A neural complexity measure applied to MEG data in Alzheimerʹs disease

Objective: A measure of neural complexity (CN) (Proc. Natl Acad. Sci. USA 91 (1994) 5033) was applied to magnetoencephalography (MEG) data to test the hypothesis that CN decreases when information processing in the brain is impaired, as is the case in patients with Alzheimerʹs Disease (AD). Methods: One hundred and fifty-one channel MEGs were recorded in 20 AD patients and 20 healthy age-matched controls in a resting condition with eyes open (EO) and eyes closed (EC). Artifact-free epochs of 117 channels were selected for analysis. CN and D2 were computed in different frequency bands, and correlated with the MMSE. Results: The Group×Frequency band interaction was significant for both CN and D2. CN was higher in AD, as compared with controls, in the 2–4 and 4–8 Hz bands, and D2 was higher in AD patients in the 14–20 and 20–30 Hz bands. The CN was higher in the EC condition compared to the EO condition, whereas the D2 was higher in the EO condition. Conclusions: The hypothesis of Tononi et al. (Proc. Natl Acad. Sci. USA 91 (1994) 5033) that the neural complexity decreases in AD patients has to be rejected. However, both neural complexity and the correlation dimension did show differences between controls and AD patients which depended on frequency band.