Action-monitoring impairment in anosognosia for hemiplegia (original) (raw)
Neuropsychologia, 2010
The current study adds to the growing empirical research into the mechanisms underlying unawareness of paralysis following stroke (anosognosia for hemiplegia or AHP) by investigating action awareness for the non-paralysed limb in a single AHP patient. Visual feedback representing patient GG's goal-directed reaching movements was either modified by a computer or left unperturbed. Unlike healthy and brain-damaged controls, GG was unable to detect computer-generated visual perturbations as large as 20°. GG also failed to report awareness of the large on-line corrective movements that he made when compensating (often unsuccessfully) for the visual perturbations. These results suggest that the motor comparators implicated in AHP are functioning, but not at optimum levels. Moreover, because the current findings reveal a deficit in awareness for reaches with the unimpaired limb, it is suggestive of common right hemisphere networks for motor awareness in both limbs and that AHP may be a global deficit in motor awareness as opposed to a specific lack of awareness for a particular motor deficit.▶ Anosognosia for Hemiplegia (AHP) involves defective sensorimotor comparisons. ▶ Large motor errors involving the unaffected arm are not consciously detected in AHP. ▶ Errors involving the unaffected arm are corrected without conscious awareness in AHP. ▶ High (conscious) and low (non-conscious) level motor awareness may dissociate in AHP. ▶ Motor awareness for both arms might involve a shared right-hemisphere mechanism.
OBJECTIVES: To confront motor awareness in anosognosia for hemiplegia (AHP), where paralyzed patients deny their motor impairment, and in motor neglect (MN), where non-paralyzed patients behave as if they were paretic. METHODS: Eight right-brain-damaged-patients, 4 hemiplegic (2 with and 2 without AHP) and 4 non-hemiplegic (2 with only perceptual-neglect and 2 with also MN) were evaluated with a bimanual motor battery, before and after examiner's reinforcement to use the contralesional limb. The requested bimanual movements could be either symmetric or asymmetric, either intransitive or transitive (with/without objects). We compared the examiner's evaluation of patients' performance with the patients' self-evaluation of their own motor capability (explicit knowledge). We also evaluated the presence/absence of compensatory unimanual strategies that, if present, suggests implicit knowledge of the motor deficit. RESULTS: We found significant differences between conditions only in MN patients, whose performance was better after the examiner's reinforcement than before it, during symmetric than asymmetric movements and during intransitive than transitive movements. As for motor awareness, we found a lack of explicit and implicit knowledge in both AHP and MN patients. CONCLUSION: Although different in terms of motor intention and motor planning, AHP and MN are both characterised by anosognosia for the motor impairment.
Imagining the impossible: Motor representations in anosognosia for hemiplegia
Neuropsychologia, 2009
Anosognosia for hemiplegia (AHP) is characterised by poor insight or underestimation of hemiplegia after brain injury. Recent explanations of AHP have used an established ‘forward model’, which proposes that normal motor awareness involves comparing the predicted and actual sensory consequences of movements. These accounts propose that AHP patients may be able to form representations of their intended movements (i.e., motor representations), but fail to register discrepancy between intended and actual movements. A prediction arising from this proposal is that AHP patients are able to generate motor representations involving their hemiplegic limb(s). Our study provides the first direct examination of this prediction in patients with AHP. We used an existing ‘grip selection task’, which investigates motor representations by comparing how patients would grasp an object and how they actually grasp the same object. Eight right hemisphere stroke patients with AHP, 10 control patients (non-AHP), and 22 age-matched healthy volunteers (HVs) completed the task. Results showed that HVs outperformed both AHP and non-AHP patients in their motor representations for the hemiplegic limb; however, the performance of AHP and non-AHP patients did not differ significantly. Motor representations for the intact limb were lower than normal in AHP patients, whereas performance in non-AHP patients was midway between the AHP and HV groups. Findings suggested that the ability to form motor representations lie on a continuum, but that impaired motor representations for the paralysed limb cannot account for AHP. Distorted motor representations, in combination with other deficits, might contribute to the pathogenesis of AHP.
Behavioural Brain Research, 2011
Anosognosia for hemiplegia (AH) is characterized by a lack of awareness of motor disorders and appears associated with fronto-temporal-parietal damage. Neuropsychological evidence indicates that behavioral indices of residual forms of motor awareness may co-exist with explicit denial of impairment. Here we explore whether the attempt by AH patients to perform an action may disclose residual forms of motor awareness and whether such forms are underpinned by different neural structures. Twelve hemiplegic patients affected by AH were tested in tasks assessing: (i) implicit awareness (IA), indexed by discrepancies between verbal reports and actual motor behavior; (ii) emergent awareness (EA), indexed by increased verbal awareness induced by the attempt to perform actions. IA and EA were found in five and three patients, respectively. Lesion analysis indicates that while the lack of IA is associated with damage to subcortical white matter anterior to the basal ganglia, lack of EA is linked to damage to cortical regions including insulo-frontal, temporal and parietal structures. Our results indicate that deficits in explicit and implicit awareness are associated with lesions involving different cortico-subcortical structures. Moreover, the results show that the attempt to perform an action may ameliorate body awareness deficits and have implications for rehabilitation.
In anosognosia for hemiplegia, patients may claim having performed willed actions with the paralyzed limb despite unambiguous evidence to the contrary. Does this false belief of having moved reflect the functioning of the same mechanisms that govern normal motor performance? Here, we examined whether anosognosics show the same temporal constraints known to exist during bimanual movements in healthy subjects. In these paradigms, when participants simultaneously reach for two targets of different difficulties, the motor programs of one hand affect the execution of the other. In detail, the movement time of the hand going to an easy target (i.e., near and large), while the other is going to a difficult target (i.e., far and small), is slowed with respect to unimanual movements (temporal coupling effect). One right-brain-damaged patient with left hemiplegia and anosognosia, six right-brain-damaged patients with left hemiplegia without anosognosia, and twenty healthy subjects were administered such a bimanual task. We recorded the movement times for easy and difficult targets, both in unimanual (one target) and bimanual (two targets) conditions. We found that, as healthy subjects, the anosognosic patient showed coupling effect. In bimanual asymmetric conditions (when one hand went to the easy target and the other went to the difficult target), the movement time of the non-paralyzed hand going to the easy target was slowed by the 'pretended' movement of the paralyzed hand going to the difficult target. This effect was not present in patients without anosognosia. We concluded that in anosognosic patients, the illusory movements of the paralyzed hand impose to the non-paralyzed hand the same motor constraints that emerge during the actual movements. Our data also support the view that coupling relies on central operations (i.e., activation of intention/programming system), rather than on online information from the periphery.
Anosognosia for hemiplegia (AHP) is characterised as a disorder in which patients are unaware of their contralateral motor deficit. Many current theories for unawareness in AHP are based on comparator model accounts of the normal experience of agency. According to such models, while small mismatches between predicted and actual feedback allow unconscious fine-tuning of normal actions, mismatches that surpass an inherent threshold reach conscious awareness and inform judgements of agency (whether a given movement is produced by the self or another agent). This theory depends on a threshold for consciousness that is greater than the intrinsic noise in the system to reduce the occurrence of incorrect rejections of self-generated movements and maintain a fluid experience of agency. Pathological increases to this threshold could account for reduced motor awareness following brain injury, including AHP. The current experiment tested this hypothesis in healthy controls by exposing them to training in which noise was applied the visual feedback of their normal reaches. Subsequent self/other attribution tasks without noise revealed a decrease in the ability to detect manipulated (other) feedback compared to training without noise. This suggests a slackening of awareness thresholds in the comparator model that may help to explain clinical observations of decreased action awareness following stroke.
The Motor Unawareness Assessment (MUNA): A new tool for the assessment of Anosognosia for hemiplegia
Journal of Clinical and Experimental Neuropsychology, 2021
Background: Anosognosia for hemiplegia (AHP) is a condition in which patients with paralysis are unaware of their motor deficits. Research into AHP is important for improving its treatment and providing insight into the neurocognitive mechanism of motor awareness. Unfortunately, most studies use assessments with widely recognized limitations. Aim: To develop a psychometrically validated assessment of AHP. Method: We developed a 40-item Motor Unawareness Assessment (MUNA) and administered it to 131 right-hemisphere stroke patients. Principal Component Analysis (PCA) was used to identify the underlying factor structure. Receiver Operating Characteristics (ROC) analysis was used to determine diagnostic cut-offs, and Area Under the Curve (AUC) analysis used to assess these cut-offs. Relationships with demographic, clinical and neuropsychological variables were explored. Results: Five factors were identified: explicit motor awareness, implicit motor awareness, impaired sense of ownership, agency and illusory movement, and emotional reactions. Established cut-offs had excellent sensitivity and specificity. Clinical, neuropsychological and demographic variables did not predict overall MUNA score but were related to specific subcomponents. The MUNA can differentiate various facets of AHP and provides a detailed profile of (un)awareness. The MUNA can therefore provide robust assessment for research purposes and assist clinicians when developing targeted rehabilitation.
'Moving' a paralysed hand: bimanual coupling effect in patients with anosognosia for hemiplegia.
Selective neurological impairments can shed light on different aspects of motor cognition. Brain-damaged patients with anosognosia for hemiplegia deny their motor deficit and believe they can still move the paralysed limb. Here we study, for the first time, if the anomalous subjective experience that their affected hand can still move, may have objective consequences that constrain movement execution with the opposite, intact hand. Using a bimanual motor task, in which anosognosic patients were asked to simultaneously trace out lines with their unaffected hand and circles with their paralysed hand, we found that the trajectories of the intact hand were influenced by the requested movement of the paralysed hand, with the intact hand tending to assume an oval trajectory (bimanual coupling effect). This effect was comparable to that of a group of healthy subjects who actually moved both hands. By contrast, brain-damaged patients with motor neglect or actual hemiplegia but no anosognosia did not show this bimanual constraint. We suggest that anosognosic patients may have intact motor intentionality and planning for the plegic hand. Rather than being merely an inexplicable confabulation, anosognosia for the plegic hand can produce objective constraints on what the intact hand does.