Biomedical subjects

Martin Kurthen

Publications and source records attributed to Martin Kurthen.

At least 19 recordsLinked to original sources

PubMed2006

Habituation of auditory evoked potentials in intracranial and extracranial recordings.

Effects of stimulus repetition are investigated in short-term habituation experiments. In these experiments, trains of stimuli are applied with longer intervals of no stimulation between the trains. In scalp recordings, an amplitude and latency decrease of the auditory N100 is usually observed at the beginning of the train. This contrasts to a recent finding with intracranial recordings, exhibiting an effect on N100 amplitude, but not on its latency. In the current study, P50 and N100 were simultaneously recorded intra- and extracranially in epilepsy patients. The amplitudes of P50 and N100 decreased in both recordings, whereas the P50 latency was not significantly affected. A latency decrease was revealed for the extracranially recorded N100, but not for the intracranial N100. This dissociation between the intracranial and scalp recordings might be explained by a different sensitivity of the two measurements for N100 generators.

Adult↗

PubMed2006

Mesial temporal lobe epilepsy impairs advanced social cognition.

PURPOSE: Although memory, language, and executive functions have been extensively studied in patients with mesial temporal lobe epilepsy (MTLE), investigations into advanced social cognitive abilities have been neglected. In the present study, we investigated the ability to detect social faux pas and studied possible mediating clinical and demographic variables in patients with MTLE compared with patients with an epilepsy not originating within the MTLE and healthy controls. METHODS: The 27 MTLE patients (16 were investigated pre- and 11 postoperatively), 27 patients with an extramesiotemporal epilepsy (except frontal lobe epilepsy), and 12 healthy controls performed a shortened version of the faux-pas test. Additionally, we used standardized tests to measure intelligence. Only patients with intact reading-comprehension abilities were included in the study. RESULTS: MTLE patients, both pre- and postoperative, performed the faux-pas test significantly worse than patients with extramesiotemporal lobe epilepsy and healthy controls. The latter two groups showed comparable performance. No statistical association was found between the MTLE patients' deficit in recognizing a faux pas and the variables IQ, age, age at seizure onset, and duration of epilepsy. CONCLUSIONS: We report for the first time that patients with MTLE are specifically impaired in recognizing faux pas, suggesting that MTLE as such is a specific etiology of deficits in higher-order social cognition.

Adult↗

PubMed2006

Mid-latency auditory-evoked responses and sensory gating in focal epilepsy: a preliminary exploration.

The relationship between epilepsy and psychosis is not well defined. Sensory gating is a possible endophenotype for psychosis, and has not been fully examined in epileptic patients. The authors examined 29 patients with focal epilepsy who were on antiepileptic medications, and 29 age-matched healthy comparison subjects, using a paired-stimulus (S1-S2) paradigm. P50 and N100 amplitudes or gating did not differ between the groups. The P200 was significantly smaller and did not gate as well in epileptic patients. Though alteration of sensory gating can be demonstrated in epileptic patients, it seems to be qualitatively different from alterations reported in association with schizophrenia.

Acoustic Stimulation↗

PubMed2006

Novelty detection and encoding for declarative memory within the human hippocampus.

Intracranial recordings of cognitive potentials within the human hippocampal system have identified N400 potentials in the anterior mesial temporal lobe (AMTL-N400) that correlate with verbal memory performance and are associated with novelty detection. Their amplitudes to "new" but not "old" words in a verbal recognition task correlate with the neuronal density of the hippocampal CA1-region and can be reduced selectively by the NMDA-receptor blocker ketamine. Moreover, it could be shown that NMDA-receptor dependent long-term potentiation (LTP), a form of synaptic plasticity with Hebbian characteristics, can be readily induced in human hippocampal slices but not in patients with hippocampal sclerosis. In these latter patients, we also found a reduction of AMTL-N400 amplitudes similar to the one induced by ketamine. In addition, we could show that hippocampal novelty detection is associated with successful encoding for declarative memory. Together, our findings suggest that successful encoding for declarative memory is at least in part mediated by NMDA-receptor dependent novelty detection within the human hippocampal system.

Animals↗

PubMed2006

Stimulation mapping via implanted grid electrodes prior to surgery for gliomas in highly eloquent cortex.

OBJECTIVE: To evaluate whether preoperative mapping of higher cortical functions with subdural grid electrodes can help to maximize resection in functional areas and avoid permanent injury. METHODS: A consecutive series of 16 patients (female: n = 7, male: n = 9, mean age of 38 yr) with a history of seizures and without focal deficit was reviewed, harboring gliomas located in the dominant hemisphere adjacent to or in the F3 gyrus/Broca area (n = 11), parietal/perisylvian area (n = 5) and additionally the pre- or postcentral area (n = 15). All patients in this series were operated for cytoreductive purposes only and not for treatment of intractable seizures. To preoperatively define and intraoperatively tailor the extent of resection all patients had a presurgical grid implantation for functional brain mapping. RESULTS: No permanent morbidity/mortality was observed after grid implantation and resective surgery. On postoperative MRI the resection was complete (100%), nearly complete (>90%) in n = 9 and subtotal (60% to <90%) in n = 5 cases. Twice, only biopsies were taken according to the results of mapping. All patients with high-grade gliomas had adjuvant treatment with radiation and chemotherapy. After a mean follow up of 20.4 months, no tumor relapse or growth was seen in all cases of resection. CONCLUSION: Preoperative grid mapping is a safe and precise instrument to evaluate language and/or associated left perisylvian functions in patients with gliomas. It may be considered a valid alternative to awake craniotomy to maximize safe resection.

Adolescent↗

PubMed2005

Subdural recordings of the mismatch negativity (MMN) in patients with focal epilepsy.

Mismatch negativity (MMN) is elicited by discernible changes in an otherwise regular stream of auditory stimulation and reflects a pre-attentive detection mechanism. In the current study, auditory evoked potentials were recorded intracranially and electrode contacts sensitive for stimulus deviance were selected in order to further elucidate the contribution of different brain areas to MMN generation. Data were obtained from patients with frontal and temporal lobe epilepsy undergoing a presurgical evaluation by subdural and depth electrodes. In 13 of 29 patients under investigation an intracranial MMN could be observed, while in four other patients a response recovery of the N100 was revealed, mimicking an MMN. Most electrodes with an MMN signal were located in or close to the superior temporal lobe. In two patients an MMN was observed at electrode contacts over the lateral inferior frontal cortex and in one patient at a frontal interhemispheric electrode strip, giving evidence for a participation of the frontal gyrus in MMN generation. Current findings have, however, to be interpreted with caution owing to the placement and limited extension of the used electrode arrays.

Acoustic Stimulation↗

PubMed2005

Episodic depersonalization in focal epilepsy.

In this report a patient with episodic depersonalization is described. As the depersonalization episodes had been attributed to partial seizures, this patient was treated with antiepileptic medication. However, clinical evaluation with long-term video/EEG revealed no evidence of seizure activity during the depersonalization episodes. On the other hand, further evaluation revealed findings that are frequently associated with focal epilepsy. In addition to episodic depersonalization, this patient had secondary generalized seizures. The relationship between episodic depersonalization, temporal lobe pathology, and epilepsy is discussed against the background of this case.

Adult↗

PubMed2005

The influence of repetition and famousness on the intracranially recorded temporobasal N200.

It is still a matter of debate at which time point faces are recognized as familiar, with some studies claiming a relatively early face recognition and others later effects of familiarity. The authors report on effects of famousness of depicted persons and stimulus repetition on intracranially recorded event-related potentials. Famousness resulted in an increased latency of the N200 component, as well as in an increased amplitude of a later long-lasting potential (N700). In contrast, repetition led to an increased amplitude of the N200 but no increase of its latency. They suppose that the recognition of faces becomes observable within the N200 latency range and that the increased N200 latency reflects a feature processing additional to the holistic face processing.

Adult↗

PubMed2005

Limbic system abnormalities associated with Ammon's horn sclerosis do not alter seizure outcome after amygdalohippocampectomy.

PURPOSE: To evaluate whether limbic system abnormalities associated with Ammon's horn sclerosis alter seizure outcome after selective amgydalohippocampectomy. METHODS: In 45 patients with unilateral mesial temporal lobe epilepsy, histologically proven Ammon's horn sclerosis, and uneventful postoperative course, volumes of the hippocampus, hemisphere, amygdala, entorhinal cortex, mamillary body, and fornix were measured by using a T(1)-weighted 3-D gradient-echo sequence with roughly isotropic (1.17 x 1.17 x 1-mm) voxels. In addition, signal intensity of the hippocampus and of the temporal lobe white matter was visually assessed and graded on a coronal T(2)-weighted fast-spin-echo sequence with 2-mm-thick slices. Volumetric measurements and visual analysis were compared between seizure-free and non-seizure-free patients examined 12 months after surgery. RESULTS: Hippocampal, hemispheric, entorhinal cortex, mamillary body, and fornix volumes, but not amygdalar volumes, were significantly smaller on the operated-on than on the non-operated-on side and significantly smaller in patients compared with controls. No volume differences of the hippocampus, hemisphere, amygdala, entorhinal cortex, mamillary body, and fornix existed between seizure-free (Engel class IA) and non-seizure-free patients (Engel class IB-IV). Increased temporal lobe white matter signal was observed in 15 patients but did not alter seizure outcome. CONCLUSIONS: Limbic system abnormalities are not a surrogate marker to predict postsurgical seizure outcome in patients with unilateral Ammon's horn sclerosis.

Adolescent↗

PubMed2005

Unilateral intracarotid amobarbital procedure for language lateralization.

PURPOSE: The determination of language dominance as part of the presurgical workup of patients with pharmacoresistant epilepsies has experienced fundamental changes. With the introduction of noninvasive functional magnetic resonance imaging (fMRI), the number of patients receiving intracarotid amobarbital procedures (IAPs) for assessment of language dominance has decreased considerably. However, recent studies show that because of methodologic limitations of fMRI, IAP remains an important tool for language lateralization. The current study examines whether unilateral instead of bilateral IAP is an adequate way to apply IAP with reduced invasiveness. METHODS: We retrospectively examine the predictive value of unilateral IAP for the results of bilateral IAP based on a sample of 75 patients with various types of language dominance. Target parameters are the prediction of the language-dominant hemisphere and the identification of patients with atypical language dominance. For language assessment based on unilateral IAP, we introduce the measure hemispheric language capacity (HLC). RESULTS: Unilateral IAP performed on the side of intended surgery quantifies language capacity contralateral to the intended surgery. It detects atypical (bilateral or right) language dominance in the majority of patients. Experience with a separate series of 107 patients requiring presurgical language lateralization shows that in >80%, bilateral IAPs are redundant. CONCLUSIONS: Unilateral IAP is principally sufficient for language lateralization in the presurgical evaluation of patients with pharmacoresistant epilepsies. Necessity of bilateral IAP is restricted to few indications (e.g., callosotomy). In times of noninvasive language lateralization, we propose unilateral IAP as the method of choice for the verification of doubtful (bilateral) fMRI activation patterns.

Adolescent↗

PubMed2004

Short-term habituation of the intracranially recorded auditory evoked potentials P50 and N100.

At an interstimulus interval (ISI) of 500-ms stimulus repetition leads to a strong decrease in cortical response. The functional foundation of this response suppression (or sensory gating) is yet not fully understood. Experiments on short-term habituation using the same stimulus material as sensory gating experiments and same ISI might help to elucidate the mechanisms behind the P50 suppression. Event-related potentials were recorded intracranially in epileptic patients undergoing presurgical evaluation with subdural and depth electrodes. Stimulus material consisted of trains of six clicks, with the last stimulus deviating in pitch and duration. P50 and N100 were calculated for each stimulus in the train separately and compared by analysis of variance (ANOVA). A highly significant amplitude reduction was found from the 1st to 2nd stimulus for both P50 and N100. From the 2nd to 5th stimulus no further amplitude decrease was observable. The deviating 6th stimulus led to a response recovery of both components, but the P50 elicited by the 6th stimulus was still smaller than the P50 of the 1st stimulus. Current results indicate that the P50 suppression as investigated in sensory gating experiments seems to be completed after the 2nd stimulus.

Acoustic Stimulation↗

PubMed2004

Do neural correlates of consciousness cause conscious states?

Neural correlates of consciousness (NCCs) have been defined as neural systems and states of those systems, which are correlated with certain states of consciousness and which are minimally sufficient for these states of consciousness to occur. Here, it is discussed whether based on the identification of a NCC one may claim that this neural correlate causes the corresponding state of consciousness. In a strict sense, neural states and corresponding states of consciousness should occur simultaneously according to the definition of NCCs. However, two causally related events should occur consecutively in time according to the general view. Thus, within the NCC framework the question of a causal psychoneural relationship is only valid under the premise of a small and practically unobservable time shift between neural states and corresponding states of consciousness. The term causality is usually applied either in the sense of efficient causation or in the sense of explanatory causation. Efficient causality addresses the physical relation of two events and the criterion of an energy exchange between both events. Explanatory causality, on the other hand, refers to the law-like character of the conjoined occurrence of two events. Under a dualistic point of view, the interpretation that neural states effectively cause consciousness would not be justified, since effective causation, as understood in physical sciences, should be associated with energy transfer. But such an energy transfer between the domain of consciousness and the neural domain would violate presently accepted physical laws. Therefore, it is argued that one may state that neural states cause states of consciousness only in the broad sense of explanatory causality with regard to the observation of a law-like psychoneural relation. Within the viewpoint of identity theory, however, one would rather claim that certain states of consciousness basically are neural states.

Causality↗

PubMed2004

Persistent severe amnesia due to seizure recurrence after unilateral temporal lobectomy.

Anterograde amnesia is a severely disabling state which has been reported as a consequence of bilateral mesiotemporal lesions in humans. In the present paper, recurrent epileptic seizures after temporal lobectomy are described as a rare cause of severe amnesia in two patients. Diffusion-weighted MRI in one patient showed cytotoxic edema during a nonconvulsive status epilepticus and subsequent progressive hippocampal atrophy within the following month. In the other patient, repeated conventional MRI revealed no structural abnormalities in the contralateral temporal lobe.

Adult↗

PubMed2004

Chronic epilepsy and cognition.

Cognitive profiles in epilepsy are as heterogenous as the epileptic syndromes themselves; causes, topography of epileptogenic areas, pathogenetic mechanisms, and the diverse features characterising the clinical course all contribute to the effect on cognition. Chronic epilepsy generally impairs cognition, but it also induces processes of functional reorganisation and behavioural compensation. In most idiopathic epilepsies, cognition is only mildly deteriorated or even normal by clinical standards. Localisation-related cryptogenic and symptomatic epilepsy disorders are accompanied by focal deficits that mirror the specific functions of the respective areas. Poor cognitive outcome is generally associated with an early onset and a long duration of the disease and with poor seizure control. There is evidence that cognitive functions are already impaired at the onset of the disease, and that the maturation of cognitive functions in children is susceptible to the adverse influence of epilepsy. In adults, cognitive decline progresses very slowly over decades with an age regression similar to that of people without epilepsy. Successful epilepsy surgery can stop or partly reverse the unfavourable cognitive development, but left-temporal resections in particular have a high risk of additional postoperative verbal memory impairment. Cognitive recovery in the adult brain after successful surgery indicates functional compensation and, to some degree, functional reorganisation or a reactivation of functions previously suppressed by influence from distant but connected epileptogenic areas.

Chronic Disease↗

PubMed2004

Pharmacorefractory status epilepticus due to low vitamin B6 levels during pregnancy.

We report a patient with pyridoxine-dependent epileptic seizures during early childhood. She had been completely seizure free for 23 years until she became pregnant. During the week 14 of her pregnancy, status epilepticus developed and was refractory to antiepileptic drugs but responded to intravenous administration of vitamin B6. Vitamin B6 levels were found to be decreased during pregnancy, although the patient reported continued and regular oral supplementation. Possible reasons for decreased vitamin B6 levels leading to status epilepticus are discussed.

Adult↗

PubMed2004

Neural bases of cognitive ERPs: more than phase reset.

Up to now, two conflicting theories have tried to explain the genesis of averaged event-related potentials (ERPs): Whereas one hypothesis claims that ERPs originate from an event-related activation of neural assemblies distinct from background dynamics, the other hypothesis states that ERPs are produced by phase resetting of ongoing oscillatory activity. So far, this question has only been addressed for early ERP components. Late ERP components, however, are generally thought to represent superimposed activities of several anatomically distinct brain areas. Thus, the question of which mechanism underlies the genesis of late ERP components cannot be easily answered based on scalp recordings. In contrast, two well-investigated late ERP components recorded invasively from within the human medial temporal lobe (MTL) in epilepsy patients, the so-called MTL-P300 and the anterior MTL-N400 (AMTL-N400), are based on single source activity. Hence, we investigated whether the MTL-P300 and the AMTL-N400 are based on an event-related activity increase, a phase reset of ongoing oscillatory activity or both. ERPs were recorded from the hippocampus and rhinal cortex in subjects performing a visual oddball paradigm and a visual word recognition paradigm. With wavelet techniques, stimulus-related phase-locking and power changes were analyzed in a frequency range covering 2 to 48 Hz. We found that the MTL-P300 is accompanied by both phase reset and power increase and that both effects overlap partly in time. In contrast, the AMTL-N400 is initially associated with phase locking without power increase and only later during the course of the AMTL-N400 we observed an additional power increase. In conclusion, both aspects, event-related activation of neural assemblies and phase resetting of ongoing activity seem to be involved in the generation of late ERP components as recorded in cognitive tasks. Therefore, separate analysis of event-related power and phase-locking changes might reveal specific insights into the mechanisms underlying different cognitive functions.

Adult↗

PubMed2003

Chronic epilepsy and cognition: a longitudinal study in temporal lobe epilepsy.

It remains unclear whether uncontrolled epilepsy causes mental decline. This longitudinal study contrasts change of memory and nonmemory functions in 147 surgically and 102 medically treated patients with temporal lobe epilepsy. All participants were evaluated at baseline (T1) and after 2 to 10 years (T3). Surgical patients underwent additional testing 1 year postoperatively (T2). Data were analyzed on an individual and group level. Sixty-three percent of the surgical and 12% of the medically treated patients were seizure-free at T3. Fifty percent of the medically treated and 60% of the surgical patients showed significant memory decline at T3 with little change in nonmemory functions (difference not significant). Surgery anticipated the decline seen in the medically treated group and exceeded it when surgery was performed on the left, or if seizures continued postoperatively. Seizure-free surgical patients showed recovery of nonmemory functions at T2 (p < 0.001) and of memory functions at T3 (T3, p = 0.03). Multiple regression indicated retest interval, seizure control, and mental reserve capacity as predictors of performance changes. In addition, psychosocial outcome was better when seizures were controlled. In conclusion, chronic temporal lobe epilepsy is associated with progressive memory impairment. Surgery, particularly if unsuccessful, accelerates this decline. However, memory decline may be stopped and even reversed if seizures are fully controlled.

Adult↗

PubMed2002

Epilepsy surgery in patients with additional psychogenic seizures.

OBJECTIVE: To assess whether surgery to reduce or control epileptic seizures is safe and effective in patients known to have additional psychogenic seizures. DESIGN: We reviewed our computerized database of 1342 patients examined for epilepsy surgery and identified 13 patients with both epileptic and psychogenic seizures on whom postoperative outcome data were available. Data were gathered from the patients' records. Mean postoperative follow-up was 56 months. RESULTS: Epilepsy surgery led to clinically relevant improvements in 11 of 13 patients. Seven patients became free of epileptic and psychogenic seizures, 2 patients became free of epileptic seizures but continued to have infrequent psychogenic seizures, 1 patient reported more than an 80% improvement in epileptic seizure frequency and an abolishment of psychogenic attacks, and in 1 patient nondisabling epileptic seizures persisted at lower frequency but psychogenic seizures stopped. In 2 of 13 patients, epilepsy surgery failed to produce notable improvements. Although 1 patient became free of epileptic attacks and the other had fewer than 3 epileptic seizures per year, the severity or frequency of psychogenic seizures and pseudo-status epilepticus increased postoperatively. One of these patients had a preoperative diagnosis of somatization disorder; in the other, pathological illness behavior had been noted. CONCLUSION: A diagnosis of additional psychogenic seizures should not be considered an absolute contraindication to epilepsy surgery, although patients should undergo careful preoperative psychiatric evaluation.

Adolescent↗