Abnormalities in brain synchronization are correlated with cognitive impairment in multiple sclerosis.

ABSTRACT

BACKGROUND: Cognitive functions are supported by brain networks and they are highly dependent on the integrity of long white matter tracts that mediate the information flow between such distant cortical areas. Brain damage in multiple sclerosis (MS) may produce cognitive impairment by preferentially damaging these tracts, thereby impairing brain synchrony. Auditory amplitude modulation following responses (AMFR), are oscillatory steady-state responses to rhythmic auditory stimuli that indirectly measure brain synchrony. OBJECTIVE: To study the effect of MS lesions in brain synchrony and its relationship with cognitive function. METHODS: We assessed the correlation between cognitive performance, as assessed with the brief repeatable battery-neuropsychology (BRB-N), and the AMFR in a group of 27 MS patients and 22 healthy controls. RESULTS: The maximal AMFR frequency - but not the amplitude - in the 30-60 Hz range was lower in patients with cognitive impairment than in patients with no cognitive impairment or the healthy controls (39.79 Hz, 43.85 Hz, and 43.84 Hz, respectively, P < 0.05). Indeed, the frequency of the AMFR was negatively correlated with the scores obtained in verbal memory, attention, and executive function. The multiple regression analysis indicates that the AMFR was the best predictor of the BRB-N scores after controlling for potential confounding factors such as age, education, disability, and years of disease evolution. CONCLUSIONS: These results suggest that the loss of synchronization in different central nervous system (CNS) pathways caused by demyelinating lesions might involve both the slowing of brain oscillatory activity and less efficient cognitive processing.