Characterization of inhibitory failure in Multiple Sclerosis: Evidence of impaired conflict resolution

Introduction: Inhibitory control deficits are frequently reported in Multiple Sclerosis (MS), although it is unclear whether these deficits represent a global or process-specific failure. Notably, most models of inhibitory control recognize at least two dissociable processes, the most consistent being: (a) the inhibition of a dominant response: response suppression, and (b) the inhibition of a dominant response and initiation of a nondominant response: executive control. This study aimed to ascertain the processes underlying inhibitory failure in MS. Method: Twenty-three MS patients and 25 healthy controls completed a battery of commonly used inhibitory tasks, with measures from each task entered into a principal components analysis with orthogonal (varimax) rotation. Results: As anticipated, two components emerged, with tasks evaluating response suppression (stop signal, go/no go) loading on a common component, and tasks evaluating executive control (Stroop, antisaccade, endogenously-cued saccade) loading on a separate common component. Composite scores were generated for each component and compared between groups. Unlike response suppression scores, executive control scores were significantly poorer for MS patients. Conclusions: Inhibitory control deficits in MS may reflect poor resolution in the context of competing processes, rather than difficulty in preventing the execution of an inappropriate response.