The role of motor intention in motor awareness: an experimental study on anosognosia for hemiplegia.

Recent theories propose that anosognosia for hemiplegia (AHP) results from specific impairments in motor planning. However, no study has hitherto directly investigated the role of motor intention in the observed non-veridical awareness of action in AHP. We developed the following paradigm to investigate the role of motor planning in awareness in patients with AHP: Four hemiplegic patients with and four without anosognosia were provided with false visual feedback of movement in their left paralysed arm through a prosthetic rubber hand. We examined whether the ability to detect presence or absence of movement based on visual evidence varied according to whether the patient had planned to move their limb or not. Motor intention had a selective effect on patients with AHP; they were more likely than controls (U = 16, P < 0.001) to ignore the visual feedback of a motionless hand and claim that they moved it when they had the intention to do so (self-generated movement) than when they expected an experimenter to move their own hand (externally generated movement), or there was no expectation of movement. By contrast, patients without AHP were not influenced by these manipulations, and did not claim they moved their hand when the hand remained still. This is the first direct demonstration that altered awareness of action in AHP reflects a dominance of motor intention prior to action over sensory information about the actual effects of movement.