P002 Abnormal surround inhibition of finger tapping task and cerebellar hyper-activation of functional MRI in patients with focal hand dystonia

Abstract

Introduction Surround inhibition is one physiological mechanism to select neuronal responses and to focus neural activity in the central nervous system. Within the motor system, it is a mechanism by which basal ganglia circuits selectively execute desired motor programs. Clinical features of focal hand dystonia (FHD) are task specific abnormal posturing due to sustained muscle contractions interfering with the performance of the skilled motor tasks. In dystonic patients, abnormal involuntary co-contraction of the hand muscles is associated with a disruption of SI. Objectives The aim of the study is to research the relationship with disrupted SI and function of central nervous system during motor performance using functional MRI. Patients & methods Seven healthy subjects (mean ages 34.7 ± 9.1 years, all men) and seven patients with writer cramp (mean ages 53.7 ± 17 years, 4 men and 2 women) were enrolled. Surrounding inhibition study: the experiment of surround inhibition was done according to Beck and Hallett. The EMG were recorded in both right first dorsal interosseus muscle (FDI) and abductor polices brevis muscle (APB). SI was evaluated as the ratio of MEP size of APB to that of FDI. Their right hand put on a side-table with their index finger on small tip of force transducer. Subjects pushed down on a small force transducer using their index finger as quickly as possible after an acoustic start signal. MEPs were measured by using single TMS which was given before signal and 100 ms, 150 ms and 1200 ms after signal. The time course of SI was constructed. And also cortical silent periods were measured for the evaluation of cortical inhibition during finger movement. Functional magnetic imaging for task and testing procedures: Subject was required to tap the second finger with the thumb at the speed of about 1 Hz for ten seconds of one session. Each subject participated in two sessions during they performed right-hand tapping or left-hand tapping. Functional MRI contrast analysis of activity was collected during tapping versus rest block. Blood oxygen level-dependent (BOLD) images were recorded. All imaging data were analyzed using analysis of SPM2 software in. Activation area was imaged by statistically activation of BOLD. For functional MRI, epoch-related fMRI design to map regional changes in BOLD signal under the condition of grip task and finger tapping task. Results In normal subjects, significant SI (smaller MEP of APB to FDI) was found within 150 ms after finger tapping. However, FHD showed no SI during finger tapping. In FHD, BOLD activity of contralateral SMA and cerebellum and excessive activation in PMA were observed in four of 7 patients. Hyperactive area around SMA in FHD extended broader than normal subjects. And also hyperactive areas were observed in ipsilateral SMA. Finger tapping task than grip task produced stronger activation in cerebellum and SMA in FHD. Discussion: In normal subjects, significant SI was found within 150 ms during pinching task with 10% Fmax. However, FHD showed no SI during pinching task. In FHD, the finding of fMRI showed BOLD hyper-activation of SMA and excessive activation in PMA. And also hyperactivity is observed in both cerebellar hemispheres. Tapping task than grip task produced hyperactivity in SMA and cerebellum. These findings suggest that skilled task must make less surround inhibition in central nervous system network. The finding of hyperactive BOLD signal suggests that dis-inhibition of central nervous system network. There may be any relationship with a disrupted SI and hyper-activation of cerebellum in fMRI during voluntary movement. Conclusion Our findings showed FHD with disrupted SI had cerebellar hyper activation of cerebellum in fMRI during voluntary movement.