Impaired sensorimotor integration in focal hand dystonia patients in the absence of symptoms C Carolyn Wu, 1 Scott L Fairhall, 2 Nicolas A McNair, 1 Jeff P Hamm, 1 Ian J Kirk, 1 Ross Cunnington, 3 Tim Anderson, 4 Vanessa K Lim 1 ABSTRACT Background Functional imaging studies of people with focal hand dystonia (FHD) have indicated abnormal activity in sensorimotor brain regions. Few studies however, have examined FHD during movements that do not provoke symptoms of the disorder. It is possible, therefore, that any differences between FHD and controls are confounded by activity due to the occurrence of symptoms. Thus, in order to characterise impairments in patients with FHD during movements that do not induce dystonic symptoms, we investigated the neural correlates of externally paced finger tapping movements. Methods Functional MRI (fMRI) was used to compare patients with FHD to controls with respect to activation in networks modulated by task complexity and hand used to perform simple and complex tapping movements. Results In the ‘complexity network,’ patients with FHD showed significantly less activity relative to controls in posterior parietal cortex, medial supplementary motor area (SMA), anterior putamen and cerebellum. In the ‘hand network,’ patients with FHD showed less activation than controls in primary motor (M1) and somatosensory (S1) cortices, SMA and cerebellum. Conjunction analysis revealed that patients with FHD demonstrated reduced activation in the majority of combined network regions (M1, S1 and cerebellum). Conclusion Dysfunction in FHD is widespread in both complexity and hand networks, and impairments are demonstrated even when performing tasks that do not evoke dystonic symptoms. These results suggest that such impairments are inherent to, rather than symptomatic of, the disorder. INTRODUCTION Focal hand dystonia (FHD) is a movement disorder characterised by excessive co-contraction of agonist and antagonist muscles during specific tasks, such as writing or playing an instrument. 1 2 The underlying causes of the disorder are still unclear, although impairments in sensorimotor regions of the brain are evident in patients with FHD. 3e8 However, conflicting findings exist in the literature. Both abnormally increased and decreased func- tional activation have been reported in sensori- motor regions. For example, studies that have implemented symptom-inducing tasks (eg, writing and playing guitar) have demonstrated reduced activation in the contralateral primary motor (M1), supplementary motor area (SMA) 3 and premotor areas 7 of patients with FHD compared with healthy control participants. In contrast, other studies have reported abnormally increased activa- tion in the above regions, 5 as well as in the cere- bellum and thalamus. 6 Another study reported less activation in SMA, but increased activation in M1 and primary somatosensory cortex (S1), in their FHD group compared with controls. 4 These contradictory results may be accounted for by the variability in tasks and degree of symptoms that were induced in these studies. For example, factors such as duration of tapping or writing can influence the severity of dystonia. 4 Moreover, sustained excitability in the basal ganglia has been found after the cessation of movement during bimanual finger tapping tasks that induced dystonia, and the resultant delayed return to baseline may mask dysfunction in these regions in some studies. 9 Less is known about changes in sensorimotor function during non-symptomatic movement in FHD. Investigating the effects of FHD using tasks that do not induce dystonic symptoms may contribute to understanding the neurological abnor- malities of the disorder, as it ensures that variability in performance is controlled for and avoids discom- fort for patients. A previous functional MRI (fMRI) study used such a task, where patients with FHD held their right wrist horizontally and either bent their wrist downward (relaxation) or upward (contraction). 10 Compared with healthy controls, decreased activity was found during the tasks in M1, S1 and SMA in patients with FHD. However, such tasks do not elucidate dysfunction that may arise during finer movement of the fingers. These finer finger movements have been addressed using PET, which demonstrated significantly decreased activa- tion for patients with FHD compared with control participants during writing tasks that induced dystonic movements, but not a finger-tapping task which did not induce dystonia. 3 However, abnor- malities in EEG have been found during similar finger tapping tasks that did not induce dystonic symp- toms. 11 In the present study, we used fMRI to investigate these types of finer movement tasks to ensure that movement performance was similar in patients and controls, and included simple and complex movements in order to examine possible complexity effects. Previous PET and fMRI research has demon- strated that the extent of brain motor activation is reflected in the complexity of the movement. For example, simple tasks (eg, tapping one finger against the thumb) require activity of the contra- lateral M1, S1 and ipsilateral cerebellum. 12e14 In contrast, complex unimanual movements (eg, sequential tapping of the fingers) additionally 1 Department of Psychology, The University of Auckland, Auckland, New Zealand 2 Neuroimaging Laboratory, Fondazione Santa Lucia IRCCS, Rome, Italy 3 Queensland Brain Institute and School of Psychology, The University of Queensland, Brisbane, Australia 4 Van der Veer Institute for Parkinson’s & Brain Research, The University of Otago, Christchurch, New Zealand Correspondence to Dr Vanessa K Lim, Department of Psychology, Research Centre for Cognitive Neuroscience, The University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand; v.lim@auckland.ac.nz Received 14 July 2009 Revised 11 October 2009 Accepted 6 November 2009 J Neurol Neurosurg Psychiatry 2010;81:659e665. doi:10.1136/jnnp.2009.185637 659 Research paper