Suzana V. Schönwald

Benchmarking matching pursuit to find sleep spindles

The aim of this study is to evaluate performance of Matching Pursuit (MP) algorithm against visual analysis for automatic sleep spindle (SS) detection in a sample of sleep stages 2-4 and REM pertaining to nine healthy young subjects. MP-SS voltage, frequency and duration characteristics were investigated for the amplitude threshold (AT) that maximized yield between test sensitivity and specificity. Parameter distribution curves were also built for correctly detected (true positive) and false-positive events. For sleep stage 2, MP reached 80.6% sensitivity and specificity for an AT value of 58.8. For all stages together, 81.2% sensitivity and specificity were reached for an AT value of 46.6. Specificity curves were adequate for all stages; sensitivity was lower for S3+4. Sigma frequency range activity with atypical characteristics was detected within REM sleep. Prevalence indexes obtained with MP were much higher than visual prevalence indexes for all stages; similar voltage, frequency and duration distribution curves were obtained for true positive and false positive events. For this sample of young male healthy subjects, the free-ware MP algorithm showed satisfactory performance for SS detection in sleep stage 2 as reported earlier, acceptable performance in sleep stages 3+4, although with lowered sensitivity, and sigma frequency range activity within REM sleep that needs better understanding. Within NREM sleep, correspondence between the MP automatic and the visual method was supported.

Topography-specific spindle frequency changes in Obstructive Sleep Apnea

BackgroundSleep spindles, as detected on scalp electroencephalography (EEG), are considered to be markers of thalamo-cortical network integrity. Since obstructive sleep apnea (OSA) is a known cause of brain dysfunction, the aim of this study was to investigate sleep spindle frequency distribution in OSA. Seven non-OSA subjects and 21 patients with OSA (11 mild and 10 moderate) were studied. A matching pursuit procedure was used for automatic detection of fast (≥13Hz) and slow (<13Hz) spindles obtained from 30min samples of NREM sleep stage 2 taken from initial, middle and final night thirds (sections I, II and III) of frontal, central and parietal scalp regions.ResultsCompared to non-OSA subjects, Moderate OSA patients had higher central and parietal slow spindle percentage (SSP) in all night sections studied, and higher frontal SSP in sections II and III. As the night progressed, there was a reduction in central and parietal SSP, while frontal SSP remained high. Frontal slow spindle percentage in night section III predicted OSA with good accuracy, with OSA likelihood increased by 12.1%for every SSP unit increase (OR 1.121, 95% CI 1.013 - 1.239, p=0.027).ConclusionsThese results are consistent with diffuse, predominantly frontal thalamo-cortical dysfunction during sleep in OSA, as more posterior brain regions appear to maintain some physiological spindle frequency modulation across the night. Displaying changes in an opposite direction to what is expected from the aging process itself, spindle frequency appears to be informative in OSA even with small sample sizes, and to represent a sensitive electrophysiological marker of brain dysfunction in OSA.

Characteristics of human EEG sleep spindles assessed by Gabor transform

The aim of this study is to show an application of the Gabor transform on the detection and characterization of human sleep EEG spindles in a sample of 10 healthy young adults, trying to identify the most useful parameters that can be used for the automatic detection and characterization of such events.

WHOQOL-OLD assessment of quality of life in elderly patients with Parkinson's disease: influence of sleep and depressive symptoms

OBJECTIVE Parkinsons disease is a neurodegenerative disease with a number of motor and non-motor features that can affect quality of life. In this study, we aimed to assess quality of life, as well as to evaluate the potential determinants of quality of life, such as sleep quality, motor and depressive symptoms, in elderly patients with Parkinsons disease. METHOD This was a cross-sectional study in which we applied the World Health Organization Quality of Life Assessment for Older Adults in 57 Parkinsons disease patients over 60 years of age. RESULTS Total World Health Organization Quality of Life Assessment for Older Adults score was found to be associated with Parkinsons disease severity (rs = -0.43; p < 0.001). World Health Organization Quality of Life Assessment for Older Adults scores for sensory abilities (facet 1) and social participation (facet 4) were higher among the patients with mild Parkinsons disease than among those in the more advanced stages (rs = -0.43; p < 0.001). Facet 1 scores were found to be associated with Pittsburgh Sleep Quality Index and Parkinsons Disease Sleep Scale score (rp = -0.46 and rp = 0.41; p < 0.001, respectively). The Geriatric Depression Scale score showed an association with the total score on the World Health Organization Quality of Life Assessment for Older Adults (rp = -0.70; p < 0.001) CONCLUSION Quality of life in Parkinsons disease patients can be assessed by the World Health Organization Quality of Life Assessment for Older Adults. Greater Parkinsons disease severity can worsen patient quality of life, as can the presence of depressive symptoms.

Psychometric properties of the Parkinson's Disease Sleep Scale – Brazilian version

Parkinsons Disease Sleep Scale (PDSS) is a specific scale for the assessment of sleep disturbances in subjects with Parkinsons Disease (PD). This cross-sectional study set out to validate the PDSS in a Brazilian Portuguese Version (PDSS-BR). Ninety-five patients with PD participated in the study; their PD symptoms were evaluated by Unified Parkinsons Disease Rating Scale (UPDRS sections I-IV) and Hoehn and Yahr scale. Patients completed Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), Beck Depression Inventory (BDI) and PDSS-BR. PDSS-BR internal consistency was satisfactory (Cronbachs alpha: 0.82; all PDSS-BR items were significantly and positively associated with total score). Test-retest reliability for total PDSS-BR score was 0.94. PDSS-BR score was highly correlated with sleep PSQI scale (r(s) = -0.63; p < 0.0001) and moderately with ESS (r(s) = -0.32; p < 0.001) and UPDRS sections I (r(s) = -0.38; p < 0.0001) and II (r(s) = -0.36; p < 0.0001) and BDI (r(s) = -0.55; p < 0.0001). Depressive symptoms, as determined by the BDI, were associated with significantly worse quality of nocturnal sleep, as measured by the PDSS-BR. The psychometric attributes of the PDSS-BR were satisfactory and consistent with those of previous studies. In summary, PDSS-BR can be useful for clinical and research purposes in Brazil.

Loss of sleep spindle frequency deceleration in Obstructive Sleep Apnea

OBJECTIVE Sleep spindles have been suggested as surrogates of thalamo-cortical activity. Internal frequency modulation within a spindles time frame has been demonstrated in healthy subjects, showing that spindles tend to decelerate their frequency before termination. We investigated internal frequency modulation of slow and fast spindles according to Obstructive Sleep Apnea (OSA) severity and brain topography. METHODS Seven non-OSA subjects and 21 patients with OSA contributed with 30min of Non-REM sleep stage 2, subjected to a Matching pursuit procedure with Gabor chirplet functions for automatic detection of sleep spindles and quantification of sleep spindle internal frequency modulation (chirp rate). RESULTS Moderate OSA patients showed an inferior percentage of slow spindles with deceleration when compared to Mild and Non-OSA groups in frontal and parietal regions. In parietal regions, the percentage of slow spindles with deceleration was negatively correlated with global apnea-hypopnea index (rs=-0.519, p=0.005). DISCUSSION Loss of physiological sleep spindle deceleration may either represent a disruption of thalamo-cortical loops generating spindle oscillations or some compensatory mechanism, an interesting venue for future research in the context of cognitive dysfunction in OSA. SIGNIFICANCE Quantification of internal frequency modulation (chirp rate) is proposed as a promising approach to advance description of sleep spindle dynamics in brain pathology.

Quantifying chirp in sleep spindles.

Sleep spindles are considered as a marker of integrity for thalamo-cortical circuits. Recently, attention has been given to internal frequency variation in sleep spindles. In this study, a procedure based on matching pursuit with a Gabor-chirplet dictionary was applied in order to measure chirp rate in atoms representing sleep spindles, also categorized into negative, positive or zero chirp types. The sample comprised 707 EEG segments containing visual sleep spindles, labeled TP, obtained from nine healthy male volunteers (aged 20-34, average 24.6 y). Control datasets were 333 non-REM (NREM) sleep background segments and 287 REM sleep intervals, each with 16s duration. Analyses were carried out on the C3-A2 EEG channel. In TP and NREM groups, the proportion of non-null chirp types was non-random and total chirp distribution was asymmetrical towards negative values, in contrast to REM. Median negative chirp rate in the TP and NREM groups was significantly lower than in REM (-0.4 Hz/s vs -0.3 Hz/s, P < 0.05). Negative chirp atoms outnumbered positives by 50% in TP, while in NREM and REM, they were, respectively, only 22% and 12% more prevalent. TP negative chirp atoms were significantly higher in amplitude compared to positive or zero types. Considering individual subjects, 88.9% had a TP negative/positive chirp ratio above 1 (mean ± sd=1.64 ± 0.65). We propose there is increasing evidence, corroborated by the present study, favoring systematic measurement of sleep spindle chirp rate or internal frequency variation. Preferential occurrence of negatively chirping spindles is consistent with the hypothesis of electrophysiological modulation of neocortical memory consolidation.

Synchronization and Propagation of Global Sleep Spindles

Sleep spindles occur thousands of times during normal sleep and can be easily detected by visual inspection of EEG signals. These characteristics make spindles one of the most studied EEG structures in mammalian sleep. In this work we considered global spindles, which are spindles that are observed simultaneously in all EEG channels. We propose a methodology that investigates both the signal envelope and phase/frequency of each global spindle. By analysing the global spindle phase we showed that 90% of spindles synchronize with an average latency time of 0.1 s. We also measured the frequency modulation (chirp) of global spindles and found that global spindle chirp and synchronization are not correlated. By investigating the signal envelopes and implementing a homogeneous and isotropic propagation model, we could estimate both the signal origin and velocity in global spindles. Our results indicate that this simple and non-invasive approach could determine with reasonable precision the spindle origin, and allowed us to estimate a signal speed of 0.12 m/s. Finally, we consider whether synchronization might be useful as a non-invasive diagnostic tool.

NREM sleep alpha and sigma activity in Parkinson’s disease: Evidence for conflicting electrophysiological activity?

OBJECTIVES Sleep EEG spectral patterns were investigated in eight newly diagnosed, non-depressed, non-demented, drug-naïve Parkinsons disease patients compared to nine controls. METHODS Mean relative spectral power density calculated for 0.25 Hz frequency bins and for classical EEG frequency bands. RESULTS Differences between patients and controls were most prominent in non-REM sleep, specially around 8.6 Hz (slow alpha), 12.5 Hz (fast alpha/slow sigma) and 15 Hz (fast sigma). Slow alpha showed lower p-values over frontal and occipital electrodes, whereas fast sigma activity was more important on central and parietal sites. Significantly increased NREM sleep alpha activity was found in left and right frontal (Mann-Whitney U=12,000, p=.021; U=14,000, p=.036), left and right central (U=14,000, p=.036), left parietal and left occipital (U=13,000, p=.027; U=15,000, p=.046) areas. Increased sigma activity was found in right frontal (U=14,000, p=.036), left central (U=12,000, p=.021), left and right parietal (U=12,000, p=.021; U=13,000, p=.027) and left occipital (U=15,000, p=.046) areas. CONCLUSIONS Concomitantly increased scalp EEG alpha and sigma activity was found during NREM sleep in initial Parkinsons disease. SIGNIFICANCE These non-REM sleep microstructure changes may represent evidence for altered electrophysiological mechanisms leading to sleep-wake instability in early disease stages.

Overnight S100B in Parkinson’s Disease: A glimpse into sleep-related neuroinflammation

Calcium-binding protein B (S100B), a primary product of astrocytes, is a proposed marker of Parkinsons Disease (PD) pathophysiology, diagnosis and progression. However, it has also been implicated in sleep disruption, which is very common in PD. To explore the relationship between S100B, disease severity, sleep symptoms and polysomnography (PSG) findings, overnight changes in serum S100B levels were investigated for the first time in PD. 17 fully treated, non-demented, moderately advanced PD patients underwent PSG and clinical assessment of sleep symptoms. Serum S100B samples were collected immediately before and after the PSG. Results are shown as median [interquartile range]. Night and morning S100B levels were similar, but uncorrelated (rs=-0.277, p=0.28). Morning S100B levels, as opposed to night levels, positively correlated with the Unified Parkinsons Disease rating scale (UPDRS) subsections I and II (rs=0.547, p=0.023; rs=0.542, p=0.025). Compared to those with overnight S100B reduction, patients with overnight S100B elevation had higher H&Y scores (2.5 [0.87] vs. 2 [0.25], p=0.035) and worse total Pittsburgh Sleep Quality Index (PSQI) and Parkinsons Disease Sleep Scores (10 [3.2] vs. 8 [4.5], p=0.037; 92.9 [39] vs. 131.4 [28], p=0.034). Correlation between morning S100B levels and total UPDRS score was strengthened after controlling for total PSQI score (rs=0.531, p=0.034; partial rs=0.699, p=0.004, respectively). Overnight S100B variation and morning S100B were associated with PD severity and perceived sleep disruption. S100B is proposed as a putative biomarker for sleep-related neuroinflammation in PD. Noradrenergic-astrocytic dysfunction is hypothesized as a possible mechanism underlying these findings.