Mental simulation of whole-body movements in patients with isolated cervical dystonia

Objective: To explore mental transformation of whole-body images in patients with isolated cervical dystonia (CD). Background: Mental transformation of bodies or of body-part images is performed by simulating one’s own actual movements, and is likely to rely upon brain systems involved in motor planning and execution. Patients with CD have various clinical presentations with different degrees of postural abnormality consistent with severity of dystonia. Previous evidence showed that CD patients were slower and less accurate than healthy controls in mentally rotating both affected (neck) and unaffected (hands and feet) body parts, but they also showed a non-significant decrement in their ability to mentally transform noncorporeal objects (Fiorio et al. 2007). Thus, it cannot be established whether CD patients are unable to simulate one’s own body movements (embodied simulation) or have a more general deficit in mental rotation. Here, we tested embodied simulation processes in CD patients by a whole-body transformation task. Methods: Eighteen patients with isolated CD under treatment with botulinum toxin and no general cognitive disorders, as assessed by formal neuropsychological examination, and 18 healthy controls, matched for age and education, underwent the whole-body transformation task. Participants had to perform left-right judgments on a schematic figure representing a front-facing or a back-facing human body in different spatial orientations (Conson et al. 2014). Both Reaction Times (RTs) and error rates were recorded. Results: A four-way mixed-design ANOVA was performed on correct RTs, with stimulus posture (frontfacing and back-facing) and stimulus orientation (0°, 90°, 180° and 270°) as within-subject factors, and with group (CD patients and controls) as a between-subject factor. The main result was a significant interaction among the three factor, F(3,102)=3,350, p= .047, partial h2 = .107, demonstrating that CD patients were slower than controls when judging back-facing, but not front-facing bodies, in specific spatial orientations. Conclusions: These findings showing that CD patients were specifically impaired in mentally transforming back-facing body images suggest that simulation of whole-body movements is impaired in this clinical population when embodied simulation processes come into play.