Anosognosia for Motor Impairments as a Delusion: Anomalies of Experience and Belief Evaluation

We put forward a two-factor account of anosognosia for hemiplegia—more generally, anosognosia for motor impairments—considered as a delusion. Anosognosia is a patient’s lack of knowledge of their illness or impairment, and patients who lack knowledge of their motor impairments believe that they can still move limbs that are, in reality, paralysed. This belief fits the DSM-5 definition of delusion. In our two-factor account of anosognosia as a continued-belief delusion, the first factor—an impairment of the motor control system—results in an anomaly of experience. When patients try, but fail, to move their left arm, there is an anomalous absence of immediate bodily experience of movement failure—perhaps accompanied by an illusory experience of successful movement. However, even without immediate experience of movement failure, other evidence of the motor impairments would be available—including evidence from everyday mishaps consequent on the motor impairments. The second factor in our two-factor account results in patients being unable to use this evidence to evaluate and reject the delusional belief and achieve knowledge of their motor impairments. Cognitive impairments of memory, error detection, executive function or working memory are candidate second factors that could result in this failure of belief evaluation.