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Biomedical subjects

M Kurthen

Publications and source records attributed to M Kurthen.

At least 19 recordsLinked to original sources
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↗
PubMed1994

Right hemisphere restitution of language and memory functions in right hemisphere language-dominant patients with left temporal lobe epilepsy.

Concomitant with the right hemispheric restitution of language functions after early left hemisphere lesions, suppression effects on originally right hemispheric visuospatial/constructional functions have repeatedly been reported. The present study evaluated this issue in 10 right hemisphere language-dominant patients with temporal lobe epilepsy. Left hemisphere language-dominant patients with left (n = 10) or right (n = 10) temporal lobe epilepsy served as controls. The following results were obtained: in all but one of the right dominant patients, left hemisphere lesions, left hemisphere foci and histories of early left brain damage indicated that secondary language transfer rather than a genetically determination is the more likely cause of the right hemisphere dominance. Despite this transfer, the language functions (comprehension, fluency, reasoning) of the right dominant patients remained significantly impaired. Language generally appeared to be better preserved in patients with an onset of epilepsy before the third year of life or a circumscribed left hemisphere lesion. No suppression effects could be detected on the level of complex cortical language and non-language functions. In contrast, on the level of temporo-limbic memory functions, verbal learning and recognition were left largely intact, albeit mostly at the expense of visuo-spatial learning and memory. The findings of the study thus indicate that the cerebral plasticity of the right hemisphere differs according to the extent of the left-hemisphere lesion, the onset of structural/functional damage and the complexity of the functions requiring restitution. Assuming that language and memory represent neocortical and palaeocortical functions, respectively, the restitution process is seemingly governed by their status in a phylogenetically determined hierarchy of functional importance.

Brain Diseases↗
PubMed1993

[The determination of cerebral speech dominance with the intracarotid amobarbital test].

In neuropsychological diagnostics of lateralisation of cognitive functions, the intracarotid amobarbital procedure (IAP) is a well established method for the determination of cerebral language dominance. In this review, different frameworks of classification of dominance patterns are discussed, ranging from the simple left/right/bilateral-dominance framework to a quantitative analysis according to a computed lateralisation index. Evidence from IAP studies concerning the cerebral organisation of linguistic subfunctions like naming and reading are discussed. A critical evaluation of rivalling approaches like electrical stimulation mapping or visual hemifield studies suggests that these methods mainly yield results complementary to IAP data and hence should not be taken as substitutes of that procedure.

Amobarbital↗
PubMed1993

[Does lateralized hemispheric control of cardiovascular activity exist? A Wada test study].

The question of whether the influence of the cerebral hemispheres on cardiovascular activity exhibits left/right differences is important for the understanding of the psychophysiology of the autonomous nervous system. Experimental results have been contradictory. One experimental procedure used is the intracarotid amobarbital test (Wada test: short anesthesia of one cerebral hemisphere). Even with this test contradictory results have been obtained in various studies, although all involved relatively small of numbers of patients. Some authors have described increases in heart rate following anesthesia of the left hemisphere, while others found little or no effect at all. We therefore searched for evidence of lateralization in a larger number of patients (36) with complex partial seizures. These patients underwent the Wada test as part of the preoperative diagnostic evaluation. In this study, inactivation of the left or right hemisphere did not lead to significantly different effects on heart rate, or on systolic or diastolic blood pressure.

Adolescent↗
PubMed1993

[Neuroradiologic methods and findings prior to the surgical treatment of epilepsy in children].

Epilepsy in childhood is often caused by morphological abnormalities and is frequently pharmacoresistant. Therefore it represents a challenge to the neuroradiologist because early and accurate diagnosis of abnormal morphology is the basis for planning surgical intervention with a high chance of controlling seizures and a low risk of complications. Both morphological (radiography, CT, MRI and angiography) and functional examinations [intracarotid amobarbital test (IAT)] are essential parts of the presurgical evaluation. In most cases MRI has proved to be most sensitive in detecting lesions except for some calcifications. Routine protocols for brain examinations are not sufficient, missing about 22% of lesions. Therefore a refined MRI and CT protocol is proposed. Even in very young children IAT can be performed at very low risk; these tests contribute highly valuable information about actual hemispheric dominance and other functions in more than 80% of procedures that is indispensable if postoperative neurological and neuropsychological deficits are to be avoided.

Adolescent↗
PubMed1993

[The intracarotid amobarbital test. Neuroradiologic and neuropsychologic aspects].

In presurgical evaluation of epilepsy, unilateral cerebral inactivation by means of intracarotid injection of amobarbital is used for the determination of cerebral dominance for language and memory functions. This intracarotid amobarbital test (IAT) is intended to yield prognoses concerning postsurgical neuropsychological and neurological deficits. In the present review, neuroradiological and neuropsychological aspects of the procedure are discussed. Each IAT is preceded by a cerebral angiography to exclude or detect vascular anomalies that might be relevant to the interpretation of neuropsychological test data. The main methodological problems of the IAT are interference of various cognitive deficits and monitoring of the course of amobarbital action. Alternative procedures of determination of hemispheric asymmetries--positron emission tomography, electrical stimulation mapping, and noninvasive methods like tachistoscopy--mainly yield data complementary to the results of the IAT and hence are not taken as substitutes of that technique.

Amobarbital↗
PubMed1993

[The selective amobarbital test in epileptology].

Epileptic foci in the frontal or parieto-occipital cortex often cause epileptiform EEG changes in both hemispheres. Therefore, delineation of the primary epileptogenic area, which is necessary for epilepsy surgery, is not possible by electrophysiological methods. A temporary inactivation of the epileptogenic area by a selective injection of the short-acting barbiturate amobarbital (selective amobarbital test, SAT) can prove the relation between generalized EEG changes and a circumscribed epileptogenic area. The SAT may also be used for evaluation of the risk for additional functional deficits after epilepsy surgery in certain brain areas. During temporary inactivation of the brain area to be resected, the function of the motor system, speech and memory can be tested.

Amobarbital↗
PubMed1992

Correlations between verbal memory performance and electrocorticographically determined suppression of electrical brain activity in intracarotid amobarbital tests.

As a part of presurgical evaluation, bilateral intracarotid amobarbital procedures (IAPs) were performed in 42 patients (84 tests) with long-standing, medically intractable complex-partial seizures. During the IAPs, electrocorticographic (ECoG) recording was carried out via bilaterally implanted subdural electrodes. Five distinct patterns of suppression of electrical brain activity were observed: (1) an isoelectric line; (2) a burst-suppression pattern; (3) polyphasic waves; (4) high-voltage beta; and (5) low-voltage beta activity. Further, two types of specific reactions of the epileptic focus were detectable: (1) spike-burst-suppression patterns (SBS; 11 left; 7 right; 6 in both IAPs) and amobarbital-induced spikes (7 left; 4 right). ECoG suppression patterns as well as SBS and spike induction showed great variability in duration and overall occurrence. To determine the influence of these amobarbital-induced ECoG changes on results of IAP memory testing, performance in a verbal learning task was analyzed according to the ECoG patterns predominant during encoding. In left IAPs, it was found that SBS at the beginning of or during encoding had a significant negative effect on verbal memory. In right IAPs, verbal memory performance improved significantly with the decline of ECoG suppression. Hence, verbal memory performance in IAPs is significantly affected by specific ECoG suppression patterns and activation of the epileptic focus.

Adolescent↗
PubMed1992

Interhemispheric dissociation of expressive and receptive language functions in patients with complex-partial seizures: an amobarbital study.

Bilateral intracarotid amobarbital procedures (IAP) were performed in 144 patients with medically intractable complex-partial seizures. As a result of language testing, 29 patients (20.1%) were found to have bilateral language representation to different degrees. In four (2.8%) of these patients--all right-handers with early onset of epilepsy and/or evidence of early brain damage--there was strong evidence of an interhemispheric dissociation of expressive and receptive language functions. Two of these patients had circumscribed temporal foci (one left, one right), and receptive language functions were represented in the hemisphere contralateral to the focus. One patient with a right frontal focus showed left-hemisphere dominance for expressive functions, while the fourth patient exhibited left-hemisphere dominance for receptive functions associated with a right temporo-parietal focus. It is argued that in these four cases the circumscribed functional and/or structural impairments have led to a shift of the anatomically associated language functions to the opposite hemisphere (rather than to neighboring regions of the same hemisphere). These findings substantiate the hypothesis that in special circumstances the anterior (expressive) language area can be located in one hemisphere and the posterior (receptive) area in the other.

Adolescent↗
PubMed1992

Linguistic perseveration in dominant-side intracarotid amobarbital tests.

148 patients with medically intractable complex-partial seizures received bilateral intracarotid amobarbital tests. In 21 patients (14.2%), there were inappropriate responses (intrusions: N = 10; perseverations: N = 11) to a series repetition task (counting backwards) given immediately before amobarbital injection. Five cases from the perseveration subgroup are discussed in detail. In these patients, linguistic perseveration occurred with left-sided amobarbital injection, although they were all found to have left hemispheric speech dominance according to language testing during the amobarbital procedure. It is argued that these perseverations are best explained as a right hemispheric continuation of a speech motor program previously initiated by the left hemisphere.

Adolescent↗
PubMed1992

Recent developments in neurosurgical spinal cord monitoring.

In a review 8 years ago, the then current status of intraoperative spinal cord monitoring (SCM) was discussed. Concerning future developments, that article concluded that the major challenge lay in (a) the improvement of the reliability and clinical relevance of somatosensory evoked potential (SEP) monitoring, where the incidence of false-negative and false-positive results had to be reduced, and (b) the application of new techniques like motor evoked potential (MEP) monitoring, which might turn out to be a method complementary to the SEP approach. Since that time, there has been a considerable amount of newly published results from intraoperative SCM, although clinical articles on exclusively neurosurgical SCM are rare (Table I). A selective literature search for the present review (primarily for the time from 1988 to 1992) yielded more than 200 citations. Eighty-one studies entered into the final evaluation; among these were 3 conference proceedings, 6 book chapters, and 10 review articles. Further, 40 clinical articles, and 22 articles on experimental work were counted. In particular, experimental studies in animals have given support to clinical monitoring by exploring the usefulness of new stimulation and recording techniques. This reappraisal only considers recent work on SEP and MEP in neurosurgical SCM with some experimental studies relevant to clinical SCM. Spinal cord monitoring in orthopaedic surgery is not evaluated in this review for reasons detailed in the article.

Evoked Potentials↗
PubMed1992

[The intra-carotid amobarbital test--indications--procedure--results].

In presurgical assessment of epilepsy, the intracarotid amobarbital procedure (IAP) is used for the detection of functional asymmetries of the cerebral hemispheres with respect to cognitive functions. The IAP permits a precise and reliable determination of patterns of language dominance, although analysis of the lateralization of specific memory functions is constrained by methodological problems. In addition, the IAP yields information on the lateralization of other cognitive functions such as attention, consciousness, and emotion. It may also serve as a means of delineating the primary epileptic focus. Furthermore, the IAP may also be helpful in the assessment of non-epileptic patients prior to elective operations in brain regions relevant to cognition.

Amobarbital↗
PubMed1992

[Are cognitive processes in a phase relation with 40 Hz EEG?].

A coherent EEG-rhythm occurring in the 40 Hz range has been shown to correlate with cognitive processes of attention in a large number of studies. We intended to evaluate whether this frequency is of specific functional significance, and whether it may represent a rhythm of excitability for cognitive processes. The model of a rhythm of excitability assumes the 40 Hz-EEG to be a timer and organizer for information processing. Event-related potentials of 12 healthy normal subjects were recorded in an experiment of attention (auditory click stimulation). In order to evaluate whether the phases of the 40 Hz-EEG represent a rhythm of excitability, responses to stimuli having similar phases at the beginning of the stimulus were selected and averaged. An effect of the different 40 Hz-phases could not be demonstrated on the amplitude and latency of N100 and P200, components of the event-related potential associated with information processing. These findings suggest that a possible timer for cognitive processes of attention is not linked to the phases of the 40 Hz-surface-EEG.

Adult↗