Mobile Brain/Body Imaging of cognitive-motor impairment in multiple sclerosis: deriving EEG-based neuro-markers during a dual-task walking study

ABSTRACTIndividuals with a diagnosis of multiple sclerosis (MS) often present with deficits in the cognitive as well as the motor domain. The ability to perform tasks that rely on both domains may therefore be particularly impaired. Yet, behavioral studies designed to measure costs associated with performing two tasks at the same time such as dual-task walking have yielded mixed results. Patients may mobilize additional brain resources to sustain good levels of performance. To test this hypothesis, we acquired event-related potentials (ERP) in thirteen individuals with MS and fifteen healthy control (HC) participants performing a Go/NoGo response inhibition task while sitting (i.e., single task) or walking on a treadmill (i.e., dual-task). In previous work, we showed that the nogo-N2 elicited by the cognitive task was reduced when healthy adults are also asked to walk, and that nogo-N2 reduction was accompanied by sustained dual-task performance. We predicted that some MS patients, similar to their healthy peers, may mobilize N2-indexed brain resources and thereby reduce costs. Somewhat to our surprise, the HC group performed the Go/NoGo task more accurately while walking, thus showing a dual-task benefit, whereas, in line with expectation, the MS group showed a trend towards dual-task costs. The expected nogo-N2 reduction during dual-task walking was found in the HC group, but was not present at the group level in the MS group, suggesting that this group did not modulate the nogo-N2 process in response to higher task load. Regression analysis for the pooled sample revealed a robust link between nogo-N2 reduction and better dual-task performance. We conclude that impaired nogo-N2 adaptation reflects a neurophysiological marker of cognitive-motor dysfunction in MS.