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G Benedek

Publications and source records attributed to G Benedek.

At least 19 recordsLinked to original sources
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↗
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↗
PubMed2001

[Surgery without boundaries].

Surgery at the turn of the century and at the millennium is characterised by an extremely rapid development. There are no boundaries anymore among the different branches of medicine, in different anatomical regions of the human body, between the living human and the artificial tissues, between the reality and the virtual reality. Nanotechnology and robotics offer new possibilities for minimally invasive procedures. By the introduction of telepresence surgery there are no more surgical limits among countries and continents, between Earth and Space as well. A new chapter in history of medicine is the Cyber Surgery. The future has already arrived. Even in this new world we have to follow the ethical requirements summarised in the Hyppocrates Oath.

Ethics, Medical↗
PubMed2000

Visual information processing in patients with schizophrenia: evidence for the impairment of central mechanisms.

Patients with schizophrenia are especially impaired in the detection of spatial location if the briefly presented target stimulus is followed by a mask in a close temporal proximity (target location backward masking (BM) paradigm). It has been suggested that this phenomenon is related to the impairment of low spatial and high temporal frequency-sensitive transient (magnocellular) visual channels. To test this hypothesis, we measured target location BM and visual contrast sensitivity (CS) in clinically remitted patients with schizophrenia. In the BM task, subjects were asked to indicate the position of letters appearing at four possible spatial locations. In the CS test, a two-alternative forced choice method was used to measure the minimal contrast level required for the detection of horizontal gratings set at low spatial and high temporal frequencies (0.5 cycle/degree and 8 Hz, respectively). We found that the schizophrenia patients with normal CSs (spared transient channel functions) showed a marked deficit in the target location BM task. This suggests that the abnormality of subcortical transient channels does not explain some visual information processing dysfunctions in schizophrenia. Instead, deficient cortical interactions of rapidly changing environmental signals may be involved.

Adult↗
PubMed2000

Coding of spatial co-ordinates on neurones of the feline visual association cortex.

The receptive field properties of 131 visual neurons lying along the anterior ectosylvian sulcus were studied with extracellular recordings in barbiturate-anaesthetized, immobilised, artificially ventilated cats. A stationary visual noise pattern was presented in an area of 24x32 degrees, in which an 8x8 degrees portion moved randomly at a speed of 10 deg/s. A definite best area characterized by maximal firing rate was found, from where the firing rate declined monotonously towards the periphery of the receptive field. The best area locations were distributed in a 40x40 degrees region around the area centralis. These results seem to verify a rather robust capacity in AEV neurones for stimulus localization, in spite of their immense receptive fields.

Analysis of Variance↗
PubMed2000

Bifurcating projections from the cerebellar fastigial neurons to the thalamic suprageniculate nucleus and to the superior colliculus.

A double-labeling fluorescence microscopic study was performed on the mesencephalic and thalamic distribution of fastigial efferents. Anesthetized cats were injected with 2% fast blue into the suprageniculate nucleus and with 0.5% nuclear yellow into the superior colliculus. Analysis of serial sections through the cerebellar fastigial nucleus revealed that 25% of the neurons projecting to the superior colliculus and 10% of those projecting to the thalamus were double labeled. The results suggest that bifurcating fastigial fibers to the mesencephalon and to the visual thalamus may play a role in cerebellar visual control.

Amidines↗
PubMed2000

P300 component of visual event-related potentials distinguishes patients with idiopathic parkinson's disease from patients with essential tremor.

A considerable rate of misdiagnosis has recently been reported in movement disorders. One of the most difficult clinical problems is the differentiation of Parkinson's disease and essential tremor. In this study, we have examined whether event-related potentials (ERPs) could aid in the solution of this differential diagnostic problem. Visual ERPs were obtained by using an "oddball" paradigm in 20 patients with idiopathic Parkinson's disease (IPD), 20 patients with essential tremor (ET), and 20 age-matched control subjects. We found that the P300 amplitudes were selectively reduced in the IPD group at the midline (Fz, Cz, Pz) electrode sites, whereas the ET group exhibited selectively elevated P300 amplitudes at the left parietal and frontal (F3, P3) recording sites. The patients with IPD, but not ET, showed a significant prolongation of the P300 latency at each electrode site. Similarly, only the IPD patients were significantly slower in responding to the target stimulus. The primary visual evoked potential (P100) did not distinguish among the IPD, ET, and control subjects. These results suggest that visual ERPs might provide a useful diagnostic method for differentiating IPD from ET.

Aged↗
PubMed2000

Early and late components of visual categorization: an event-related potential study.

We examined the characteristics of early and late components of event-related potentials (ERPs) accompanying the visual categorization of natural scenes. In the first experiment, ERPs were recorded in an animal-non-animal categorization task (CT), whereas the second experiment included a spatial frequency discrimination task (DT). In the CT, there were more negative potentials for non-animals in the time windows of 150-250 ms (N1) and 350-500 ms (N2), and a more positive potential for animals in the time window of 250-350 ms (P2). In the DT, spatial frequency gratings evoked only a short-duration difference N1 at the frontal sites. Our results suggest that N1 may be related to higher-level categorization processes.

Adult↗