Aikaterini Fotopoulou and her colleagues have shown that some patients fitting this description have a residual, subconscious awareness of their disability.
The researchers recruited 14 brain-damaged patients with a completely paralysed left arm, half of whom denied their paralysis (ie they had anosognosia). Next, all the patients were presented with a series of sentences for which they had to provide the final word. The twist to the task is that the word had to be completely unrelated in meaning to its adjoining sentence.
Some of the sentences were emotionally neutral (about cars), some were negatively emotional (about violence), and finally some pertained to stroke and physical disabilities. The patients with anosognosia performed no differently from the paralysed controls on the neutral and negative sentences, but they took longer to complete the sentences about stroke and disabilities. This was taken as a sign of competition between subconscious self-threatening information about disability and the task requirement to find an unrelated word. It suggests the anosognosic patients had a subconscious awareness of their own disability.
The patients were also asked to rate the same set of sentences for their self-relevance - this was an explicit test of their awareness. Again, the anosognosic patients differed from controls on precisely the sentences that pertained to stroke and disability. This time, as you might expect, they tended to say such sentences were less relevant to them than did the controls.
A final component of the study involved scanning the brains of all fourteen of the patients. This showed that the patients with anosognosia had damage in brain regions involved in motor control (including the basal ganglia) and body representation (including the anterior insula) that were unaffected in patients without anosognosia.
Fotopoulou's theory is that patients with anosognosia have a subconscious awareness of their deficits but that the brain circuits responsible for creating an up-to-date representation of self are compromised. Consistent with this, in previous research, patients with anosnognosia have shown greater insight when describing their impairments from a third-person perspective and also after viewing themselves on video. A related theory is that patients with anosognosia have intact motor planning brain circuits but that their feedback circuits are damaged. So, when asked to move, they feel that they've sent a successful motor command to their limb but are left unaware that the command wasn't enacted.
One reason anosognosia is so intriguing is that it has both neurobiological and psychological components. Some experts have interpreted it as a form of Freudian defence against the emotional trauma of paralysis. Consistent with this, when insight into their paralysis has been achieved, previously anosognosic patients have subsequently suffered from an increase in depressive symptoms.
'The combination of our behavioural and neural findings suggest that an explicit, affectively personalised sensorimotor awareness requires the re-representation of sensorimotor information in the insular cortex, with possible involvement of limbic areas and basal ganglia circuits,' the researchers said. 'The delusional features of anosognosia for hemiplegia can be explained as a failure of this re-representation.'
Fotopoulou, A., Pernigo, S., Maeda, R., Rudd, A., and Kopelman, M. (2010). Implicit awareness in anosognosia for hemiplegia: unconscious interference without conscious re-representation. Brain, 133 (12), 3564-3577 DOI: 10.1093/brain/awq233