The physiology of motor delusions in anosognosia for hemiplegia: implications for current models of motor awareness

Schizophrenia and the bodily self

Despite the historically consolidated psychopathological perspective, on the one hand, contemporary organicistic psychiatry often highlights abnormalities in neurotransmitter systems like dysregulation of dopamine transmission, neural circuitry, and genetic factors as key contributors to schizophrenia. Neuroscience, on the other, has so far almost entirely neglected the first-person experiential dimension of this syndrome, mainly focusing on high-order cognitive functions, such as executive function, working memory, theory of mind, and the like. An alternative view posits that schizophrenia is a self-disorder characterized by anomalous self-experience and awareness. This view may not only shed new light on the psychopathological features of psychosis but also inspire empirical research targeting the bodily and neurobiological changes underpinning this disorder. Cognitive neuroscience can today address classic topics of phenomenological psychopathology by adding a new level of description, finally enabling the correlation between the first-person experiential aspects of psychiatric diseases and their neurobiological roots. Recent empirical evidence on the neurobiological basis of a minimal notion of the self, the bodily self, is presented. The relationship between the body, its motor potentialities and the notion of minimal self is illustrated. Evidence on the neural mechanisms underpinning the bodily self, its plasticity, and the blurring of self-other distinction in schizophrenic patients is introduced and discussed. It is concluded that brain-body function anomalies of multisensory integration, differential processing of self- and other-related bodily information mediating self-experience, might be at the basis of the disruption of the self disorders characterizing schizophrenia.

Modulation of Motor Awareness: A Transcranial Magnetic Stimulation Study in the Healthy Brain

Previous studies on the mechanisms underlying willed actions reported that the premotor cortex may be involved in the construction of motor awareness. However, its exact role is still under investigation. Here, we investigated the role of the dorsal premotor cortex (PMd) in motor awareness by modulating its activity applying inhibitory rTMS to PMd, before a specific motor awareness task (under three conditions: without stimulation, after rTMS and after Sham stimulation). During the task, subjects had to trace straight lines to a given target, receiving visual feedback of the line trajectories on a computer screen. Crucially, in most trials, the trajectories on the screen were deviated, and to produce straight lines, subjects had to correct their movements towards the opposite direction. After each trial, participants were asked to judge whether the line seen on the computer screen corresponded to the line actually drawn. Results show that participants in the No Stimulation condition did not recognize the perturbation until 14 degrees of deviation. Importantly, active, but not Sham, rTMS significantly modulated motor awareness, decreasing the amplitude of the angle at which participants became aware of the trajectory correction. These results suggest that PMd plays a crucial role in action self-monitoring.

Key constructs of body awareness impairments post-stroke: a scoping review of assessment tools and interventions

PURPOSE

To summarise body awareness assessment tools and interventions relevant for stroke rehabilitation using a framework that categorises key body awareness constructs, disorders and impairments.

MATERIALS AND METHODS

Online electronic databases and trial registries were searched from inception until July 2021, in addition to hand searching reference lists of included studies and reviews. Study selection included any study design where the investigation involved assessing and/or intervening in body awareness following stroke. Data were extracted based on predefined criteria by two independent reviewers and mapped to the emergent framework.

RESULTS

The final analysis included 144 papers that reported 43 assessment tools and 8 types of interventions for body awareness. Consensus was reached on a synthesised body awareness framework. This comprised specific impairments and disorders, constructs, sub-categories and main categories leading to the overarching term of body awareness. Clinical and psychometric properties of the assessment tools were not reported or poorly evaluated, and the interventions lacked robust study designs and rigorous methods.

CONCLUSIONS

The framework produced will enable future research and clinical practice to be based on consistent concepts and definitions. Clinicians can also use this information to cautiously select assessment tools and/or interventions but are reminded of the limitations identified in this review.Implications for rehabilitationThere is limited understanding, compounded by inconsistent terminology and definitions regarding body awareness after stroke.A synthesized framework to define key constructs and definitions of body awareness is proposed.Assessment tools and interventions reported in the literature are mapped to the proposed framework.Psychometric properties of available tools are reported.Significant work remains to refine concepts of body awareness, develop and evaluate assessment tools and interventions.

Moving without sensory feedback: online TMS over the dorsal premotor cortex impairs motor performance during ischemic nerve block

The study investigates the role of dorsal premotor cortex (PMd) in generating predicted sensory consequences of movements, i.e. corollary discharges. In 2 different sessions, we disrupted PMd and parietal hand's multisensory integration site (control area) with transcranial magnetic stimulation (TMS) during a finger-sequence-tapping motor task. In this TMS sham-controlled design, the task was performed with normal sensory feedback and during upper-limb ischemic nerve block (INB), in a time-window where participants moved without somatosensation. Errors and movement timing (objective measures) and ratings about movement perception (subjective measures) were collected. We found that INB overall worsens objective and subjective measures, but crucially in the PMd session, the absence of somatosensation together with TMS disruption induced more errors, less synchronized movements, and increased subjective difficulty ratings as compared with the parietal control session (despite a carryover effect between real and sham stimulation to be addressed in future studies). Contrarily, after parietal area interference session, when sensory information is already missing due to INB, motor performance was not aggravated. Altogether these findings suggest that the loss of actual (through INB) and predicted (through PMd disruption) somatosensory feedback degraded motor performance and perception, highlighting the crucial role of PMd in generating corollary discharge.

Case report of anosognosia for hemiplegia: A fMRI study

OBJECTIVE

The aim of this study is to verify the functional activation in a patient with anosognosia for hemiplegia following left brain lesions.

METHODS

We report a case of a 53-year-old right-handed female patient. She came to our rehabilitative unit with a diagnosis of an ischemic major stroke in the left internal carotid artery and important hemiplegia to the right side. She underwent functional magnetic resonance imaging (fMRI), during which she performed a motor imagery task.

RESULTS

The fMRI assessment showed an ischemic lesion in the frontotemporal and insular left areas. In the fMRI experiment, we revealed activation of the residual neural patterns of both hemispheres.

CONCLUSION

We underlined an interest in the compensation mechanism that involved neural networks near brain lesions and some areas of the contro-lesional hemisphere, suggesting that the synaptic plasticity permitted an intra and inter-hemispheric reorganization of the cerebral system.

The 'healthy side' of anosognosia for hemiplegia: Increased sense of agency for the unimpaired limb or motor compensation?

OBJECTIVES

Anosognosic patients show a lack of awareness for their hemiplegia coupled with a distorted sense of agency for the actions performed by the plegic limbs. Since anosognosia is often associated with right brain damage, this hemisphere seems to play a dominant role in monitoring awareness for motor actions. Therefore, we would expect that anosognosic patients show distorted awareness and sense of agency also for actions performed with the unimpaired limb.

METHOD

To test this hypothesis, we induced illusory actions that could be congruent or incongruent with a preceding verbal command. A group of 16 right brain-damaged patients performed this task and then rated i) their ability to anticipate the actions, ii) their sense of agency and iii) their sense of ownership for each limb. Measures of awareness, neglect and motor impairment were also considered for the patient group.

RESULTS

Following incongruent actions with the unimpaired limb, less aware patients showed a relatively mild distortion in all three aspects. In addition, we also found a crucial relationship between motor impairment (for the plegic limb) and sense of agency for both plegic and healthy limbs.

CONCLUSION

Although the distortion linked to both limbs supports the initial hypothesis that the right hemisphere is responsible for monitoring awareness for action for the whole body, our data also suggest that the observed distortion may be linked to a motor compensatory phenomenon, not necessarily related to awareness processes.

Brain Abnormalities in Individuals with a Desire for a Healthy Limb Amputation: Somatosensory, Motoric or Both? A Task-Based fMRI Verdict

Body integrity dysphoria (BID), a long-lasting desire for the amputation of physically healthy limbs, is associated with reduced fMRI resting-state functional connectivity of somatosensory cortices. Here, we used fMRI to evaluate whether these findings could be replicated and expanded using a task-based paradigm. We measured brain activations during somatosensory stimulation and motor tasks for each of the four limbs in ten individuals with a life-long desire for the amputation of the left leg and fourteen controls. For the left leg, BID individuals had reduced brain activation in the right superior parietal lobule for somatosensory stimulation and in the right paracentral lobule for the motor task, areas where we previously found reduced resting-state functional connectivity. In addition, for somatosensory stimulation only, we found a robust reduction in activation of somatosensory areas SII bilaterally, mostly regardless of the stimulated body part. Areas SII were regions of convergent activations for signals from all four limbs in controls to a significantly greater extent than in subjects with BID. We conclude that BID is associated with altered integration of somatosensory and, to a lesser extent, motor signals, involving limb-specific cortical maps and brain regions where the first integration of body-related signals is achieved through convergence.

The relations between cognitive and motivational components of anosognosia for left-sided hemiplegia and the right hemisphere dominance for emotions: A historical survey

Since the description of anosognosia for hemiplegia by Babinski (who also stressed the links between anosognosia and right hemisphere damage) both motivational and cognitive mechanisms have been advanced to explain this awareness disorder. In this review I will discuss first the neurophysiological mechanisms that can impede the discovery of the motor deficits contralateral to the brain lesion and then suggest that some instances of anosognosia for left-sided hemiplegia may also be due to motivational mechanisms of denial. Among the cognitive mechanisms, sensory feedback and intentional feed-forward disorders can lead to a poor awareness of the motor defects, whereas denial mechanisms could result from an interaction between the right hemisphere dominance for emotions and the anxiety raised by the catastrophic consequences of the brain damage. In particular, a maladaptive reaction to the personal implications of the brain lesion could be revealed by the presence of an implicit acknowledgement of the motor defect.

Exploring the Interaction Between Handedness and Body Parts Ownership by Means of the Implicit Association Test

The experience of owning a body is built upon the integration of exteroceptive, interoceptive, and proprioceptive signals. Recently, it has been suggested that motor signals could be particularly important in producing the feeling of body part ownership. One thus may hypothesize that the strength of this feeling may not be spatially uniform; rather, it could vary as a function of the degree by which different body parts are involved in motor behavior. Given that our dominant hand plays a leading role in our motor behavior, we hypothesized that it could be more strongly associated with one’s self compared to its non-dominant counterpart. To explore whether this possible asymmetry manifests as a stronger implicit association of the right hand (vs left hand) with the self, we administered the Implicit Association Test to a group of 70 healthy individuals. To control whether this asymmetric association is human-body specific, we further tested whether a similar asymmetry characterizes the association between a right (vs left) animal body part with the concept of self, in an independent sample of subjects (N = 70, 140 subjects total). Our results revealed a linear relationship between the magnitude of the implicit association between the right hand with the self and the subject’s handedness. In detail, the strength of this association increased as a function of hand preference. Critically, the handedness score did not predict the association of the right-animal body part with the self. These findings suggest that, in healthy individuals, the dominant and non-dominant hands are differently perceived at an implicit level as belonging to the self. We argue that such asymmetry may stem from the different roles that the two hands play in our adaptive motor behavior.

Direct electrical stimulation of the premotor cortex shuts down awareness of voluntary actions

A challenge for neuroscience is to understand the conscious and unconscious processes underlying construction of willed actions. We investigated the neural substrate of human motor awareness during awake brain surgery. In a first experiment, awake patients performed a voluntary hand motor task and verbally monitored their real-time performance, while different brain areas were transiently impaired by direct electrical stimulation (DES). In a second experiment, awake patients retrospectively reported their motor performance after DES. Based on anatomo-clinical evidence from motor awareness disorders following brain damage, the premotor cortex (PMC) was selected as a target area and the primary somatosensory cortex (S1) as a control area. In both experiments, DES on both PMC and S1 interrupted movement execution, but only DES on PMC dramatically altered the patients’ motor awareness, making them unconscious of the motor arrest. These findings endorse PMC as a crucial hub in the anatomo-functional network of human motor awareness.

Here, using electrical stimulation on patients undergoing awake brain surgery, the authors show that disruption of the premotor cortex makes patients unconscious of motor arrest. This finding suggests the premotor cortex is crucial for motor awareness.

Building the bodily self-awareness: Evidence for the convergence between interoceptive and exteroceptive information in a multilevel kernel density analysis study

Exteroceptive and interoceptive signals shape and sustain the bodily self-awareness. The existence of a set of brain areas, supporting the integration of information coming from the inside and the outside of the body in building the sense of bodily self-awareness has been postulated, yet the evidence remains limited, a matter of discussion never assessed quantitatively. With the aim of unrevealing where in the brain interoceptive and exteroceptive signals may converge, we performed a meta-analysis on imaging studies of the sense of body ownership, modulated by external visuotactile stimulation, and studies on interoception, which involves the self-awareness for internal bodily sensations. Using a multilevel kernel density analysis, we found that processing of stimuli of the two domains converges primarily in the supramarginal gyrus bilaterally. Furthermore, we found a right-lateralized set of areas, including the precentral and postcentral, and superior temporal gyri. We discuss these results and propose this set of areas as ideal candidates to match multiple body-related signals contributing to the creation of a multidimensional representation of the bodily self.

The Representation of Objects in Apraxia: From Action Execution to Error Awareness

Apraxia is a well-known syndrome characterized by the sufferer's inability to perform routine gestures. In an attempt to understand the syndrome better, various different theories have been developed and a number of classifications of different subtypes have been proposed. In this article review, we will address these theories with a specific focus on how the use of objects helps us to better understand upper limb apraxia. With this aim, we will consider transitive vs. intransitive action dissociation as well as less frequent types of apraxia involving objects, i.e., constructive apraxia and magnetic apraxia. Pantomime and the imitation of objects in use are also considered with a view to dissociating the various different components involved in upper limb apraxia. Finally, we discuss the evidence relating to action recognition and awareness of errors in the execution of actions. Various different components concerning the use of objects emerge from our analysis and the results show that knowledge of an object and sensory-motor representations are supported by other functions such as spatial and body representations, executive functions and monitoring systems.

When I am (almost) 64: The effect of normal ageing on implicit motor imagery in young elderlies

Motor imagery (M.I.) is a cognitive process in which movements are mentally evoked without overt actions. Behavioral and fMRI studies show a decline of explicit M.I. ability (e.g., the mental rehearsal of finger oppositions) with normal ageing: this decline is accompanied by the recruitment of additional cortical networks. However, none of these studies investigated behavioral and the related fMRI ageing modifications in implicit M.I. tasks, like the hand laterality task (HLT). To address this issue, we performed a behavioral and fMRI study: 27 younger subjects (mean age: 31 years) and 29 older subjects (mean age: 61 years) underwent two event-related design fMRI experiments. In the HLT, participants were asked to decide whether a hand rotated at different angles was a left or right hand. To test the specificity of any age related difference in the HLT, we used a letter rotation task as a control experiment: here subjects had to decide whether rotated letters were presented in a standard or a mirror orientation. We did not find any group difference in either behavioral task; however, we found significant additional neural activation in the elderly group in occipito-temporal regions: these differences were stronger for the HLT rather than for the LRT with group by task interactions effects in right occipital cortices. We interpret these results as evidence of compensatory processes associated with ageing that permit a behavioral performance comparable to that of younger subjects. This process appears to be more marked when the task specifically involves motor representations, even when these are implicitly evoked.

Action-monitoring impairment in anosognosia for hemiplegia

Every movement begins with action programming, and ends with a produced effect. Anosognosia for hemiplegia (AH), involving unawareness of motor deficits after brain damage, is a striking but also poorly understood symptom in clinical neurology. It has been suggested that it may result from a combination of cognitive and sensorimotor dysfunctions, including impairments in monitoring motor action and detecting the mismatch between intention and outcome. Here we investigated the relationship between motor action awareness and monitoring of self-produced movements by using a motor imaginary task, which was performed with either the intact or the affected limb. We tested 10 right brain-damaged patients, including 5 with AH, in comparison with 5 healthy controls. In a first phase, participants were asked to either realize or imagine a movement with their right or left arm. In a subsequent recognition phase, the participants had to recall whether the movement was a realized or imagined and which arm was used. AH patients performed significantly worse relative to no-AH patients and healthy controls for the left movements. Specifically, we found that AH patients believed they had realized movements with their (paralyzed) left arm even when they failed in the left execution condition. However, they also made more errors for movements actually realized with the right hand. These findings confirm that impaired action monitoring may contribute to AHP. Furthermore, our results support the notion of an action control system integrating "feedforward" signals through a comparison process between the intention and execution of movement, but also indicate that monitoring deficits in AHP are not strictly unilateral. Combined together, dysfunction of motor comparator processes and more general monitoring deficits may add up to lead to unawareness of paralysis.

Selective improvement of anosognosia for hemiplegia during transcranial direct current stimulation: a case report

Right brain damage patients may not complain of a left sided paralysis up to the point of denying it or even claiming of having just moved an otherwise paralyzed limb. This condition is known as anosognosia for hemiplegia (AHP). Recent behavioural experiments suggest that some residual intentionality might be preserved in patients with anosognosia and that the false belief of having moved originates from a failure to notice discrepancies between movement expectancies and the actual state of the motor system. This failure may be caused by a lack of afferent sensory information concerning the movement or alternatively by a direct dysfunction of the brain regions involved in actions' motor monitoring (i.e., the comparator system). Here we examined the effect of anodal transcranial direct current stimulation (tDCS) of the right premotor cortex in a patient with a bilateral lesion, involving predominantly the right hemisphere, and a dense unawareness for his left hemiplegia. During sham or anodal tDCS the patient was requested to judge his ability to perform simple motor actions (i) without actually executing the movement itself ("offline" condition) and after having performed a series of verbally cued finger opposition movements ("online" condition) with (i) eyes-closed or (ii) eyes-open. We found that anodal tDCS induces a significant remission of the false experience of movement only when the patient is requested to actually perform the movement with eyes open. Conversely, the patient's awareness does not improve in both the "offline" condition (in which the patient does not attempt to perform the movement) and in the "online" condition, when vision is precluded ("online" condition, eyes-closed). We conclude that the stimulation of the premotor cortex by tDCS activates brain regions involved in motor monitoring, temporary restoring the ability of the motor comparator system to correctly appreciate afferent information and build up a veridical motor awareness.

A New Perspective on Delusional States - Evidence for Claustrum Involvement

Delusions are a hallmark positive symptom of schizophrenia, although they are also associated with a wide variety of other psychiatric and neurological disorders. The heterogeneity of clinical presentation and underlying disease, along with a lack of experimental animal models, make delusions exceptionally difficult to study in isolation, either in schizophrenia or other diseases. To date, no detailed studies have focused specifically on the neural mechanisms of delusion, although some studies have reported characteristic activation of specific brain areas or networks associated with them. Here, we present a novel hypothesis and extant supporting evidence implicating the claustrum, a relatively poorly understood forebrain nucleus, as a potential common center for delusional states.