MEG analysis in Alzheimer´s disease computing approximate entropy for different frequency bands

The goal of this study was to analyze the magnetoencephalogram (MEG) background activity in patients with Alzheimer´s disease (AD) using a regularity measure: approximate entropy (ApEn). This measure was computed for a broad band (0.5-40 Hz) as well as typical frequency bands (delta, theta, alpha, beta and gamma). Five minutes of recording were acquired with a 148-channel whole-head magnetometer in 15 patients with probable AD and 15 elderly control subjects. Our results showed that AD patients´ MEGs were more regular than controls´ recordings at all frequency bands, with the exception of beta. Additionally, there were statistically significant differences (p <; 0.01, Student´s t-test) at the broad and delta bands. Using receiver operating characteristic curves, the highest accuracy (83.33%) was reached at delta band. These results suggest the usefulness of ApEn to gain a better understanding of dynamical processes underlying the MEG recording.