Reality monitoring in anosognosia for hemiplegia

The dual-path hypothesis for the emergence of anosognosia in Alzheimer's disease

Although neurocognitive models have been proposed to explain anosognosia in Alzheimer's disease (AD), the neural cascade responsible for its origin in the human brain remains unknown. Here, we build on a mechanistic dual-path hypothesis that brings error-monitoring and emotional processing systems as key elements for self-awareness, with distinct impacts on the emergence of anosognosia in AD. Proceeding from the notion of anosognosia as a dimensional syndrome, varying between a lack of concern about one's own deficits (i.e., anosodiaphoria) and a complete lack of awareness of deficits, our hypothesis states that (i) unawareness of deficits would result from primary damage to the error-monitoring system, whereas (ii) anosodiaphoria would more likely result from an imbalance between emotional processing and error-monitoring. In the first case, a synaptic failure in the error-monitoring system, in which the anterior and posterior cingulate cortices play a major role, would have a negative impact on error (or deficits) awareness, preventing patients from becoming aware of their condition. In the second case, an impairment in the emotional processing system, in which the amygdala and the orbitofrontal cortex play a major role, would prevent patients from monitoring the internal milieu for relevant errors (or deficits) and assigning appropriate value to them, thus biasing their impact on the error-monitoring system. Our hypothesis stems on two scientific premises. One comes from preliminary results in AD patients showing a synaptic failure in the error-monitoring system along with a decline of awareness for cognitive difficulties at the time of diagnosis. Another comes from the somatic marker hypothesis, which proposes that emotional signals are critical to adaptive behavior. Further exploration of these premises will be of great interest to illuminate the foundations of self-awareness and improve our knowledge of the underlying paths of anosognosia in AD and other brain disorders.

Updating beliefs beyond the here-and-now: the counter-factual self in anosognosia for hemiplegia

The syndrome of anosognosia for hemiplegia, 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 anosognosia for hemiplegia is a modality-specific deficit of sensorimotor monitoring, or whether domain-general processes of attention and belief-updating converge to cause anosognosia for hemiplegia. Using a Bayesian learning framework, we formalized 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 anosognosia for hemiplegia 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 anosognosia for hemiplegia patients: (i) standardized, 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 anosognosia for hemiplegia. 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.

Mnemonic monitoring in anosognosia for memory loss

OBJECTIVE

Anosognosia, or unawareness, for memory loss has been proposed to underlie cognitive functions such as memory and executive function. However, there is an inconsistent association between these constructs. Recent studies have shown that compromise ongoing self-monitoring of one's memory associates with anosognosia for memory loss. Yet to date it is unclear which memory monitoring mechanisms are impaired in these patients. In this study, we examined the extent to which temporal monitoring or orbitofrontal reality filtering (e.g., ability to monitor the temporal relevance of a memory) and source monitoring (e.g., the ability to distinguish which memories stem from internal as opposed to external sources) are associated with awareness of memory deficits.

METHOD

A total of 35 patients (M = 69 years; M = 14 years of education) with memory difficulties following a stroke were recruited from outpatient clinics. Patients were assessed with measures of self-awareness of memory difficulties, cognitive abilities and 2 experimental paradigms assessing source and temporal monitoring.

RESULTS AND CONCLUSION

Results showed that patients unaware of their memory difficulties were more likely to externalize the source of their memories. Specifically, those unaware of their deficits were more likely to assign an external source to memories that were internally produced (e.g., imagined). No differences were observed in relation to temporal monitoring between patients aware and unaware of their deficits. This study informs current theoretical models of self-awareness of memory loss. Future studies should attempt to replicate these findings and explore different memory monitoring mechanisms in relation to anosognosia for memory loss. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Cross domain self-monitoring in anosognosia for memory loss in Alzheimer's disease

Anosognosia for memory loss is a common feature of Alzheimer's disease (AD). Recent theories have proposed that anosognosia, a disruption in awareness at a global level, may reflect specific deficits in self-monitoring, or local awareness. Though anosognosia for memory loss has been shown to relate to memory self-monitoring, it is not clear if it relates to self-monitoring deficits in other domains (i.e., motor). The current study examined this question by analyzing the relationship between anosognosia for memory loss, memory monitoring, and motor monitoring in 35 individuals with mild to moderate AD. Anosognosia was assessed via clinical interview before participants completed a metamemory task to measure memory monitoring, and a computerized agency task to measure motor monitoring. Cognitive and psychological measures included memory, executive functions, and mood. Memory monitoring was associated with motor monitoring; however, anosognosia was associated only with memory monitoring, and not motor monitoring. Cognition and mood related differently to each measure of self-awareness. Results are interpreted within a hierarchical model of awareness in which local self-monitoring processes are associated across domain, but appear to only contribute to a global level awareness in a domain-specific fashion.

Cortico-thalamic disconnection in a patient with supernumerary phantom limb

Supernumerary phantom limb (SPL) designates the experience of an illusory additional limb occurring after brain damage. Functional neuroimaging during SPL movements documented increased response in the ipsilesional supplementary motor area (SMA), premotor cortex (PMC), thalamus and caudate. This suggested that motor circuits are important for bodily related cognition, but anatomical evidence is sparse. Here, we tested this hypothesis by studying an extremely rare patient with chronic SPL, still present 3 years after a vascular stroke affecting cortical and subcortical right-hemisphere structures. Anatomical analysis included an advanced in vivo reconstruction of white matter tracts using diffusion-based spherical deconvolution. This reconstruction demonstrated a massive and relatively selective disconnection between anatomically preserved SMA/PMC and the thalamus. Our results provide strong anatomical support for the hypothesis that cortico-thalamic loops involving motor-related circuits are crucial to integrate sensorimotor processing with bodily self-awareness.

Monitoring what is real: The effects of modality and action on accuracy and type of reality monitoring error

Reality monitoring refers to processes involved in distinguishing internally generated information from information presented in the external world, an activity thought to be based, in part, on assessment of activated features such as the amount and type of cognitive operations and perceptual content. Impairment in reality monitoring has been implicated in symptoms of mental illness and associated more widely with the occurrence of anomalous perceptions as well as false memories and beliefs. In the present experiment, the cognitive mechanisms of reality monitoring were probed in healthy individuals using a task that investigated the effects of stimulus modality (auditory vs visual) and the type of action undertaken during encoding (thought vs speech) on subsequent source memory. There was reduced source accuracy for auditory stimuli compared with visual, and when encoding was accompanied by thought as opposed to speech, and a greater rate of externalization than internalization errors that was stable across factors. Interpreted within the source monitoring framework (Johnson, Hashtroudi, & Lindsay, 1993), the results are consistent with the greater prevalence of clinically observed auditory than visual reality discrimination failures. The significance of these findings is discussed in light of theories of hallucinations, delusions and confabulation.

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.

Inter-individual variability in metacognitive ability for visuomotor performance and underlying brain structures

Metacognition refers to the ability to discriminate between one's own correct and incorrect decisions. The neurobiological underpinnings of metacognition have mainly been studied in perceptual decision-making. Here we investigated whether differences in brain structure predict individual variability in metacognitive sensitivity for visuomotor performance. Participants had to draw straight trajectories toward visual targets, which could unpredictably deviate around detection threshold, report such deviations when detected, and rate their confidence level for such reports. Structural brain MRI analyses revealed that larger gray-matter volume (GMV) in the left middle occipital gyrus, left medial parietal cortex, and right postcentral gyrus predicted higher deviation detection sensitivity. By contrast, larger GMV in the right prefrontal cortex but also right anterior insula and right fusiform gyrus predicted higher metacognitive sensitivity. These results extend past research by linking metacognitive sensitivity for visuomotor behavior to brain areas involved in action agency (insula), executive control (prefrontal cortex) and vision (fusiform).

Implicit awareness in anosognosia: clinical observations, experimental evidence, and theoretical implications

Unawareness  of deficits caused by brain damage or neurodegeneration, termed anosognosia, has been demonstrated in a number of different neurological conditions. Clinical observation suggests that unawareness paradoxically can be accompanied by signs of understanding or representation of deficit, but not explicitly expressed. Such "implicit awareness," an apparent oxymoron, is implied by or inferred from actions or statements of the person with neurological disorder. In the current paper, we review clinical observations and experimental evidence which suggest the occurrence of implicit awareness in dementia and hemiplegia, and explore the clinical and theoretical implications of this phenomenon. We present a theoretical framework to understand implicit awareness in these two conditions.

The riddle of anosognosia: does unawareness of hemiplegia involve a failure to update beliefs?

Anosognosia for hemiplegia (AHP) is defined as a lack of awareness for motor incapacity after a brain lesion. The causes of AHP still remain poorly understood. Many associations and dissociations with other deficits have been highlighted but no specific cognitive or neurological impairment has been identified as a unique causative factor. We hypothesized that a failure to update beliefs about current state might be a crucial component of AHP. Here, we report results from a new test that are compatible with this view. We examined anosognosic and nosognosic brain-damaged patients, as well as healthy controls, on a task where they had to guess a target word based on successive clues, with increasing informative content. After each clue, participants had to propose a word solution and rated their confidence. Compared to other participants, anosognosic patients were abnormally overconfident in their responses, even when information from the clues was insufficient. Furthermore, when presented with new clues incongruent with their previous response, they often stuck to their former "false" beliefs instead of modifying them. This impairment was unrelated to global deficits in reasoning or memory, and all patients eventually identified the correct solution of riddles after the last, fully informative, clue. These results suggest that a deficit in the generation and adjustment of beliefs may be a key factor contributing to the occurrence and persistence of anosognosia, when associated with concomitant losses in motor, proprioceptive, and/or attentional functions. Patients may remain unaware of their deficit partly because they cannot "update" their beliefs about current state.

Confabulation and delusion: a common monitoring framework

Confabulations and delusions both involve the production of false claims. Although they may have different types of content, they share several characteristics. For example, they are often held with considerable conviction and are resistant to counter evidence, they may be acted upon, and they may be accompanied by a lack of concern about the false claim or its implications. Confabulations and delusions may initially arise from failures in different systems (e.g., mnemonic vs. perceptual or affective). However, their shared characteristics raise the possibility that the monitoring deficits involved might be the same, resulting in failure to reject the confabulatory or delusional ideas. In this paper we will focus on the nature of these common monitoring deficits. Critically, we argue that monitoring in confabulation and delusion involves both unconscious and conscious processes. We propose that an unconscious process is responsible for tagging suspect content which needs to be checked for veracity by a separate set of conscious evaluative processes. Failure of these monitoring processes would allow ideas which ought to be checked and rejected to instead be uncritically accepted: This would result in the production of confabulations or delusions. Importantly, inclusion of both unconscious and conscious monitoring stages allows the model to account for both "endorsement" and "explanation" delusions, and both "primary" and "secondary" confabulations. Our hope is that this model may provide a theoretical framework to guide empirical investigation of the commonalities and differences between the conditions.

Recent advances in the understanding of neglect and anosognosia following right hemisphere stroke

This article highlights the latest findings regarding the cognitive-behavioral syndromes of neglect and anosognosia for hemiplegia that occur following right hemisphere stroke. We review papers published in the past 2 years pertaining to neurophysiology, assessment, and intervention for these two syndromes.

Motor awareness in anosognosia for hemiplegia: experiments at last!

Anosognosia for hemiplegia (AHP) is the apparent inability to acknowledge contralesional paralysis, typically following right-hemisphere lesions. Here, we review studies that regard AHP as a specific deficit of motor awareness and explain its symptoms by employing an established computational model of motor control. These accounts propose that AHP arises from a breakdown in the monitoring of intended and actual movement. First, we critically examine physiological and behavioural experiments, which attempt to provide an account of AHP by verifying the presence or absence of motor intentions. We then review more recent experiments that endeavour to empirically address the hitherto unexplored role of motor intentions and internal representations of movements in AHP patients' non-veridical (illusory) awareness of movement. Finally, we consider implications of AHP research for clinical practice and the understanding of motor awareness more generally. We conclude that the false experience of movement in AHP may provide insight into what occurs when the mechanism responsible for monitoring and correcting significant discrepancies between predicted and executed actions is impaired. The system seems to continue to operate by deceiving awareness.