title: Defective sensorimotor integration in preparation for reaction time tasks in patients with multiple sclerosis.
abstract: Slowness of voluntary movements in patients with multiple sclerosis (MS) may be due to various factors, including attentional and cognitive deficits, delays in motor conduction time, and impairment of specific central nervous system circuits. In 13 healthy volunteers and 20 mildly disabled, relapsing-remitting MS patients, we examined simple reaction time (SRT) tasks requiring sensorimotor integration in circuits involving the corpus callosum and the brain stem. A somatosensory stimulus was used as the imperative signal (IS), and subjects were requested to react with either the ipsilateral or the contralateral hand (uncrossed vs. crossed SRT). In 33% of trials, a startling auditory stimulus was presented together with the IS, and the percentage reaction time change with respect to baseline SRT trials was measured (StartReact effect). The difference between crossed and uncrossed SRT, which requires interhemispheric conduction, was significantly larger in patients than in healthy subjects (P = 0.021). The StartReact effect, which involves activation of brain stem motor pathways, was reduced significantly in patients with respect to healthy subjects (uncrossed trials: P = 0.015; crossed trials: P = 0.005). In patients, a barely significant correlation was found between SRT delay and conduction abnormalities in motor and sensory pathways (P = 0.02 and P = 0.04, respectively). The abnormalities found specifically in trials reflecting interhemispheric transfer of information, as well as the evidence for reduced subcortical motor preparation, indicate that a delay in reaction time execution in MS patients cannot be explained solely by conduction slowing in motor and sensory pathways but suggest, instead, defective sensorimotor integration mechanisms in at least the two circuits examined.
authors.affiliation: EMG Unit, Neurology Department, Hospital Clinic, and Institut d'Investigació Augustí Pi i Sunyer, Facultat de Medicina, University of Barcelona, Barcelona, Spain; and.
authors.forename: Christopher
authors.initials: C
authors.lastname: Cabib
authors.affiliation: Center for Neuroimmunology, Neurology Department, Hospital Clínic, and Institut d'Investigació August Pi i Sunyer, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Sara
authors.initials: S
authors.lastname: Llufriu
authors.affiliation: EMG Unit, Neurology Department, Hospital Clinic, and Institut d'Investigació Augustí Pi i Sunyer, Facultat de Medicina, University of Barcelona, Barcelona, Spain; and.
authors.forename: Jordi
authors.initials: J
authors.lastname: Casanova-Molla
authors.affiliation: Center for Neuroimmunology, Neurology Department, Hospital Clínic, and Institut d'Investigació August Pi i Sunyer, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Albert
authors.initials: A
authors.lastname: Saiz
authors.affiliation: EMG Unit, Neurology Department, Hospital Clinic, and Institut d'Investigació Augustí Pi i Sunyer, Facultat de Medicina, University of Barcelona, Barcelona, Spain; and jvalls@clinic.ub.es.
authors.forename: Josep
authors.initials: J
authors.lastname: Valls-Solé
mesh_terms: D000328:Adult; D001307:Auditory Perception; D001933:Brain Stem / Q000503:physiopathology; D016022:Case-Control Studies; D003337:Corpus Callosum / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000503:physiopathology*; D011597:Psychomotor Performance; D011930:Reaction Time; D066191:Sensorimotor Cortex / Q000503:physiopathology
keywords: StartReact effect; crossed reaction time task; motor preparation; multiple sclerosis; simple reaction time