PubMed Health⌕ Search

Biomedical subjects

M Seeck

Publications and source records attributed to M Seeck.

53 records · Page 3Linked to original sources
PubMed1999

Left temporal rhythmic electrical activity: a correlate for psychosis? A case report.

It is well recognized that epileptic patients are at higher risk for acute or chronic psychotic states than non-epileptic subjects. Here we present intracranial depth electrode recordings during a psychotic episode in a 20-year-old woman who was referred for presurgical evaluation. Unrelated to her seizures, she presented acoustic hallucinations and delusions and became agitated for a duration of 18-24 hours. During this period, a new unusual pattern of sharp slow waves was seen semi-rhythmically every 2-3 sec from left anterior neocortical temporal areas. Her condition responded well to a treatment with Haloperidol, but not with Benzodiazepines. Ictal and interictal scalp- and depth-EEG recordings outside the psychotic episode as well as MRI-based volumetry, PET, SPECT and neuropsychological testing gave evidence of bilateral temporal and frontal dysfunction. This case report suggests that psychosis in epileptic patients may be based on a bilateral cerebral dysfunction linked together in a pathological network, but with a focal (here: left temporal) driving mechanism.

Adult↗
PubMed1999

Semantically-triggered reading epilepsy: an experimental case study.

Primary reading epilepsy (PRE) is a rare syndrome in which epileptic seizures are electively provoked by reading. Cognitive neuropsychology has demonstrated the existence of at least two pathways for reading, the sublexical pathway involved in converting graphemes to phonemes, and the lexical pathway used when meaning is conveyed. Which of these specific pathways is relevant in triggering epileptic discharges remains largely unknown. We report the case of a patient suffering from PRE in which the two routes were distinguished on the basis of the reading material employed. Significantly less epileptic discharges were observed when the patient read non-words than words. In view of our findings, we tentatively contrast a lexical form of PRE, triggered by the activation of semantic knowledge structures, with a sublexical form, triggered by non-word reading. Evidence from the literature suggests that the former is characterized by bilateral EEG activating patterns, whereas the latter involves preferentially the left hemisphere.

Electroencephalography↗
PubMed1999

Frequency domain EEG source localization of ictal epileptiform activity in patients with partial complex epilepsy of temporal lobe origin.

The aim of this study was to investigate whether EEG source localization in the frequency domain, using the FFT dipole approximation (Lehmann, D. and Michel, C.M. Electroenceph. clin. Neurophysiol., 1990, 76: 271-276), would be useful for quantifying the frequency content of epileptic seizure activity. Between one and 7 extracranially recorded seizures were analyzed in each of 7 patients with mesolimbic epilepsy, who were seizure-free after temporal lobe resection. The full scalp frequency spectrum for the first 4 s after seizure onset, as well as for subsequent periods, was determined. Power peaks in the spectra were identified, and an instant dipole fit was performed for the frequencies corresponding to these peaks. Ictal frequencies, ranging between 3.5 and 8.5 Hz, showed a variable degree of stability over time in the different patients. For a particular frequency, dipole results were similar during the different phases of seizure development. In patients with more than one prominent frequency, dipole results for the different frequencies were similar. Dipole results were also similar between patients. We conclude that dipole localization of dominant frequencies, as obtained from full scalp FFT analysis, gives quite reproducible results for seizures originating in the mesial temporal area. The method may become a useful tool for the pre-surgical identification of patients with mesolimbic epilepsy.

Adult↗
PubMed1999

Spatiotemporal EEG analysis and distributed source estimation in presurgical epilepsy evaluation.

In the attempts to localize electric sources in the brain on the basis of multichannel EEG and/or MEG measurements, distributed source estimation procedures have become of increasing interest. Several commercial software packages offer such localization programs and results using these methods are seen more and more frequently in the literature. It is crucial that the users understand the similarities and differences of these methods and that they become aware of the advantages and limitations that are inherent to each approach. This review provides this information from a theoretical as well as from a practical point of view. The theoretical part gives the algorithmic basis of the electromagnetic inverse problem and shows how the different a priori assumptions are formally integrated in these equations. The authors restrict this formalism to the linear inverse solutions i.e., those solutions in which the inversion procedure can be represented as a matrix applied to the data. It will be shown that their properties can be best characterized by their resolution kernels and that methods with optimal resolution matrices can be designed. The authors also discuss the important problem of regularization strategies that are used to minimize the influence of noise. Finally, a new kind of inverse solution, termed ELECTRA (for ELECTRical Analysis), is presented that is based on constraining the source model on the basis of the currents that can actually be measured by the scalp recorded EEG. The practical part of the review illustrates the localization procedures with different clinical data sets. Three aspects become important when working with real data: 1) Clinical data is usually far from ideal (limited number of electrodes, noise, etc.). The behavior of inverse procedures in such unfortunate situations has to be evaluated. 2) The selection of the time points or time periods of interest is crucial, especially in the analysis of spontaneous EEG. 3) Additional information coming from other modalities is usually available and can be incorporated. The authors are illustrating these important points in the case of interictal and ictal epileptiform activity. Spike averaging, frequency domain source localization, and temporal segmentation based on electric field topographies will be discussed. Finally, the technique of EEG-triggered functional magnetic resonance imaging (fMRI) will be illustrated, where EEG is recorded in the magnet and is used to synchronize fMRI acquisition with interictal events. The analysis of both functional data, i.e. the EEG in terms of three-dimensional source localization and the EEG-triggered fMRI, combines the advantages of the two techniques: the temporal resolution of the EEG and the spatial resolution of the fMRI.

Adult↗
PubMed1999

Psychosocial functioning in chronic epilepsy: relation to hippocampal volume and histopathological findings.

MRI volumetric measurements of the ipsi- and contralateral hippocampal volume (HV) were performed in a group of 37 patients with lesional and non-lesional temporal (TLE), and extratemporal lobe (ETLE) lobe epilepsy. Twenty-six patients underwent surgery and the resected tissues subjected to histopathological examination. Psychosocial scores were calculated on the basis of employment, partnership/family status and presence of a positive psychiatric history. Poorest values were obtained for the group with right lesional and non-lesional TLE (RTLE, p < 0.001). In this group, significant positive correlations between psychosocial functioning and the left hippocampal volume or age of onset were observed. We found that the left hippocampal volume in RTLE was smaller with increasing epilepsy duration. We conclude that patients with RTLE represent a particular group with regard to the structural and psychosocial consequences of chronic epilepsy. With regard to histopathological analysis, no particular type of lesion was identified as the major determinant of the results described above.

Adult↗
PubMed1998

Non-invasive epileptic focus localization using EEG-triggered functional MRI and electromagnetic tomography.

We present a new approach for non-invasive localization of focal epileptogenic discharges in patients considered for surgical treatment. EEG-triggered functional MR imaging (fMRI) and 3D EEG source localization were combined to map the primary electrical source with high spatial resolution. The method is illustrated by the case of a patient with medically intractable frontal lobe epilepsy. EEG obtained in the MRI system allowed triggering of the fMRI acquisition by the patient's habitual epileptogenic discharges. fMRI revealed multiple areas of signal enhancement. Three-dimensional EEG source localization identified the same active areas and provided evidence of onset in the left frontal lobe. Subsequent electrocorticography from subdural electrodes confirmed spike and seizure onset over this region. This approach, i.e. the combination of EEG-triggered fMRI and 3D EEG source analysis, represents a promising additional tool for presurgical epilepsy evaluation allowing precise non-invasive identification of the epileptic foci.

Adolescent↗
PubMed1998

Childhood epilepsy with neuropsychological regression and continuous spike waves during sleep: epilepsy surgery in a young adult.

We describe the case of a man with a history of complex partial seizures and severe language, cognitive and behavioural regression during early childhood (3.5 years), who underwent epilepsy surgery at the age of 25 years. His early epilepsy had clinical and electroencephalogram features of the syndromes of epilepsy with continuous spike waves during sleep and acquired epileptic aphasia (Landau-Kleffner syndrome), which we considered initially to be of idiopathic origin. Seizures recurred at 19 years and presurgical investigations at 25 years showed a lateral frontal epileptic focus with spread to Broca's area and the frontal orbital regions. Histopathology revealed a focal cortical dysplasia, not visible on magnetic resonance imaging. The prolonged but reversible early regression and the residual neuropsychological disorders during adulthood were probably the result of an active left frontal epilepsy, which interfered with language and behaviour during development. Our findings raise the question of the role of focal cortical dysplasia as an aetiology in the syndromes of epilepsy with continuous spike waves during sleep and acquired epileptic aphasia.

Adult↗
PubMed1998

Comprehensive postictal neuropsychology improves focus localization in epilepsy.

In recent years, new techniques such as single photon emission computed tomography (SPECT), positron emission tomography (PET) and magnetic resonance imaging (MRI) have been used to improve the localization of epileptic foci during the noninvasive evaluation procedure for epilepsy surgery. Since ictal/or immediate postictal SPECT studies were shown to localize epileptic foci better than interictal SPECT, we addressed the question of whether immediate postictal neuropsychological examination would show the same effect. Neuropsychological examinations were carried out postictally and interictally using a broad range of tests. Postictal results were analyzed with regard to lateralizing and localizing information about the epileptogenic region. Seventeen patients suffering from temporal and extratemporal pharmacoresistant epilepsy were investigated postictally with a subset of tests used for the interictal neuropsychological examination. A significant improvement in focus localization was seen in comparison with interictal neuropsychology (p = 0.014). We conclude that neuropsychology can yield lateralizing and sometimes localizing information, even for extratemporal foci, if carried out during the postictal period and based on a global analysis of the clinical neuropsychological picture.

Adolescent↗
PubMed1998

Ictal agraphia: a patient study.

We present a case of "pure" or "apraxic" agraphia, a recognized writing disturbance, caused by intermittent focal seizures from the left posterior parasagittal parieto-occipital region. Pure agraphia has been described in focal lesions or as part of a generalized confusional syndrome. The posterior cerebral vascular territory is the characteristic site for the transient neurologic syndromes associated with cyclosporine toxicity. Our patient was at risk for this complication while recovering from a lung transplant, with elevated cyclosporine levels.

Agraphia↗
PubMed1997

Evidence for rapid face recognition from human scalp and intracranial electrodes.

It is still generally believed that complex visual analysis is not carried out within the first 100 ms. Here we show that intra- and extracranial visual evoked potentials (VEPs) differentiate previously seen faces from novel faces as early as 50 ms after stimulus onset. EEG was recorded from scalp electrodes in 12 male healthy volunteers (group I) and intracranially from implanted depth electrodes in the temporal and frontal cortex of seven epilepsy patients (group II). Both groups were engaged in a face recognition task. All subjects showed significant differential responses which occurred very early (50-90 ms) and later (190-600 ms). In group II, the early responses were recorded more frequently in the right hemisphere, whereas the late differential VEPs were found in both hemispheres. Both types of VEPs were more frequent in the temporal neocortex, underlining its role as a major contributor to these fast recognition processes.

Adult↗
PubMed1997

Extracranial localization of intracranial interictal epileptiform activity using LORETA (low resolution electromagnetic tomography).

Besides the standard clinical methods of EEG waveshape analysis, mathematical models for reconstruction of dipolar sources from the digitized surface EEG have been introduced in epilepsy research. Although useful for localizing focal sources, these methods are inadequate for analyzing widespread epileptiform activity. A recently introduced alternative method called LORETA (low resolution electromagnetic tomography, Pascual-Marqui et al., 1994), directly computes the current distribution throughout the full brain volume, assuming that neighboring neuronal populations are simultaneously and synchronously activated. In mathematical terms the method selects the smoothest of all possible 3-dimensional current distributions, inherently introducing a certain amount of dispersion. In 7 patients, undergoing simultaneous EEG recording from 10 intracranial (subdural) and 22 extracranial electrodes, 111 subdural discharges (61 subtemporal and 50 lateral temporal) were identified. The exact time point of maximal intracranial activity was automatically identified, and the LORETA solution at that timepoint was computed from the surface EEG. Statistical comparison revealed significantly higher LORETA current density in the area corresponding to the subdurally recorded spike compared to other areas, and a more anterior and more medial LORETA location for subtemporal compared to lateral temporal spikes. This study indicates that the LORETA technique may become a useful method to localize electrical activity in the brain.

Adolescent↗
PubMed1997

Neurophysiologic correlates of implicit face memory in intracranial visual evoked potentials.

Visual evoked potentials were recorded in the amygdala, hippocampus, mid- and inferotemporal cortex, orbitofrontal cortex, and lateral frontal cortex of seven epileptic patients while they were engaged in a difficult task requiring the discrimination between repeated and nonrepeated faces. The explicit recognition of previously seen faces was at chance levels, as measured by the accuracy of push-button responses. Nevertheless, all subjects showed clear-cut differential evoked responses to repeated versus nonrepeated faces, indicating implicit encoding of the distinction between the two types of stimuli. Differential responses were more frequent in neocortical recording sites (especially in the mid- and inferotemporal leads) than in limbic recording sites such as the amygdala and hippocampus. The authors conclude that implicit encoding processes are modulated by neocortical visual association areas of the temporal lobes.

Adult↗
PubMed1996

Three- to five-dimensional biomedical multisensor imaging for the assessment of neurological (dys) function.

This report describes techniques and protocols implemented at the Geneva Canton University Hospitals (HUG) for the combination of various biomedical imaging modalities and sensors including electromagnetic tomography, to study, assess, and localize neurological (dys) function. The interest for this combination stems from the broad variety of information brought out by (functional) magnetic resonance imaging, magnetic resonance spectroscopy, computed tomography, single-photon emission tomography, positron emission tomography, and electromagnetic tomography. Combining these data allows morphology, metabolism, and function to be studied simultaneously, the complementary nature of the information from these modalities becoming evident when studying pathologies reflected by metabolic or electrophysiologic dysfunctions. Compared with other current multimodality approaches, the one at the HUG is totally compatible with both clinical and research protocols, and efficiently addresses the multidimensional registration and visualization issues. It also smoothly integrates electrophysiology and related data as fully featured modalities.

Computer Graphics↗
PubMed1995

Selectively distributed processing of visual object recognition in the temporal and frontal lobes of the human brain.

Evoked potentials to visually driven cognitive tasks were recorded through depth electrodes placed bilaterally within the amygdala, hippocampus, midtemporal and inferotemporal cortex, and lateral frontal cortex of 6 epileptic patients. Task-related differential response patterns were used to identify the recording sites engaged by specific aspects of visual encoding. In this group of 6 patients, the amygdala was most frequently engaged in encoding the familiarity of faces; midtemporal and inferotemporal cortex, in encoding perceptual identity and object categorization; and lateral frontal cortex, in holding visual object information in working memory. The two aspects of encoding that most frequently engaged the hippocampal region were related to working memory and object categorization. The processing of complex visual knowledge is thus anatomically distributed but regionally specialized. These experiments also showed that identical input and output parameters can engage different areas of the brain depending on the nature of the instructional set.

Adult↗
PubMed1993

Differential neural activity in the human temporal lobe evoked by faces of family members and friends.

In 6 patients, depth electrodes revealed differential evoked responses to familiar versus novel faces. These differential responses were obtained in the amygdala, hippocampus, and temporal neocortex but not in the dorsolateral frontal or cingulate cortex. The limbic and temporal structures that differentiated novel from familiar faces did not respond differentially to variations in luminance. Limbic structures and temporal cortex thus appear to participate in face recognition and in encoding the familiarity of visual experiences.

Adult↗
PubMed1992

Category-related components in visual evoked potentials: photographs of faces, persons, flowers and tools as stimuli.

One hundred and sixty black-and-white photographs of faces, persons, tools and flowers constituted the four stimulus categories in the first experimental paradigm. In the second paradigm, 160 black-and-white photographs of persons in a neutral (side view), fighting, greeting and "depressed" postures were used. The same nine female and nine male students volunteered as subjects in both paradigms. EEG responses were recorded through the electrodes F3, F4, Cz, Oz, T5 and T6 and referenced to "linked" mastoid electrodes. Individually averaged EPs and grand averages of the EPs for all 18 subjects were computed as well as bipolar responses for selected pairs of electrodes. Category-related components in the evoked potentials (EPs) were found mainly in the recordings through the midline and the frontal electrodes. These category-specific differences were more prominent, however, in the bipolar recordings between these electrodes and the respective ipsilateral electrodes (T5 or T6) than in the monopolar recordings. Monopolar and bipolar EPs could be divided into those evoked by person stimuli and by non-person stimuli. Category-related differences were demonstrated by computing EP-difference curves related to pairs of stimulus categories. In addition to the statistical analysis of peak amplitudes and peak latencies of the individual curves, a "running" Wilcoxon test was applied and cross-correlation functions between the EPs evoked by different stimulus categories were computed. The "face-related" components of the EPs described in earlier studies could be confirmed. They were prominent in the waves peaking between 130 and 150 ms and between 200 and 230 ms and were stronger when faces rather than full-figure "neutral persons" were used as stimuli. No significant hemispheric differences could be found between any of the EPs. In the second paradigm, EEG responses evoked by person stimuli in a neutral, fighting, greeting or depressed posture exhibited only slight differences, if at all. The "person-responsive" components in the EPs evoked by the photographs of a neutral standing person (side view) were smaller between 120 and 200 ms than in the other three categories in which "expressive" persons were the stimuli.

Adult↗