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Hubert Preissl

Publications and source records attributed to Hubert Preissl.

At least 19 recordsLinked to original sources
PubMed2006

Fetal magnetoencephalography.

The assessment of the neurological integrity of the human fetus in utero is a technically challenging problem. New brain imaging devices can substantially improve our capabilities to describe functional brain activity in the fetus. It has been well established by fetal behavioral studies and investigations in preterm and term newborns that the brain is functional in utero. The major effort required to perform effective neurological functional investigations is designation of an integrated approach to neurological assessment and the generation of normative data. Currently, it is possible to record evoked brain activity elicited by auditory and visual stimulation from the fetus. In addition, there is growing evidence that spontaneous brain activity can be recorded in the fetus. This paper explores the current status of the brain-imaging field for fetal investigations and currently available data.

Brain↗
PubMed2006

Language lateralization in magnetoencephalography: two tasks to investigate hemispheric dominance.

Hemispheric specialization for language has been the focus of many studies, mainly using functional magnetic resonance imaging. Here, we used magnetoencephalography to investigate hemispheric dominance and time-dependent aspects of cortical language processing. We implemented a verb generation task and a newly designed vowel identification task. Eleven healthy adults were investigated. By using oscillatory magnetoencephalography spectral analysis, significant hemispheric differences were found for both tasks in cerebral language areas. Robust left-lateralization in frontal brain regions was observed with the verb generation task, confirming previous functional magnetic resonance imaging and magnetoencephalography studies. Our new vowel identification task yields significant left-lateralization in posterior language regions, making this silent and child-friendly task a valuable alternative for non-invasive language assessment in difficult populations.

Brain↗
PubMed2006

The cerebrocortical response to hyperinsulinemia is reduced in overweight humans: a magnetoencephalographic study.

Animal studies have shown that the brain is an insulin-responsive organ and that central nervous insulin resistance induces obesity and disturbances in glucose metabolism. In humans, insulin effects in the brain are poorly characterized. We used a magnetoencephalography approach during a two-step hyperinsulinemic euglycemic clamp to (i) assess cerebrocortical insulin effects in humans, (ii) compare these effects between 10 lean and 15 obese subjects, and (iii) test whether the insulin receptor substrate (IRS)-1 Gly972Arg polymorphism in the insulin-signaling cascade modifies these effects. Both spontaneous and stimulated (mismatch negativity) cortical activity were assessed. In lean humans, stimulated cortical activity (P = 0.046) and the beta and theta band of spontaneous cortical activity (P = 0.01 and 0.04) increased with insulin infusion relative to saline. In obese humans, these effects were suppressed. Moreover, the insulin effect on spontaneous cortical activity correlated negatively with body mass index and percent body fat (all r < -0.4; all P < 0.05) and positively with insulin sensitivity of glucose disposal (theta band, r = 0.48, P = 0.017). Furthermore, insulin increased spontaneous cortical activity (beta band) in carriers of wild-type IRS-1, whereas, in carriers of the 972Arg allele, this insulin effect was absent (P = 0.01). We conclude that, in lean humans, insulin modulates cerebrocortical activity, and that these effects are diminished in obese individuals. Moreover, cerebrocortical insulin resistance is found in individuals with the Gly972Arg polymorphism in IRS-1, which is considered a type 2 diabetes risk gene.

Adult↗
PubMed2006

Serial magnetoencephalographic study of fetal and newborn auditory discriminative evoked responses.

The mismatch negativity (MMN) response elicited to auditory stimuli is an indicator for cognitive function of sound discrimination in humans. MMN was successfully recorded in previous studies in newborns and fetuses (33-40 weeks of gestation) with magnetoencephalography (MEG). The aim of our study was to perform systematic serial MMN recordings on fetuses starting at 28 weeks of gestation with a follow up recording within 2 weeks after birth. The recording of weak magnetic fields from the fetal brain were performed with the 151 channel MEG system called SARA (SQUID Array for Reproductive Assessment). Two tone bursts were presented in a sequence of a standard complex tone of 500 Hz intermixed with a deviant complex tone of 750 Hz in 12% of the stimuli, inter-stimulus interval 800+/-100 ms. Eighteen pregnant women between 28th and 39th gestational weeks participated in the study. Measurements were performed every two weeks and once after delivery. The averaged evoked responses to standard and deviant tones were obtained and subtraction between them was calculated. A successful detection of response to the frequency change was found in 66% of the fetal data and 89% of the neonatal data. Responses to the standard tone were detected in 56% of all records. In the 28-39 week gestational age group, the discriminative brain responses to tone frequency change could be detected as early as 28 weeks. Although not statistically significant, a decrease in latency was observed with increase in gestational age. The ability of the fetus to detect changes in sounds is a prerequisite to normal development for cognitive function; related to language learning and clinical aspects of auditory disorders.

Acoustic Stimulation↗
PubMed2006

Subjective feeling of appetite modulates brain activity: an fMRI study.

Obesity and overweight are important risk factors for the development of diabetes mellitus type 2 and associated chronic diseases, and therefore, they have become serious global problems in the western and developed countries. But little is known about the neuroanatomical correlates of eating behavior and its influences on the central nervous processing in humans. We used functional magnetic resonance imaging (fMRI) to measure the cortical activation in 12 lean healthy humans during visual stimulation with food-related and nonfood pictures after a fasting period of at least 5 h. Compared to the nonfood pictures, the food stimuli elicited a significantly greater activity in the left orbitofrontal cortex and the insular/opercular cortex bilaterally with a stronger focus on the left side. Subjective ratings of appetite during the presentation of food-related stimuli modulated the activity in the insula bilaterally, the left operculum and the right putamen. These results provide further insights in the central nervous processing of food relevant stimuli in humans, specifically with respect to the subjective experience of appetite.

Adult↗
PubMed2006

Magnetoencephalography in healthy neonates.

OBJECTIVE: To describe magnetoencephalography (MEG) recordings in a cohort of healthy neonates. METHODS: We performed MEG and single channel EEG concomitantly in 21 healthy newborns. MEG and EEG signals were reviewed for gross comparison of general patterns and individual waveform characteristics. Spectral analysis was performed to quantify the signals. RESULTS: Our MEG recordings showed patterns comparable to classical neonatal EEG. Seventy-nine percent of the subjects exhibited the 'continuous polyfrequency activity' at some point in their recording. Sixty-three percent had the 'continuous slow' pattern, and 47% had the 'trace alternant' pattern. Spectral analysis revealed maximal power at frequencies of less than 4 Hz (delta band) in both MEG and EEG with a decline towards higher frequencies. CONCLUSIONS: Neonatal MEG is feasible and shares the basic EEG features and frequency content, with predominant activity in the slow frequency delta band. The latter corresponds to reports from earlier neonatal EEG studies. SIGNIFICANCE: MEG may prove to be useful in studies of neonatal brain functions.

Brain↗
PubMed2005

Do cortical maps depend on the timing of sensory input? Experimental evidence and computational model.

Fast adaptations in the functional organization of primary sensory cortex are generally assumed to result from changes of network connectivity. However, the effects of intrinsic neuronal excitability alterations due to the activation of neighboring cortical representational zones, which might as well account for the changes of cortical representative maps, have been paid little attention to. In a recent experiment (Braun et al. 2000b) we showed by neuromagnetic source imaging that random or fixed sequence stimulation of three digits of both hands led to stimulation-timing-induced changes in primary somatosensory (SI) cortical maps. The distance between the cortical representation of thumb and middle finger became significantly shorter during the fixed sequence stimulation. The analysis on the time course of the cortical map changes revealed that these reorganizations occurred within minutes and were fully reversible. The previously reported results were interpreted as the involvement of a superordinate center responsible for detecting and activating the appropriate maps. Here we present an alternative parsimonious explanation that is supported by a computational model. Based on the experimental evidence, we developed a simple model that took intrinsic neuronal excitability together with subthreshold activation into account and assumed partial cortical overlap of the representational zones of neighboring digits. Furthermore, in the model the neuronal excitability decayed slowly with respect to the stimulation frequency. The observed cortical map changes in the experiment could be reproduced by the two-layer feed-forward computational network. Our model thus suggests that the dynamic shifts of cortical maps can be explained by the state and time course of intrinsic neuronal excitability and subthreshold activation, without involving changes in network connectivity.

Adult↗
PubMed2005

Synchronization analysis of the uterine magnetic activity during contractions.

BACKGROUND: Our objective was to quantify and compare the extent of synchronization of the spatial-temporal myometrial activity over the human uterus before and during a contraction using transabdominal magnetomyographic (MMG) recordings. Synchronization can be an important indicator for the quantification of uterine contractions. METHODS: The spatialtermporal myometrial activity recordings were performed using a 151-channel noninvasive magnetic sensor system called SARA. This device covers the entire pregnant abdomen and records the magnetic field corresponding to the electrical activity generated in the uterine myometrium. The data was collected at 250 samples/sec and was resampled with 25 samples/sec and then filtered in the band of 0.1-0.2 Hz to study the primary magnetic activity of the uterus related to contractions. The synchronization between a channel pair was computed. It was inferred from a statistical tendency to maintain a nearly constant phase difference over a given period of time even though the analytic phase of each channel may change markedly during that time frame. The analytic phase was computed after taking Hilbert transform of the magnetic field data. The process was applied on the pairs of magnetic field traces (240 sec length) with a stepping window of 20 sec duration which is long enough to cover two cycle of the lowest frequency of interest (0.1 Hz). The analysis was repeated by stepping the window at 10 sec intervals. The spatial patterns of the synchronization indices covering the anterior transabdominal area were computed. For this, regional coil-pairs were used. For a given coil, the coil pairs were constructed with the surrounding six coils. The synchronization indices were computed for each coil pair, averaged over the 21 coil-pairs and then assigned as the synchronization index to that particular coil. This procedure was tested on six pregnant subjects at the gestational age between 29 and 40 weeks admitted to the hospital for contractions. The RMS magnetic field for each coil was also computed. RESULTS: The results show that the spatial patterns of the synchronization indices change and follow the periodic pattern of the uterine contraction cycle. Spatial patterns of synchronization indices and the RMS magnetic fields show similarities in few window frames and also show large differences in few other windows. For six subjects, the average synchronization indices were: 0.346 +/- 0.068 for the quiescent baseline period and 0.545 +/- 0.022 at the peak of the contraction. DISCUSSION: These results show that synchronization indices and their spatial distributions depict uterine contractions and relaxations.

Action Potentials↗
PubMed2005

Sound frequency change detection in fetuses and newborns, a magnetoencephalographic study.

The mismatch negativity (MMN) response to auditory stimuli has been successfully recorded in newborns thus demonstrating the discriminative cognitive ability. The aim of our study was to determine whether and when such an MMN response could be detected in the human fetus. The recordings of weak magnetic fields from the fetal brain were performed with the 151 channel MEG system called SARA (SQUID Array for Reproductive Assessment). Two tone bursts were presented in a sequence of a standard complex tone of 500 Hz intermixed with a deviant complex tone of 750 Hz in 12% of the stimuli. Sound intensity delivered over the maternal abdomen was 110 dB. The interstimulus interval (ISI) varied between 500 ms and 1100 ms. Fetal response, corresponding to sound frequency change detection, was calculated from the records where responses to standard and deviant tones were observed. A successful response was found in 60% of 25 fetal recordings. The MMN response with an average latency of 321 ms was observed in 48% of the fetal data. In 12% of the fetal data, a late component, referred to as the late discriminative negativity (LDN) response, was detected with an average latency of 458 ms. The same paradigm was applied in 5 newborns after birth. The capability for sound discrimination is a prerequisite for normal speech development. The investigation of sound discrimination and related cortical activity of the fetus can help to identify and determine the nature of deficits caused by central processes in the auditory system at very early stages.

Acoustic Stimulation↗
PubMed2005

Ellipsoidal head model for fetal magnetoencephalography: forward and inverse solutions.

Fetal magnetoencephalography (fMEG) is a non-invasive technique where measurements of the magnetic field outside the maternal abdomen are used to infer the source location and signals of the fetus' neural activity. There are a number of aspects related to fMEG modelling that must be addressed, such as the conductor volume, fetal position and orientation, gestation period, etc. We propose a solution to the forward problem of fMEG based on an ellipsoidal head geometry. This model has the advantage of highlighting special characteristics of the field that are inherent to the anisotropy of the human head, such as the spread and orientation of the field in relationship with the localization and position of the fetal head. Our forward solution is presented in the form of a kernel matrix that facilitates the solution of the inverse problem through decoupling of the dipole localization parameters from the source signals. Then, we use this model and the maximum likelihood technique to solve the inverse problem assuming the availability of measurements from multiple trials. The applicability and performance of our methods are illustrated through numerical examples based on a real 151-channel SQUID fMEG measurement system (SARA). SARA is an MEG system especially designed for fetal assessment and is currently used for heart and brain studies. Finally, since our model requires knowledge of the best-fitting ellipsoid's centre location and semiaxes lengths, we propose a method for estimating these parameters through a least-squares fit on anatomical information obtained from three-dimensional ultrasound images.

Algorithms↗
PubMed2005

Fetal magnetoencephalography--a multimodal approach.

Past studies have shown the feasibility of recording fetal evoked responses to external stimuli using a non-invasive technique called magnetoencephalography (MEG). These studies were all performed using either auditory or visual stimuli and showed a fairly low detection rate for each modality, thus making this technology currently unreliable for fetal clinical applications. This study is based on the hypothesis that a multimodal approach of applying both auditory and visual stimulation paradigms in successive recording sessions could improve the probability of obtaining a fetal evoked response. A total of 34 studies were performed on 11 normal healthy fetuses at different stages of gestation starting as early as 28 weeks with a 151-channel fetal MEG system. The success rate of obtaining a response to either (or both) stimuli from a study at a given gestation age was 91%. All the 11 fetuses showed a response at least once over the gestation period the recordings were performed. A multimodal testing approach can improve the ability of the MEG technique to reliably monitor the functional development of the fetal brain.

Acoustic Stimulation↗
PubMed2005

Development of auditory evoked fields in human fetuses and newborns: a longitudinal MEG study.

OBJECTIVE: To investigate the maturation of the auditory cortex by non-invasive recording of auditory evoked magnetic fields in human fetuses and newborns with the relatively novel and completely non-invasive technology of MEG. METHODS: Serial recordings were performed every 2 weeks on 18 fetuses beginning from week 27 of gestational age until term with a follow-up recording on the newborn. Auditory stimulation consisted of tone bursts in an oddball design with standard tones and deviant tones. RESULTS: In 52 of 63 fetal and in all of the neonatal recordings an auditory evoked magnetic field was obtained. A decrease in latency with increasing age of the subjects was observed in the combined analysis of fetuses and neonates. CONCLUSIONS: With advanced study using MEG, 83% of the measurements showed auditory evoked fields in fetuses that correspond with existing literature in electrophysiology in the past. These findings indicate that MEG is a technique that can be used to investigate maturation of the auditory cortex based on auditory evoked fields in fetuses and neonates. SIGNIFICANCE: Maturational changes have been examined in the past. With the use of this novel technique, applied to a serial study, it is possible to trace the development of auditory responses in utero and newborns.

Adult↗
PubMed2005

Objective measurement of tactile mislocalization.

Stimulating the skin with intensities close to the sensory threshold causes erroneous localization of the site of stimulation. Previous studies using manual methods for applying faint tactile stimuli have shown that localization errors obey a somatotopic principle in which tactile stimuli are preferentially mislocalized to sites adjacent to the stimulated skin region. However, manual testing of mislocalization is time consuming and only partially objective because results depend on the skills of the tester. To improve the testing procedure, an automated apparatus was developed. The procedure adjusted stimulus intensity adaptively during testing to remain near the individual subject's sensory threshold, so that mislocalizations occurred often enough to assess somatotopic organization. The new method was applied to 12 healthy subjects. In each subject, the five digits of the right hand were stimulated singly in random order. Localization errors were distributed preferentially to fingers close to the stimulated finger rather than to distant fingers. The profile of mislocalization differed significantly from that expected on the basis of response bias or guessing behavior. The present results replicate previous findings obtained for manual testing with improved sensitivity and indicate that the new technique is a useful tool for the study of somatosensory processing on a perceptual level.

Adult↗
PubMed2005

Benign partial epilepsy in childhood: selective cognitive deficits are related to the location of focal spikes determined by combined EEG/MEG.

PURPOSE: Benign partial epilepsy (BPE) in childhood is characterized by the occurrence of interictal stereotyped focal spikes with variable localization in the EEG. Children with BPE often exhibit neuropsychological deficits. It is unclear whether a correlation exists between these deficits and the localization of spikes, several EEG studies giving inconsistent results. Magnetoencephalography (MEG) improves the accuracy of spike localization. Therefore by using combined MEG/EEG, we investigated the topographic relation between focal spikes and neuropsychological findings in children with BPE. METHODS: Twenty-seven children diagnosed consecutively with BPE were enrolled in the study. All were examined by combined MEG/EEG and magnetic resonance imaging (MRI). Location of spikes was determined by dipole source estimation. A standardized neuropsychological assessment was conducted, including Kaufman ABC battery, language tests, and motor performance series. All children with sufficient MEG data were included in the correlation analysis (N = 20). RESULTS: Focal spikes were located in the perisylvian region in 13 children, in the occipital region in seven, and in the frontal region in one. Five children had bilateral or multiple foci. Children with left perisylvian spikes did not differ from the others in global IQ, but performed significantly lower in language tests (p = 0.01). Children with occipital spikes performed significantly lower in simultaneous information processing (p = 0.01), especially in visual transformation tasks. CONCLUSIONS: Combined MEG/EEG investigation is a useful tool to examine interictal focal spikes. Our results show a correlation between the location of spikes and selective cognitive deficits in children with BPE. These findings indicate that focal interictal spikes may interfere with complex cognitive functions.

Brain Mapping↗
PubMed2004

The right hand knows what the left hand is feeling.

The mislocalization profile, describing incorrect localization of faint tactile stimuli to different regions of the body, has been shown to provide insight into the processing of tactile stimuli. Interhemispheric somatosensory processing was examined in 15 subjects by studying the interference of left-hand stimulation on right-hand perception. In different conditions supra-threshold interference stimuli were applied to the left thumb or little finger either 200 or 500 ms prior to the application of a test stimulus on the right hand. Data show that interference stimuli applied to the left hand massively altered localization responses for stimuli applied to the right side. Stimulating the left thumb yielded an increased number of mislocalizations to the right thumb. Similarly, stimulating the left little finger caused a shift in localization responses towards the right ring finger. Results support the hypothesis that interaction of somatosensory information originating from different sides of the body follows a somatotopic organization.

Adult↗
PubMed2004

A simple wavelet-based test for evoked responses.

Statistically valid detection of evoked responses from magnetoencephalographic (MEG) sensors is complicated by temporal autocorrelation. By decorrelating time series and transforming them toward normality, the discrete wavelet transform (DWT) allows the analyst to test for an association between stimulus and sensor time series with appropriate degrees of freedom. Eswaran et al. (Neurosci. Lett. 2002a;331:128-32) used a 151-channel fetal MEG system to obtain serial recordings from 10 pregnant subjects. There were 3-8 recordings per subject. In each recording session, the fetus was stimulated by 500Hz and 1KHz tones with a relative frequency of 80-20%, respectively. In this new analysis of the same data, the fetal MEG signals were compared to two different stimulus waveforms: the frequent tone and the Novel stimulus, defined as a change in pitch. WaveDetect was developed to determine whether there was a significant association between the stimuli and the MEG traces. This test is performed by taking the DWT of each series and then computing the Spearman correlation between the wavelet coefficients for an appropriate scale. A significant response (i.e., correlated stimulus-sensor pair) was detected from each patient. This result suggests that the combination of serial recordings and WaveDetect may ensure reliable detection of auditory evoked responses.

Acoustic Stimulation↗
PubMed2004

Influence of social support and emotional context on pain processing and magnetic brain responses in fibromyalgia.

OBJECTIVE: To examine the effects of social support provided by the presence of patient's significant other on pain ratings, pain thresholds, and brain activity associated with tactile stimulation in 18 fibromyalgia (FM) patients and 18 migraine patients (controls), and to assess the influence of emotional context on thermal pain perception and processing of non-pain-related information. METHODS: Thermal pain thresholds and somatosensory brain magnetic responses elicited by tactile stimulation at the elbow (a painful tender point in the FM group) and at the finger (nonpainful site) were evaluated under 2 experimental conditions of social support: patient alone and patient's significant other present. Brain activity was recorded using a 151-channel whole-head magnetoencephalography system. Additionally, the emotional context during presentation of tactile stimuli was manipulated by presenting aversive, pain-related pictures and neutral pictures and asking the patients to imagine that they were experiencing the situations depicted. RESULTS: Thermal pain thresholds indicated greater sensitivity in FM patients than in migraine patients, as well as enhanced sensitivity at the elbow than at the fingers. Specifically, in FM patients, there were significant reductions in pain sensitivity and subjective pain ratings when patients were stimulated at the painful tender point in the presence of their significant others as compared with the ratings when the patients were alone. Brain activity elicited by elbow stimulation was also significantly reduced in FM patients when a significant other was present as compared with the activity when the patient was alone. These effects were not observed in the migraine patients. CONCLUSION: When the significant other was present, FM patients reported less pain and thermal pain sensitivity and showed diminished brain activity elicited upon tactile stimulation of a tender point compared with these levels when the patients were alone. These findings are consistent with the hypothesis that social support through the presence of a significant other can influence pain processing at the subjective-behavioral level as well as the central nervous system level.

Adult↗