EEG harmonic responses to photic stimulation in normal aging and Alzheimer's disease: differences in interhemispheric coherence.
OBJECTIVE
The distinction between electroencephalogram (EEG) driving responses in normal aging and Alzheimer's disease (AD) is unclear. This study was conducted to explore the structure of harmonic responses of EEG coherence during photic stimulation (PS) in AD.


METHODS
EEG interhemispheric coherence was analyzed for each harmonic responses during PS (white flickers at 5, 10 and 15 flashes/sec) in younger subjects (20-25 years), non-demented elderly subjects (50-67 years) and AD patients (43-66 years).


RESULTS
The elderly subjects had higher interhemispheric coherence during PS than the younger subjects, with significant differences found in the 6th (30Hz) and 8th (40Hz) harmonic responses to 5Hz PS. The AD patients had significantly smaller coherence than the elderly subjects in the 2nd (10Hz) and 4th (20Hz) harmonic responses to 5Hz PS, and in the fundamental (10Hz) and 2nd (20Hz) harmonic responses to 10Hz PS. These coherence values did not correlate with duration of the disease or with cognitive functioning as evaluated by MMSE score.


CONCLUSIONS
A failure of stimulation-related brain activation in AD patients was observed in alpha-related frequencies, suggesting that AD is not the end result of normal aging of the brain, at least in terms of the mechanisms which are involved in PS-related functional organization.
Kikuchi
Mitsuru
M
Department of Psychiatry and Neurobiology, Graduate School of Medical Science, Kanazawa University, 13-1 Takara-machi, Japan. mitsuru@zc4.so-net.ne.jp
Wada
Yuji
Y
Takeda
Tsutomu
T
Oe
Hiroyasu
H
Hashimoto
Takuma
T
Koshino
Yoshifumi
Y
D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D000513:Alpha Rhythm; D000544:Alzheimer Disease / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology*; D002540:Cerebral Cortex / Q000000981:diagnostic imaging / Q000473:pathology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D018450:Disease Progression; D004569:Electroencephalography / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009474:Neurons / Q000473:pathology*; D009483:Neuropsychological Tests; D012016:Reference Values; D015899:Tomography, Emission-Computed, Single-Photon