Cognitive-motor interference refers to dual-tasking (DT) interference (DTi) occurring when the simultaneous performance of a cognitive and a motor task leads to a percentage change in one or both tasks. Several theories exist to explain DTi in humans: the capacity-sharing, the bottleneck and the cross-talk theories. Numerous studies investigating whether a specific brain locus is associated with cognitive-motor DTi have been conducted, but not systematically reviewed. We aimed to review the evidences on brain activity associated with the cognitive-motor DT, in order to better understand the neurological basis of the CMi. Results were reported according to the technique used to assess brain activity. Twenty-three articles met the inclusion criteria. Out of them, nine studies used functional magnetic resonance imaging to show an additive, under-additive, over- additive, or a mixed activation pattern of the brain. Seven studies used near-infrared spectroscopy, and seven neurophysiological instruments. Yet a specific DT locus in the brain cannot be concluded from the overall current literature. Future studies are warranted to overcome the shortcomings identified.

Purposeful, safe locomotion requires higher-level cortical processes, to meet the real-life demands of walking while performing concurrent cognitive tasks (e.g. recalling a shopping list or attending to a conversation). The assessment of walking and a secondary cognitive task under these 'dual tasking' conditions may represent a more valid outcome measure in multiple sclerosis (MS), by examining the occurrence and magnitude of the cognitive-motor interference of walking. This topical review provides a state-of-the-art overview of research into dual-tasking during walking in persons with MS, based on 14 recent papers. Studies consistently demonstrate a slowing of ambulation under dual tasking, regardless of the cognitive task demand, the stage of the disease and the disability level. The reciprocal effect of walking on the cognitive tasks was rarely assessed. We present our main findings, highlight the different factors contributing to dual-task deficits, identify methodological shortcomings and offer recommendations for constructing dual-tasking paradigms useful in clinical practice and research.

More than one-third of PwMS showed walking-related motor fatigue during the 6MWT, with its prevalence greatest in more disabled persons (up to 51%) and in those with progressive MS phenotype (up to 50%). Identification of walking-related motor fatigue may lead to better-tailored interventions.