Biomedical subjects

P Achermann

Publications and source records attributed to P Achermann.

At least 19 recordsLinked to original sources

PubMed2006

Sleep-wake disturbances in sporadic Creutzfeldt-Jakob disease.

BACKGROUND: The prevalence and characteristics of sleep-wake disturbances in sporadic Creutzfeldt-Jakob disease (sCJD) are poorly understood. METHODS: Seven consecutive patients with definite sCJD underwent a systematic assessment of sleep-wake disturbances, including clinical history, video-polysomnography, and actigraphy. Extent and distribution of neurodegeneration was estimated by brain autopsy in six patients. Western blot analyses enabling classification and quantification of the protease-resistant isoform of the prion protein, PrPSc, in thalamus and occipital cortex was available in four patients. RESULTS: Sleep-wake symptoms were observed in all patients, and were prominent in four of them. All patients had severe sleep EEG abnormalities with loss of sleep spindles, very low sleep efficiency, and virtual absence of REM sleep. The correlation between different methods to assess sleep-wake functions (history, polysomnography, actigraphy, videography) was generally poor. Brain autopsy revealed prominent changes in cortical areas, but only mild changes in the thalamus. No mutation of the PRNP gene was found. CONCLUSIONS: This study demonstrates in sporadic Creutzfeldt-Jakob disease, first, the existence of sleep-wake disturbances similar to those reported in fatal familial insomnia in the absence of prominent and isolated thalamic neuronal loss, and second, the need of a multimodal approach for the unambiguous assessment of sleep-wake functions in these patients.

Aged↗

PubMed2006

Trait-like individual differences in the human sleep electroencephalogram.

We aimed to examine whether commonly observed individual differences in sleep architecture and the sleep electroencephalogram reflect individual traits, which are amenable to a genetic investigation of human sleep. We studied intra-individual stability and inter-individual variation in sleep and sleep electroencephalogram spectra across four baseline recordings of eight healthy young men. A similarity concept based on Euclidean distances between vectors was applied. Visually scored sleep variables served as feature vector components, along with electroencephalogram power spectra in non-rapid-eye-movement and rapid-eye-movement sleep. The distributions of similarity coefficients of feature vectors revealed a clear distinction between high within-subject similarity (i.e. stability), and low between-subject similarity (i.e. variation). Moreover, a cluster analysis based on electroencephalogram spectra in both non-rapid-eye-movement and rapid-eye-movement sleep segregated all four baseline nights of each individual into a distinct cluster. To investigate whether high and low sleep pressure affects the similarity coefficients, normalized non-rapid-eye-movement sleep electroencephalogram spectra of the first and second half of the recordings were compared. Because the electroencephalogram changes systematically in the course of the night, within-subject variation no longer differed from between-subject variation. In conclusion, our data provide evidence for trait-like characteristics in the sleep electroencephalogram. Further studies may help to identify distinct phenotypes to search for genes underlying functional aspects of undisturbed human sleep.

Adult↗

PubMed2005

Analysis of oscillatory patterns in the human sleep EEG using a novel detection algorithm.

The different brain states during sleep are characterized by the occurrence of distinct oscillatory patterns such as spindles or delta waves. Using a new algorithm to detect oscillatory events in the electroencephalogram (EEG), we studied their properties and changes throughout the night. The present approach was based on the idea that the EEG may be described as a superposition of stochastically driven harmonic oscillators with damping and frequency varying in time. This idea was implemented by fitting autoregressive models to the EEG data. Oscillatory events were detected, whenever the damping of one or more frequencies was below a predefined threshold. Sleep EEG data of eight healthy young males were analyzed (four nights per subject). Oscillatory events occurred mainly in three frequency ranges, which correspond roughly to the classically defined delta (0-4.5 Hz), alpha (8-11.5 Hz) and sigma (11.5-16 Hz) bands. Their incidence showed small intra- but large inter-individual differences, in particular with respect to alpha events. The incidence and frequency of the events was characteristic for sleep stages and non-rapid eye movement (REM)-REM sleep cycles. The mean event frequency of delta and sigma (spindle) events decreased with the deepening of sleep. It was higher in the second half of the night compared with the first one for delta, alpha and sigma oscillations. The algorithm provides a general framework to detect and characterize oscillatory patterns in the EEG and similar signals.

Algorithms↗

PubMed2005

Exposure to pulse-modulated radio frequency electromagnetic fields affects regional cerebral blood flow.

We investigated the effects of radio frequency electromagnetic fields (RF EMF) similar to those emitted by mobile phones on waking regional cerebral blood flow (rCBF) in 12 healthy young men. Two types of RF EMF exposure were applied: a 'base-station-like' and a 'handset-like' signal. Positron emission tomography scans were taken after 30 min unilateral head exposure to pulse-modulated 900 MHz RF EMF (10 g tissue-averaged spatial peak-specific absorption rate of 1 W/kg for both conditions) and sham control. We observed an increase in relative rCBF in the dorsolateral prefrontal cortex on the side of exposure. The effect depended on the spectral power in the amplitude modulation of the RF carrier such that only 'handset-like' RF EMF exposure with its stronger low-frequency components but not the 'base-station-like' RF EMF exposure affected rCBF. This finding supports our previous observation that pulse modulation of RF EMF is necessary to induce changes in the waking and sleep EEG, and substantiates the notion that pulse modulation is crucial for RF EMF-induced alterations in brain physiology.

Adult↗

PubMed2004

Interhemispheric coherence of the sleep electroencephalogram in mice with congenital callosal dysgenesis.

Regional differences in the effect of sleep deprivation on the sleep electroencephalogram (EEG) may be related to interhemispheric synchronization. To investigate the role of the corpus callosum in interhemispheric EEG synchronization, coherence spectra were computed in mice with congenital callosal dysgenesis (B1) under baseline conditions and after 6-h sleep deprivation, and compared with the spectra of a control strain (C57BL/6). In B1 mice coherence was lower than in controls in all vigilance states. The level of coherence in each of the three totally acallosal mice was lower than in the mice with only partial callosal dysgenesis. The difference between B1 and control mice was present over the entire 0.5-25 Hz frequency range in non-rapid eye movement sleep (NREM sleep), and in all frequencies except for the high delta and low theta band (3-7 Hz) in rapid eye movement (REM) sleep and waking. In control mice, sleep deprivation induced a rise of coherence in the Delta band of NREM sleep in the first 2 h of recovery. This effect was absent in B1 mice with total callosal dysgenesis and attenuated in mice with partial callosal dysgenesis. In both strains the effect of sleep deprivation dissipated within 4 h. The results show that EEG synchronization between the hemispheres in sleep and waking is mediated to a large part by the corpus callosum. This applies also to the functional changes induced by sleep deprivation in NREM sleep. In contrast, interhemispheric synchronisation of theta oscillations in waking and REM sleep may be mediated by direct interhippocampal connections.

Analysis of Variance↗

PubMed2004

Sleep and rest facilitate auditory learning.

Sleep is superior to waking for promoting performance improvements between sessions of visual perceptual and motor learning tasks. Few studies have investigated possible effects of sleep on auditory learning. A key issue is whether sleep specifically promotes learning, or whether restful waking yields similar benefits. According to the "interference hypothesis," sleep facilitates learning because it prevents interference from ongoing sensory input, learning and other cognitive activities that normally occur during waking. We tested this hypothesis by comparing effects of sleep, busy waking (watching a film) and restful waking (lying in the dark) on auditory tone sequence learning. Consistent with recent findings for human language learning, we found that compared with busy waking, sleep between sessions of auditory tone sequence learning enhanced performance improvements. Restful waking provided similar benefits, as predicted based on the interference hypothesis. These findings indicate that physiological, behavioral and environmental conditions that accompany restful waking are sufficient to facilitate learning and may contribute to the facilitation of learning that occurs during sleep.

Acoustic Stimulation↗

PubMed2004

The dynamics of spindles and EEG slow-wave activity in NREM sleep in mice.

A quantitative analysis of spindles and spindle-related EEG activity was performed in C57BL/6 mice. The hypothesis that spindles are involved in sleep regulatory mechanisms was tested by investigating their occurrence during 24 h and after 6 h sleep deprivation (SD; n = 7). In the frontal derivation distinct spindle events were characterized as EEG oscillations with a dominant frequency approximately at 11 Hz. Spindles were most prominent during NREM sleep and increased before NREM-REM sleep transitions. Whereas spindles increased concomitantly with slow wave activity (SWA, EEG power between 0.5 and 4.0 Hz) at the beginning of the NREM sleep episode, these measures showed an opposite evolution prior to the transition to REM sleep. The 24-h time course of spindles showed a maximum at the end of the 12-h light period, and was a mirror image of SWA in NREM sleep. After 6 h SD the spindles in NREM sleep were initially suppressed, and showed a delayed rebound. In contrast, spindles occurring immediately before the transition to REM sleep were enhanced during the first 2 h of recovery. The data suggest that spindles in NREM sleep may be involved in sleep maintenance, while spindles heralding the transition to REM sleep may be related to mechanisms of REM sleep initiation.

Action Potentials↗

PubMed2003

Dimensional complexity and spectral properties of the human sleep EEG. Electroencephalograms.

OBJECTIVE: The relevance of the dimensional complexity (DC) for the analysis of sleep EEG data is investigated and compared to linear measures. METHODS: We calculated DC of artifact-free 1 min segments of all-night sleep EEG recordings of 4 healthy young subjects. Non-linearity was tested by comparing with DC values of surrogate data. Linear properties of the segments were characterized by estimating the self-similarity exponent alpha based on the detrended fluctuation analysis which quantifies the persistence of the signal and by calculating spectral power in the delta, theta, alpha and sigma bands, respectively. RESULTS: We found weak nonlinear signatures in all sleep stages, but most pronounced in sleep stage 2. Strong correlations between DC and linear measures were established for the self-similarity exponent alpha and delta power, respectively. CONCLUSIONS: The dimensional complexity of the sleep EEG is influenced by both linear and nonlinear features. It cannot be directly interpreted as a nonlinear synchronization measure of brain activity, but yields valuable information when combined with the analysis of linear measures.

Adult↗

PubMed2002

Electromagnetic fields, such as those from mobile phones, alter regional cerebral blood flow and sleep and waking EEG.

Usage of mobile phones is rapidly increasing, but there is limited data on the possible effects of electromagnetic field (EMF) exposure on brain physiology. We investigated the effect of EMF vs. sham control exposure on waking regional cerebral blood flow (rCBF) and on waking and sleep electroencephalogram (EEG) in humans. In Experiment 1, positron emission tomography (PET) scans were taken after unilateral head exposure to 30-min pulse-modulated 900 MHz electromagnetic field (pm-EMF). In Experiment 2, night-time sleep was polysomnographically recorded after EMF exposure. Pulse-modulated EMF exposure increased relative rCBF in the dorsolateral prefrontal cortex ipsilateral to exposure. Also, pm-EMF exposure enhanced EEG power in the alpha frequency range prior to sleep onset and in the spindle frequency range during stage 2 sleep. Exposure to EMF without pulse modulation did not enhance power in the waking or sleep EEG. We previously observed EMF effects on the sleep EEG (A. A. Borbély, R. Huber, T. Graf, B. Fuchs, E. Gallmann and P. Achermann. Neurosci. Lett., 1999, 275: 207-210; R. Huber, T. Graf, K. A. Cote, L. Wittmann, E. Gallmann, D. Matter, J. Schuderer, N. Kuster, A. A. Borbély, and P. Achermann. Neuroreport, 2000, 11: 3321-3325), but the basis for these effects was unknown. The present results show for the first time that (1) pm-EMF alters waking rCBF and (2) pulse modulation of EMF is necessary to induce waking and sleep EEG changes. Pulse-modulated EMF exposure may provide a new, non-invasive method for modifying brain function for experimental, diagnostic and therapeutic purposes.

Adult↗

PubMed2002

Power and coherence of sleep spindle frequency activity following hemispheric stroke.

Brainstem and thalamic structures are known to play a critical role in modulating sleep-wake cycles, but the extent to which the cerebral hemispheres are involved remains unclear. To study the role of the cerebral hemispheres in generating sleep EEG patterns, all-night polysomnographic recordings were collected in subjects with brain damage (n = 30) caused by hemispheric stroke and in hospitalized controls (n = 12). Recordings were made in the acute (< or =10 days post-stroke), subchronic (11-35 days post-stroke) and chronic (>60 days post-stroke) phases of stroke. Bipolar and referential EEG derivations were recorded. Standard sleep stage scoring was conducted using the referential derivation placed opposite the lesion. Sleep stage 2 power and coherence spectra were calculated based on recordings from bipolar derivations. In the mean spectra, the highest spindle frequency peak was identified and its size was calculated relative to the background spectrum. Analysis of visually scored EEG data indicated that, compared with controls, acute phase brain-damaged subjects had lower sleep efficiency and increased waking after sleep onset. The durations of rapid eye movement and non-rapid eye movement sleep stages did not differ significantly between brain-damaged subjects and hospitalized controls. Spectral analyses revealed that, compared with hospitalized controls, brain-damaged subjects had significantly reduced spindle peak sizes in the power and coherence spectra from derivations ipsilateral to the lesion. Within-subject comparisons across time demonstrated that the power and coherence of sleep spindle frequency activity increased significantly from the acute to the chronic phases of stroke, suggesting that plastic mechanisms allowed the possibility of recovery. Our findings provide novel evidence that the cerebral hemispheres are important in generating coherent sleep spindles in humans, and they are consonant with prior empirical and theoretical evidence that corticothalamic projections modulate the generation of synchronous spindle oscillations. Because spindle oscillations are thought to be involved in blocking sensory input to the cortex during sleep, the decrease in synchronous spindle frequency activity following hemispheric stroke may contribute to the observed reduction in sleep continuity.

Adolescent↗

PubMed2001

Brain sources of EEG gamma frequency during volitionally meditation-induced, altered states of consciousness, and experience of the self.

Multichannel EEG of an advanced meditator was recorded during four different, repeated meditations. Locations of intracerebral source gravity centers as well as Low Resolution Electromagnetic Tomography (LORETA) functional images of the EEG 'gamma' (35-44 Hz) frequency band activity differed significantly between meditations. Thus, during volitionally self-initiated, altered states of consciousness that were associated with different subjective meditation states, different brain neuronal populations were active. The brain areas predominantly involved during the self-induced meditation states aiming at visualization (right posterior) and verbalization (left central) agreed with known brain functional neuroanatomy. The brain areas involved in the self-induced, meditational dissolution and reconstitution of the experience of the self (right fronto-temporal) are discussed in the context of neural substrates implicated in normal self-representation and reality testing, as well as in depersonalization disorders and detachment from self after brain lesions.

Brain Mapping↗

PubMed2001

Unihemispheric enhancement of delta power in human frontal sleep EEG by prolonged wakefulness.

EEG power spectra exhibit site-specific and state-related differences in specific frequency bands. In the present study we investigated the effect of total sleep deprivation on sleep EEG topography. Eight healthy, young, right-handed subjects were recorded during baseline sleep and recovery sleep after sleep deprivation. Forty hours of sleep deprivation affected power spectra in all derivations. However, hemispheric asymmetries were observed in the delta range. Sleep deprivation enhanced the anterior predominance of delta activity in the left hemisphere but not in the right one. This effect may reflect a functional asymmetry between the dominant and non-dominant hemisphere. The results provide further evidence for the presence of both global and local aspects of sleep regulation.

Adult↗

PubMed2001

High frequency repetitive transcranial magnetic stimulation (rTMS) of the left dorsolateral cortex: EEG topography during waking and subsequent sleep.

Repetitive transcranial magnetic stimulation (rTMS) is a novel research tool in neurology and psychiatry. It is currently being evaluated as a conceivable alternative to electroconvulsive therapy for the treatment of mood disorders. Eight healthy young (age range 21-25 years) right-handed men without sleep complaints participated in the study. Two sessions at a 1-week interval, each consisting of an adaptation night (sham stimulation) and an experimental night (rTMS in the left dorsolateral prefrontal cortex or sham stimulation; crossover design), were scheduled. In each subject, 40 trains of 2-s duration of rTMS (inter-train interval 28 s) were applied at a frequency of 20 Hz (i.e. 1600 pulses per session) and at an intensity of 90% of the motor threshold. Stimulations were scheduled 80 min before lights off. The waking EEG was recorded for 10-min intervals approximately 30 min prior to and after the 20-min stimulations, and polysomnographic recordings were obtained during the subsequent sleep episode (23.00-07.00 h). The power spectra of two referential derivations, as well as of bipolar derivations along the antero-posterior axis over the left and right hemispheres, were analyzed. rTMS induced a small reduction of sleep stage 1 (in min and percentage of total sleep time) over the whole night and a small enhancement of sleep stage 4 during the first non-REM sleep episode. Other sleep variables were not affected. rTMS of the left dorsolateral cortex did not alter the topography of EEG power spectra in waking following stimulation, in the all-night sleep EEG, or during the first non-REM sleep episode. Our results indicate that a single session of rTMS using parameters like those used in depression treatment protocols has no detectable side effects with respect to sleep in young healthy males.

Adult↗

PubMed2001

Individual 'fingerprints' in human sleep EEG topography.

The sleep EEG of eight healthy young men was recorded from 27 derivations during a baseline night and a recovery night after 40 h of waking. Individual power maps of the nonREM sleep EEG were calculated for the delta, theta, alpha, sigma and beta range. The comparison of the normalized individual maps for baseline and recovery sleep revealed very similar individual patterns within each frequency band. This high correspondence was quantified and statistically confirmed by calculating the Manhattan distance between all pairs of maps within and between individuals. Although prolonged waking enhanced power in the low-frequency range (0.75-10.5 Hz) and reduced power in the high-frequency range (13.25-25 Hz), only minor effects on the individual topography were observed. Nevertheless, statistical analysis revealed frequency-specific regional effects of sleep deprivation. The results demonstrate that the pattern of the EEG power distribution in nonREM sleep is characteristic for an individual and may reflect individual traits of functional anatomy.

Adult↗

PubMed2001

Functional topography of the human nonREM sleep electroencephalogram.

The sleep EEG of healthy young men was recorded during baseline and recovery sleep after 40 h of waking. To analyse the EEG topography, power spectra were computed from 27 derivations. Mean power maps of the nonREM sleep EEG were calculated for 1-Hz bins between 1.0 and 24.75 Hz. Cluster analysis revealed a topographic segregation into distinct frequency bands which were similar for baseline and recovery sleep, and corresponded closely to the traditional frequency bands. Hallmarks of the power maps were the frontal predominance in the delta and alpha band, the occipital predominance in the theta band, and the sharply delineated vertex maximum in the sigma band. The effect of sleep deprivation on EEG topography was determined by calculating the recovery/baseline ratio of the power spectra. Prolonged waking induced an increase in power in the low-frequency range (1-10.75 Hz) which was largest over the frontal region, and a decrease in power in the sigma band (13-15.75 Hz) which was most pronounced over the vertex. The topographic pattern of the recovery/baseline power ratio was similar to the power ratio between the first and second half of the baseline night. These results indicate that changes in sleep propensity are reflected by specific regional differences in EEG power. The predominant increase of low-frequency power in frontal areas may be due to a high 'recovery need' of the frontal heteromodal association areas of the cortex.

Adult↗

PubMed2000

Exposure to pulsed high-frequency electromagnetic field during waking affects human sleep EEG.

The aim of the study was to investigate whether the electromagnetic field (EMF) emitted by digital radiotelephone handsets affects brain physiology. Healthy, young male subjects were exposed for 30 min to EMF (900 MHz; spatial peak specific absorption rate 1 W/kg) during the waking period preceding sleep. Compared with the control condition with sham exposure, spectral power of the EEG in non-rapid eye movement sleep was increased. The maximum rise occurred in the 9.75-11.25 Hz and 12.5-13.25 Hz band during the initial part of sleep. These changes correspond to those obtained in a previous study where EMF was intermittently applied during sleep. Unilateral exposure induced no hemispheric asymmetry of EEG power. The present results demonstrate that exposure during waking modifies the EEG during subsequent sleep. Thus the changes of brain function induced by pulsed high-frequency EMF outlast the exposure period.

Adult↗

PubMed2000

Dual electroencephalogram markers of human sleep homeostasis: correlation between theta activity in waking and slow-wave activity in sleep.

To investigate the relationship between markers of sleep homeostasis during waking and sleep, the electroencephalogram of eight young males was recorded intermittently during a 40-h waking episode, as well as during baseline and recovery sleep. In the course of extended waking, spectral power of the electroencephalogram in the 5-8Hz band (theta activity) increased. In non-rapid eye movement sleep, power in the 0.75-4.5Hz band (slow-wave activity) was enhanced in the recovery night relative to baseline. Comparison of individual records revealed a positive correlation between the rise rate of theta activity during waking and the increase in slow-wave activity in the first non-rapid eye movement sleep episode. A topographic analysis based on 27 derivations showed that both effects were largest in frontal areas. From these results, we suggest that theta activity in waking and slow-wave activity in sleep are markers of a common homeostatic sleep process.

Adult↗

PubMed2000

Effects of medial thalamotomy and pallido-thalamic tractotomy on sleep and waking EEG in pain and Parkinsonian patients.

OBJECTIVES: Investigation of sleep and sleep EEG before and after stereotactic neurosurgery. METHODS: All-night polysomnographic recordings were obtained in 3 neurogenic pain patients and 3 parkinsonian patients. One subject of each group was recorded in addition 3 months after surgery. Stereotactic operations were performed in the medial thalamus and on the pallido-thalamic tract to relieve neurogenic pain and parkinsonian symptoms, respectively. RESULTS: Sleep efficiency was little affected by the surgical intervention in neurogenic pain patients and a dramatic reduction in REM sleep occurred, which had recovered in the subject recorded after 3 months. After the surgery parkinsonian patients showed an increase in total sleep time and in sleep efficiency, and a decrease in REM sleep latency. Sleep efficiency remained elevated in the 3 months follow-up. Medial thalamotomy abolished spindle frequency activity (SFA) in the power and coherence spectra in non-REM sleep stage 2 systematically. Pallido-thalamic tractotomy attenuated SFA only to varying degrees. After 3 months SFA had reemerged. The alpha peak of the waking EEG was shifted to lower frequencies after surgery in 5 of 6 patients and had reverted to the original frequency 3 months later. CONCLUSIONS: Medial thalamotomy or pallido-thalamic tractotomy had acute and reversible effects on the EEG and long-term deleterious side effects of stereotactic surgery on sleep and sleep EEG are improbable. The results provide further evidence for the involvement of the human thalamus in the generation of sleep spindles.

Aged↗