Magnetoencephalographic analysis of alpha frequency light entrainment of brain activity in dementia patients

We used magnetoencephalography (MEG) to analyze the power spectrum and light entrainment in patients with symptoms of Alzheimer's disease ( AD; n = 5 ) or cerebrovascular dementia (CV; n = 1 ). A 160-channel MEG and an electroencephalogram (EEG) were recorded simultaneously in each patient while they were at rest with their eyes open and stimulated by pulses of light ( 8-10.5 Hz at 0.5-Hz intervals). A spectral analysis was carried out and the amplitude of each frequency determined. The results show that the AD patients did not entrain at some frequencies, whereas the CV patients exhibited entrainment of the alpha wave, although the amplitude was smaller than in normal subjects.