Atypical sleep architecture and altered EEG spectra in Williams syndrome.

BACKGROUND: Williams syndrome (WS) is a neurodevelopmental genetic disorder characterised by physical abnormalities and a distinctive cognitive profile with intellectual disabilities (IDs) and learning difficulties. METHODS: In our study, nine adolescents and young adults with WS and 9 age- and sex-matched typically developing (TD) participants underwent polysomnography. We examined sleep architecture, leg movements and the electroencephalogram (EEG) spectra of specific frequency bands at different scalp locations. RESULTS: We found an atypical, WS characteristic sleep pattern with decreased sleep time, decreased sleep efficiency, increased wake time after sleep onset, increased non-rapid eye movement percentage, increased slow wave sleep, decreased rapid eye movement sleep percentage, increased number of leg movements and irregular sleep cycles. Patients with WS showed an increased delta and slow wave activity and decreased alpha and sigma activity in the spectral analysis of the EEG. CONCLUSIONS: Sleep maintenance and organisation are significantly affected in WS, while EEG spectra suggest increases in sleep pressure.

Correlation of visuospatial memory ability with right parietal EEG spindling during sleep.

Individual differences in human sleep EEG spindling were shown to be associated with psychometric measures of cognitive ability. Previous results revealed a frequency- and region specificity of this effect, suggesting that only fast, but not slow spindle-related oscillatory activity over the frontal region correlated with cognitive performance. Our aim is to test the hypothesis that region-specific spindle-type oscillatory activity is related to specific cognitive abilities reflecting the cortical localization of the corresponding cognitive function. The visuospatial abilities are the focus of the present report. Nineteen healthy volunteers were tested with the Rey-Osterrieth Complex Figure (ROCF) test and memory performances correlated with the spindle analysis of the second night's polysomnographic recordings. Correlations were age-corrected and subjected to descriptive data analysis. ROCF recall performances at 3 and 30 minutes delay, correlated positively and significantly with fast sleep spindle density measured over the right parietal area. No significant relationship between recognition performance and sleep EEG variables emerged. Slow spindle density did not correlate with test performances. Our findings converge with other data suggesting the involvement of right parietal functioning in visuospatial abilities. Moreover, these results support the hypothesis that region-specific differences in fast sleep spindling could be markers of specific neuropsychological performances.

Rhythmic hippocampal slow oscillation characterizes REM sleep in humans.

Hippocampal rhythmic slow activity (RSA) is a well-known electrophysiological feature of exploratory behavior, spatial cognition, and rapid eye movement (REM) sleep in several mammalian species. Recently, RSA in humans during spatial navigation was reported, but systematic data regarding human REM sleep are lacking. Using mesio-temporal corticography with foramen ovale electrodes in epileptic patients, we report the presence of a 1.5-3-Hz synchronous rhythmic hippocampal oscillation seemingly specific to REM sleep. This oscillation is continuous during whole REM periods, is clearly observable by visual inspection, and appears in tonic and phasic REM sleep episodes equally. Quantitative analysis proved that this 1.5-3-Hz frequency band significantly differentiates REM sleep from waking and slow-wake sleep (SWS). No other frequency band proved to be significant or showed this high rhythmicity. Even in temporo-lateral surface recordings, although visually much less striking, the relative power of the 1.5-3-Hz frequency band differentiates REM sleep from other states with statistical significance. This could mean that the 1.5-3-Hz hippocampal RSA spreads over other cortical areas in humans as in other mammals. We suggest that this oscillation is the counterpart of the hippocampal theta of mammalian REM sleep, and that the 1.5-3-Hz delta EEG activity is a basic neurophysiological feature of human REM sleep.