Impaired sleep-associated modulation of post-exercise corticomotor depression in multiple sclerosis

To compare the beneficial effect of nap versus rest on the recovery of motor evoked potentials (MEPs) after a fatiguing exercise performed in patients with multiple sclerosis (MS) and healthy controls.

In 12 MS patients and 12 healthy controls, MEPs were recorded from the adductor pollicis muscle before, 10 and 60 min (T0, T10, and T60) after an effort of thumb adduction at 25% of maximal voluntary contraction force for 24 min. After the effort, the subject was maintained at rest or invited to have a nap while monitored with polysomnography. The two sessions (nap and rest) were randomly performed in each subject during the same day. The impact of nap and rest on post-exercise changes in MEP amplitude were studied in each group (patients and controls) and then compared between the two groups.

Although MEP amplitude at baseline was lower in MS patients than in controls, post-exercise corticomotor depression (PECD), expressed as T10/T0 MEP amplitude ratio, was similar in both groups. Regarding MEP amplitude recovery at T60, nap was significantly more beneficial than rest in healthy subjects, but not in MS patients.

Motor recovery from PECD following a fatiguing exercise can be enhanced by sleep (at least a short nap) in healthy subjects. In MS patients, sleep restorative effect is reduced or lost, maybe contributing to the excessive fatigue or fatigability characterized in these patients.