitant non-nociceptive somatosensory input has a strong spinal component, we reasoned that, if the afferent input underlying the TGI originates at spinal level, then the TGI should be inhibited by a concomitant non-nociceptive somatosensory input. Conversely, if TGI is the result of supraspinal processing, then no effect of touch on TGI would be expected. We elicited TGI sensations in a purely thermal condition without tactile input, and found no evidence that tactile input affected the TGI. These results provide further evidence against a spinal mechanism generating the afferent input producing the TGI, and indicate that the peculiar burning sensation of the TGI results from supraspinal interactions between thermoceptive and nociceptive systems.

Control of wrist movement in deafferented man: evidence for a mixed strategy of position and amplitude control.

There is a continuing debate about control of voluntary movement, with conflicted evidence about the balance between control of movement vectors (amplitude control) that implies knowledge of the starting position for accuracy, and equilibrium point or final position control, that is independent of the starting conditions. We tested wrist flexion and extension movements in a man with a chronic peripheral neuronopathy that deprived him of proprioceptive knowledge of his wrist angles. In a series of experiments, we demonstrate that he could scale the amplitude of his wrist movements in flexion/extension, even without visual feedback, and appeared to adopt a strategy of moving via a central wrist position when asked to reach target angles from unknown start locations. When examining the relationship between positional error at the start and end of each movement in long sequences of movements, we report that he appears to have three canonical positions that he can reach relatively successfully, in flexion, in extension and in the centre. These are consistent with end-point or position control. Other positions were reached with errors that suggest amplitude control. Recording wrist flexor and extensor EMG confirmed that the flexion and extension canonical positions were reached by strong flexor and extensor activity, without antagonist activity, and other positions were reached with graded muscle activation levels. The central canonical position does not appear to be reached by either maximal co-contraction or by complete relaxation, but may have been reached by matched low-level co-contraction.

Subliminal modulation of voluntary action experience: A neuropsychological investigation.

Human voluntary actions are often associated with a distinctive subjective experience termed 'sense of agency'. This experience could be a reconstructive inference triggered by monitoring one's actions and their outcomes, or a read-out of brain processes related to action preparation, or some hybrid of these. Participants pressed a key with the right index finger at a time of their own choice, while viewing a rotating clock. Occasionally they received a mild shock on the same finger. They were instructed to press the key as quickly as possible if they felt a shock. On some trials, trains of subliminal shocks were also delivered, to investigate whether such subliminal cues could influence the initiation of voluntary actions, or the subjective experience of such actions. Participants' keypress were always followed by a tone 250 ms later. At the end of each trial they reported the time of the keypress using the rotating clock display. Shifts in the perceived time of the action towards the following tone, compared to a baseline condition containing only a keypress but no tone, were taken as implicit measures of sense of agency. The subliminal shock train enhanced this "action binding" effect in healthy participants, relative to trials without such shocks. This difference could not be attributed to retrospective inference, since the perceptual events were identical in both trial types. Further, we tested the same paradigm in a patient with anarchic hand syndrome (AHS). Subliminal shocks again enhanced our measure of sense of agency in the unaffected hand, but had a reversed effect on the 'anarchic' hand. These findings suggest an interaction between internal volitional signals and external cues afforded by the external environment. Damage to the neural pathways that mediate interactions between internal states and the outside world may explain some of the clinical signs of AHS.

Children who stutter show reduced action-related activity in the rostral cingulate zone.

Previous studies have indicated that children who stutter show not only speech-related problems, but also wider difficulties in self-control. In this study we test the novel hypothesis that children who stutter may experience difficulties with inhibitory control over voluntary actions. We used functional MRI to compare brain activity between children who stutter and children who do not stutter in a task that captures key cognitive aspects of voluntary action control. Participants performed a rolling marble task, in which they were instructed to press a key to stop a rolling marble from crashing on some of the trials (instructed action condition). They were also asked to choose voluntarily whether to execute or inhibit this prepotent response in other trials (volition condition). Children who stutter reported less motor and cognitive impulsivity and had shorter stop-signal reaction times when controlled for IQ, consistent with greater inhibition, compared to children who do not stutter. At the neural level, children who stutter showed decreased activation in the rostral cingulate zone during voluntary action selection compared to children who do not stutter. This effect was more pronounced for children who were rated as showing more stuttered syllables in the stutter screening, and was furthermore correlated with stop-signal reaction times and impulsivity ratings. These findings suggest that stuttering in childhood could reflect wider difficulties in self-control, also in the non-verbal domain. Understanding these neural mechanisms could potentially lead to more focused treatments of stuttering.

Voluntary or involuntary? A neurophysiologic approach to functional movement disorders.

Patients with functional movement disorders (FMD) experience movements as involuntary that share fundamental characteristics with voluntary actions. This apparent paradox raises questions regarding the possible sources of a subjective experience of action. In addition, it poses a yet unresolved diagnostic challenge, namely how to describe or even quantify this experience in a scientifically and clinically useful way. Here, we describe recent experimental approaches that have shed light on the phenomenology of action in FMD. We first outline the sources and content of a subjective experience of action in healthy humans and discuss how this experience may be created in the brain. Turning to FMD, we describe implicit, behavioral measures that have revealed specific abnormalities in the awareness of action in FMD. Based on these abnormalities, we propose a potential, new solution to the paradox of volition in FMD.

Emotional valence, sense of agency and responsibility: A study using intentional binding.

We investigated how the emotional valence of an action outcome influences the experience of control, in an intentional binding experiment. Voluntary actions were followed by emotionally positive or negative human vocalisations, or by neutral tones. We used mental chronometry to measure a retrospective component of sense of agency (SoA), triggered by the occurrence of the action outcome, and a prospective component, driven by the expectation that the outcome will occur. Positive outcomes enhanced the retrospective component of SoA, but only when both occurrence and the valence of the outcome were unexpected. When the valence of outcomes was blocked - and therefore predictable - we found a prospective component of SoA when neutral tones were expected but did not actually occur. This prospective binding was absent, and reversed, for positive and negative expected outcomes. Emotional expectation counteracts the prospective component of SoA, suggesting a distancing effect.

Laser-Evoked Vertex Potentials Predict Defensive Motor Actions.

The vertex potential is the largest response that can be recorded in the electroencephalogram of an awake, healthy human. It is elicited by sudden and intense stimuli, and is composed by a negative-positive deflection. The stimulus properties that determine the vertex potential amplitude have been well characterized. Nonetheless, its functional significance remains elusive. The dominant interpretation is that it reflects neural activities related to the detection of salient stimuli. However, given that threatening stimuli elicit both vertex potentials and defensive movements, we hypothesized that the vertex potential is related to the execution of defensive actions. Here, we directly compared the salience and motoric interpretations by investigating the relationship between the amplitude of laser-evoked potentials (LEPs) and the response time of movements with different defensive values. First, we show that a larger LEP negative wave (N2 wave) predicts faster motor response times. Second, this prediction is significantly stronger when the motor response is defensive in nature. Third, the relation between the N2 wave and motor response time depends not only on the kinematic form of the movement, but also on whether that kinematic form serves as a functional defense of the body. Therefore, the N2 wave of the LEP encodes key defensive reactions to threats.

Voluntary control of a phantom limb.

Voluntary actions are often accompanied by a conscious experience of intention. The content of this experience, and its neural basis, remain controversial. On one view, the mind just retrospectively ascribes intentions to explain the occurrence of actions that lack obvious triggering stimuli. Here, we use EEG frequency analysis of sensorimotor rhythms to investigate brain activity when a participant (CL, co-author of this paper) with congenital absence of the left hand and arm, prepared and made a voluntary action with the right or the phantom "left hand". CL reported the moment she experienced the intention to press a key. This timepoint was then used as a marker for aligning and averaging EEG. In a second condition, CL was asked to prepare the action on all trials, but then, on some trials, to cancel the action at the last moment. For the right hand, we observed a typical reduction in beta-band spectral power prior to movement, followed by beta rebound after movement. When CL prepared but then cancelled a movement, we found a characteristic EEG pattern reported previously, namely a left frontal increase in spectral power close to the time of the perceived intention to move. Interestingly, the same neural signatures of positive and inhibitory volition were also present when CL prepared and inhibited movements with her phantom left hand. These EEG signals were all similar to those reported previously in a group of 14 healthy volunteers. Our results suggest that conscious intention may depend on preparatory brain activity, and not on making, or ever having made, the corresponding physical body movement. Accounts that reduce conscious volition to mere retrospective confabulation cannot easily explain our participant's neurophenomenology of action and inhibition. In contrast, the results are consistent with the view that specific neural events prior to movement may generate conscious experiences of positive and negative volition.

Exploring implicit and explicit aspects of sense of agency.

Sense of agency refers to the sense of initiating and controlling actions in order to influence events in the outside world. Recently, a distinction between implicit and explicit aspects of sense of agency has been proposed, analogous to distinctions found in other areas of cognition, notably learning. However, there is yet no strong evidence supporting separable implicit and explicit components of sense of agency. The so-called 'Perruchet paradigm' offers one of the few convincing demonstrations of separable implicit and explicit learning systems. We adopted this approach to evaluate the implicit-explicit distinction in the context of a simple task in which outcomes were probabilistically caused by actions. In line with our initial predictions, we found evidence of a dissociation. We discuss the implications of this result for theories of sense of agency.

Increased plasticity of the bodily self in eating disorders.

BACKGROUND: The rubber hand illusion (RHI) has been widely used to investigate the bodily self in healthy individuals. The aim of the present study was to extend the use of the RHI to examine the bodily self in eating disorders (EDs). METHOD: The RHI and self-report measures of ED psychopathology [the Eating Disorder Inventory - 3 (EDI-3) subscales of Drive for Thinness, Bulimia, Body Dissatisfaction, Interoceptive Deficits, and Emotional Dysregulation; the 21-item Depression, Anxiety and Stress Scale (DASS-21); and the Self-Objectification Questionnaire (SOQ)] were administered to 78 individuals with an ED and 61 healthy controls. RESULTS: Individuals with an ED experienced the RHI significantly more strongly than healthy controls on both perceptual (i.e. proprioceptive drift) and subjective (i.e. self-report questionnaire) measures. Furthermore, both the subjective experience of the RHI and associated proprioceptive biases were correlated with ED psychopathology. Approximately 23% of the variance for embodiment of the fake hand was accounted for by ED psychopathology, with interoceptive deficits and self-objectification significant predictors of embodiment. CONCLUSIONS: These results indicate that the bodily self is more plastic in people with an ED. These findings may shed light on both aetiological and maintenance factors involved in EDs, particularly visual processing of the body, interoceptive deficits, and self-objectification.

Extrastriate body area underlies aesthetic evaluation of body stimuli.

Humans appear to be the only animals to have developed the practice and culture of art. This practice presumably relies on special processing circuits within the human brain associated with a distinct subjective experience, termed aesthetic experience, and preferentially evoked by artistic stimuli. We assume that positive or negative aesthetic judgments are an important function of neuroaesthetic circuits. The localisation of these circuits in the brain remains unclear, though neuroimaging studies have suggested several possible neural correlates of aesthetic preference. We applied repetitive transcranial magnetic stimulation (rTMS) over candidate brain areas to disrupt aesthetic processing while healthy volunteers made aesthetic preference judgments between pairs of dance postures, or control non-body stimuli. Based on evidence from visual body perception studies, we targeted the ventral premotor cortex (vPMC) and extrastriate body area (EBA), in the left and right hemispheres. rTMS over EBA reduced aesthetic sensitivity for body stimuli relative to rTMS over vPMC, while no such difference was found for non-body stimuli. We interpret our results within the framework of dual routes for visual body processing. rTMS over either EBA or vPMC reduced the contributions of the stimulated area to body processing, leaving processing more reliant on the unaffected route. Disruption of EBA reduces the local processing of the stimuli and reduced observers' aesthetic sensitivity. Conversely, disruption of the global route via vPMC increased the relative contribution of the local route via EBA and thus increased aesthetic sensitivity. In this way, we suggest a complementary contribution of both local and global routes to aesthetic processing.

EEG activations during intentional inhibition of voluntary action: an electrophysiological correlate of self-control?

An important aspect of volition is the internal decision whether to act or to withhold an action. We used EEG frequency analysis of sensorimotor rhythms to investigate brain activity when people prepare and then cancel a voluntary action. Participants used a rotating clock-hand to report when they experienced the intention to press a key with their right hand, even on trials where they freely decided to inhibit movement at the last moment. On action trials, we observed the classical pattern of reduced beta-band spectral power prior to movement, followed by beta rebound after movement. On inhibition trials where participants prepared but then cancelled a movement, we found a left frontal increase in spectral power (event-related synchronisation: ERS) peaking 12 ms before the perceived intention to move. This neural correlate of intentional inhibition was significantly different from the activity at the corresponding moment in action trials. The results are discussed in the context of a recent model of voluntary action (WWW model; Brass & Haggard, 2008). Planned actions can be subjected to a final predictive check which either commits actions for execution or suspends and withholds them. The neural mechanism of intentional inhibition may play an important role in self-control.

Lexicality drives audio-motor transformations in Broca's area.

Broca's area is classically associated with speech production. Recently, Broca's area has also been implicated in speech perception and non-linguistic information processing. With respect to the latter function, Broca's area is considered to be a central area in a network constituting the human mirror system, which maps observed or heard actions onto motor programs to execute analogous actions. These mechanisms share some similarities with Liberman's motor theory, where objects of speech perception correspond to listener's intended articulatory gestures. The aim of the current series of behavioral, TMS and fMRI studies was to test if Broca's area is indeed implicated in such audio-motor transformations. More specifically, using a classical phonological rhyme priming paradigm, we investigated whether the role of Broca's area could be purely phonological or rather, is lexical in nature. In the behavioral baseline study, we found a large priming effect in word prime/target pairs (W-W) and no effect for pseudo-words (PW-PW). Online TMS interference of Broca's area canceled the priming difference between W-W and PW-PW by enhancing the effects for PW-PW. Finally, the fMRI study showed activation of Broca's area for W-W pairs, but not for PW-PW pairs. Our data show that Broca's area plays a significant role in speech perception strongly linked to the lexicality of a stimulus.

Action observation and execution: what is shared?

Performing an action and observing it activate the same internal representations of action. The representations are therefore shared between self and other (shared representations of action, SRA). But what exactly is shared? At what level within the hierarchical structure of the motor system do SRA occur? Understanding the content of SRA is important in order to decide what theoretical work SRA can perform. In this paper, we provide some conceptual clarification by raising three main questions: (i) are SRA semantic or pragmatic representations of action?; (ii) are SRA sensory or motor representations?; (iii) are SRA representations of the action as a global unit or as a set of elementary motor components? After outlining a model of the motor hierarchy, we conclude that the best candidate for SRA is intentions in action, defined as the motor plans of the dynamic sequence of movements. We shed new light on SRA by highlighting the causal efficacy of intentions in action. This in turn explains phenomena such as inhibition of imitation.

Towards a sensorimotor aesthetics of performing art.

The field of neuroaesthetics attempts to identify the brain processes underlying aesthetic experience, including but not limited to beauty. Previous neuroaesthetic studies have focussed largely on paintings and music, while performing arts such as dance have been less studied. Nevertheless, increasing knowledge of the neural mechanisms that represent the bodies and actions of others, and which contribute to empathy, make a neuroaesthetics of dance timely. Here, we present the first neuroscientific study of aesthetic perception in the context of the performing arts. We investigated brain areas whose activity during passive viewing of dance stimuli was related to later, independent aesthetic evaluation of the same stimuli. Brain activity of six naïve male subjects was measured using fMRI, while they watched 24 dance movements, and performed an irrelevant task. In a later session, participants rated each movement along a set of established aesthetic dimensions. The ratings were used to identify brain regions that were more active when viewing moves that received high average ratings than moves that received low average ratings. This contrast revealed bilateral activity in the occipital cortices and in right premotor cortex. Our results suggest a possible role of visual and sensorimotor brain areas in an automatic aesthetic response to dance. This sensorimotor response may explain why dance is widely appreciated in so many human cultures.

Disruption of sitting balance after stroke: influence of spoken output.

OBJECTIVES: To identify the extent of dual task interference between cognitive and motor tasks, (cognitive motor interference (CMI)) in sitting balance during recovery from stroke; to compare CMI in sitting balance between stroke and non-stroke groups; and to record any changes to CMI during sitting that correlate with functional recovery. METHOD: 36 patients from stroke rehabilitation settings in three NHS trusts. Healthy control group: 21 older volunteers. Measures of seated postural sway were taken in unsupported sitting positions, alone, or concurrently with either a repetitive utterance task or an oral word category generation task. Outcome measures were variability of sway area, path length of sway, and the number of valid words generated. RESULTS: Stroke patients were generally less stable than controls during unsupported sitting tasks. They showed greater sway during repetitive speech compared with quiet sitting, but did not show increased instability to posture between repetitive speech and word category generation. When compared with controls, stroke patients experienced greater dual task interferences during repetitive utterance but not during word generation. Sway during repetitive speech was negatively correlated with concurrent function on the Barthel ADL index. CONCLUSIONS: The stroke patients showed postural instability and poor word generation skills. The results of this study show that the effort of verbal utterances alone was sufficient to disturb postural control early after stroke, and the extent of this instability correlated with concomitant Barthel ADL function.

Action observation and acquired motor skills: an FMRI study with expert dancers.

When we observe someone performing an action, do our brains simulate making that action? Acquired motor skills offer a unique way to test this question, since people differ widely in the actions they have learned to perform. We used functional magnetic resonance imaging to study differences in brain activity between watching an action that one has learned to do and an action that one has not, in order to assess whether the brain processes of action observation are modulated by the expertise and motor repertoire of the observer. Experts in classical ballet, experts in capoeira and inexpert control subjects viewed videos of ballet or capoeira actions. Comparing the brain activity when dancers watched their own dance style versus the other style therefore reveals the influence of motor expertise on action observation. We found greater bilateral activations in premotor cortex and intraparietal sulcus, right superior parietal lobe and left posterior superior temporal sulcus when expert dancers viewed movements that they had been trained to perform compared to movements they had not. Our results show that this 'mirror system' integrates observed actions of others with an individual's personal motor repertoire, and suggest that the human brain understands actions by motor simulation.