P300 amplitude and response speed relate to preserved cognitive function in relapsing-remitting multiple sclerosis

To explore if cognitive impairment in relapsing-remitting multiple sclerosis (RRMS) is associated with abnormal neural function and if there is evidence of neural compensatory mechanisms.

Seventy-two RRMS patients and 89 healthy control subjects were included in a cross-sectional study. Event-related brain potential (P300) and response time (RT) were recorded with visual and auditory choice reaction tasks. Cognitive function was evaluated with an 18 item test battery.

Patients had a decrease in cognitive function (p<0.001 for global score) and increased visual P300 amplitude frontally. P300 amplitude was normal in other brain areas and RT was normal. P300 latency was normal except for an increase in auditory latency occipitally. Cognitive performance correlated positively with parietal P300 amplitude in patients but not in controls. Cognition had stronger correlation (negative) with RT in patients than in controls.

Patients with low P300 amplitude and long RT were more often cognitively impaired. This indicates that general factors such as signal amplitude and speed are limiting for cognitive function in RRMS patients. The increase in frontal P300 amplitude may be a compensatory effect.

Our findings suggest that high amplitude and fast speed may be protective against cognitive impairment.