Abnormalities in the awareness and control of action

Much of the functioning of the motor system occurs without awareness. Never theless, we are aware of some aspects of the current state of the system an d we can prepare and make movements in the imagination. These mental repres entations of the actual and possible states of the system are based on two sources: sensory signals from skin and muscles, and the stream of motor com mands that have been issued to the system. Damage to the neural substrates of the motor system can lead to abnormalities in the awareness of action as well as defects in the control of action. We provide a framework for under standing how these various abnormalities of awareness can arise. Patients w ith phantom limbs or with anosognosia experience the illusion that they can move their limbs. We suggest that these representations of movement are ba sed on streams of motor commands rather than sensory signals. Patients with utilization behaviour or with delusions of control can no longer properly link their intentions to their actions. In these cases the impairment lies in the representation of intended movements. The location of the neural dam age associated with these disorders suggests that representations of the cu rrent and predicted state of the motor system are in parietal cortex, while representations of intended actions are found in prefrontal and premotor c ortex.