Biomedical subjects

Krisztina Benedek

Publications and source records attributed to Krisztina Benedek.

14 recordsLinked to original sources

PubMed2007

Hypobaric hypoxia reduces the amplitude of oscillatory potentials in the human ERG.

PURPOSE: To explore the retinal functions in healthy volunteers during acute hypoxic exposure, applying a set of electrophysiological tests. METHODS: Standard electroretinograms (ERGs) of the retina (rod-(scotopic) ERGs, cone-(photopic) ERGs, maximal responses and oscillatory potentials (OPs)) and 30-Hz flicker ERGs were recorded according to ISCEV (International Society of Clinical Electrophysiology of Vision) recommendations in 14 healthy volunteers during a 15-min exposure to a simulated altitude of 5500 m. RESULTS: The mean arterial oxygen saturation level was significantly reduced (P < 0.001) during the hypobaric challenge. It returned to the normal level very shortly after the end of the hypoxic exposure. No significant change in the latency or amplitude of the slow components of the ERG was found in any recording. The OPs of the ERG, however, revealed a significant decrease in amplitude during hypoxic exposure. Both OP1 and OP2 amplitudes were significantly different (P < 0.05) from the baseline values during hypoxia. Partial recovery of these waves occurred after termination of the hypoxia. CONCLUSIONS: These results appear to support the notion that the inner layers of the retina presumed to be the main source of the OPs, display the highest sensitivity towards circulatory and/or hypoxic challenges.

Adolescent↗

PubMed2006

[Headache: diagnosis and treatment].

Headache is the most common reason why patients visit a neurologist. Approximately 70% of the population suffer from headache. The symptoms in this condition are rather simple and a well-controlled therapy is mostly available, but there are still frequent failures in the diagnosis and therapy of headaches. Failures in the treatment are caused mainly by the fact the doctors are not able to set the appropriate diagnosis. It is recommended that patients with persisting headache should turn to headache centers. The therapy should be determined by the frequency and duration of the headache, its severity, the accompanying symptoms and preceding therapeutic history. This survey may be of assistance on the state-of-the-art diagnostics and therapy of headaches in neurological practice.

Brain Diseases↗

PubMed2006

[Parallel processing of visual information].

This is a survey on the function of parallel visual pathway with a special emphasis on its clinical implications. It is based on data in the literature and own results of our group. The paper primarily deals with the X, Y, W pathways and by the magnocellular, parvocellular and koniocellular visual pathways characterized by cells of various size as well as by nerve fibers of various thickness. Electrophysiological, microelectrode recording of single-unit activity makes the distinction between the pathways available in animal model. Much more difficulties arise if we intend to characterize the pathways in humans or to detect the selective damage of one of these pathways in patients. The non-invasive diagnostic methods that could be used in the diagnosis are detailed here, too. Finally, the neurological, ophthalmological and psychological diseases are discussed in which a selective damage of any visual pathway is suspected. Summing it up, the survey provides evidences for the introduction of the novel concept of parallel pathways into the diagnostic aspects of ophthalmology, neurology and psychiatry.

Humans↗

PubMed2006

Electrophysiological findings in patients with nonarteritic anterior ischemic optic neuropathy.

OBJECTIVE: Nonarteritic ischemic optic neuropathy (NAION) is one of the most frequent causes of sudden visual loss in middle-aged or elderly patients. Although several electrophysiological methods are available for an objective evaluation of the visual deficits, these are not generally used in the assessment of the clinical condition of NAION patients. To evaluate the severity of the optic nerve and retinal damage, electrophysiological tests were performed on 8 patients with NAION. METHODS: Visual evoked potentials (VEPs), scotopic, photopic and flicker electroretinograms (ERGs), multifocal ERGs and pattern ERGs were recorded. RESULTS: The results demonstrated that the VEPs fairly reliably reflected the visual loss caused by NAION. The VEPs were extinguished in cases with a serious visual acuity loss, while a decrease in amplitude and a lengthening of the P100 latency were observed in cases with good visual acuity and a severe visual field loss and in the nonattacked fellow eye of the patients with monocular involvement. The pattern ERGs failed to show signs of retrograde degeneration. The photopic, scotopic and flicker ERGs, and the oscillatory potentials (OPs) were close to normal in these NAION patients. CONCLUSIONS: Our observations permit the conclusion that electrophysiological methods can provide an objective indication of the clinical condition of these patients. The new data obtained promote an understanding of the pathomechanism of the disease. SIGNIFICANCE: Electrophysiological tests are suitable for monitoring of the progression of the disease in NAION patients.

Adult↗

PubMed2006

The effects of reward and punishment contingencies on decision-making in multiple sclerosis.

Many patients with multiple sclerosis (MS) show cognitive and emotional disorders. The purpose of this study is to evaluate the role of contingency learning in decision-making in young, non-depressed, highly functioning patients with MS (n=21) and in matched healthy controls (n=30). Executive functions, attention, short-term memory, speed of information processing, and selection and retrieval of linguistic material were also investigated. Contingency learning based on the cumulative effect of reward and punishment was assessed using the Iowa Gambling Test (IGT). In the classic ABCD version of the IGT, advantageous decks are characterized by immediate small reward but even smaller future punishment. In the modified EFGH version, advantageous decks are characterized by immediate large punishment but even larger future reward. Results revealed that patients with MS showed significant dysfunctions in both versions of the IGT. Performances on neuropsychological tests sensitive to dorsolateral prefrontal functions did not predict and did not correlate with the IGT scores. These results suggest that patients with MS show impaired performances on tasks designed to assess decision-making in a situation requiring the evaluation of long-term outcomes regardless of gain or loss, and that this deficit is not a pure consequence of executive dysfunctions.

Adult↗

PubMed2006

Longitudinal changes in cortical glucose hypometabolism in children with intractable epilepsy.

In children with partial epilepsy, there is increasing evidence to suggest that not all cortical regions showing glucose hypometabolism on positron emission tomography (PET) represent epileptogenic cortex but that some hypometabolic areas might be the result of repeated seizures. Most of the supportive data, however, have come from cross-sectional imaging studies. To evaluate longitudinal changes in cortical glucose hypometabolism, we compared two sequential [(18)F]fluorodeoxyglucose (FDG) PET scans performed 7 to 44 months apart in 15 children with intractable nonlesional partial epilepsy. The extent of hypometabolic cortex on the side of the electroencephalography-verified epileptic focus and its changes between the two PET scans were measured and correlated to clinical seizure variables. The change in seizure frequency between the two PET scans correlated positively with the change in the extent of cortical glucose hypometabolism (r = .8, P <.001). Most patients with persistent or increased seizure frequency (one or more seizures per day) showed enlargement in the area of hypometabolic cortex on the second PET scan. In contrast, patients whose seizure frequency had decreased below daily seizures between the first and second PET scans showed a decrease in the size of the hypometabolic cortex. These results support the notion that the extent of cortical glucose hypometabolism on PET scanning can undergo dynamic changes, and these are, at least partly, related to the frequency of seizures. The findings have implications on how aggressively persistent seizures should be treated in children. (J Child Neurol 2006;21:26-31).

Adolescent↗

PubMed2005

Non-arteritic ischaemic optic neuropathy (NAION) in patients under 50 years of age.

PURPOSE: The goal of our study was to compare the case histories and clinical findings in three young patients (aged<50 years) who had undergone their first attack of non-arteritic ischaemic optic neuropathy (NAION). We intended to consider whether NAION at a relatively young age might comprise a separate pathological and diagnostic entity. RESULTS: All three cases revealed some common characteristics. All of them experienced recurrent attacks with bilateral manifestations that led to severe loss of vision and visual field defects. The patients had also suffered from diabetes mellitus for a long time, but none of them had diabetic retinopathy. CONCLUSION: The case histories of these relatively young patients showed some differences, including recurrences and more severe loss of vision, to those of elderly patients. However, all the signs we found had been reported previously, although much less frequently, in NAION cases among elderly patients. The clinical and laboratory findings definitely exclude the possibility of an alternative diagnosis. Hence, our results do not support the notion of a different pathomechanism of NAION at a young age and its existence as a separate disease entity.

Adult↗

PubMed2004

[New chapter in the study of visual evoked potentials--clinical application of the multifocal VEP method].

The multifocal visual evoked potentials are the evoked responses over the visual cortex in response to the stimulation of circumscribed small areas in the central 30 degree region of the retina. The recording of multifocal visual evoked potentials was made possible by the computer algorhythm elaborated by Sutter in 1991. Multifocal electroretinography, developed upon the same theoretical principles, is already an routine clinical examination method for the topographic analysis of functional damages in the central part of the retina and for the differential diagnostics in neuro-ophthalmology. The multifocal visual evoked potential, however, has not been introduced into the clinical practice, although it displays the function of ganglion cells in a given region of the retina in a more detailed way than the sensitivity threshold in the perimetry. This examination makes the objective verification of defects possible in the visual pathway, too. In our department the recording of multifocal visual evoked potentials was started in 2002. In this paper we present the basics of this method and also deal with the problems concerning its application and its status in the history of visual evoked potentials.

Electroretinography↗

PubMed2004

Quantitative visualization of ictal subdural EEG changes in children with neocortical focal seizures.

OBJECTIVE: To quantify the ictal subdural electroencephalogram (EEG) changes using spectral analysis, and to delineate the quantitatively defined ictal onset zones on high-resolution 3D MR images in children with intractable neocortical epilepsy. METHODS: Fourteen children with intractable neocortical epilepsy (age: 1-16 years) who had subsequent resective surgery were retrospectively studied. The subjects underwent a high-resolution MRI and prolonged subdural EEG recording. Spectral analysis was applied to 3 habitual focal seizures. After fast Fourier transformation of the EEG epoch at ictal onset, an amplitude spectral curve (square root of the power spectral curve) was created for each electrode. The EEG magnitude of ictal rhythmic discharges was defined as the area under the amplitude spectral curve within a preset frequency band including the ictal discharge frequency, and calculated for each electrode. The topography mapping of ictal EEG magnitude was subsequently displayed on a surface-rendered MRI. Finally, receiver operating characteristic (ROC) analysis was performed to evaluate the consistency between quantitatively and visually defined ictal onset zones. RESULTS: The electrode showing the maximum of the averaged ictal EEG magnitude was part of the visually defined ictal onset zone in all cases. ROC analyses demonstrated that electrodes showing >30% of the maximum of the averaged ictal EEG magnitude had a specificity of 0.90 and a sensitivity of 0.74 for the concordance with visually defined ictal onset zones. SIGNIFICANCE: Quantitative ictal subdural EEG analysis using spectral analysis may supplement conventional visual inspection in children with neocortical epilepsy by providing an objective definition of the onset zone and its simple visualization on the patient's MRI.

Adolescent↗

PubMed2004

Metabolic changes of subcortical structures in intractable focal epilepsy.

PURPOSE: Intractable focal epilepsy is commonly associated with cortical glucose hypometabolism on interictal 2-deoxy-2[18F]-fluoro-D-glucose (FDG) positron emission tomography (PET). However, subcortical brain structures also may show hypometabolism on PET and volume changes on magnetic resonance imaging (MRI) studies, and these are less well understood in terms of their pathophysiology and clinical significance. In the present study, we analyzed alterations of glucose metabolism in subcortical nuclei and hippocampus by using FDG-PET in young patients with intractable epilepsy. METHODS: Thirty-seven patients (mean age, 7.5 years; age range, 1-27 years) with intractable frontal (n = 23) and temporal (n = 14) lobe epilepsy underwent FDG-PET scanning as part of their presurgical evaluation. Normalized glucose metabolism was measured in the thalamus and caudate and lentiform nuclei, as well as in hippocampus, both ipsi- and contralateral to the epileptic focus, and correlated with duration and age at onset of epilepsy, presence or absence of secondary generalization, location of the epileptic focus, and extent of cortical glucose hypometabolism. RESULTS: Long duration of epilepsy was associated with lower glucose metabolism in the ipsilateral thalamus and hippocampus. Duration of epilepsy was a significant predictor of ipsilateral thalamic glucose metabolism in both temporal and frontal lobe epilepsy. Presence of secondarily generalized seizures also was associated with lower normalized metabolism in the ipsilateral thalamus and hippocampus. Extent of cortical hypometabolism did not correlate with subcortical metabolism, and glucose metabolism in the caudate and lentiform nuclei did not show any correlation with the clinical variables. CONCLUSIONS: The findings suggest that metabolic dysfunction of the thalamus ipsilateral to the seizure focus may become more severe with long-standing temporal and frontal lobe epilepsy, and also with secondary generalization of seizures.

Adolescent↗

PubMed2004

Is intraoperative electrocorticography reliable in children with intractable neocortical epilepsy?

PURPOSE: To study the relation between the spike frequency during intraoperative electrocorticography (ECoG) under general anesthesia with isoflurane and that during extraoperative ECoG monitoring in children with intractable neocortical epilepsy. METHODS: Twenty-one children (age, 1-16 years; 15 boys and six girls) who underwent intraoperative and extraoperative ECoG monitoring with subdural electrode arrays were studied. The spike frequency and the spatial pattern of spike frequency were compared between intraoperative and extraoperative ECoGs for each patient (by using Wilcoxon signed-ranks and Spearman's rank correlation, respectively). RESULTS: In 15 of 21 patients, the spike frequency was significantly lower during intraoperative than during extraoperative ECoG (mean z = -6.3; p < 0.001). In four of 21 patients, no significant difference was found in the spike frequency between intraoperative and extraoperative recordings. In two of 21 patients, spike frequency reached one spike/min neither during intraoperative nor extraoperative recording; therefore appropriate comparison of spike frequency was not possible. A significant positive correlation in the spike-frequency pattern was seen between intraoperative and extraoperative recordings in nine of nine cases who had > or = 10 spikes/min during intraoperative ECoG (mean rho = 0.62; p < 0.01), in five of six cases with one to nine spikes/min (mean rho = 0.50; p < 0.01), and in none of five cases with less than one spike/min (mean rho = 0.13). CONCLUSIONS: General anesthesia often decreases the spike frequency in children with neocortical epilepsy, yet intraoperative ECoG can reliably reflect the awake interictal spiking pattern when spike frequency exceeds one spike/min during intraoperative ECoG recording.

Adolescent↗

PubMed2003

The scotopic low-frequency spatial contrast sensitivity develops in children between the ages of 5 and 14 years.

The purpose of this study was to investigate the development of visual contrast sensitivity (CS) in children between 5 and 14 years of age. Six spatial frequencies and static (0 Hz) and dynamic (8 Hz) conditions were used at photopic and scotopic luminance levels. The results revealed significant maturation of CS, which reached the adult-like values by 11-12 years of age. The development was more pronounced at low spatial frequencies (<2 cycles/degree) and in the dynamic condition. The scotopic CS exhibited slower development than the photopic CS. These results suggest the late maturation of the magnocellular visual pathway.

Adolescent↗

PubMed2003

Human scotopic spatiotemporal sensitivity: a comparison of psychophysical and electrophysiological data.

The aim of the study was to investigate spatiotemporal visual functions under scotopic and photopic conditions in order to acquire human psychophysical and electrophysiological data that are comparable with contrast sensitivities based on single-unit recordings in animal experiments. Static and dynamic contrast sensitivities (CSs) and steady-state visual evoked potentials (VEPs) were measured under photopic and scotopic conditions in healthy volunteers. The results from the CS experiment indicated that the inclusion of temporal modulation and the application of scotopic luminance levels uniformly resulted in a relatively increased sensitivity for low spatial frequencies. Similarly, analysis of the second harmonic component of the VEPs demonstrated a shift from band-pass to low-pass functions. These results suggest that, under scotopic conditions, human visuospatial processing is characteristically predominated by the functional activity of the magnocellular pathways.

Adolescent↗

PubMed2002

Short-term hypobaric hypoxia enhances visual contrast sensitivity.

The effect of hypoxia on early visual functions remains a controversial area of research. To explore this question, we measured static and dynamic visual contrast sensitivity in 14 healthy volunteers at a simulated altitude of 5500 m. In comparison with the baseline condition (mean arterial oxygen saturation: 98.4%), contrast sensitivity significantly increased after 5, 10 and 15 min of hypoxic exposure (saturation: 82.9%, 77.0%, 74.3%, respectively). After 10 min, this enhancement was markedly pronounced under dynamic conditions. Returning to the baseline altitude (saturation: 97.7%), contrast sensitivity recovered, mostly at the lower spatial frequencies. There was a significant negative relationship between arterial oxygen saturation and contrast sensitivity values at low and medium spatial frequencies (0.5-4.8 c/deg). These results suggest that early visual processing may be enhanced during short-term hypoxic challenge.

Adult↗