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.