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D Shoham

Publications and source records attributed to D Shoham.

At least 19 recordsLinked to original sources
PubMed2000

Visual cortex maps are optimized for uniform coverage.

Cat visual cortex contains a topographic map of visual space, plus superimposed, spatially periodic maps of ocular dominance, spatial frequency and orientation. It is hypothesized that the layout of these maps is determined by two constraints: continuity or smooth mapping of stimulus properties across the cortical surface, and coverage uniformity or uniform representation of combinations of map features over visual space. Here we use a quantitative measure of coverage uniformity (c') to test the hypothesis that cortical maps are optimized for coverage. When we perturbed the spatial relationships between ocular dominance, spatial frequency and orientation maps obtained in single regions of cortex, we found that cortical maps are at a local minimum for c'. This suggests that coverage optimization is an important organizing principle governing cortical map development.

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PubMed1999

Imaging cortical dynamics at high spatial and temporal resolution with novel blue voltage-sensitive dyes.

Conventional imaging techniques have provided high-resolution imaging either in the spatial domain or in the temporal domain. Optical imaging utilizing voltage-sensitive dyes has long had the unrealized potential to achieve high resolution in both domains simultaneously, providing subcolumnar spatial detail with millisecond precision. Here, we present a series of developments in voltage-sensitive dyes and instrumentation that make functional imaging of cortical dynamics practical, in both anesthetized and awake behaving preparations, greatly facilitating exploration of the cortex. We illustrate this advance by analyzing the millisecond-by-millisecond emergence of orientation maps in cat visual cortex.

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PubMed1997

Spatial relationships among three columnar systems in cat area 17.

In the primary visual cortex, neurons with similar response properties are arranged in columns. As more and more columnar systems are discovered it becomes increasingly important to establish the rules that govern the geometric relationships between different columns. As a first step to examine this issue we investigated the spatial relationships between the orientation, ocular dominance, and spatial frequency domains in cat area 17. Using optical imaging of intrinsic signals we obtained high resolution maps for each of these stimulus features from the same cortical regions. We found clear relationships between orientation and ocular dominance columns: many iso-orientation lines intersected the borders between ocular dominance borders at right angles, and orientation singularities were concentrated in the center regions of the ocular dominance columns. Similar, albeit weaker geometric relationships were observed between the orientation and spatial frequency domains. The ocular dominance and spatial frequency maps were also found to be spatially related: there was a tendency for the low spatial frequency domains to avoid the border regions of the ocular dominance columns. This specific arrangement of the different columnar systems might ensure that all possible combinations of stimulus features are represented at least once in any given region of the visual cortex, thus avoiding the occurrence of functional blind spots for a particular stimulus attribute in the visual field.

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PubMed1997

Spatio-temporal frequency domains and their relation to cytochrome oxidase staining in cat visual cortex.

Spatial and temporal frequencies are important attributes of the visual scene. It is a long-standing question whether these attributes are represented in a spatially organized way in cat primary visual cortex. Using optical imaging of intrinsic signals, we show here that grating stimuli of different spatial frequencies drifting at various speeds produce distinct activity patterns. Rather than observing a map of continuously changing spatial frequency preference across the cortical surface, we found only two distinct sets of domains, one preferring low spatial frequency and high speed, and the other high spatial frequency and low speed. We compared the arrangement of these spatio-temporal frequency domains with the cytochrome oxidase staining pattern, which, based on work in primate striate cortex, is thought to reflect the partition of the visual cortex into different processing streams. We found that the cytochrome oxidase blobs in cat striate cortex coincide with domains engaged in the processing of low spatial and high temporal frequency contents of the visual scene. Together with other recent results, our data suggest that spatiotemporal frequency domains are a manifestation of parallel streams in cat visual cortex, with distinct patterns of thalamic inputs and extrastriate projections.

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PubMed1995

Optical imaging of the layout of functional domains in area 17 and across the area 17/18 border in cat visual cortex.

Optical imaging based on intrinsic signals was used to investigate the functional architecture of cat area 17 and the border between areas 17 and 18. The visual stimuli were gratings of different spatial frequencies moving at different angles, in different directions and with different speeds. In area 17 the iso-orientation domains were usually organized in patches rather than as elongated bands. Patches with different orientation preferences were arranged radially forming 'pinwheels' around 'orientation centres'. The pinwheel density was approximately 1.7-fold higher than in area 18. To explore clustering according to direction of motion, stimuli having the same orientation but moving in opposite directions were used. These two stimuli yielded very similar activity maps giving no indication of robust directionality clustering. Using near infrared light we were able to simultaneously image ocular-dominance and iso-orientation domains. A quantitative assessment of the relative strengths of the two subsystems showed that in upper cortical layers clustering according to orientation preference was three-fold stronger than clustering according to ocular dominance. The functional organization of spatial frequency was also examined. When we compared the activated regions by stimuli having different spatial frequency and moving at different velocities we observed that neurons were clustered also in these respects. We also investigated the functional architecture at the area 17/18 border and found that orientation maps at both sides of the border were not independent of each other. The map of area 17 smoothly blended into that of area 18. Similarly, the preferred spatial frequency of the neurons changed gradually over a distance of approximately 0.8 mm at the region of the area 17/18 border.

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PubMed1995

Coherent spatiotemporal patterns of ongoing activity revealed by real-time optical imaging coupled with single-unit recording in the cat visual cortex.

1. We examined the spatiotemporal organization of ongoing activity in cat visual areas 17 and 18, in relation to the spontaneous activity of individual neurons. To search for coherent activity, voltage-sensitive dye signals were correlated with the activity of single neurons by the use of spike-triggered averaging. In each recording session an area of at least 2 x 2 mm of cortex was imaged, with 124 diodes. In addition, electrical recordings from two isolated units, the local field potential (LFP) from the same microelectrodes, and the surface electroencephalogram (EEG) were recorded simultaneously. 2. The optical signals recorded from the dye were similar to the LFP recorded from the same site. Optical signals recorded from different cortical sites exhibited a different time course. Therefore real-time optical imaging provides information that is equivalent in many ways to multiple-site LFP recordings. 3. The spontaneous firing of single neurons was highly correlated with the optical signals and with the LFP. In 88% of the neurons recorded during spontaneous activity, a significant correlation was found between the occurrence of a spike and the optical signal recorded in a large cortical region surrounding the recording site. This result indicates that spontaneous activity of single neurons is not an independent process but is time locked to the firing or to the synaptic inputs from numerous neurons, all activated in a coherent fashion even without a sensory input. 4. For the cases showing correlation with the optical signal, 27-36% of the optical signal during spike occurrence was directly related to the occurrence of spontaneous spikes in a single neuron, over an area of 2 x 2 mm. In the same cortical area, 43-55% of the activity was directly related to the visual stimulus. 5. Surprisingly, we found that the amplitude of this coherent ongoing activity, recorded optically, was often almost as large as the activity evoked by optimal visual stimulation. The amplitude of the ongoing activity that was directly and reproducibly related to the spontaneous spikes of a single neuron was, on average, as high as 54% of the amplitude of the visually evoked response that was directly related to optimal sensory stimulation, recorded optically. 6. Coherent activity was detected even at distant cortical sites up to 6 mm apart.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1987

Human muscle-derived, tissue specific, myocytotoxic T cell lines in dermatomyositis.

Mononuclear cells were isolated from the inflamed muscle tissue of a patient suffering from dermatomyositis (DM). These were expanded in long-term culture and maintained in the presence of IL-2 containing culture medium. Two cell lines were established, one of the helper/inducer (OKT4+) and the other of the suppressor/cytotoxic phenotype (OKT8+). The OKT4+ cell line exhibited a non HLA-restricted, tissue-specific, myocytotoxic effect on rat muscle cell culture. Its lymphoproliferative response to human muscle antigen was HLA-restricted. The OKT8+ cell line exhibited a non HLA-restricted, tissue-specific response to muscle antigens and no myocytotoxic activity in in vitro rat muscle cell culture. It is likely that clones of OKT4+ lymphocytes in patients suffering from DM are associated with the pathogenesis of the disease--they probably mediate the diffuse damage to skeletal muscle through their myocytotoxic activity.

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PubMed1986

Isolation of a paramyxovirus from pigs in Israel and its antigenic relationships with avian paramyxoviruses.

During surveillance of the swine population in Israel a haemagglutinating agent was isolated and identified as a paramyxovirus (PMV). Serological studies based on haemagglutination and neuraminidase inhibition (HI and NI) tests displayed a close antigenic relationship between the isolate and the prototype strain of a variety of the avian PMV serotype 3 (PMV-3). However, comprehensive HI and NI cross-reaction tests between the isolate and PMV-3 reference strains, on the one hand, and the other eight avian PMV serotypes, on the other hand, showed that the viruses compared differed in terms of their antigenic interrelationships with the other avian PMVs and also in the quantitative values of the cross-reactivity. This is interpreted to mean that the swine isolate and the avain PMV-3 prototype strain are different viruses, although very closely related, but are not different isolations of the same virus from avian and mammalian hosts.

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