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L Deecke

Publications and source records attributed to L Deecke.

At least 37 records · Page 2Linked to original sources
PubMed2001

False recognition depends on depth of prior word processing: a magnetoencephalographic (MEG) study.

Brain activity was measured with a whole head magnetoencephalograph (MEG) during the test phases of word recognition experiments. Healthy young subjects had to discriminate between previously presented and new words. During prior study phases two different levels of word processing were provided according to two different kinds of instructions (shallow and deep encoding). Event-related fields (ERFs) associated with falsely recognized words (false alarms) were found to depend on the depth of processing during the prior study phase. False alarms elicited higher brain activity (as reflected by dipole strength) in case of prior deep encoding as compared to shallow encoding between 300 and 500 ms after stimulus onset at temporal brain areas. Between 500 and 700 ms we found evidence for differences in the involvement of neural structures related to both conditions of false alarms. Furthermore, the number of false alarms was found to depend on depth of processing. Shallow encoding led to a higher number of false alarms than deep encoding. All data are discussed as strong support for the ideas that a certain level of word processing is performed by a distinct set of neural systems and that the same neural systems which encode information are reactivated during the retrieval.

Adult↗
PubMed2001

Physiological evidence of gender differences in word recognition: a magnetoencephalographic (MEG) study.

Magnetic field recordings were made in order to describe brain processes during a word recognition experiment. We investigated 26 healthy young subjects (14 females) and focused on gender differences related to recognition performance and brain activity. From about 200 ms to 350 ms after word onset the event-related field (ERF) patterns differed significantly between women and men, although the mean recognition performances did not. Differences were due to different strengths of activation as well as due to the involvement of different neural structures as underlined with statistical analysis. We interpret that our physiological findings demonstrate that different mental strategies are used for correct word recognition in the brains of women and men as assessed with magnetoencephalography (MEG). Our data might be linked to previous findings about the hemispheric asymmetry in male subjects (left lateralized) compared to women in whom both hemispheres seem to be equally involved in word processing.

Adult↗
PubMed2001

Neuromagnetic activity in alpha and beta bands reflect learning-induced increases in coordinative stability.

OBJECTIVE: To investigate how learning induced increases in stability on a syncopation task are manifest in the dynamics of cortical activity. METHOD: Magnetoencephalography was recorded from 143 sensors (CTF Systems, Inc). A pre-training procedure determined the critical frequency (F(c)) for each subject (n=4). Subjects either syncopated or synchronized to a metronome that increased in frequency from 1.2 to 3.0 Hz in 0.2 Hz steps. The F(c) was the point at which subjects spontaneously switched from syncopation to synchronization. Subjects then underwent 100 training trials (with feedback) at F(c). Following the learning phase the pre-training procedure was repeated. RESULTS: An increase in the F(c) occurred indicating that practice improved the stability of syncopation. The transition delay was also observed in the phase of the time-averaged signal in sensors over the contralateral sensorimotor area and in power analysis in the 8-12 Hz and 18-24 Hz frequency bands. Initially, reduced power was observed bilaterally during syncopation compared to synchronization. Following training, these differences were reduced or eliminated. CONCLUSION: Pre-training power differences can be explained by the greater difficulty of the syncopation task. The reduction in power differences following training suggests that at the cortical level, syncopation became more similar to synchronization possibly reflecting a decrease in task and/or attention demands.

Acoustic Stimulation↗
PubMed2000

Improvement of presurgical patient evaluation by generation of functional magnetic resonance risk maps.

Recent functional magnetic resonance imaging (FMRI) replication studies show a high variability of active voxels within subjects and across runs - a potentially harmful situation for clinical applications. We tried to reduce these uncertainties inherent in current presurgical FMRI. For this, a new high quality head fixation device was used to detect reliably activated voxels over repeated measurements. In addition high correlation thresholds were applied to define the areas with highest probability of activation. The results show a focussing of such functional high risk areas to only a few voxels which localized close to intraoperative cortical stimulation. The generation of such FMRI risk maps may improve validity of clinical localization and facilitate the development of currently missing standards for maximized but still safe tumor resection.

Adult↗
PubMed2000

Reduced activation of midline frontal areas in human elderly subjects: a contingent negative variation study.

Contingent negative variation (CNV) was recorded from electrodes F7, F3, Fz, F4, F8, T7, C3, Cz, C4, T8, P7, P3, Pz, P4 and P8 in 19 young (mean age: 23 years) and 15 elderly (mean age: 66 years) healthy right-handed subjects, using a S2-choice paradigm. Young subjects showed early peak negativity shortly after the warning stimulus over mid-frontal areas, whereas for the remaining electrodes the negativity increased continuously. The amplitude of the early CNV was selectively reduced in elderly subjects over midline but not lateral frontal areas. We conclude that the activation of frontal midline areas as pre-supplementary motor area or anterior cingulate might be impaired in higher age.

Acoustic Stimulation↗
PubMed2000

[123I]beta-CIT SPECT in multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration.

Differentiation between Parkinson's disease (PD) and other neurodegenerative disorders with parkinsonian features, such as multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD), is difficult on clinical grounds. We studied the pattern of dopaminergic degeneration in 18 patients with probable MSA, 8 patients with PSP, 4 patients with CBD, 48 patients with PD and a similar degree of disability, and 14 control subjects performing single photon emission computed tomography (SPECT) 20 hours after injection of [123I]beta-CIT. Overall striatal binding was significantly reduced in MSA (-51% of normal mean), PSP (-60%), CBD (-35%), and PD (-58%), without overlap with control values. Asymmetry of striatal beta-CIT binding was significantly increased in patients with CBD and PD, as compared with control subjects. Although asymmetry seemed to be less pronounced in MSA and PSP than in PD, this was not statistically significant. Putamen-caudate nucleus ratios in patients with PD, MSA, and PSP, but not with CBD, were significantly reduced, as compared with control subjects. In conclusion, [123I]beta-CIT SPECT reliably enables the visualization of the presynaptic dopaminergic lesion in patients with MSA, PSP, and CBD. In most patients, however, it does not seem to be possible to differentiate these disorders from PD with this method.

Adult↗
PubMed2000

Supplementary motor area activation preceding voluntary movement is detectable with a whole-scalp magnetoencephalography system.

Despite the fact that the knowledge about the structure and the function of the supplementary motor area (SMA) is steadily increasing, the role of the SMA in the human brain, e.g., the contribution of the SMA to the Bereitschaftspotential, still remains unclear and controversial. The goal of this study was to contribute further to this discussion by taking advantage of the increased spatial information of a whole-scalp magnetoencephalography (MEG) system enabling us to record the magnetic equivalent of the Bereitschaftspotential 1, the Bereitschaftsfeld 1 (BF 1) or readiness field 1. Five subjects performed a complex, and one subject a simple, finger-tapping task. It was possible to record the BF 1 for all subjects. The first appearance of the BF 1 was in the range of -1.9 to -1.7 s prior to movement onset, except for the subject performing the simple task (-1 s). Analysis of the development of the magnetic field distribution and the channel waveforms showed the beginning of the Bereitschaftsfeld 2 (BF 2) or readiness field 2 at about -0.5 s prior to movement onset. In the time range of BF 1, dipole source analysis localized the source in the SMA only, whereas dipole source analysis containing also the time range of BF 2 resulted in dipole models, including dipoles in the primary motor area. In summary, with a whole-head MEG system, it was possible for the first time to detect SMA activity in healthy subjects with MEG.

Adult↗
PubMed2000

Spatiotemporal analysis of neuromagnetic events underlying the emergence of coordinative instabilities.

A full-head 143-channel superconducting quantum interference device was used to study changes occurring in the magnetic activity of the human brain during performance of an auditory-motor coordination task in which the rate of coordination was systematically increased. Previous research using the same task paradigm demonstrated that spontaneous switches in timing behavior that arise with higher coordination rates are accompanied by qualitative changes in spatiotemporal brain activity measured by electro- and magnetoencephalography. Here we show how these patterns can be decomposed into basic physiological events, i.e., evoked brain responses to acoustic tones and self-initiated finger movements. The frequency dependence of the amplitudes of these component responses may shed new light onto why spontaneous timing transitions occur in the first place.

Evoked Potentials, Auditory↗
PubMed2000

High resolution DC-EEG mapping of the Bereitschaftspotential preceding simple or complex bimanual sequential finger movement.

The present set of experiments investigated the Bereitschaftspotential (BP) preceding voluntary bimanual sequential simple (task 1) and complex movements (task 2) in supplementary/cingulate and primary motor areas (SCMA, MIs) using 64-channel direct current electroencephalography analysis in 16 right-handed healthy subjects. The results showed that: (1) onset times of BPs preceding the two tasks were significantly earlier at Cz than at C3 and C4, (2) the complex task induced significantly larger amplitudes than the simple task over the SCMA 1.1 s before EMG onset (BPI period), over the SCMA and both MIs for the BP2 period, extending from the SCMA and MIs to all frontocentral, central, centroparietal, and frontal areas during the motor potential period, (3) task difference prior to 0.96 s mainly appeared in the SCMA rather than in either MI, (4) the BP had a significantly larger amplitude in the SCMA than in the MIs, the differences being asymmetric between the left and the right hemisphere motor areas, and (5) the sinks of BP current source density (CSD) preceding the two tasks were found in the frontocentral midline; and the regions and intensities of CSD maps were larger and stronger in task 2 than they were in task I at the same times of the epoch. The results suggested that: (1) the SCMA and MIs participate in bimanual sequential simple or complex movements, (2) the SCMA appears to not only serve as a trigger command for voluntary movement but also seems to design the different motor modes, (3) the amplitude, duration, onset time, CSD region, and intensity of BP all increase with the level of complexity of the movement, (4) the greater the complexity of the action, the earlier the preparation and the larger the extent of activated neuronal populations in the SCMA, (5) activation of the SCMA occurred prior to that of the MI, and (6) the activation suggests an asymmetry between left and right MIs in simultaneous bilateral finger movement, but this asymmetry seems to be less pronounced for complex movements.

Adult↗
PubMed2000

False recognition in a verbal memory task: an event-related potential study.

Brain potentials were recorded from 15 healthy young subjects during the performance of a word recognition task. During the study phase, subjects had to intentionally memorise a series of words. These words were presented again together with the same number of new words in a following test phase where the instruction was to discriminate between repeated words and new words. We compared event-related potentials (ERPs) evoked by correctly identified repeated words (hits) and ERPs evoked by incorrectly classified new words (false alarms). Although both types of words were thought to be repeated the ERPs indicated differences between these two conditions starting at about 450 ms after the stimulus onset. These differences were mostly pronounced over frontal scalp locations but occurred also over parietal scalp locations (false alarms produced significantly more negative going ERPs than hits). We interpret that frontal and parietal brain areas show greater activation during false recognition because of a more intensive search for item representations.

Adult↗
PubMed2000

High resolution spatiotemporal analysis of the contingent negative variation in simple or complex motor tasks and a non-motor task.

OBJECTIVES: Since the characteristics of the Bereitschaftspotential (BP) - voluntary movement paradigm of internally-driven movements - have been established recently by our group using high resolution DC-EEG techniques, it was of great interest to apply similar techniques to the other slow brain potential--contingent negative variation (CNV) of externally-cued movements--with the same motor tasks using the same subjects. METHODS: The CNV for simple bimanual sequential movements (task 1), complex bimanual sequential movements (task 2) and a non-motor condition (task 3) was recorded on the scalp using a 64 channel DC-EEG in 16 healthy subjects, and the data were analyzed with high resolution spatiotemporal statistics and current source density (CSD). RESULTS: (1) The CNV was distributed over frontal, frontocentral, central and centroparietal regions; a negative potential was found at the frontal pole and a positive potential was found over occipital regions. (2) CNV amplitudes were higher for task 2 than for task 1, and there was no late CNV for task 3. (3) A high resolution spatiotemporal analysis revealed that during the early CNV component, statistical differences existed between the motor tasks (tasks 1 and 2) and the non-motor task (task 3), which occurred at frontocentral, central, centroparietal, parietal and parieto-occipital regions. During the late CNV component, additional significant differences were found not only between the motor tasks and the non-motor task but also between motor task 1 and task 2 at frontocentral, central and centroparietal regions. (4) Comparison of the CNV between the frontomesial cortex (situated over the supplementary/cingulate areas, SCMA) and both lateral pre-central areas (situated over the primary motor areas, MIs) showed that there was no statistically significant difference between the two cortical motor areas except for the early CNV. (5) Comparison of the CNV between the 3 tasks over the cortical motor areas showed that there were significant differences between the motor tasks and the non-motor task regarding the auditory evoked potential (AEP) and the early CNV component, and between all 3 tasks in the late CNV, the visual evoked potential (VEP(2)) and the N-P component. (6) The ranges and the densities of the CSD maps were larger and higher for complex than for simple tasks. The current sinks of the AEP and the early CNV were located at Fz, the late CNV at FCz and surrounding regions. As to be expected, current sources of the VEPs were located at the occipital lobes. The CNV was a current sink (negative) except for the VEP's main component which was a current source (positive). CONCLUSIONS: (1) The CNV topography over the scalp varied with the complexity of motor tasks and between motor and non-motor conditions. (2) The origin of the early CNV may rest in the frontal lobes, while the late CNV may stem from more extensive cortical areas including SCMA, MIs, etc. (3) The late CNV component is not identical with the BP.

Adult↗
PubMed2000

Neuromagnetic recordings in temporal lobe epilepsy.

The introduction of whole-head magnetoencephalography (MEG) systems facilitating simultaneous recording from the entire brain surface has established MEG as a clinically feasible method for the evaluation of patients with temporal lobe epilepsy (TLE). In mesial TLE, two types of MEG spike dipoles could be identified: an anterior vertical and an anterior horizontal dipole. Dipole orientations can be used to attribute spike activity to temporal lobe subcompartments. Whereas the anterior vertical dipole is compatible with epileptic activity in the mediobasal temporal lobe, the anterior horizontal dipole can be explained by epileptic activity of the temporal tip cortex. In nonlesional TLE, medial and lateral vertical dipoles were found which could distinguish between medial and lateral temporal seizure onset zones as evidenced from invasive recordings. In lesional TLE, MEG could clarify the spatial relationship of the structural lesion to the irritative zone. Evaluation of patients with persistent seizures after epilepsy surgery may represent another clinical important application of MEG because magnetic fields are less influenced than electric fields by the prior operation. Simultaneous MEG and invasive EEG recordings indicate that epileptic activity restricted to mesial temporal structures cannot reliably be detected on MEG and that an extended cortical area of at least 6 to 8 cm2 involving also the basal temporal lobe is necessary to produce a reproducible MEG signal. In lateral neocortical TLE MEG seems to be more sensitive than scalp-EEG which further underlines the potential role of MEG for the study of nonlesional TLE. Whole-head MEG therefore can be regarded as a valuable and clinically relevant noninvasive method for the evaluation of patients with TLE.

Atrophy↗
PubMed2000

Magnetoencephalography in focal epilepsy.

The introduction of whole-head magnetoencephalographic (MEG) systems facilitating simultaneous recording from the entire brain surface has led to a major breakthrough in the MEG evaluation of epilepsy patients. MEG localizations estimates of the interictal spike zone showed excellent agreement with invasive electrical recordings and were useful to clarify the spatial relationship of the irritative zone and structural lesions. MEG appears to be especially useful for study of patients with neocortical epilepsy, and helped to guide the placement of subdural grid electrodes in patients with nonlesional epilepsies. MEG could differentiate between patients with mesial and lateral temporal seizure onset. Spike propagation in the temporal lobe and the spatio-temporal organization of the interictal spike complex could be studied noninvasively. MEG was useful to delineate essential brain regions before surgical procedures adjacent to the central fissure. MEG appears to be more sensitive than scalp EEG for detection of epileptic discharges arising from the lateral neocortex, whereas only highly synchronized discharges arising from mesial temporal structures could be recorded. A major limitation of MEG has been the recording of seizures because long-term recordings cannot be performed on a routine basis with the available technology. Because MEG and EEG yield both complementary and confirmatory information, combined MEG-EEG recordings in conjunction with advanced source modeling techniques should improve the noninvasive evaluation of epilepsy patients and further reduce the need for invasive procedures.

Brain Mapping↗
PubMed2000

Electrophysiological, neuropsychological and clinical findings in multiple sclerosis patients receiving interferon beta-1b: a 1-year follow-up.

We assessed serial event-related potentials (ERPs) as well as neuropsychological and clinical test findings in a group of multiple sclerosis (MS) patients (n = 14) treated with interferon beta-1b (INF-beta-1b) compared to normal controls (n = 14). All investigations were done within 1 week before INF-beta-1b therapy was started and 12 months later. An auditory oddball paradigm was employed. No significant differences in the N100, P200, N200 or P300 latencies between patients and control group were found, but 3 out of 14 MS patients developed abnormal P300 latencies (more than 2 standard errors from the mean) after 1 year of INF-beta-1b therapy. This was not reflected by the respective neurological impairment as assessed by the Expanded Disability Status Scale score. ERPs might be a useful tool in clinical studies in order to evaluate drug effects on cognition, but for a final statement, the analysis of ERPs in a larger group of patients is required.

Adjuvants, Immunologic↗
PubMed2000

Modulation of spatial orientation processing by mental imagery instructions: a MEG study of representational momentum.

Under appropriate conditions, an observer's memory for the final position of an abruptly halted moving object is distorted in the direction of the represented motion. This phenomenon is called "representational momentum" (RM). We examined the effect of mental imagery instructions on the modulation of spatial orientation processing by testing for RM under conditions of picture versus body rotation perception and imagination. Behavioral data were gathered via classical reaction time and error measurements, whereas brain activity was recorded with the help of magnetoencephalography (MEG). Due to the so-called inverse problem and to signal complexity, results were described at the signal level rather than with the source location modeling. Brain magnetic field strength and spatial distribution, as well as latency of P200m evoked fields were used as neurocognitive markers. A task was devised where a subject examined a rotating sea horizon as seen from a virtual boat in order to extrapolate either the picture motion or the body motion relative to the picture while the latter disappeared temporarily until a test-view was displayed as a final orientation candidate. Results suggest that perceptual interpretation and extrapolation of visual motion in the roll plane capitalize on the fronto-parietal cortical networks involving working memory processes. Extrapolation of the rotational dynamics of sea horizon revealed a RM effect simulating the role of gravity in rotational equilibrium. Modulation of the P200m component reflected spatial orientation processing and a non-voluntary detection of an incongruity between displayed and expected final orientations given the implied motion. Neuromagnetic properties of anticipatory (Contingent Magnetic Variation) and evoked (P200m) brain magnetic fields suggest, respectively, differential allocation of attentional resources by mental imagery instructions (picture vs. body tilt), and a communality of neural structures (in the right centro-parietal region) for the control of both RM and mental rotation processes. Finally, the RM of the body motion is less prone to forward shifts than that of picture motion evidencing an internalization of the implied mass of the virtual body of the observer.

Adult↗
PubMed2000

The relation between erythrocyte volume and folate levels is influenced by a common mutation in the methylenetetrahydrofolate reductase (MTHFR) gene (C677T).

BACKGROUND: The enzyme 5,10 methylenetetrahydrofolate reductase (MTHFR) plays an important role in folate metabolism and folate-dependent reactions. Homozygosity for a common polymorphism in the MTHFR gene (C677T, Ala to Val) is associated with an increased risk of neural tube defects and hyperhomocysteinemia in individuals with low folate levels. Homozygous carriers of the polymorphism with adequate folate levels, on the other hand, seem to be at lower risk for colorectal cancer. Homozygous carriers of the polymorphism (5-15% of the white population) probably represent a subpopulation with increased folate needs. Hematological sequelae of folate deficiency have been recognized for a long time. However, no data exist concerning the relation between the C677T MTHFR polymorphism, folate levels, and hematological parameters. METHODS: We investigated associations between the C677T MTHFR polymorphism, folate levels, total plasma homocysteine, and hematological parameters in 94 patients with cerebrovascular disease (transient ischemic attack/minor stroke) and in 82 healthy subjects. RESULTS: Homozygous carriers (VV) of the polymorphism with low folate levels showed significantly higher homocysteine levels than mutation-negative (AA) and heterozygous (AV) subjects (P = 0.038). Furthermore, VV subjects in the lowest folate quartile exhibited significantly higher mean erythrocyte volumes (MCV) and a tendency towards higher erythrocyte hemoglobin content (MCH) than AA and AV subjects (P = 0.008 and 0.069, respectively). Although MCV was not influenced by folate levels in AA and AV subjects, in VV subjects a significant inverse correlation with folate levels could be demonstrated (P = 0.544 and 0.020, respectively). CONCLUSION: We demonstrate an association between the C677T polymorphism, folate levels, and hematological parameters. The elevation of MCV in homozygous carriers of the polymorphism with low folate levels indicates impaired DNA synthesis and/or methylation in these subjects. Considering our data and the results of previous studies, the polymorphism may have contrary effects on homocysteine metabolism and DNA synthesis/methylation dependent on a subject's folate supply. Although the polymorphism is disadvantageous in homozygous carriers with low folate levels, its presence may be beneficial in individuals with adequate folate supply.

Adult↗