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Biomedical subjects

H G Wieser

Publications and source records attributed to H G Wieser.

At least 19 recordsLinked to original sources

Human hippocampus establishes associations in memory.

Studies of amnesia have demonstrated that the hippocampus is necessary for long-term memory, but its precise role in memory is unknown. We designed a positron emission tomography experiment with tailored encoding and retrieval tasks that permitted the isolation of different mnemonic functions theorized to be mediated by the hippocampus. These functions included encoding single items, establishing interitem associations, novelty detection, and retrieving recently formed associations. Of these, we found hippocampal and parahippocampal activation only during associative learning. Our results indicate that the hippocampal formation may be particularly involved in the establishment of associations among components of an episode in memory.

Association

The anterior and posterior selective temporal lobe amobarbital tests: angiographic, clinical, electroencephalographic, PET, SPECT findings, and memory performance.

The techniques, results, and problems of three types of selective temporal lobe (TL) amobarbital procedures (balloon technique with temporary occlusion of the internal carotid artery distal to the origin of the anterior choroidal artery (acha) [n = 19]; selective anterior catheterization of the acha [n = 20]; and selective catheterization of the peduncular P2-segment of the posterior cerebral artery [n = 5]) are described in a group of 40 patients with medically refractory complex partial seizures of mesial TL origin. Selective amobarbital tests were carried out before surgery to predict the memory deficit after an intended selective amygdalohippocampectomy. The effects of selective anaesthetization of TL were correlated with clinical data, pattern and duration of amobarbital induced EEG changes, and performance on verbal and nonverbal memory tasks measured during the test. In 4 patients the effect of selective amobarbital injection on regional and global metabolism was studied with 18F-FDG-PET, with the PET tracer being injected intravenously immediately after amobarbital. More recently in 2 patients the vascular territory perfused by amobarbital in the acha test was studied with SPECT using 99m Tc ECD injected immediately prior to the amobarbital into the acha. Whereas the PET studies showed a rather widespread and bilateral amobarbital-induced decrease of metabolism, the SPECT studies confirmed the selective distribution of the tracer in the vascular territory of the acha, i.e., in amygdala and hippocampus. The comparison of selective TL amobarbital test performance with postoperative neuropsychological performance showed that the predictive value of this test is rather good for the postoperative verbal memory but underestimates postoperative nonverbal ("figural") memory performance.

Adult

Untroubled musical judgement of a performing organist during early epileptic seizure of the right temporal lobe.

The case of a professional musician with a right temporal lobe epilepsy is presented. Whilst playing an organ concert (John Stanley's Voluntary VIII, Op. 5), he suffered a complex partial seizure. The recorded concert performance (with the seizure) was analysed and compared with other available exercise records and with the composition. The musical analysis of the seizure-induced variations reveals that at the beginning of the seizure, the left hand started to become unprecise in time and deviated from the score, whereas the right hand remained faultless at this time. With increasing duration of the seizure discharge, the dissociation of both hands from the score increased but the right hand compensated for the errors of the left hand in a musically meaningful way, i.e. with the aim to compensate for the seizure-induced errors of the left hand. The case illustrates untroubled musical judgement during epileptic activity in the right temporal lobe at the beginning of the seizure. Whereas the temporal formation of the performance was markedly impaired, the ability of improvisation-in the sense of a 'perfect musical solution' to errors of the left hand-remained intact.

Adult

Learning and retention of words and designs following excision from medial or lateral temporal-lobe structures.

We sought to elucidate the contributions of the amygdala, hippocampus and temporal neocortex to learning and memory for verbal and visuospatial material. Two matched learning tasks, using abstract words versus abstract designs, were administered to patients with unilateral neocorticectomy (NCE; Dublin), selective amygdalohippocampectomy (AHE; Zurich) or anterior temporal-lobe resection invading the amygdala and hippocampus (ATL; Montreal). Data were analysed according to side and type of resection. Learning and recall for words was impaired in groups with resection from the left temporal lobe, irrespective of whether mediobasal structures were spared or temporal neocortex was spared. All right-resection groups were unimpaired. Learning for abstract designs was impaired across all trials in the right AHE and NCE groups, and on the last two trials in the right ATL group. Restricted deficits of lower magnitude were observed on some trials in left-resection groups. These results show a partial dissociation between side of excision and type of material, but the finding of similar deficits in all resection types was unexpected. We propose that excision from either the hippocampal region or temporal neocortex may result in a disconnection, giving a similar functional outcome, as both types of resection interrupt a circuit likely to be essential for normal storage and retrieval of information.

Amygdala

Thalamic glucose metabolism in temporal lobe epilepsy measured with 18F-FDG positron emission tomography (PET).

Thalamic glucose metabolism has been studied in 24 patients suffering from temporal lobe epilepsy (TLE) using interictal 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). A total of 17 patients had a unilateral TL seizure onset, 11 of these patients had a mesial temporal lobe epilepsy syndrome (MTLE), with mesial gliosis and a mesial TL seizure origin. Three patients had a lateral TL seizure origin, and 3 patients had mesial TL tumors. Bilateral TLE was assumed in 7 patients. Only in the patient group with MTLE (n = 11), the ipsilateral thalamic glucose uptake showed a statistically significant lower value when compared to the thalamus of the contralateral side (Wilcoxon paired sign test, P = 0.012). There was a more pronounced hypometabolism in right TLE compared to left TLE. A 'hypersynchronous seizure onset pattern' in ictal EEG was only seen in 6 (26%) patients (1 patient with bilateral, 5 with unilateral TLE). No correlation existed between the thalamic, temporal glucose metabolism and the 'hypersynchronous seizure onset pattern'.

Adult

Increased excitatory amino acid levels in brain cysts of epileptic patients.

We studied two epileptic patients with arachnoid brain cysts by proton magnetic resonance spectroscopy (1H MRS). In addition, histochemical analyses of surgical specimens, cerebrospinal fluid, and cystic fluid were performed in one of the patients. In both patients, greatly increased levels of excitatory amino acids (EAAs) glutamate and aspartate were present in the cystic fluid, while there was only a moderate increase of glutamate in the epileptogenic brain tissue adjacent to the cyst in one of the patients. In non epileptic brain regions, no elevations of the EAAs were present. Since EAAs are involved in induction and maintenance of epileptogenesis, their extremely high concentrations in the cystic fluid may explain seizures in some patients with such brain cysts. Our findings may have therapeutical consequences for patients with drug resistant epilepsy, in whom elevated concentrations of EAAs in the cysts can be verified. Surgery with the aim to create a communication between the cyst and the subarachnoidal space may prevent an accumulation of the EAAs and thus result in a relief of seizures.

Adolescent

Musicogenic epilepsy: review of the literature and case report with ictal single photon emission computed tomography.

PURPOSE: We report a case of musicogenic epilepsy with ictal single photon emission computed tomography (SPECT) study and discuss the findings of this patient in the context of 76 cases with musicogenic epilepsy described in the literature and seven other cases followed in Zurich. METHODS: We analyzed the 83 patients according to the precipitating musical factors, type of epilepsy, presumed localization of seizure onset, and demographic data. RESULTS: Fourteen of 83 patients (17%) had seizures triggered exclusively by music. At time of examination, music was the only known precipitating stimulus in 65 of 83 patients (78%). Various characteristics of the musical stimulus were significant, e.g., musical category, familiarity, and instruments. CONCLUSIONS: Musicogenic epilepsy is a particular form of epilepsy with a strong correlation to the temporal lobe and a right-sided preponderance. A high musial standard might predispose for musicogenic epilepsy. Moreover, the majority of cases do not fall into the category of a strictly defined "reflex epilepsy," but appear to depend on the indermediary of a certain emotional reaction mediated through limbic mesial temporal lobe structures.

Acoustic Stimulation

[Future perspectives in epilepsy treatment].

The primary goal of a causal (= curative) therapy of the epilepsies is the correction of the causes of the epilepsy syndrome. Unfortunately, at present, this is only possible to a limited extent. Recent advances have been achieved in the discovery of the possible causes of resistance to common antiepileptic drugs (increased activity of P-glycoprotein drug efflux-pump in the epileptogenic focus), in the discovery of the pathophysiology of some epilepsy syndromes as autoimmune diseases (Rasmussen encephalitis), as well as in the understanding of a few epilepsy forms as a genetically determined aberrations. Much expectation for a more accurate biochemical in-vivo characterization of epilepsy syndromes presently lies in the noninvasive proton magnetic resonance spectroscopy, with the ultimate goal of a more specific pharmacological therapy with antiepileptic drugs. Technical advances, which might gain importance for epilepsy therapy in the near future, are 'radiosurgery' and probably also gene-therapy, i.e. the treatment of focal epilepsies by intracerebral grafting of GABA- and adenosine-releasing cells developed in transgenic mice.

Animals

[Treatment of epilepsy: where are we today?].

The modern treatment of epilepsy has improved considerably in all three pillars. More than a century has passed, however, since Sir Charles Locock introduced the bromides in 1857 and Sir Victor Horsely pioneered epilepsy surgery in 1886 (18). In drug therapy, the 'classic AED' of the last decades, i.e. phenobarbital (Hauptmann, 1912) and phenytoin (Putnam and Merrit, 1938) are being largely displaced by valproate (Meunir, 1963) and carbamazepine (Lorge, 1963). Only ethosuximide (Zimmermann, 1951) has continued to maintain its position in 3/s spikewave-absence epilepsy, in particular in the USA (28, 29). Although it is an excellent drug against absences, it has the unpleasant property that it may induce GM seizures and should therefore be combined with a so-called 'GM protector' (mostly phenobarbital). For this reason ethosuximide has been relegated to second place in Europe by valproate. Thus, the decision as to which AED should be employed at the outset has been simplified considerably: actually, with valproate as the drug of first choice, which displays a very broad spectrum of action, we are on the right track for virtually all forms of epilepsy, perhaps with the exception of focal epilepsy (11). Especially in the event of focal epilepsy of temporal origin we employ carbamazepine as the preparation of first choice. In some countries (Denmark), because of the less severe side effects, oxcarbazepine is already preferred (Mogens Dam, personal communication). Considerable experience and knowledge are still required, however, when resistance has developed to traditionally applied classic monotherapy. Here, the range of further treatment can also be greatly extended by the availability of the 'new AED'. A generally accepted protocol for the replacement of one preparation with another first- or second-choice drug and, above all, for the 'right' combination with third-choice preparations can as yet not be compiled. What we need here is the expert epileptologist who has experience with 'theoretically useful' combinations and has an insight into the interactions occurring with such combinations. For several specific epileptic syndromes the 'Königsteiner Working Group of German-Speaking Epileptologists' has given clear and binding recommendations for AED therapy (e.g. for benign juvenile myoclonic epilepsy--Janz syndrome). This working group has also made recommendations for the necessary clinical and laboratory controls in AED therapy with potentially severe side effects (e.g. valproate therapy in high-risk children), which were published and/or are being published and discussed in the 'Epilepsie-Blätter' of the German League against Epilepsy (4). Despite all advances in drug therapy, the number of epilepsy patients not satisfactorily treatable with drug therapy has not been dramatically reduced statistically, so that the other two pillars of epilepsy therapy, i.e. epileptic surgery and behavioural therapy, continue to be very important.

Anticonvulsants

Bilateral medial temporal lobe damage without amnesic syndrome: a case report.

After the case report H.M. [42], unilateral neurosurgical interventions in the mediotemporal area have no longer been performed, if damage to the contralateral mediotemporal region was present, because of running the risk of provoking a postoperative amnesic syndrome. We present a patient with bilateral mediotemporal cysts and medically refractory complex partial seizures originating in the left mediotemporal region. Although our patient had additional right mediotemporal damage and poor non-verbal learning and memory, the left amygdaloid body and the left hippocampal formation were resected because the patient passed a selective anterior temporal lobe Amobarbital test. Postoperatively, our patient's non-verbal memory recovered to normal, but his verbal memory declined. Nevertheless, he was non-amnesic and seizure-free.

Age of Onset

"One-way asynchrony' of burst-suppression activity.

In a patient with traumatic intracerebral lesions, we recorded two subsequent electroencephalograms with burst-suppression activity. Between the two measurements, the clinical condition of the patient deteriorated. The first EEG showed symmetrical interhemispheric asynchrony of bursts. In the second EEG, however, we noted synchrony from one hemisphere to the other, but asynchrony in the opposite direction. We propose a simple model that can explain why one-way asynchrony of burst-suppression activity is prognostically more severe than symmetrical asynchrony.

Adult

Epilepsy surgery.

Surgical therapy of epilepsy, although still underutilized, is presently well accepted and performed world-wide with increasing frequency. In the last decade the following changes have been noticed: non-invasive pre-surgical evaluation is increasingly carried out in close collaboration with referring centres so that often no (or only a very short) hospitalization is necessary in highly specialized epilepsy centres for this purpose. Stereoelectro-encephalography (SEEG) is used less often in invasive evaluation while the subdural strip and grid electrode-techniques are used more often. There is a general trend for a more flexible and collaborative multidisciplinary and multi-method approach utilizing the whole spectrum of modern diagnostic facilities in a more patient-oriented and therefore more cost-effective way. The main objective of the pre-surgical evaluation is to determine the onset area of the patient's spontaneous habitual seizures. The primary epileptogenic zone is not necessarily synonymous with the so-called lesional zone, although in the great majority of patients they are related. In a small percentage of candidates for epilepsy surgery additional special examinations are necessary to prevent and/or predict the degree of post-operative deficits. At present selective Amytal tests are often used but these invasive procedures might be replaced in the future by functional PET and functional MR studies. Surgery in patients with epilepsy can be categorized into: (i) lesion-oriented surgery (lesionectomy sensu stricto), (ii) epilepsy-oriented lesional surgery, (iii) surgery for epilepsy sensu stricto. Surgery is performed with a 'curative (= causal)' or a 'palliative' intention. Furthermore surgery can be categorized into standardized epilepsy surgery (such as anterior temporal lobe resection, selective amygdalohippeocampectomy, anterior callosotomy); and individually tailored surgical interventions. It is obvious that also so-called standardized operations are tailored to some degree, usually based on pre-operative findings as well as on intraoperative corticography and/or other intra-operative neurophysiological tests (functional mapping). Individually tailored operations comprise smaller topectomies and larger resections. Surgery for temporal lobe epilepsy still prevails. For mesial temporal lobe epilepsy more selective operations, such as the selective amygdalohippocampectomy, are increasingly performed. Today the majority of patients suffering from this syndrome can be evaluated non-invasively (or 'semi-invasively' with the foramen ovale electrode technique) in combination with MRI (including volumetry of the hippocampus) and PET or SPECT. In general one has the impression that extratemporal resections without a lesion are performed less often. But, if a morphological abnormality is present, pre-surgical evaluation (using grids), and surgery making use of 'functional mapping' are increasingly offered from more and more centres. Anterior callosal sections and functional hemispherectomies have also witnessed a renaissance. The most important standardized operations are reviewed.

Amygdala

Intracranial temperature across 24-hour sleep-wake cycles in humans.

The 24 h time course of intracranial temperature, recorded subdurally at the parahippocampal gyrus in six patients (19 24 h periods), exhibited a prominent 24 h rhythm with its crest located at 20-21 h. The declining trend of intracranial temperature between lights off and sleep onset persisted in the first nonREM sleep episode (studied in two patients, seven sleep episodes). The correlation between EEG slow-wave activity (SWA) in nonREM sleep and the change in temperature explained < 25% of the variance. Although the change in temperature tended to be more positive in REM sleep episodes than in nonREM sleep episodes, no significant increase was observed in REM sleep. The data indicate that intracranial temperature exhibits a marked 24 h rhythm, the time course of which is only slightly affected by nonREM/REM sleep and EEG synchronization.

Adult

On the sensitivity of the human brain to magnetic fields: evocation of epileptiform activity.

Evocation of epileptiform activity by DC magnetic fields of between 0.9 and 1.8 millitesla (mT) has been demonstrated in 6 epileptic patients undergoing presurgical evaluation. The activity was monitored by electroencephalography (EEG) recording from both electrodes attached to the scalp as well as from intracranial electrodes inserted via the foramen ovale. Epileptiform activity evoked by the magnetic field application was distinguished from background levels by comparing the number of epileptiform discharges in the 10-s intervals before and after field applications. In nearly all cases, a delay of up to several seconds was observed between the application of the magnetic field and the onset of epileptiform firing. Removal of the field also appeared to cause firing in some instances, but this has not yet been investigated systematically. In all 6 patients, subsequent seizures confirmed that the epileptiform activity monitored during the experiments was originating from the primary epileptogenic zones of the patients.

Adult

[Comparison of valproate level in human plasma, cerebrospinal fluid and brain tissue following administration of various preparations of valproate and valpromide].

The concentration of valproate was measured in plasma, CSF and brain tissue of patients who underwent resective surgical treatment because of severe temporal lobe epilepsy after pretreatment with either a sustained release formulation of valproate (Depakine Chrono: 5 patients), the conventional formulation of valproate (Depakine: 6 patients) or valpromide (Depamide: 2 patients). With a mean serum value for all 13 patients of 32.3 micrograms/g valproate, the mean brain/serum ratio was 15.1% (SD 6.1%). The valproate concentration of the hippocampus was significantly higher than that of the amygdala, and patients who had the sustained release formulation had significantly higher valproate concentration in the CSF and in the hippocampal formation than those patients who had the conventional valproate. Since a few patients had tumors, whereas others had varying degrees of gliosis, it cannot be ruled out that these differences are the result of different histopathological conditions with related differences in blood-brain barrier functions.

Adolescent

Treatment of refractory epilepsy with intravenous immunoglobulins. Results of the first double-blind/dose finding clinical study.

Sixty-one refractory epileptic patients (46 with partial epilepsy) were treated with intravenous immunoglobulins in a controlled double-blind/dose finding clinical trial; 18 (7 females, mean age 18.5 years) received placebo, while 14 (3 females, mean age 26.2 years, 2 excluded), 14 (4 females, mean age 24.6 years, 1 excluded) and 15 (5 females, mean age 24.4 years) patients received 100, 250 and 400 mg/kg per infusion of intravenous immunoglobulins, respectively. Seven perfusions were scheduled, four the 1st week, and thereafter one during the 2nd, 3rd and 6th week. The patients were followed for 6 months. An optional infusion was given at the end of the study. A comparison of the mean number of seizures per day was made between the baseline (4 weeks before the first infusion) and the 6th month after the first infusion. Patients were considered responders if they had a decrease of at least 50% in daily seizure frequency at the end of the study compared with the baseline. We did not find severe adverse events. One patient had to stop infusions for possible related side effects (vomiting). When all patients were analyzed together, we found a positive trend in favor of intravenous immunoglobulin treatment, but this was not significant (P = 0.095). There was no relationship between dose and efficacy (P = 0.31). When the largest group with partial epilepsy was analyzed separately, we noted 19 responders in the test group, compared with 2 in the placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent