Mental rotation of body parts and non-corporeal objects in patients with idiopathic cervical dystonia

Mental rotation of body parts is performed through inner simulation of actual movements, and is likely to rely upon cortical and subcortical systems (e.g. motor and premotor areas and basal ganglia) involved in motor planning and execution. Studies indicate that sensory and motor deficits, such as for example pain, limb amputation or focal hand dystonia, bring about a specific impairment in mental rotation of the affected body parts. Here we explored the ability of patients affected by idiopathic cervical dystonia (CD) to mentally rotate affected (neck) and unaffected (hands and feet) body districts. The experimental stimuli consisted of realistic photos of left or right hands or feet and the head of a young men with a black patch on the left or the right eye. As non-corporeal stimulus the front view of a car with a black patch on the left or the right headlight was used. The stimuli were presented at six different degrees of orientations. Twelve CD patients and 12 healthy participants were asked to verbally report whether the hands or feet were left or right, or whether the patch was on the left or the right eye or headlight. Reaction times and accuracy in performing the laterality tasks on the four stimuli were collected. Results showed that CD patients are slow in mental rotation of stimuli representing body parts, namely hand, foot and head. This abnormality was not due to a general impairment in mental rotation per se, since patients' ability to rotate a non-corporeal object (a car) was not significantly different from that of healthy participants. We posit that the deficit in mental rotation of body parts in CD patients may derive from a defective integration of body- and world-related knowledge, a process that is likely to allow a general representation of "me in the external world".