Citation

Cabib C, Llufriu S, Casanova-Mollà J, Saiz A, Valls-Solé J. J. Neurophysiol. 2014; 113(5): 1462-1469.

Affiliation

Hospital Clínic. Universitat de Barcelona. jvalls@clinic.ub.es.

Copyright

(Copyright © 2014, American Physiological Society)

DOI

10.1152/jn.00591.2014

PMID

25475350

Abstract

Delayed movement execution in reaction time tasks in 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 brainstem. A somatosensory stimulus was used as 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 correlated with interhemispheric conduction time (r=0.520, p=0.019), was significantly larger in patients than in healthy subjects (p=0.021). The StartReact effect, which involves activation of brainstem motor pathways, was significantly reduced 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/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 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.

Language: en