Interaction Between Eye and Hand Movements in Multiple Sclerosis Patients With Intention Tremor Peter Feys, PhD, 1–4 Werner F. Helsen, PhD, 1 * Xuguang Liu, MD, PhD, 2 Bart Nuttin, MD, PhD, 3 Ann Lavrysen, 1 Stephan P. Swinnen, PhD, 1 and Pierre Ketelaer, MD 4 1 Department of Kinesiology, Katholieke Universiteit Leuven, Leuven, Belgium 2 Division of Neuroscience and Psychological Medicine, Charing Cross Hospital, Imperial College, London, United Kingdom 3 Department of Neurosciences and Psychiatry, Katholieke Universiteit Leuven, Leuven, Belgium 4 National Multiple Sclerosis Center, Melsbroek, Belgium Abstract: Deficient eye and hand movements are present in patients with multiple sclerosis. In the present study, eye and hand movements were simultaneously measured during visu- ally guided wrist step-tracking tasks in 16 patients with inten- tion tremor and 15 healthy controls. The coupling between eye and hand movements was analyzed during simultaneous eye– hand tracking, and interactions were studied by comparing the coordinated eye– hand condition with isolated eye- or hand- tracking conditions. Despite movement abnormalities, the onset of eye and hand movements was highly correlated and an invariant coupling between the saccadic completion time and hand peak velocity was found, suggesting that the temporal coupling was very much preserved. The differences between the experimental tracking conditions suggest that, in MS pa- tients with intention tremor, the ocular system influenced the hand movements. Intention tremor amplitude was reduced when there was no preceding saccadic eye movement, whereas conversely, eye movements were not affected by different hand tremor severity. © 2005 Movement Disorder Society Key words: multiple sclerosis; intention tremor; eye; inter- action; step tracking Symptoms in both the ocular and limb motor systems are present in patients with multiple sclerosis (MS). Intention tremor in the upper limb and eye movement deficits such as unsteady fixation and saccadic dysmetria are frequently observed and are both related to damage of the cerebellum or closely related structures such as the brainstem. 1–6 Eye movement deficits have been reported to coexist with upper limb coordination disorders in MS patients. 5,7,8 Abnormal eye movements appear closely related to hand tremor severity during goal-directed aim- ing tasks. 8 In patients with cerebellar deficits, both eye and hand ramp-tracking movements are also less accu- rate compared to healthy controls. 9 It has been concluded that the inaccurate eye movements contributed to inac- curacy of the hand movements and vice versa. In normal subjects, the performance of discrete goal- directed movements toward a visual target is character- ized by two movement phases: first, a primary large saccadic eye movement and a primary hand movement typically undershoot and end near the target, respec- tively, followed by corrective movements bringing the eyes and the hand on the target. The primary eye and hand movements are temporally coupled: eye and hand movement onset are closely related with the eyes invari- antly fixating the target well before the primary hand movement is completed. Saccadic completion time is temporally coupled with peak acceleration and peak ve- locity of the hand, ensuring that the eyes are in an optimal position to provide retinal information of the target position for adjustments during hand decelera- tion. 10 –14 Eye and hand movements in MS patients have been studied mainly in isolation. 4,7,8,15–17 Therefore, two ma- jor questions were addressed in the present study: (1) Do *Correspondence to: Dr. Werner F. Helsen, Katholieke Universiteit Leuven, Department of Kinesiology, Motor Learning Laboratory, Ter- vuursevest 101, B-3001 Leuven, Belgium. E-mail: werner.helsen@faber.kuleuven.be Received 10 February 2004; Revised 9 September 2004; Accepted 10 September 2004 Published online 16 February 2005 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/mds.20382 Movement Disorders Vol. 20, No. 6, 2005, pp. 705–713 © 2005 Movement Disorder Society 705