Awareness is in the Eye of the Observer: Preserved Third-Person Awareness of Deficit in Anosognosia for Hemiplegia

In recent decades, the research traditions of (first-person) embodied cognition and of (third-person) social cognition have approached the study of self-awareness with relative independence. However, neurological disorders of self-awareness offer a unifying perspective to empirically investigate the contribution of embodiment and social cognition to self-awareness. This study focused on a neuropsychological disorder of bodily self-awareness following right-hemisphere damage, namely anosognosia for hemiplegia (AHP). A previous neuropsychological study has shown AHP patients, relative to neurological controls, to have a specific deficit in third-person, allocentric inferences in a story-based, mentalisation task. However, no study has tested directly whether verbal awareness of motor deficits is influenced by either perspective-taking or centrism, and if these deficits in social cognition are correlated with damage to anatomical areas previously linked to mentalising, including the supramarginal and superior temporal gyri and related limbic white matter connections. Accordingly, two novel experiments were conducted with right-hemisphere stroke patients with (n = 17) and without AHP (n = 17) that targeted either their own (egocentric, experiment 1) or another stooge patient’s (experiment 2) motor abilities from a first-or-third person (allocentric in Experiment 2) perspective. In both experiments, neurological controls showed no significant difference between perspectives, suggesting that perspective-taking deficits are not a general consequence of right-hemisphere damage. More specifically, experiment 1 found AHP patients were more aware of their own motor paralysis when asked from a third compared to a first-person perspective, using both group level and individual level analysis. In experiment 2, AHP patients were less accurate than controls in making allocentric, third-person perspective judgements about the stooge patient, but with only a trend towards significance and with no within-group, difference between perspectives. Deficits in egocentric and allocentric third-person perspective taking were associated with lesions in the middle frontal gyrus, superior temporal and supramarginal gyri, with white matter disconnections more predominate in deficits in allocentricity. This study confirms previous clinical and empirical investigations on the selectivity of first-person motor awareness deficits in anosognosia for hemiplegia and experimentally demonstrates for the first time that verbal egocentric 3PP-taking can positively influence 1PP body awareness.

REHABILITATION AND MODULATION AIMED AT AMELIORATING AWARENESS IN ANOSOGNOSIA FOR HEMIPLEGIA

Anosognosia for hemiplegia is a multifaceted syndrome that has a detrimental impact on the patient. Various theories based on behavioural and neuroanatomical data have been proposed to explain the mechanisms underlying the symptoms. These approaches have resulted in the development of a number of different proce- dures aimed at reducing symptoms or enhancing residual aware- ness. The article reviews rehabilitation attempts and their effects on individual cases and groups of patients. A selection of material was made using indexed articles published between 1987 and 2019. The inclusion criteria were: i) the presence of a neuropsychological assessment and ii) the presence of one or more methods specifically used to reduce AHP symptoms, or to enhance residual forms of awareness. The review indicates that intervention procedures have moved from bottom-up to more cognitive and metacognitive approaches. In fact, initially anosognosia for hemiplegia was considered to be a co-oc- current symptom of other neuropsychological conditions (e.g. spa- tial neglect) and interventions were borrowed from the rehabilitation techniques that had had success in relieving these other disorders. When anosognosia was identified as an independent syndrome and residual forms of awareness were demonstrated, procedures attempting to modulate awareness started to focus on specific components of the disease, such as visual perspective, motor monitoring and the updating of beliefs. Although further research is needed in this field, the most recent approaches seem to give more stable, lasting results than earlier methods. A timeline for interventions relating to anosognosia is suggested, and ethical issues are also discussed.

Updating Beliefs Beyond the Here-and-Now: The Counter-factual Self in Anosognosia for Hemiplegia

The syndrome of anosognosia for hemiplegia (AHP), or the lack of awareness for one’s paralysis following right hemisphere stroke, can provide unique insights into the neurocognitive mechanisms of self-awareness. Yet it remains unclear whether AHP is a modality-specific deficit of sensorimotor monitoring, or whether domain-general processes of attention and belief-updating converge to cause AHP. Using a Bayesian learning framework, we formalised and empirically investigated the hypothesis that failures to update anosognosic beliefs can be explained by abnormalities in the relative uncertainty (i.e. precision) ascribed to prior beliefs versus sensory information in different contexts. We designed a new motor belief-updating task that manipulated both the temporal (prospective and retrospective) and spatial (hemispace most affected by inattention and hemispace less affected by inattention) conditions in which beliefs had to be updated, and we validated its sensitivity to AHP in 26 patients with right hemisphere stroke. We then computed and empirically tested two different Bayesian predictors of prospective beliefs using two proxies for precision in AHP patients: (i) standardised, neuropsychological measures of objective attention abilities, i.e. visuospatial neglect scores, and (ii) subjective uncertainty reports, i.e. confidence ratings. Our results suggest that while neglect does not affect local, sensorimotor error monitoring, it does seem to affect the degree to which observed errors are used to update more general, prospective beliefs about counterfactual motor abilities in AHP. Difficulties in such ‘counterfactual’ belief-updating were associated with disruptions in tracts of the ventral attentional network (i.e. superior longitudinal fasciculus connecting the temporo-parietal junction and ventral frontal cortex) and associated lesions to the insula, inferior parietal cortex and superior temporal regions. These results suggest that self-awareness extends beyond local, retrospective monitoring, requiring also salience-based, convergence of beliefs about the self that go beyond the ‘here-and-now’ of sensorimotor experience.