Electroencephalographic activities during wakefulness and sleep in the frontal cortex of healthy older people: links with "thinking".

STUDY OBJECTIVE: Separate studies have shown for the frontal cortex that: i) sleep electroencephalogram (EEG) activity less than 1 Hz may be linked to waking recovery, and ii) waking frontal theta activity may reflect "cortical workload." We explored the potential linkage between (i) and (ii) in relation to specific waking theta frequencies and 0.5-Hz to 1.0-Hz activity in sleep.

DESIGN: A correlational study

SETTING: Laboratory-based waking EEGs under different (eyes-closed) contrived "thinking" conditions (mostly localized to the left frontal area), and night sleep EEGs at home.

PARTICIPANTS: Twelve right-handed, healthy, good-sleeping, older adults (mean age, 67.3 years)

MEASUREMENT & RESULTS: EEGs comprised 4 bipolar derivations (Fp1-F3; Fp2-F4; O1-P3; O2-P4). Power in the 7-8-Hz bin was the only waking frequency significantly (positively) correlated with power in the 0.5- to 1.0-Hz bin during the first NREM period and only for the left frontal EEG. Interestingly, 7- to 8-Hz power immediately after lights out at bedtime, and before the appearance of EEG sleepiness, showed an even higher positive correlation with 0.5- to 1.0-Hz power during sleep. This wake-sleep EEG link was confirmed in another sample of 8 similar participants. Waking frontal 7- to 8-Hz EEG may not be typical theta, but "kappa" activity, believed to be associated with thinking

CONCLUSIONS: Within limits of the EEG, and for the left frontal area, waking thinking may be reflected by putative cortical reorganization during the first NREM period.