Biomedical subjects

R Vogels

Publications and source records attributed to R Vogels.

At least 37 records · Page 2Linked to original sources

PubMed2000

Three-dimensional shape coding in inferior temporal cortex.

Neurons in the rostral lower bank of the superior temporal sulcus (TEs), part of the inferior temporal cortex, respond selectively to three-dimensional (3D) shapes. We have investigated how these neurons represent disparity-defined 3D structure. Most neurons were selective for either first-order (disparity gradients) or second-order (disparity curvature) disparities. The latter selectivity proved remarkably vulnerable to disparity discontinuities, such as sharp edges or steps in disparity. The majority of the neurons remained selective for small disparity variations within the stimulus. 3D shape selectivity was preserved when the frontoparallel position or the stimulus size was altered. Thus, in TEs, 3D shape is coded by first- and second-order disparity-selective neurons, which are highly sensitive to spatial variations of disparity.

Action Potentials↗

PubMed1999

Macaque inferior temporal neurons are selective for disparity-defined three-dimensional shapes.

Real-world objects are three-dimensional (3D). Yet, it is unknown whether the neurons of the inferior temporal cortex, which is critical for object recognition, are selective for the 3D shape of objects. We tested for such selectivity by comparing responses to stereo-defined curved 3D shapes derived from identical pairs of monocular images. More than one-third of macaque inferior temporal neurons were selective for 3D shape. In the vast majority of those neurons, this selectivity depended on the global binocular disparity gradient and not on the local disparity. Thus, inferior temporal cortex processes not only two-dimensional but also 3D shape information.

Animals↗

PubMed1999

Effect of image scrambling on inferior temporal cortical responses.

Imaging studies compared activations elicited by images of objects and scrambled versions of these same images in order to localize human brain regions involved in object recognition. Given these studies and the known role of macaque temporal cortex in object recognition, I determined the effect of image scrambling on the responses of macaque inferior temporal neurons. Images of natural objects were scrambled to different degrees. The response of most neurons decreased with increasing degrees of scrambling. In 26% of the neurons, response was reduced by 50% when the image was scrambled using only four parts, but most neurons tolerated higher degrees of scrambling, suggesting that these neurons code object parts instead of entire objects. These results are related to human functional imaging studies.

Action Potentials↗

PubMed1999

Temporal resolution deficits in the visual fields of MS patients.

We assessed the relationship between temporal resolution and MS-induced neuropathy. A diagnostic strategy comprising assessments of temporal resolution at 16 points in the extra-foveal visual field up to 12 degrees from the fovea was first compared with foveal temporal resolution and with a standard VEP procedure in the same MS patients. At the group level, foveal temporal resolution was less sensitive to demyelination than the 16-point diagnostic strategy, the detection rate of which was comparable to that of the VEP procedure. Cross-sensitivity of the VEP and the 16-point diagnostic procedure was low. Subsequently, the average severity of MS-induced temporal resolution deficits was studied at three retinal loci of the same size but different eccentricities. Foveal deficits were not significantly greater than more peripheral deficits within the central 12 degrees.

Adult↗

PubMed1999

Ganciclovir-mediated in vivo elimination of myeloid leukemic cells expressing the HSVtk gene induces HSVtk loss variants.

The in vivo elimination of suicide gene-expressing tumor cells with prodrug treatment can induce protective immunity against wild-type tumors. In this study, we determined the efficacy and safety of the in vivo elimination of HSVtk expressing cells with ganciclovir treatment of a bystander cell killing-insensitive leukemic cell line. The retroviral construct pLTk+NeoDeltaMo, containing the HSVtk gene and the NeoR gene in a bicistronic unit, was introduced into rat leukemic LT12 cells. LT12/Tk+N cells showed a 1000- to 10 000-fold increased sensitivity to ganciclovir in vitro. In vitro mixing experiments demonstrated that LT12 cells were not susceptible to bystander cell lysis by LT12/Tk+N-2 cells exposed to ganciclovir. Rats injected s.c. with cloned LT12/Tk+N-2 cells developed tumors reaching a diameter of 3-4 cm after 40 days. Rats treated with gan- ciclovir twice daily for 5 consecutive days starting at day 7 did not develop s.c. tumors. Large established s.c. LT12/Tk+N-2 tumors completely regressed after ganciclovir treatment. However, recurrences of s.c. tumors were observed that were no longer sensitive to ganciclovir treatment. In vitro analysis of aspirates from the recurrent tumors demonstrated loss of HSVtk expression. In vitro culture of LT12/Tk+N-2 cells in soft agar in the presence of ganciclovir indicated that the frequency with which HSVtk-loss variants occurred is approximately one per 104 cells. The in vivo occurrence of HSVtk-loss variants escaping ganciclovir-induced elimination may have important implications for vaccination protocols using HSVtk gene expressing tumor cells that are not susceptible to bystander cell killing.

Animals↗

PubMed1999

Categorization of complex visual images by rhesus monkeys. Part 1: behavioural study.

In order to study how visual categories are coded by the activities of single neurons, it is necessary to first demonstrate that the animal subjects can categorize the visual stimuli employed in the single-unit recordings. Thus, rhesus monkeys were trained in a visual categorization task designed to minimize rote learning of individual exemplars and to allow testing of transfer from old to novel exemplars of the category. The stimuli were presented during controlled fixation. The monkeys learned to distinguish complex colour images of trees from other objects and generalized from old to novel exemplars. An extensive series of tests with probe stimuli showed that simple form, colour and texture features had insufficient stimulus control to account for the categorization performance. Scrambling the images impaired categorization performance, suggesting that the configuration of stimulus components controlled the categorization. The animals also learned a fish/non-fish categorization, but more slowly than a tree/non-tree categorization. These results indicate that rhesus monkeys can learn to categorize socially neutral, complex, natural visual images and suggest that this categorization is based on a combination of low-level features.

Animals↗

PubMed1999

Categorization of complex visual images by rhesus monkeys. Part 2: single-cell study.

In order to investigate the neural coding of ordinate-level visual categories, single-cell recordings were made in the anterior temporal cortex of two rhesus monkeys performing a categorization of colour images of trees versus images of other objects. Neurons showed a high average degree of selectivity for these complex colour images. Although most neurons responded to trees and non-trees, about a quarter responded in a category-specific manner, e.g. to trees but not non-trees, and about one-tenth responded almost exclusively to exemplars of the trained category. The responses of these neurons were largely invariant for stimulus transformations, e. g. changes in position or size, and decreased with the degree of image scrambling, mimicking the behavioural results. However, the responses of single neurons were insufficiently stimulus invariant to accommodate the entire range of variability present in the features of exemplars within the same category. This strong within-category selectivity challenges the idea that a prototype is represented at the single neuron level, but suggests that ordinate-level categorization is based on a population of neurons, each selective for a limited set of exemplars.

Animals↗

PubMed1999

Shape interactions in macaque inferior temporal neurons.

Missal et al. observed that the responses of inferior temporal (IT) neurons to a shape were reduced markedly when this shape partially overlapped a larger second shape, suggesting that shape interactions determine IT responses. In the present study, we compared the responses of IT neurons with combinations of two shapes which did or did not overlap and studied the effect of the relative and absolute positions of the two shapes. In a first test, a preferred shape (figure) was presented at the fixation point while a second, nonpreferred, shape was displayed either in the background of the figure (overlap) or at one of four peripheral positions (nonoverlap). Controls consisted of presentations of either shape in isolation at each of the five positions. The stimuli were presented during a fixation task. The responses to these combinations of two shapes were, on average, reduced compared with those elicited by the preferred shape presented in isolation. This suppression occurred whether or not the two shapes overlapped, but the degree of suppression in the overlap and nonoverlap conditions did not correlate. These interactions were stronger when the interacting stimulus was located in the contralateral compared with the ipsilateral hemifield. The position of the interacting stimulus within a hemifield significantly affected the suppression associated with combined shapes in some neurons. The strength of the interactions of the two nonoverlapping shapes depended on the shape of the interacting stimulus in half of the neurons. In a second test, the preferred shape and interacting stimulus could appear either at the fixation point or at one eccentric position. Here we found that the suppression was, on average, strongest when the interacting stimulus, rather than the preferred shape, was presented at the fixation position. Also, in 40% of the neurons, the response reduction was similar in overlap and nonoverlap conditions if effects of stimulus position were taken into account. In both tests, we also measured the responses to combinations of a nonpreferred shape and the interacting stimulus and showed that the response to a combination of two nonpreferred shapes was, in general, smaller than the response to a combination of the preferred and nonpreferred shape. Overall the results indicate that stimulus interactions in the receptive fields of IT neurons can be position and shape selective; this can contribute to the coding for the relationships between object parts.

Animals↗

PubMed1998

Second gene expression in bicistronic constructs using short synthetic intercistrons and viral IRES sequences.

In this study, we describe the efficiency of second gene translation in bicistronic constructs containing either a short (36bp) synthetic intercistron or known internal ribosomal entry sites (IRES). Experiments were performed using two different gene combinations: Herpes simplex virus-thymidine kinase (HSV-TK) and neomycine (NEO) or human glucocerebrosidase (hGC) and a methotrexate (MTX) resistant mutant dihydrofolate reductase (DHFR). We demonstrate that upon transfection, second gene translation is efficient using either an IRES or a 36-bp intercistron. Infection with retrovirus carrying the TK and NEO genes linked via a 36-bp intercistron resulted in both G418R (NEO expression) and gancyclovir (GCV) sensitivity (TK expression), indicating that both genes were expressed and thus that the genomic DNA and RNA of this bicistronic construct were intact. Likewise, retrovirus carrying the hGC and mutant DHFR gene separated by a short intercistron was harvested from MTXR murine PsiCRE cells. However, infection of PA317 cells with this virus supernatant did not result in the presence of hGC enzyme activity in these murine cells. Proviral DNA and RNA analyses indicated that the hGC coding region was lost from the original construct in the infected PA317 cells. In contrast, retrovirus carrying the hGC and DHFR cDNAs was linked via an IRES functioned as expected. Based on these results, we conclude that the efficiency of second gene translation using short synthetic intercistrons might prove useful in bicistronic constructs, depending on the gene combination used.

Animals↗

PubMed1998

The neuronal machinery involved in successive orientation discrimination.

Following our strategy of using simple discrimination tasks to investigate the primate visual system, we trained both human and monkey subjects for two orientation discrimination tasks: an identification and a successive discrimination. Contrasting these two tasks allowed us to isolate the temporal comparison component and to relate this component to activity in right fusiform gyrus using Positron Emission Tomography (PET) and to infero-temporal cortex using a lesion approach in monkeys. Single-cell recordings in infero-temporal cortex demonstrated that neurons in this region can contribute to the three processes underlying temporal comparison: (1) sensorial representation of visual stimuli, (2) maintaining a trace of the preceding stimulus, and (3) comparison of the incoming stimulus with that trace. By the same token, a comparison of these two tasks, which use the same input and the same attribute, demonstrates the task dependency of processing in the human and non-human primate visual system.

Adult↗

PubMed1998

Regions in the human brain activated by simultaneous orientation discrimination: a study with positron emission tomography.

In order to compare regional cerebral activity involved in simultaneous as opposed to successive orientation discrimination, we used positron emission tomography to measure regional cerebral blood flow, in two threefold sets of conditions, in a large number of subjects. The first such triad involved simultaneous orientation discrimination, orientation identification and detection, with all tasks using the same pair of gratings. The second triad consisted of successive orientation discrimination with its corresponding identification and detection tasks. Comparisons between tasks within each triad isolate attention to orientation and, respectively, spatial or temporal comparison. The subtraction of detection from simultaneous discrimination revealed activation of right fusiform, right lingual, left precentral, left cingulate and left temporal cortex, in addition to right insula, cerebellum and left thalamus. Only the fusiform, insular and precentral activations remained when the corresponding identification was subtracted from simultaneous discrimination. In contrast, most of the non-visual activation sites remained when simultaneous discrimination was compared with successive discrimination, which also revealed a left lingual activation. These experiments provide further evidence for task-dependent processing in the human visual system and suggest that the right fusiform cortex is involved in spatial as much as temporal comparisons.

Adult↗

PubMed1998

Quality and cost impacts: prevention of post-operative clean wound infections.

This paper report the effectiveness of a nursing quality assurance program over three years, which demonstrates improvement in the incidence and severity of post-operative clean wound infections and the associated extended length of hospital stay and cost. General surgery categories included cardiovascular, orthopaedic, neurosurgery, kidney, abdominal, mammary and other. Cardiovascular categories included coronary artery bypass graft (CABG), heart transplant, and atrial valve replacement. Hip replacement and total knee replacement procedures were included in the orthopaedic category. Additional length of stay and concomitant hospital costs were calculated. Results show that early reporting of observations and implementation of appropriate treatment will decrease the incidence, severity and associated costs of post-operative clean wound infections.

Australia↗

PubMed1997

Ocular torsion induced by static and dynamic visual stimulation and static whole body roll.

By means of real-time infra-red video-oculography we studied eye torsion in 12 normal healthy subjects. Ocular torsion was induced by visual stimulation or static whole body roll with and without visual orientation ("head-fixed" or "earth-fixed"). Visual stimulation was achieved by a horizontal grating that oscillated sinusoidally in a frontal plane. The oscillation frequency varied from 0 to 0.6 Hz while amplitude varied from 6 degrees to 33 degrees. Visual orientation during whole body roll was established by mounting a 32 lx illuminated horizontal grating either on a tilting device (head-fixed) or on the wall in the frontal plane (earth-fixed). Maximum visual-induced eye torsion gain was reached at about 0.2 Hz. No eye torsion was observed in static (0 Hz) visual tilts of the grating. Maximum gain was about 0.36 at amplitudes between 6 degrees and 10 degrees. Eye torsion gain decreased with increasing amplitude and increasing frequency (> 0.2 Hz). Static whole body roll in the dark up to 180 degrees clockwise and counterclockwise induced static ocular counter rolling with a maximum amplitude of 12 degrees and a maximum gain of 0.22. Gain decreased with increasing roll down to zero at 180 degrees. Visual orientation with either head or earth fixed did not affect the amplitude or gain of the body roll induced ocular counter-rolling. The results are interpreted in terms of improving the reliability of clinical statolith testing and understanding the processes involved in motion sickness.

Adult↗

PubMed1997

Responses of macaque inferior temporal neurons to overlapping shapes.

We tested whether macaque inferior temporal neurons can signal the presence of their preferred shape independently of other shapes simultaneously present, by comparing the responses and selectivity of TE neurons to shapes (figures), either presented in isolation or overlapping another shape (background). The two overlapping shapes differed in color or texture and thus were easily segmentable. We found that the response and selectivity of TE neurons to the figure can be dramatically altered, most commonly reduced, when the figure is overlapping the background. This reduction in response was also present when the monkey was required to actively discriminate the figures from varying backgrounds during recording. The level of suppression depended on the shape of the background and on whether or not figure and background can be discriminated. These results indicate that responses of TE cells are not only determined by the properties of the figures but also are influenced by the properties of stimuli in the background.

Animals↗

PubMed1997

Effects of inferior temporal lesions on two types of orientation discrimination in the macaque monkey.

Rhesus monkeys with transection of the forebrain commissures were trained in two different tasks in which grating orientation was the discriminandum. In the temporal same-different task, the monkeys had to judge whether or not two successively presented gratings differed in orientation. In the identification task, we measured how well the monkey could judge the orientation of the grating. The performance in any task was affected neither by a unilateral anterior temporal cortical area lesion nor by a subsequent posterior temporal cortical area lesion in the same hemisphere resulting in a two-stage inferior temporal (IT) lesion. However, a single stage IT (combined anterior and posterior temporal cortical areas) lesion of the other hemisphere severely disrupted the performance in the temporal same-different task, but only barely increased just noticeable differences in orientation in the identification task. This indicates that the impairment in a temporal comparison task after an IT lesion is not due to a perceptual coding deficit, but is related to the temporal comparison per se. Thus, IT is involved in the temporal comparison of successively presented stimuli. On the other hand, the two IT lesions, each having a different history (single versus two stage) had dramatically different behavioural effects, suggesting an important role for adult brain plasticity in determining the behavioural outcome of a brain lesion.

Animals↗

PubMed1997

Human brain activity related to orientation discrimination tasks.

In order to relate regional activity in the human brain to the different components of discrimination tasks, we compared regional cerebral blood flow, measured with positron emission tomography, under four conditions: successive orientation discrimination, orientation identification, detection and passive viewing. By adding successive discrimination and passive viewing at a second, lower rate we were able to investigate the main effects and interaction between task and presentation rate. Four occipital regions--the posterior calcarine region bilaterally, the right lingual gyrus and the right interior occipital cortex--displayed a main effect of presentation rate. Two regions--a right posterolateral occipital region and a right posterior fusiform region--displayed a significant main effect of task. The involvement of this posterior fusiform region in successive discrimination was also revealed by the subtraction of detection from successive discrimination, as was that of the right middle fusiform gyrus. Finally, a more anterior right middle fusiform region was differentially active in successive discrimination compared to identification, suggesting that activity in this region is related to the temporal comparison of orientation.

Adult↗

PubMed1996

Diazepam decreases performance in a long-term memory task using visual shapes.

We designed a memory task involving visual recognition sensitive enough to demonstrate the long-term amnesic effect of diazepam. Following memorization of a list of abstract visual stimuli (Fourier), subjects were evaluated on recognition performance immediately following acquisition and after a 3-day drug clearance interval. Administration of 15 mg diazepam 1 h before acquisition imposed a significant (10-24%) deficit only in delayed recognition. In contrast, a drug-free acquisition followed by a diazepam-challenged delayed recognition did not influence recognition. Moreover, 1 h after administration, diazepam did not significantly impair detection or visual discriminative performances. Given the persistence of an important deficit in recognition memory in the absence of any drug, this paradigm promises to be useful for studying regional cerebral blood flow during long-term memory performance.

Adolescent↗

PubMed1996

Herpes simplex virus thymidine kinase gene therapy for rat malignant brain tumors.

Transfer of a herpes simplex virus-derived thymidine kinase (HSV-tk) gene into brain tumor cells and subsequent ganciclovir (GCV) treatment has been shown by others to be an effective treatment in rats with intracerebrally inoculated 9L gliosarcomas. Mechanism of action and reproducibility are, however, still a matter of debate. We have used the same model to test the therapeutic effects of both retrovirus- and adenovirus-mediated transfer of the HSV-tk gene followed by GCV treatment. Survival time of rats with intracerebral 9L tumors was significantly prolonged after a single administration of adenovirus carrying a HSV-tk gene as compared to controls. Retrovirus-mediated gene transfer also resulted in significantly prolonged survival time when recombinant retrovirus-producing cells were transplanted. Direct injection of the recombinant retrovirus, HSV-tk-expressing cells, virus-producing cells without GCV administration and recombinant retrovirus-lacZ or interleukin-2 (IL-2)-producing cells did not result in tumor cell kill. In the present study, no significant difference in survival of 9L brain tumor carrying rats was found after treatment with adenovirus as compared to retrovirus-mediated HSV-tk-mediated gene transfer and subsequent GCV treatment.

Adenoviruses, Human↗