Differential brain compensation for cognitive versus motor processes in early relapsing-remitting multiple sclerosis subjects without clinical impairment.
|Title||Differential brain compensation for cognitive versus motor processes in early relapsing-remitting multiple sclerosis subjects without clinical impairment.|
|Publication Type||Journal Article|
|Authors||Burke MA, Mahurin RK, Bowen JD|
Objective: To assess regional cortical alterations of functional MRI (fMRI) brain activation in relapsing-remitting multiple sclerosis (RRMS) versus controls by a parallel design utilizing standardized clinical cognitive measures in conjunction with functional brain imaging with identical tasks. Background: Clinical staging and disability status in MS are frequently based on results from clinical cognitive assessment. However, it is unclear to what extent cognitive test performance within normal ranges reflects integrity of associated brain networks. Design/Methods: We studied 15 RRMS (mean age 43.6 SD 8.2 years, mean EDSS=4.5) and 10 control (mean age 45.2 SD 9.6 years) right-handed subjects. Outcome measures included global CNS function, cognitive, and motor tests. Each fMRI task followed a boxcar paradigm on a GE 1.5-T scanner. The two fMRI tasks consisted of a verbal numeric reasoning task (logical reasoning) and a simple motor task (fingertap). fMRI results were compared to prescan performance of identical computer-based versions of the same tasks (NeuroCog Assessment Battery). Results: The prescan logical reasoning task showed no significant difference between MS and controls (p>0.05); however, MS subjects reported significantly greater perceived effort than controls (p<0.01). Statistical parametric mapping of fMRI data revealed greater activation in MS subjects than controls. Between-group differences were found in the orbitofrontal cortex and cerebellum for the logical reasoning fMRI task. Performance on prescan fingertap showed no significant difference between MS and control subjects (p>0.05), with no between-group differences noted on level and extent of brain activation within the left motor cortex and supplementary motor area. Conclusions: Increased brain activations during a logical reasoning task compensates for minor cognitive disability in MS, suggesting that compensatory mechanisms enabled MS subjects to attain control performance levels for the computerized task, but with more perceived effort. This effect was not found for a simple motor task in subjects without motor impairment. These compensatory cognitive processes appear to arise earlier in the disease course than for simple motor activity.