In a study applying EEG power spectroscopy to assess AD, high-risk ApoE gene carriers without dementia and healthy controls (22), it was found that for EEG in the resting, closed-eye state, there were differences mainly in AD patients, whereas for EEG in the hyperventilation state, there were differences mainly in high-risk ApoE gene carriers without dementia (or pre-AD), suggesting that EEG spectrum power in different states may represent different periods of cognitive impairment. Here, APOE is linked to Alzheimer disease.