Brain connectivity of patients with Alzheimer's disease by coherence analysis of electroencephalograms

The Alzheimer's disease (AD) is known as a degenerative brain disease. AD is usually diagnosed by patient history and neuropsychological tests. The functional brain imaging can help exclude other cerebral diseases. The electroencephalogram (EEG) examination provides a convenient means of disclosing brain function and connectivity. In the present study, 11 AD patients and 11 normal subjects were enrolled. Twenty-channel EEGs during baseline and photic stimulation were respectively preprocessed by ocular-artifact reduction using blind source separation. The power spectra of EEGs as well as inter-brain area coherence were computed. Our results showed significant decrease of delta power and significant increase of alpha power at left frontal and left posterior regions during baseline in AD group, implying a selected attenuation of brain functions. In addition, significantly reduced short-range delta coherences were elicited by photic stimulation around left and right frontal regions and left posterior regions in AD group, corresponding to the impairment of cortical associations. The short-range EEG coherences as well as selective spectral power may be useful for differentiating AD from normal subjects. The subsequent investigations upon the behavior at different stages would be beneficial for developing EEG indexes as neurophysiological markers for AD.