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Biomedical subjects

M Kurthen

Publications and source records attributed to M Kurthen.

At least 19 recordsLinked to original sources
PubMed2001

Memory and epilepsy: characteristics, course, and influence of drugs and surgery.

Memory processing in humans is essential for consciousness, cognitive-behavioral development and individual biography. In epilepsy, declarative memory functions show characteristic patterns of impairment when mesiotemporal and associated neocortical structures are affected by lesions, ongoing epileptic activity, or the undesired effects of conservative or operative treatment. Major issues are thus the etiology, onset and course of memory impairment, as well as the prevention of further memory decline during treatment. New input in the field has resulted from improved imaging techniques, sophisticated experimental study designs, more selective surgical approaches, and new antiepileptic drugs.

Animals↗
PubMed2000

SATSCOM--Selective amobarbital test intraarterial SPECT coregistered to MRI: description of a method assessing selective perfusion.

For evaluation of potential functional deficits, an intraarterial amobarbital test is performed prior to neurosurgical or neuroradiological interventions. To visualize individual amobarbital perfusion patterns, simultaneous injection of (99m)Tc-HMPAO was performed previously. The present study describes for the first time a method of coregistration of intraarterial SPECT during selective amobarbital test to MRI. Three patients undergoing selective amobarbital test of the posterior cerebral artery were included. SATSCOM (Selective amobarbital test intraarterial SPECT coregistered to MRI) was performed by skull extraction in SPECT and MRI followed by surface matching. In all three patients, SATSCOM revealed accurate matching results. With this functional-anatomical mapping, suppression of higher cortical functions can be correlated to anatomical regions. Furthermore, a more precise mapping of amobarbital effect improves planning invasive interventions, particularly those close to eloquent areas.

Adult↗
PubMed2000

[Temporal lobe epilepsy: longitudinal clinical, neuropsychological and psychosocial follow-up of surgically and conservatively managed patients].

Little is known about the differential long-term outcome from surgical and nonsurgical therapy in patients with chronic epilepsy. In the present study, 161 surgically or nonsurgically treated patients with drug-resistant temporal lobe epilepsy (TLE) were re-evaluated according to a detailed clinical, neuropsychological, and psychosocial protocol with a mean follow-up interval of 58 months. Freedom from seizures was achieved in 64% of the surgical group; yet 23% of the nonsurgical patients became seizure-free as a result of modifications in drug therapy. Generally, socioeconomic development was poorer in nonsurgical than in surgical patients. Freedom from seizures, employment, and the absence of depression were significant determinants of better quality of life. As for neuropsychological outcome, verbal memory impairment was common after left-sided temporal resection; however, there was no evidence of a marked progression of cognitive impairment after the first postoperative year. In nonsurgical patients, too, cognitive capacities were surprisingly stable over time, although persisting seizures and good baseline performance predicted a poorer neuropsychological outcome.

Adult↗
PubMed2000

Cortical motor reorganization following early brain damage and hemispherectomy demonstrated by transcranial magnetic stimulation.

BACKGROUND: Transcranial magnetic stimulation (TMS) was utilized to study 7 patients who had undergone hemispherectomy for control of longstanding intractable epilepsy to assess cortical motor reorganization and MEP (motor evoked potentials) ipsilateral to the remaining hemisphere. Five patients were seizure-free post-operatively. All patients displayed a spastic hemiparesis, were able to walk, raise and bend the paretic arm and use the paretic hand to different degrees. METHODS: We examined MEP threshold, site of maximal response to TMS, and latency to the biceps brachii, abductor pollicis brevis and the anterior tibial muscles using a 7 and 12 cm diameter round coil. RESULTS: The following results were obtained: (1) No MEP could be induced to either side by use of the small coil. (2) When using the large coil MEP-threshold was elevated also when stimulating the non-affected hemisphere in comparison to normal controls. (3) Ipsilateral MEP were found to: be non-inducible in two patients, demonstrate largely increased latencies in 3 and be identical to contralateral MEP in two patients. (4) Ipsilateral MEP could be evoked more often in distal than proximal muscles. (5) The site of maximal ipsilateral MEP response was found approximately 2 cm anteriorly to that of the contralateral MEP to the non-affected side of the body (6) No correlation was found between the degree of hemiparesis and inducability of MEP. CONCLUSIONS: The pattern of reorganization of ipsilateral motor control following early brain damage and hemispherectomy appears to be extremely diverse and does not correlate with the degree of neurological impairment.

Adult↗
PubMed2000

Localizing value of epileptic visual auras.

It is difficult to differentiate between seizures of occipital or temporal lobe origin in patients with focal epileptic seizures associated with visual aura. These are often suspected to originate from the visual cortex, which causes reluctance to propose resection as treatment for the affected patient. To determine the value of localizing different types of visual auras, we report on 20 patients experiencing visual aura from a series of 878 surgically treated patients suffering from intractable focal seizures. In all of these patients, a morphological abnormality was identified on MRI (n = 18) or cranial CT (n = 2). These abnormalities were shown to represent the morphological correlate of the epileptogenic zone in each case, as demonstrated by intracranial ictal EEG recordings and/or seizure freedom after focal resective surgery. Elementary hallucinations, illusions and visual loss were reported not only by all patients with occipital lobe epilepsy, but also by patients with occipitotemporal and anteromedial temporal seizure onset. Complex hallucinations never occurred in occipital lobe seizures but were present in the two other groups. The same correlation was found for concentric changes of visual field (tunnel vision), a newly described ictal phenomenon. We conclude that elementary hallucinations, illusions and visual loss, although typical for occipital lobe epilepsy, can also occur in anteromedial temporal or occipitotemporal seizures and are therefore not a discordant feature in presurgical evaluation of patients with suspected temporal lobe epilepsy. Complex hallucinations and tunnel vision, however, should be considered concordant only with the assumption of an anteromedial temporal or occipitotemporal seizure onset.

Adolescent↗
PubMed1999

Evidence relating human verbal memory to hippocampal N-methyl-D-aspartate receptors.

Studies in rodents and nonhuman primates have linked the activity of N-methyl-D-aspartate (NMDA) receptors within the hippocampus to animals' performance on memory-related tasks. However, whether these receptors are similarly essential for human memory is still an open question. Here we present evidence suggesting that hippocampal NMDA receptors, most likely within the CA1 region, do participate in human verbal memory processes. Words elicit a negative event-related potential (ERP) peaking around 400 ms within the anterior mesial temporal lobe (AMTL-N400). Ketamine, an NMDA-receptor antagonist, reduces the amplitude of the AMTL-N400 (in contrast to other hippocampal potentials) on initial presentation, eliminates the typical AMTL-N400 amplitude reduction with repetition, and leads to significant memory impairment. Of the various hippocampal subfields, only the density of CA1 neurons correlates with the word-related ERPs that are reduced by ketamine. Altogether, our behavioral, anatomical, and electrophysiological results indicate that hippocampal NMDA receptors are involved in human memory.

Adult↗
PubMed1999

Amobarbital effects on the posterior hippocampus during the intracarotid amobarbital test.

OBJECTIVE: To relate functional effects on the hippocampus during the intracarotid amobarbital test (IAT) to its direct perfusion with amobarbital. METHODS: In 17 patients with intractable temporal lobe epilepsy, 28 hemispheres were perfused with 2.3 mL of 10% solution of 200 mg amobarbital and 37 MBq 99mTc-hexamethylpropylene amine oxime (HMPAO). For evaluation of amobarbital effects, data were combined from stereo-EEG (S-EEG) recordings from intrahippocampal depth electrodes and high-resolution SPECT after intracarotid injection of HMPAO. RESULTS: Perfusion of the entire hippocampus was observed only in hemispheres with a fetal origin of the posterior cerebral artery (PCA). In 10 hemispheres, S-EEG recordings could not unequivocally be assigned to either the anterior or the posterior part of the hippocampus. In the remaining 18 hemispheres, only the two with a fetal type of PCA showed perfusion of the entire hippocampus. In both, hippocampal electrical activity changed under the influence of amobarbital but did not differ in anterior and posterior contacts. In 15 of 16 hemispheres in which SPECT demonstrated perfusion of the anterior hippocampus only, amobarbital injection resulted in significant S-EEG activity change in both the anterior and the posterior parts of the hippocampus. CONCLUSION: S-EEG effects on the posterior hippocampus during the IAT can occur without direct perfusion of those brain areas.

Adolescent↗
PubMed1999

Conscious behavior explained.

Current neurobiological research on temporal binding in binocular rivalry settings contributes to a better understanding of the neural correlate of perceptual consciousness. This research can easily be integrated into a theory of conscious behavior, but if it is meant to promote a naturalistic theory of perceptual consciousness itself, it is confronted with the notorious explanatory gap argument according to which any statement of psychophysical correlations (and their interpretation) leaves the phenomenal character of, e.g., states of perceptual consciousness open. It is argued that research on temporal binding plays no role in a naturalistic theory of consciousness if the gap argument can be solved on internal philosophical grounds or if it turns out to be unsolvable at the time being. But there may be a way to dissolve or deconstruct it, and the accessibility of this way may well depend on scientific progress, including neurobiological research on the neural correlate of perceptual consciousness.

Brain↗
PubMed1999

Essential functions of the human self model are implemented in the prefrontal cortex.

The human self model comprises essential features such as the experiences of ownership, of body-centered spatial perspectivity, and of a long-term unity of beliefs and attitudes. In the pathophysiology of schizophrenia, it is suggested that clinical subsyndromes like cognitive disorganization and derealization syndromes reflect disorders of this self model. These features are neurobiologically instantiated as an episodically active complex neural activation pattern and can be mapped to the brain, given adequate operationalizations of self model features. In its unique capability of integrating external and internal data, the prefrontal cortex (PFC) appears to be an essential component of the neuronal implementation of the self model. With close connections to other unimodal association cortices and to the limbic system, the PFC provides an internally represented world model and internal milieu data of the organism, both serving world orientation. In the pathophysiology of schizophrenia, it is the dysfunction of the PFC that is suggested to be the neural correlate for the different clinical schizophrenic subsyndromes. The pathophysiological study of psychiatric disorders may contribute to the theoretical debate on the neuronal basis of the self model.

Body Image↗
PubMed1999

Limbic P300s in temporal lobe epilepsy with and without Ammon's horn sclerosis.

Limbic P300 potentials can be recorded within the mesial temporal lobes of patients with temporal lobe epilepsy (TLE). To delineate possible mechanisms of their generation and pathological alteration, we analysed limbic P300s in 55 TLE patients with and 29 without Ammon's horn sclerosis (AHS) and correlated their amplitudes with neuronal cell counts in 30 histopathological specimens. Limbic P300 amplitudes were reduced on the side of the epileptogenic focus only in patients with AHS. Moreover, in AHS patients, limbic P300 latencies were prolonged bilaterally; and in patients with left-sided AHS, amplitudes were reduced bilaterally. Both findings suggest bilateral functional deficits in TLE with unilateral AHS. Limbic P300 areas correlated significantly with neuronal densities of dentate gyrus granule cells but not hippocampal pyramidal cells in the CA1-4 (cornu ammonis) subfields. This finding points to a potential mechanism for the bilateral effects of unilateral AHS as both dentate gyri exhibit strong reciprocal contralateral connectivity.

Adolescent↗
PubMed1999

Prediction of postoperative seizure control by hippocampal event-related potentials.

PURPOSE: In spite of unequivocal results of the presurgical evaluation, between 10 and 30% of patients with medial temporal lobe epilepsy (MTLE) do not become seizure free by temporal lobe surgery. Because event-related potentials (ERPs) recorded within the hippocampal formation have been shown to be sensitive to the epileptogenic process, we examined whether ERPs can help to improve the prediction of postoperative seizure control. METHODS: We recorded ERPs to words from bilateral intrahippocaampal electrodes by using a visual word-recognition paradigm in 70 patients with unilateral hippocampal pathology and related these measurements to seizure outcome after temporal lobe surgery. RESULTS: Words elicited N400 potentials, which were reduced in amplitude on repetition on the side contralateral to hippocampal sclerosis. This contralateral repetition effect, however, was significantly diminished in the group of patients who experienced seizure recurrence after the operation. Contralateral repetition effects thus permitted correct prediction of postoperative seizure control in 94% of all patients. CONCLUSIONS: Recording ERPs to words within the medial temporal lobes can improve the prediction of postoperative seizure control. Reduced repetition effects contralateral to the side of hippocampal sclerosis may indicate bilateral epileptogenicity.

Adolescent↗
PubMed1998

Limbic ERPs predict verbal memory after left-sided hippocampectomy.

Surgical removal of the dominant medial temporal lobe regions runs a considerable risk of verbal memory deficits which may be compensated for postoperatively by corresponding regions in the non-dominant medial temporal lobe. We examined this possibility by recording event-related potentials (ERPs) to words from the medial temporal lobes of patients with left-sided temporal lobe epilepsy (TLE) undergoing presurgical evaluation. N400 amplitudes in the right anterior medial temporal lobe predicted the postoperative verbal recall performance of individual patients with surprising accuracy, indicating that intracranial recordings can be used to quantify the functional capacities of the right hemisphere that can compensate for the verbal memory deficits after loss of medial temporal lobe structures in the left hemisphere.

Adolescent↗
PubMed1997

Evidence of very fast memory consolidation: an intracarotid amytal study.

This study provides evidence from intracarotid amobarbital tests (IAT) in patients with epilepsy that complete suppression of the electrophysiological activity of the left language-dominant hemisphere through left IAT does not impair memory for verbal information given 1 min or immediately before the injection of the barbiturate. Although language functions were completely disrupted and patients were unable to encode new information during the left IAT, pre/post memory was as good as in the right IAT. This lack of retrograde amnesia leads to the conclusion that a relatively stable representation of events is achieved within seconds after encoding. The results contradict models which assume that short-term memory is based on purely electrophysiological processes.

Amobarbital↗
PubMed1997

Patterns of language dominance in focal left and right hemisphere epilepsies: relation to MRI findings, EEG, sex, and age at onset of epilepsy.

The present study evaluates results of language testing during intracarotid amobarbital procedures in 167 patients with either left (LHE, n = 81) or right hemisphere epilepsies (RHE, n = 86). In both groups there was a high rate of deviance from complete left hemisphere dominance of 24 and 31%, respectively. Whilst complete right hemisphere or incomplete left hemisphere language dominance were the prominent atypical patterns in LHE, RHE was associated with either bilateral dominance or incomplete left dominance. In LHE, atypical language dominance was frequently associated with an extratemporal localization of lesions or epileptic foci. The age at onset of epilepsy and the degree of right hemisphere language dominance correlated significantly in LHE but not in RHE. Finally, atypical dominance in LHE but not in RHE was associated with poorer language and nonlanguage functions, the latter being negatively correlated with the degree of right hemisphere language dominance. Conclusions are: (1) The data contradict the assumption of equipotentiality and favor the supposition of a predetermined left hemisphere superiority in language processing. (2) Atypical language dominance in LHE can largely be explained in terms of a plasticity dependent language shift as a consequence of early left hemisphere epilepsies and lesions. (3) Atypical dominance patterns in RHE appear to reflect the prevalence of genetically determined variants and the possibility of a language transfer from the right to the left hemisphere.

Age of Onset↗
PubMed1994

Quantitative and qualitative evaluation of patterns of cerebral language dominance. An amobarbital study.

As a part of presurgical evaluation, 173 patients received bilateral intracarotid amobarbital tests for determination of cerebral language dominance. Language testing during intracarotid amobarbital procedures (IAP) consisted of the following tasks: automatic speech, sentence comprehension, body commands, naming, repetition, reading, and spontaneous speech. Patterns of cerebral language dominance were evaluated and discussed on five levels of analysis: (1) quantification of language dominance on the basis of a lateralization index derived from the total language scores in each IAP; (2) determination of five dominance subpatterns (left or right dominant, strongly bilateral, and incomplete left or right dominant) according to quantification performed on level (1) and clinical judgement; (3) qualitative differentiation of three kinds of bilaterality (positive, negative, and general) according to total language performance in left and right IAP; (4) analysis of grouped linguistic subfunctions extracted from performance in specific IAP subtests; (5) extraordinary individual case histories. The distribution of lateralization indices revealed only partially continuous degrees of lateralization, especially between the left-dominant and bilateral subgroups. As for the clinically oriented classification, incomplete left dominance is frequent (16.2%), while incomplete right dominance does not occur at all. Atypical dominance patterns are mostly correlated to bilateral and/or extratemporal foci. Concerning grouped subfunctions, a rotated factor matrix statistic yields an analysis of clusters of IAP subtests, where functions involving expressive language capacities are separated from those that are purely receptive. Further analyses of bilaterality subpatterns suggest that there are mainly four bilaterality phenomena, namely interhemispheric dissociation, double representation, unilateral representation of subfunctions, and partial representation of subfunctions in either hemisphere. Application of these differentiations to individual cases yields additional evidence that can be used in patient selection for operation in order to avoid postoperative neuropsychological deficits, especially in candidates for extratemporal surgery. In conclusion, a multilevel analysis of IAP language data is recommended since it permits a detailed account of varieties of language dominance patterns and contributes to more adequate presurgical decision-making in planned operations in cognitively relevant brain areas.

Adolescent↗