Abstract
In Older Adults (OAs), Electroencephalogram (EEG) slowing in frontal lobes and a diminished muscle atonia during Rapid Eye Movement sleep (REM) have each been effective tracers of Mild Cognitive Impairment (MCI), but this relationship remains to be explored by non-linear analysis. Likewise, data provided by EEG, EMG (Electromyogram) and EOG (Electrooculogram)—the three required sleep indicators—during the transition from REM to Non-REM (NREM) sleep have not been related jointly to MCI. Therefore, the main aim of the study was to explore, with results for Detrended Fluctuation Analysis (DFA) and multichannel DFA (mDFA), the Color of Noise (CN) at the NREM to REM transition in OAs with MCI vs. subjects with good performances. The comparisons for the transition from NREM to REM were made for each group at each cerebral area, taking bilateral derivations to evaluate interhemispheric coupling and anteroposterior and posterior networks. In addition, stationarity analysis was carried out to explore if the three markers distinguished between the groups. Neuropsi and the Mini-Mental State Examination (MMSE) were administered, as well as other geriatric tests. One night polysomnography was applied to 6 OAs with MCI (68.1 ± 3) and to 7 subjects without it (CTRL) (64.5 ± 9), and pre-REM and REM epochs were analyzed for each subject. Lower scores for attention, memory and executive funcions and a greater index of arousals during sleep were found for the MCI group. Results confirmed that EOGs constituted significant markers of MCI, increasing the CN for the MCI group in REM sleep. The CN of the EEG from the pre-REM to REM was higher for the MCI group vs. the opposite for the CTRL group at frontotemporal areas. Frontopolar interhemispheric scaling values also followed this trend as well as right anteroposterior networks. EMG Hurst values for both groups were lower than those for EEG and EOG. Stationarity analyses showed differences between stages in frontal areas and right and left EOGs for both groups. These results may demonstrate the breakdown of fractality of areas especially involved in executive functioning and the way weak stationarity analyses may help to distinguish between sleep stages in OAs.
Highlights
Later, according to the results of the tests, the Older Adults (OAs) were divided in two main groups, one with normal functioning on the Neuropsi and all its scales and subscales, with undiminished daily activities or control (CTRL), and another group with similar results in the daily living tests but with at least one subscale on the Neuropsi showing three standard deviations below the mean, or with Mild Cognitive Impairment (MCI)
The Mini-mental State Examination (MMSE) and the Neuropsi scores were significantly correlated according to the Pearson correlation coefficient [r(11) = 0.65, p < 0.01]
On their sleep questionnaires more complaints appeared in the CTRL group: four members of the CTRL group declared their sleep was not very good and three of them good, while all members of the MCI group stated their sleep was good
Summary
Evidence supporting these investigations has been found involving selective REM sleep deprivation effects over the interhemispheric correlation in gamma frequencies on the recovery night in frontal lobes (Corsi-Cabrera et al, 2014) and a higher prefrontal rebound of frontal gamma synchronization during subsequent wakefulness in young subjects performing executive tasks (Corsi-Cabrera et al, 2015). Patients diagnosed with MCI may have subjective mental complaints about their cognitive functioning, corroborated by a near relative or friend, or lower performances considering age and education standards on neuropsychological tests (Petersen, 2004)
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