Zsófia Clemens

Prediction of general mental ability based on neural oscillation measures of sleep

The usual assessment of general mental ability (or intelligence) is based on performance attained in reasoning and problem‐solving tasks. Differences in general mental ability have been associated with event‐related neural activity patterns of the wakeful working brain or physical, chemical and electrical brain features measured during wakeful resting conditions. Recent evidences suggest that specific sleep electroencephalogram oscillations are related to wakeful cognitive performances. Our aim is to reveal the relationship between non‐rapid eye movement sleep‐specific oscillations (the slow oscillation, delta activity, slow and fast sleep spindle density, the grouping of slow and fast sleep spindles) and general mental ability assessed by the Raven Progressive Matrices Test (RPMT). The grouping of fast sleep spindles by the cortical slow oscillation in the left frontopolar derivation (Fp1) as well as the density of fast sleep spindles over the right frontal area (Fp2, F4), correlated positively with general mental ability. Data from those selected electrodes that showed the high correlations with general mental ability explained almost 70% of interindividual variance in RPMT scores. Results suggest that individual differences in general mental ability are reflected in fast sleep spindle‐related oscillatory activity measured over the frontal cortex.

Fine-tuned coupling between human parahippocampal ripples and sleep spindles.

Sleep‐associated memory consolidation is thought to rely on coordinated information transfer between the hippocampus and neocortex brought about during slow wave sleep (SWS) by distinct local field potential oscillations. Specifically, findings in animals have led to the concept that ripples originating from hippocampus combine with spindles to provide a fine‐tuned temporal frame for a persistent transfer of memory‐related information to the neocortex. The present study focused on characterizing the temporal relationship between parahippocampal ripple activity (80–140 Hz) and spindles recorded from frontal, parietal and parahippocampal cortices in 12 epilepsy patients implanted with parahippocampal foramen ovale electrodes. Overall, parietal and parahippocampal spindles showed closer relationships to parahippocampal ripple activity than frontal spindles, with the latter following parietal and parahippocampal spindles at a variable delay of up to 0.5 s. On a timescale of seconds, ripple activity showed a continuous increase before the peak of parietal and parahippocampal spindles, and decreased thereafter. At a fine timescale of milliseconds, parahippocampal ripple activity was tightly phase‐locked to the troughs of these spindles. The demonstration of spindle phase‐locked ripple activity in humans is consistent with the idea of a temporally fine‐tuned hippocampus‐to‐neocortex transfer of information taking place during SWS.

Twenty-four hours retention of visuospatial memory correlates with the number of parietal sleep spindles.

Recent evidence suggests that the sleep-dependent consolidation of declarative memories relies on the non-rapid eye movement (NREM) rather than the rapid eye movement (REM) phase of sleep. Moreover, a few studies both at the cellular and the behavioural levels have suggested the involvement of sleep spindles, the most synchronous oscillatory waveforms during NREM sleep stage 2, in this process. Our previous study showed that overnight verbal memory retention correlates with the total number of sleep spindles in left frontocentral areas, while spindling in other regions did not correlate with mnemonic retention. In the present study, we show that retention of visuospatial memories over a 24-h period correlates with the total number of sleep spindles detected over parietal regions during the intervening night-time sleep. This result provides further evidence for the association between sleep spindle activity and declarative memory consolidation, and suggests that visuospatial and verbal memory retention differ in the topographic distribution of the NREM spindle activity with which they are associated.

Correction of vitamin D deficiency improves seizure control in epilepsy: A pilot study

There is growing interest concerning the role of vitamin D in various medical conditions such as diabetes and oncological, cardiovascular and central nervous system disorders. Although vitamin D deficiency is known to be highly prevalent among epilepsy patients, only a single study, published nearly forty years ago, assessed the effect of vitamin D on seizure control. Here, we measured serum 25-hydroxy-vitamin D (25(OH)D) levels and normalized it by administration of vitamin D3 in 13 patients with pharmacoresistant epilepsy. To see if vitamin D3 has an impact on seizure frequency, we compared seizure numbers during a 90-day period before and after treatment onset. We found that seizure numbers significantly decreased upon vitamin D3 supplementation. Median seizure reduction was 40%. We conclude that the normalization of serum vitamin 25(OH)D level has an anticonvulsant effect.

Interictal epileptic spiking during sleep and wakefulness in mesial temporal lobe epilepsy: A comparative study of scalp and foramen ovale electrodes

Summary:  Purpose: To assess distribution of temporal lobe spikes across different states of sleep and wakefulness in simultaneous scalp and foramen ovale (Fo) recordings.

Spatio-temporal analysis of monofractal and multifractal properties of the human sleep EEG.

Fractality is a common property in nature. It can also be observed in time series representing dynamics of complex processes. Therefore fractal analysis could be a useful tool to describe the dynamics of brain electrical activities in physiological and pathological conditions. In this study, we carried out a spatio-temporal analysis of monofractal and multifractal properties of whole-night sleep EEG recordings. We estimated the Hurst exponent (H) and the range of fractal spectra (dD) in 10 healthy subjects. We found higher H values during NREM4 compared to NREM2 and REM in all electrodes. Measure dD showed an opposite trend. Differences of H and dD between NREM2 and REM reached significancy at circumscribed regions only. Our results contribute to a deeper understanding of the fractal nature of brain electrical activities and may have implications for automatic classification of sleep stages.

Comparison of fractal and power spectral EEG features: effects of topography and sleep stages.

Fractal nature of the human sleep EEG was revealed recently. In the literature there are some attempts to relate fractal features to spectral properties. However, a comprehensive assessment of the relationship between fractal and power spectral measures is still missing. Therefore, in the present study we investigated the relationship of monofractal and multifractal EEG measures (H and ΔD) with relative band powers and spectral edge frequency across different sleep stages and topographic locations. In addition we tested sleep stage classification capability of these measures according to different channels. We found that cross-correlations between fractal and spectral measures as well as between H and ΔD exhibit specific topographic and sleep stage-related characteristics. Best sleep stage classifications were achieved by estimating measure ΔD in temporal EEG channels both at group and individual levels, suggesting that assessing multifractality might be an adequate approach for compact modeling of brain activities.

Epilepsy and Vitamin D

Several disorders, both systemic and those of the nervous system, have been linked with vitamin D deficiency. Neurological disorders with a vitamin D link include but are not limited to multiple sclerosis, Alzheimer and Parkinson disease, as well as cerebrovascular disorders. Epilepsy which is the second leading neurological disorder received much less attention. We review evidence supporting a link between vitamin D and epilepsy including those coming from ecological as well as interventional and animal studies. We also assess the literature on the interaction between antiepileptic drugs and vitamin D. Converging evidence indicates a role for vitamin D deficiency in the pathophysiology of epilepsy.

Factors affecting spiking related to sleep and wake states in temporal lobe epilepsy (TLE)

The aim of the study was to investigate the influence of different clinical factors on spiking during sleep and wakefulness in temporal lobe epilepsy. The study included 38 temporal lobe epilepsy (TLE) patients who underwent long-term electroencephalography (EEG) monitoring. In addition to traditional sleep scoring, waking was subdivided into eyes opened (WEO) and eyes closed (WEC) states. The following spike measures were investigated: spiking rates for each state, mean spike rate, spiking stability across wake and sleep states and relative spike density for each state. These measures were investigated according to clinical variables, such as age, age at epilepsy onset, duration of epilepsy, seizure frequency, the presence of secondarily generalised tonic-clonic (SGTC) seizures and the data on epileptogenic lesions based on MRI. Spiking rates during most states and spiking stability showed a significant positive correlation with epilepsy duration. Relative spike density during sleep stage NREM3,4 significantly increased with age at epilepsy onset. Relative spike density during WEC was significantly higher in the presence of hippocampal sclerosis (HS). Spiking rate during REM was significantly higher if a patient had SGTC seizures. Our data provide evidence that different aspects of spiking are associated with different aspects of TLE. We suggest that spike behaviour analysis offer new aspects both for diagnosis and research.

Sleep-related painful erection is associated with neurovascular compression of basal forebrain

Sirs: Erections are normal phenomena during sleep [4–6, 9]. Sleep-related painful erection (SRPE) is a parasomnia of unknown origin characterised by penile pain, wakening the patient and possibly resulting in excessive daytime sleepiness [1, 3]. We present the case of a 65year-old technician with negative medical history. He was a “matiné idol” with many sexual relationships all his adult life, although he had wife and children. His awakenings with torturing penile pain during night-time erections started at the age of 55 years; the pain gradually increased and the frequency of unpleasant erections increased to 3–5 /night. The penile pain spread over the lower body. As soon as he was fully awake, erection and pain disappeared together; in later years, however, the pain persisted. To get rid of pains he increased sexual activity, but with no success. Then he sought medical help. Two and three years after his problems started, uro-surgical operations were performed for the ill-localised pain: first a trans-urethral-prostatic-resection (although he had no urinary retention); then an operation for anal fissure. In 1999 he was referred to our sleep-clinic. His physical status, laboratory tests, and whole spine MRI were normal. He was severely depressed. Whole-night-polysomnography (Brainquick System III MS–40) including phallography, demonstrated disrupted night-sleep with three erections 1–7 minutes after the onset of REM-sleep phases (Table). Erections lasting 3–8 minutes were accompanied by arousal and full awakening from REM sleep, then they abruptly disappeared. Repeated tests showed similar findings. Brain MRI revealed a neurovascular compression on the antero-lateral surface of the left hypothalamus by the left posterior cerebral artery (Figure). Treatment with metoprolol, clozapine and clonazepam was ineffective. After a transitory improvement on clomipramin his complaints reappeared. Our patient’s symptoms covered the criteria of SRPE. In our opinion, uro-surgical procedures, probably performed because of pain only, show the danger of unrecognised parasomnia leading to poorly justified operations. In SRPE the pain could result from erectile hyper-activity during REM-sleep, due to central overdrive. Our patient’s increased daytime sexual activity seems to support this theory; however, the short duration of his night-time erections does not. The theory that SRPE is a psycho-somatic disorder [2] is supported by the depression of our patient, but preservation of sleep-related erections also in vegetative-state-patients [9] and independence from pre-sleep sexual arousal [11] make it improbable. The anterior-hypothalamus is implicated in the control of reproductive behaviour [7]. Lesion of the medial preoptic area in rats eliminates copulations; while its stimulation induces erections and removes descending inhibition of penile reflexes [10]. Rats with this lesion exhibit non-contact erections near receptive females although copulatory behaviour is compromised. The bed nucleus of LETTER TO THE EDITORS