Biomedical subjects

Gerald Lindinger

Publications and source records attributed to Gerald Lindinger.

7 recordsLinked to original sources

PubMed2005

Combined MEG/EEG analysis of the interictal spike complex in mesial temporal lobe epilepsy.

We studied the functional organization of the interictal spike complex in 30 patients with mesial temporal lobe epilepsy (MTLE) using combined magnetoencephalography (MEG)/electroencephalography (EEG) recordings. Spikes could be recorded in 14 patients (47%) during the 2- to 3-h MEG/EEG recording session. The MEG and EEG spikes were subjected to separate dipole analyses; the MEG spike dipole localizations were superimposed on MRI scans. All spike dipoles could be localized to the temporal lobe with a clear preponderance in the medial region. Based on dipole orientations in MEG, patients could be classified into two groups: patients with anterior medial vertical (AMV) dipoles, suggesting epileptic activity in the mediobasal temporal lobe and patients with anterior medial horizontal (AMH) dipoles, indicating involvement of the temporal pole and the anterior parts of the lateral temporal lobe. Whereas patients with AMV dipoles had strictly unitemporal interictal and ictal EEG changes during prolonged video-EEG monitoring, 50% of patients with AMH dipoles showed evidence of bitemporal affection on interictal and ictal EEG. Nine patients underwent epilepsy surgery so far. Whereas all five patients with AMV dipoles became completely seizure-free postoperatively (Class Ia), two out of four patients with AMH dipoles experienced persistent auras (Class Ib). This difference, however, was not statistically significant. We therefore conclude that combined MEG/EEG dipole modeling can identify subcompartments of the temporal lobe involved in epileptic activity and may be helpful to differentiate between subtypes of mesial temporal lobe epilepsy noninvasively.

Adult↗

PubMed2004

Fatigue in a simple repetitive motor task: a combined electrophysiological and neuropsychological study.

Fatigue is one of the most common psychophysiological symptoms that interact with the control mechanisms regulating task behaviour. The cortical processes involved in preparation and feedback control of voluntary movement are associated with EEG activity time-locked to movement onset: a pre-movement Movement-Related Cortical Potential (MRCP) is followed by a post-movement potential (PMP). The aim of this study was to determine whether changes in subjective fatigue which arise in the course of a simple repetitive motor task affect cortical information processing as measured by MRCPs or PMPs. MRCPs/PMPs were recorded in 33 healthy subjects while they made 100 self-paced unilateral button presses with their left or right index finger, and then continued with the other index finger for another 100 movements. Before and after the motor tasks, subjective fatigue was assessed via questionnaire. (1) Subjects who reported a higher increase of fatigue when they had finished the motor tasks showed smaller (more negative) amplitudes of the PMP. (2) This increase of negativity was strongest during the initial part of the tasks. (3) Physical aspects of perceived fatigue had a stronger effect on PMP amplitude than cognitive aspects. Smaller amplitudes of the PMP in more fatigued subjects might be explained by reduced attention to somatosensory feedback. Adaptation of this effect may result from more automatic performance at later stages of the task when all subjects required a lower degree of attentional control. In conjunction with previous studies, effects of fatigue could be separated from habituation.

Attention↗

PubMed2004

Habituation in a simple repetitive motor task: a study with movement-related cortical potentials.

OBJECTIVE: The movement-related cortical potential (MRCP) attenuates over the right hemisphere during the performance of a complex motor sequence. Because subjects have to learn complex sequences, earlier research has attributed this decrease of negativity to motor learning. The aims of this study were (1) to examine whether such an attenuation also occurs in the course of a repetitive motor task so simple that learning is not required, and (2) whether there are any transfer effects when subjects change from one to the other hand. METHODS: MRCPs were recorded in 33 right-handed healthy subjects. In a counterbalanced crossover design, subjects made 100 self-paced unilateral button presses with their left or right index finger, and then continued on the other side of the body for another 100 movements. Tasks were performed with the same speed during the entire experiment. RESULTS: (1) The amplitude of the MRCP attenuated over the right hemisphere in the course of the tasks irrespective of the side of movement. (2) The amplitude of the MRCP decreased across the entire scalp until a minimum level was reached at the end of the earlier sequence, and then increased slightly from this low level during the following sequence made after a switch of hand. CONCLUSIONS: The right hemisphere may predominate motor activation or attentional demands directed towards movement execution or somatosensory inputs even in very simple motor tasks. The decrease and subsequent increase of negativity during the first and second sequence, respectively, may reflect the subjects' changing arousal.

Adult↗

PubMed2003

Olfaction and depth of word processing: a magnetoencephalographic study.

Using a whole-cortex magnetoencephalograph, magnetic field changes were recorded to describe brain activities related to simultaneous visual and olfactory processing and to detect odor-related influences on verbal information processing. Words had to be either shallowly (nonsemantic) or deeply (semantic) encoded by healthy young subjects, each of these tasks under two different kinds of olfactory stimulation. After each encoding phase, word recognition performance was tested. First, the odor was randomly associated with some of the study words (simultaneous stimulation; same duration as for words) for both depths of word processing conditions, and second, continuous olfactory stimulation (permanent stimulation) was provided during the whole study phases of both depths of word processing conditions. The statistical analysis of the physiological data revealed evidence of a specific odor-induced effect depending on depth of word processing and kind of olfactory stimulation. Brain activity between about 250 and 450 ms as well as between about 650 and 1000 ms after stimulus onset was found to vary as a function of odor delivery and depth of word processing. In addition, a significant effect of odor stimulation on subsequent word recognition performance occurred in case of simultaneous odor stimulation and semantic word encoding. It is interpreted that in this case, word recognition performance significantly decreased because of the presence of the odor during prior word encoding. Such a behavioral effect was missing in all other conditions. The present psychological and physiological findings support the idea that semantic word encoding is specifically affected by simultaneous olfactory information processing. It is concluded that this phenomenon is due to a competition with cortical regions related to language and olfactory information processing, as suggested by T. S. Lorig (1999, Neurosci. Biobehav. Rev. 23, 391-398).

Adult↗

PubMed2003

Olfaction and face encoding in humans: a magnetoencephalographic study.

Magnetic field changes were recorded while 20 healthy young participants performed a deep face encoding task. Some of the faces were randomly associated with a simultaneously presented odor. A recognition test, during which all faces were presented again together with the same number of new faces, followed. The task was to discriminate between repeated and new faces. During the recognition test no odor was presented. The recognition performance was significantly influenced by the simultaneously associated odor during the encoding phase. Faces associated with odor were less accurately recognized. In addition, we found significant physiological differences between 'encoded faces without odor' and 'encoded faces with odor'. In particular, two effects occurred. Between about 200 and 300 ms after stimulus onset 'encoded faces without odor' evoked higher brain activity than 'encoded faces with odor'. Between about 600 and 900 ms after stimulus onset 'encoded faces with odor' evoked higher brain activity than 'encoded faces without odor'. Whereas the latter effect is interpreted as reflecting conscious olfactory information processing, the earlier effect is suggested to reflect an odor influence on face encoding. We suggest that the simultaneous odor association distracted face encoding resulting in a significantly reduced recognition performance. These findings are suggested to represent evidence of multimodal sensoric interactions between visual face processing and olfactory information.

Adult↗

PubMed2002

Magnetoencephalography in presurgical epilepsy evaluation.

The introduction of whole-head magnetoencephalography (MEG) systems facilitating simultaneous recording from the entire brain surface has led to a major breakthrough of MEG in presurgical epilepsy evaluation. Localizations of the interictal spike zone with MEG showed excellent agreement with invasive electrical recordings, were useful to clarify the spatial relationship of the irritative spike zone to structural lesions, and could attribute epileptic activity to lobar subcompartments both in temporal lobe and extratemporal epilepsy. MEG was especially useful for the study of patients with non-lesional neocortical epilepsy and of patients with large lesions, where it provided unique information on the epileptogenic zone. It could reliably localize sensorimotor cortex prior to surgical procedures adjacent to central fissure. MEG language mapping yielded concordant results with the Wada test and cortical stimulation studies. MEG localizations of epileptic activity and essential brain regions were successfully integrated into frameless stereotaxy systems providing accurate functional information intraoperatively. Because MEG and EEG yield both complementary and confirmatory information, combined MEG-EEG recordings in conjunction with advanced source modeling techniques will further improve the noninvasive evaluation of epilepsy patients and constantly reduce the need for invasive procedures.

Brain↗

PubMed2002

Evidence of conscious and subconscious olfactory information processing during word encoding: a magnetoencephalographic (MEG) study.

The present study was meant to distinguish between unconscious and conscious olfactory information processing and to investigate the influence of olfaction on word information processing. Magnetic field changes were recorded in healthy young participants during deep encoding of visually presented words whereby some of the words were randomly associated with an odor. All recorded data were then split into two groups. One group consisted of participants who did not consciously perceive the odor during the whole experiment whereas the other group did report continuous conscious odor perception. The magnetic field changes related to the condition 'words without odor' were subtracted from the magnetic field changes related to the condition 'words with odor' for both groups. First, an odor-induced effect occurred between about 200 and 500 ms after stimulus onset which was similar in both groups. It is interpreted to reflect an activity reduction during word encoding related to the additional olfactory stimulation. Second, a later effect occurred between about 600 and 900 ms after stimulus onset which differed between the two groups. This effect was due to higher brain activity related to the additional olfactory stimulation. It was more pronounced in the group consisting of participants who consciously perceived the odor during the whole experiment as compared to the other group. These results are interpreted as evidence that the later effect is related to conscious odor perception whereas the earlier effect reflects unconscious olfactory information processing. Furthermore, our study provides evidence that only the conscious perception of an odor which is simultaneously presented to the visual presentation of a word reduces its chance to be subsequently recognized.

Adult↗