Unconscious activation of motor responses in a hemiplegic patient with anosognosia and neglect.

Unconscious processing of environmental stimuli has been convincingly demonstrated for a large number of neuropsychological syndromes. However, only few studies have successfully recorded on-line the activation of the autonomous or the motoric nervous systems. The activation of the motor system by unconscious stimuli would be a strong argument that information processing in the brain is not organized into two serial steps (stimulus identification first, response selection second). This would argue for parallel processes of stimuli identification routines and response selection mechanisms on the basis of only provisionally worked out stimulus features. Investigating an anosognostic patient we found electrodermal activity (EDA) and electromyographic responses (EMG) to bimanual tasks, mental imagery, and to the request to execute specific actions. But overt behavior remained hemiplegic and the patient was unable to feel any kind of control of her paralyzed left arm and hand. Generally, the data can be interpreted along the lines of a theory of two different routes to action, leaving the unconscious selection of action patterns intact, whereas the intentional triggering of overt behavior with the left hand and arm was impossible for the patient.