Silent event-related fMRI reveals deficient motor and enhanced somatosensory activation in orofacial dystonia

Abstract

Previous studies showed cortical dysfunction and impaired sensorimotor integration in primary generalized and focal hand dystonia. We used a whistling task and silent event-related fMRI to investigate functional changes in patients with blepharospasm and patients with a combination of blepharospasm and oromandibular dystonia (Meige's syndrome). Whistling served as a model for a skilful orofacial movement with a high demand on sensorimotor integration. It allowed us to study the oromandibular motor system that is clinically affected in Meige's syndrome but not in isolated blepharospasm. In Meige's syndrome, functional MRI revealed deficient activation of the primary motor and ventral premotor cortex within the mouth representation area during whistling. Compared with healthy controls, both forms of orofacial dystonia had increased activation of bilateral somatosensory areas and the caudal supplementary motor area (SMA) in common. While overactivity of somatosensory areas and caudal SMA in Meige patients was partly reversed by botulinum toxin treatment, impaired motor activation was not. We conclude that impaired motor activation appears to be specific for the clinically affected oromandibular motor system in Meige's syndrome while enhanced somatosensory activation is a common abnormality in both forms of orofacial dystonia independent of the affected motor system. Somatosensory overactivity indicates an altered somatosensory representation in orofacial dystonia while impaired motor activation may be a functional correlate of reduced cortical inhibition during oromandibular motor execution in Meige's syndrome.

Executive functioning in patients with blepharospasm in comparison with patients with hemifacial spasm

“…This result contrasts with the hypothesis that plastic changes in the frontal lobe following focal dystonia would be associated with impaired executive function in these patients 19 .…”

Sensorimotor network in cervical dystonia and the effect of botulinum toxin treatment: A functional MRI study

“…These observations may suggest that abnormal sensory inputs coming to SMA neurons participate in the development of dystonia. Like SMA, the dorsal premotor cortex (PMd) is a part of motor cortex generally considered to be relevant to the planning, selection and execution of motor actions [31] as well as to sensorimotor integration in normals [6]. In generalized and focal dystonia patients, PET studies have reported hyperactive PMd and hypoactive M1 during movement compared to normals [32].…”

“…Differences among task conditions, including testing of dystonia-affected and unaffected body parts can partly explain this variance. It is also a matter of debate whether different types of primary dystonias share identical pathophysiological traits [6].…”

Dystonia Pathophysiology: A Critical Review

“…However, reduced sensorimotor activation also may occur during dystonic movements (165,166). The abnormal fMRI signals for representation of digits in the primary sensory cortex (107,108) or other body parts in the basal ganglia (171) have been interpreted as a loss of neuronal selectivity.…”