Biomedical subjects

G Benedek

Publications and source records attributed to G Benedek.

At least 19 recordsLinked to original sources

PubMed2006

Measurement of the p to s wave branching ratio of 187Re beta decay from beta environmental fine structure.

The mixed occurrence of s-wave and p-wave contributions in a first forbidden unique Gamow-Teller beta decay has been investigated for the first time by measuring the beta environmental fine structure (BEFS) in a 187Re crystalline compound. The experiment has been carried out with an array of eight AgReO4 thermal detectors operating at a temperature of approximately 100 mK. A fit of the observed BEFS spectrum indicates the p-wave electron emission as the dominant channel. The complete understanding of the BEFS distortion of the 187Re beta decay spectrum is crucial for future experiments aiming at the precise calorimetric measurement of the antineutrino mass.

Journal Article↗

PubMed2006

The role of gas dynamics in operation conditions of a Pulsed Microplasma Cluster Source for nanostructured thin films deposition.

This study intends to explain the fluid dynamic characteristics of a Pulsed Microplasma Cluster Source (PMCS). An axially symmetric steady state simulation is performed for modeling the real-life three-dimensional unsteady flow of hypersonic helium inside our PMCS. Hypersonic helium flow is simulated using Realizable k-epsilon turbulent model. We obtained the jet velocity, density, and pressure field inside our PMCS for the conditions considered and discussed them with respect to our experimental observations. We also presented a qualitative discussion on the formation-termination process of this hypersonic jet. In particular, simulation, in agreement with the experiment, indicates that the middle stage of the injection process, where the Mach disk stands close to the ablation target and at the same time the mass flow rate is relatively high, is almost the appropriate time for firing the electric discharge. We simulated the jet-electrode impingement and tracked the trajectory of the ablated carbon clusters, considered as rigid spheres, inside the PMCS. We noticed that the spatial distribution of the clusters inside PMCS is highly conserved during the free expansion of the cluster beam out of the nozzle (in the vacuum chambers) and is recognizable in the deposited carbon film. This indicates that the geometry of PMCS plays a significant role in the uniformity of the deposited film.

Computer Simulation↗

PubMed2005

Spatial and temporal visual properties of single neurons in the suprageniculate nucleus of the thalamus.

The spatial and temporal visual sensitivity to drifting sinusoidal gratings was studied in 105 neurons of the suprageniculate nucleus of the feline thalamus. Extracellular single-unit recordings were performed in halothane-anesthetized, immobilized, artificially ventilated cats. Most suprageniculate nucleus cells were strongly sensitive to the direction of drifting gratings. The suprageniculate nucleus units had a clear preference for very low spatial frequencies with a mean of 0.05 cycle/deg. The spatial resolution was also very low with a mean of 0.16 cycle/deg. Most of the cells displayed low-pass spatial tuning characteristics, while the remainder of the units were band-pass tuned. The suprageniculate nucleus units were extremely narrowly tuned, to spatial frequencies with a mean spatial bandwidth of 1.07 octaves. A majority of the units responded optimally to high temporal frequencies, with a mean of 8.53 Hz. The temporal frequency tuning functions predominantly revealed a band-pass character, with a mean temporal bandwidth of 1.66 octaves. These results demonstrate that the neurons in the suprageniculate nucleus display particular spatial and temporal characteristics. The spatial and temporal tuning properties of the suprageniculate nucleus neurons are very similar to those of the superior colliculus and the anterior ectosylvian cortex, structures that provide the main visual afferentation toward the suprageniculate nucleus. This suggests their common function in motion perception, and especially in the recording of movements of the visual environment relative to the body, and the related behavioral action.

Animals↗

PubMed2005

Visual receptive field properties of excitatory neurons in the substantia nigra.

The substantia nigra has been widely regarded as a structure involved in visuomotor co-ordination, but little is known about the sensory background of its function. Here we give a detailed description of the visual receptive field properties of excitatory substantia nigra neurons. The visual responses of 59 excitatory neurons were recorded in both the substantia nigra pars reticularis and the pars compacta of halothane-anesthetized, immobilized, artificially respirated cats. The substantia nigra neurons were not responsive or exhibited very low sensitivity to stationary visual stimulation. The units responded optimally to small stimuli moving at intermediate or high velocities in their extremely large receptive field. We observed no signs of retinotopical organization within the substantia nigra. A majority of the units exhibited narrow direction tuning and high direction selectivity, while a smaller proportion of them were broadly tuned and not direction-sensitive. Our results suggest that the visual properties of the excitatory substantia nigra units are quite similar to those of the superior colliculus and other extrastriatal structures that receive tectal afferents. This supports the notion that the substantia nigra processes dynamic visual information and that its excitatory visual neurons are modulated by the extrageniculate tectal visual system of the mammalian brain.

Action Potentials↗

PubMed2004

Patients with schizophreniform disorder use verbal descriptions for the representation of visual categories.

BACKGROUND: Neuropsychological impairment is a common finding in schizophrenia. However, a significant proportion of patients are not impaired in conventional neuropsychological tests. In this study, we investigated whether remitted patients with schizophreniform disorder exhibited dysfunctions in specific cognitive tasks. METHOD: Twenty remitted, highly functioning patients with schizophreniform disorder and 20 control subjects participated in the study. In addition to background neuropsychological evaluation (WAIS-R IQ, Wisconsin Card Sorting Test (WCST), Trail Making B, Rey Osterrieth Complex Figure), subjects received a category learning task. The categories consisted of geometric shapes systematically changing in shape and size. Training included the sequential presentation of category members (visual learning) and verbal description of categories. RESULTS: The patients with schizophreniform disorder had normal IQ, executive functions/psychomotor speed (WCST and Trail Making B) and visual memory (Rey-Osterrieth Complex Figure). In contrast, they displayed impaired categorization performances after visual learning. The performance of the patients improved markedly after verbal description of categories. Verbal knowledge about categories positively correlated with categorization performance in the patients, but not in the controls. CONCLUSIONS: Category learning functions, which include decision-making under uncertainty and feature integration, are impaired in patients with schizophreniform disorder who display normal executive functions and visual memory. These patients may use verbal knowledge as a compensatory strategy in visual tasks.

Adult↗

PubMed2004

No evidence for impaired 'theory of mind' in unaffected first-degree relatives of schizophrenia patients.

OBJECTIVE: The aim of this study was to investigate the possibility that 'theory of mind' (ToM) impairments are associated with schizophrenia liability. METHOD: Forty healthy control subjects and 79 first-degree biological relatives of schizophrenia patients (32 siblings and 47 parents) received the Eyes Test, during which subjects are asked to choose the word best describes the mental state of a person whose eyes are depicted on a photograph. RESULTS: The affected relatives (n = 14) performed worse on the Eyes Test compared with the controls (P = 0.0001), whereas the unaffected relatives (n = 65) showed intact performances (P = 0.4). The Eyes Test values did not correlate with age and IQ. There was no significant difference between male and female participants. CONCLUSION: ToM deficits, as measured by the Eyes Test, are not associated with schizophrenia liability.

Adult↗

PubMed2003

Dopaminergic contributions to the visual categorization of natural scenes: evidence from Parkinson's disease.

Recent evidence raised the possibility that dopaminergic mechanisms in the neostriatum play an important role in categorization. In this study, we examined the electrophysiological correlates of natural scene categorization in Parkinson's disease (PD), which is characterized by the depletion of dopamine in the neostriatum. Event-related potentials (ERPs) were recorded in PD patients and age-matched control subjects using a natural scene categorization task. Subjects had to decide whether a briefly presented image contained animals or non-animals. In the control group, the mean amplitudes of N1 (150-250 ms) and N2 components (400-600 ms) were more negative for non-animal scenes as compared with stimuli containing animals, whereas P2 (250-350 ms) was more positive for animals. In contrast, in the PD group the mean amplitudes of N1 and N2 components were similar for both animal and non-animal stimuli, and the P2 amplitudes were reduced. In the case of N1 peak latency, there was no between-group difference, whereas the N2 and P2 components were significantly delayed in the PD group. These results suggest that both perceptual (N1) and semantic (N2) processes related to the categorization of natural scenes are specifically impaired in PD. In the temporal domain, the slowed semantic processing is preceded by a relatively normally paced perceptual analysis. These findings are in agreement with the hypothesis emphasizing the importance of striatal dopaminergic mechanisms in classification functions.

Aged↗

PubMed2003

Effects of surface cues on macaque inferior temporal cortical responses.

Humans are able to recognize objects when surface details, such as colour, texture and luminance gradients, are not available. By systematically eliminating colour, texture, shading, contrast and inner contours from given objects, we tested whether certain shape-selective inferior temporal cortex (IT) neurons of awake rhesus monkeys remain selective for these objects as the surface information is reduced. In psychophysical experiments, we established that the rhesus monkey can identify the shape of a coloured object largely independently of its surface characteristics and, to a lesser degree, of its inner contours. Shape selectivity of the neurons does not change when texture and shading are concealed. The responsiveness of the neurons is also affected by the removal of these surface attributes. The IT neurons were found to respond highly similarly to objects brighter or darker than their background. Selectivity for shape is preserved when the contrast is reversed. Deletion of the inner contours, outlining the main parts of the objects, did not affect the responses and selectivity of the IT neurons. These findings indicate that the IT can contribute to the invariant perception of objects having different surface details.

Animals↗

PubMed2003

Extents of visual, auditory and bimodal receptive fields of single neurons in the feline visual associative cortex.

Extracellular microelectrode recordings were carried out on 150 neurons in the anterior ectosylvian sulcal region of halothane-anesthetized, immobilized, artificially ventilated cats. Fifty-nine neurons were visual, 60 were auditory and 31 were bimodal visual-auditory. As the extent of the receptive fields has never been exactly determined, we introduced a quasi-objective, computer-based, statistical method in order to estimate the receptive field sizes in the anterior half of the perimeter. The visual, auditory and bimodal cells had very large receptive fields, often with portions extending well into the ipsilateral hemifield. The mean extents of the visual and auditory receptive fields in the horizontal plane were 75.75 degrees (N=59, SD: +/- 28.620, range: 15-135 degrees), and 132.5 degrees (N=60, SD: +/- 46.72 degrees, range: 15-165 degrees) respectively. These data suggest that a single visual neuron can carry information from the whole visual field of the right eye and a single auditory unit can carry information of azimuths throughout the whole area of the horizontal plane studied. The mean extent of the bimodal receptive fields in the horizontal plane was 82.1 degrees (N=31, SD: +/- 24.24 degrees, range: 30-135 degrees). In 21 of the 31 bimodal cells we observed a facilitatory interaction between visual and auditory stimuli. The mean extent of the facilitatory interactions in these cells was 75.75 degrees (N=21, SD: +/- 24.56 degrees, range: 45-135 degrees).

Animals↗

PubMed2002

Spatial contrast sensitivity of migraine patients without aura.

Visual disturbances are frequent symptoms in migraine. Since there is a possibility of separate damage in the magno- or parvo-cellular visual pathway in migraine patients, we performed a study including the measurement of static and dynamic spatial contrast sensitivity on 15 patients suffering from migraine without aura under photopic and scotopic conditions. Fifteen healthy volunteers without primary headache served as controls. The results revealed a marked decrease in contrast sensitivity at low spatial frequencies in the migraine patients. Spatial contrast sensitivity demonstrated some lateralization, as the sensitivity to low spatial frequencies obtained through separate eyes showed significantly larger side-differences in migraine patients than in control subjects. These findings suggest that the mechanisms responsible for vision at low spatial frequencies are impaired in migraine patients. This might indicate impaired function of the magnocellular pathways in this condition.

Adult↗

PubMed2001

Intact prototype learning in schizophrenia.

In this study, we examined executive functions and visual prototype learning in patients with schizophrenia (n=22) and matched healthy control subjects (n=20). The patients demonstrated marked perseveration in the Wisconsin Card Sorting Test (WCST), whereas they successfully learned prototypes of dot-pattern category exemplars. These findings are against the hypothesis of a pure generalized cognitive dysfunction in schizophrenia, providing preliminary evidence for intact neocortical mechanisms related to perceptual classification functions.

Adult↗

PubMed2001

Convergence of Y and non-Y channels onto single neurons in the superior colliculi of the cat.

Receptive field properties of single neurons in the cat superior colliculus were examined following selective conduction-block of Y-type fibers in contralateral optic nerve. Although the responses evoked by photic stimuli presented via the Y-blocked eye were significantly weaker than those evoked by stimuli presented via the normal eye, > 85% of collicular cells were binocular. Furthermore, when binocular cells were stimulated via the Y-blocked eye their median upper cut-off velocity (100 degrees /s) was significantly lower than that (400 degrees /s) for stimuli presented via the normal eye. Thus, there is a substantial degree of excitatory convergence of Y- and non-Y- information channels on single collicular neurons and the responses to high velocity of motion appear to depend on the integrity of Y-type input.

Action Potentials↗

PubMed2001

[Impaired visual information processing in unaffected siblings of schizophrenia patients].

Recent research has provided evidence that certain psychophysiological dysfunctions are present in non-psychotic biological relatives of schizophrenia patients. A new candidate for such studies is the visual backward masking (VBM) dysfunction. In this study, the authors compared the VBM and Wisconsin Card Sorting Test (WCST) performances of unaffected siblings of schizophrenia patients with that of normal volunteers with a negative family history. In the BM test, a briefly presented target letter must be recognized, which is followed by an irrelevant stimulus (mask). The WCST assesses higher-level cognitive (prefrontal) functions of categorization and attentional set-shifting. Despite their intact psychosocial and general intellectual functions, the unaffected relatives of schizophrenia patients showed lower BM performances in comparison with the controls, which was restricted to short interstimulus intervals (< 60 ms). In the controls, there was a non-linear (N-shaped) masking function, whereas in the relatives no similar effects were found. There was no significant difference in the WCST performances. These results suggest that the dysfunction of early sensory-perceptual processes is a trait marker of schizophrenia.

Adolescent↗

PubMed2001

Remitted schizophrenia-spectrum patients with spared working memory show information processing abnormalities.

Working memory and information processing abnormalities are often reported in schizophrenia. The aim of this study was to examine visual backward masking (BM) functions in remitted schizophrenia-spectrum patients with spared working memory functions. Seventy-two patients with DSM-IV schizophrenia-spectrum disorders were screened using the Wisconsin Card Sorting Test (WCST) and the digit span forward/backward tasks. Patients with spared WCST and digit span performances were selected and administered a spatial working memory test and two BM procedures (target identification and location). The schizophrenia-spectrum group with spared WCST and digit span performances included individuals with schizophreniform disorder (N=11), schizophrenia (N=2), and schizoaffective disorder (N=2). These patients were clinically remitted and demonstrated spared IQ, normal spatial working memory, and relatively high psychosocial functioning. However, there was a significant impairment in the BM procedure, most prominently in the target location task and at short interstimulus intervals. These results suggest that the BM dysfunction is a trait marker of schizophrenia-spectrum disorders and may be present in the absence of working memory abnormalities.

Adult↗

PubMed2001

Are Alzheimer's disease patients able to learn visual prototypes?

Recently, controversial results emerged regarding visual prototype learning in Alzheimer's disease (AD). The aim of this study was to elucidate this issue in a larger population of AD patients. The AD patients (N=72) and age-matched healthy control subjects (N=25) learned to recognize and to categorize visual dot patterns. In comparison with the control subjects, the AD patients as a group showed dysfunctions in the recognition task, whereas categorization was relatively spared in their case. Recognition was impaired in patients with mild AD (Mini-Mental score: 18-23) and moderate AD (Mini-Mental score<18), whereas categorization was impaired only in patients with moderate AD. These results suggest that while the medio-temporal/diencephalic explicit memory system is markedly affected even in early AD, the sensory neocortical areas mediating implicit category learning display a sufficient degree of functional capacity until later stages of the disease.

Aged↗

PubMed2001

Event-related potentials from a visual categorization task.

Investigation of the neural bases of human perceptual categorization is a continuously growing territory of visual sciences. Recently, several papers appeared on the cortical bases of human categorization performance, using functional brain imaging techniques such as positron emission tomography (PET) or functional magnetic resonance imaging (fMRI). However, the cheaper commercially available laboratory tests are not always the best methods to study multiple aspects of visual categorization. In this study, we describe the electrophysiological correlates of natural scene categorization in humans. The subject's task was to decide whether briefly presented natural scenes contained animal or non-animal items. Analysis of event-related potentials (ERPs) recorded during the categorization task, revealed more negative potentials for non-animal stimuli (NAS) in the time windows of 150-250 ms (N1) and 350-500 ms (N2), and more positive potentials for animal stimuli (AS) in the time window of 250-350 ms (P2). Our work provides an inexpensive noninvasive method to study both early perceptual and late phases of semantic information processing by recording ERPs during the categorization of natural scenes.

Evoked Potentials, Visual↗

PubMed2001

Different trait markers for schizophrenia and bipolar disorder: a neurocognitive approach.

BACKGROUND: The aim of this study was to assess visual information processing and cognitive functions in unaffected siblings of patients with schizophrenia, bipolar disorder and control subjects with a negative family history. METHODS: The siblings of patients with schizophrenia (N = 25), bipolar disorder (N = 20) and the controls subjects (N = 20) were matched for age, education, IQ, and psychosocial functioning, as indexed by the Global Assessment of Functioning scale. Visual information processing was measured using two visual backward masking (VBM) tests (target location and target identification). The evaluation of higher cognitive functions included spatial and verbal working memory, Wisconsin Card Sorting Test, letter fluency, short/long delay verbal recall and recognition. RESULTS: The relatives of schizophrenia patients were impaired in the VBM procedure, more pronouncedly at short interstimulus intervals (14, 28, 42 ms) and in the target location task. Marked dysfunctions were also found in the spatial working memory task and in the long delay verbal recall test. In contrast, the siblings of patients with bipolar disorder exhibited spared performances with the exception of a deficit in the long delay recall task. CONCLUSIONS: Dysfunctions of sensory-perceptual analysis (VBM) and working memory for spatial information distinguished the siblings of schizophrenia patients from the siblings of individuals with bipolar disorder. Verbal recall deficit was present in both groups, suggesting a common impairment of the fronto-hippocampal system.

Adult↗

PubMed2001

The synergistic antinociceptive interactions of endomorphin-1 with dexmedetomidine and/or S(+)-ketamine in rats.

UNLABELLED: Spinal administration of the endogenous mu-opioid agonist peptide, endomorphin-1, results in antinociception in rodents, but there are few data about its interaction with other antinociceptive drugs. We investigated the antinociceptive interactions at the spinal level of endomorphin-1 with the N-methyl-D-aspartate antagonist S(+)-ketamine, the alpha2-adrenoceptor agonist dexmedetomidine, or both in awake rats. Nociception was assessed by the tail-flick test. Dose-response curves were determined for endomorphin-1 (0.6-50 microg), for dexmedetomidine (0.1-10 microg), for mixtures of S(+)-ketamine (30 or 100 microg) with endomorphin-1 (2-18 microg) or of endomorphin-1 with dexmedetomidine in a fixed ratio (4:1), and for the triple combination of the three drugs after intrathecal administration. Endomorphin-1 and dexmedetomidine both produced dose-dependent antinociception. The coadministration of 100 microg S(+)-ketamine significantly enhanced the antinociceptive effect of 6 microg endomorphin-1. Isobolographic analysis of the combinations of endomorphin-1 and dexmedetomidine revealed a synergistic interaction between these drugs. The 80% effective dose for the triple combination was significantly less than that for either binary combination. These data indicate that S(+)-ketamine and dexmedetomidine, acting via different receptors, produce synergistic antinociceptive interaction with endomorphin-1 at the spinal level. Furthermore, the triple combination of an opioid agonist, an alpha2-adrenoceptor agonist, and an N-methyl-D-aspartate receptor antagonist shows potent antinociceptive activity. IMPLICATIONS: The coadministration of the N-methyl-D-aspartate antagonist receptor antagonist, S(+)-ketamine, or the specific alpha2-adrenoceptor agonist, dexmedetomidine, significantly enhances the antinociceptive effect of the endogenous mu-opioid agonist, endomorphin-1, at the spinal level. The triple combination of the three drugs causes a further improved antinociception.

Adrenergic alpha-Agonists↗