Kinaesthetic motor imagery in writer's cramp dystonia reveals writing specific abnormalities in the occipital lobe.

Abstract

Studies on motor imagery (MI) in writer's cramp (WC) dystonia are limited but may offer insights into impaired motor planning without the influence of dystonic co-contraction. This study used functional magnetic resonance imaging (fMRI) to compare executed writing and drawing of circles with kinaesthetic motor imagery in 18 WC patients and 18 healthy controls. Kinematic analysis confirmed the abnormal signature of WC by demonstrating a decreased frequency and an increased number of inversions during writing in WC patients. fMRI showed decreased BOLD activation during MI, with similar regions activated as in motor execution. Between-group differences during drawing demonstrated reduced activity in the bilateral precentral areas, left supplementary motor area, and right frontal medial area in WC patients. Imagined drawing revealed diminished activation in the left sensorimotor cortex, left superior frontal area, and right cerebellum (Vermis 4/5, Vermis 6, and Cerebellum 6) in WC patients. Writing and imagined writing led to abnormal activation in the superior occipital area and cuneus in WC patients. Direct comparison of writing and drawing in execution and MI conditions displayed a writing-specific deficit in the cuneus and occipital areas. We conclude that MI in WC dystonia offers a valuable opportunity to observe neural activity in similar regions as during motor execution. The observed writing-specific activation deficits in the occipital lobe may reflect dysfunction in the integration of printed/written features or a correlate of disrupted somatosensory processing.