Retinotopic mapping in awake monkeys suggests a different functional organization for dorsal and ventral V4

Using functional magnetic resonance imaging, we mapped the retinotopic organization throughout the visual cortex of fixating monkeys. The observed retinotopy in V1, V2 and V3 was completely consistent with the classical view. More rostrally in occipital cortex, both areas V3A and MT/V5 had a lower and upper visual field representation split by a horizontal meridian. Both areas were almost completely surrounded by a vertical meridian representa- tion. Ventral, but not dorsal V4 was rostrally bordered by a horizontal meridian. Furthermore, contrary to all other early visual areas including V4v, the eccentricity lines ran almost parallel to the areal boundaries in V4d. These results suggest a different functional organization in dorsal and ventral V4, similar to what has been observed in human

The Extraction of 3D Shape from Texture and Shading in the Human Brain

We used functional magnetic resonance imaging to investigate the human cortical areas involved in processing 3-dimensional (3D) shape from texture (SfT) and shading. The stimuli included monocular images of randomly shaped 3D surfaces and a wide variety of 2-dimensional (2D) controls. The results of both passive and active experiments reveal that the extraction of 3D SfT involves the bilateral caudal inferior temporal gyrus (caudal ITG), lateral occipital sulcus (LOS) and several bilateral sites along the intraparietal sulcus. These areas are largely consistent with those involved in the processing of 3D shape from motion and stereo. The experiments also demonstrate, however, that the analysis of 3D shape from shading is primarily restricted to the caudal ITG areas. Additional results from psychophysical experiments reveal that this difference in neuronal substrate cannot be explained by a difference in strength between the 2 cues. These results underscore the importance of the posterior part of the lateral occipital complex for the extraction of visual 3D shape information from all depth cues, and they suggest strongly that the importance of shading is diminished relative to other cues for the analysis of 3D shape in parietal regions

Stereopsis Activates V3A and Caudal Intraparietal Areas in Macaques and Humans

Stereopsis, the perception of depth from small differences between the images in the two eyes, provides a rich model for investigating the cortical construction of surfaces and space. Although disparity-tuned cells have been found in a large number of areas in macaque visual cortex, stereoscopic processing in these areas has never been systematically compared using the same stimuli and analysis methods. In order to examine the global architecture of stereoscopic processing in primate visual cortex, we studied fMRI activity in alert, fixating human and macaque subjects. In macaques, we found strongest activation to near/far compared to zero disparity in areas V3, V3A, and CIPS. In humans, we found strongest activation to the same stimuli in areas V3A, V7, the V4d topolog (V4d-topo), and a caudal parietal disparity region (CPDR). Thus, in both primate species a small cluster of areas at the parieto-occipital junction appears to be specialized for stereopsis

Changing Human Visual Field Organization from Early Visual to Extra-Occipital Cortex

BACKGROUND: The early visual areas have a clear topographic organization, such that adjacent parts of the cortical surface represent distinct yet adjacent parts of the contralateral visual field. We examined whether cortical regions outside occipital cortex show a similar organization. METHODOLOGY/PRINCIPAL FINDINGS: The BOLD responses to discrete visual field locations that varied in both polar angle and eccentricity were measured using two different tasks. As described previously, numerous occipital regions are both selective for the contralateral visual field and show topographic organization within that field. Extra-occipital regions are also selective for the contralateral visual field, but possess little (or no) topographic organization. A regional analysis demonstrates that this weak topography is not due to increased receptive field size in extra-occipital areas. CONCLUSIONS/SIGNIFICANCE: A number of extra-occipital areas are identified that are sensitive to visual field location. Neurons in these areas corresponding to different locations in the contralateral visual field do not demonstrate any regular or robust topographic organization, but appear instead to be intermixed on the cortical surface. This suggests a shift from processing that is predominately local in visual space, in occipital areas, to global, in extra-occipital areas. Global processing fits with a role for these extra-occipital areas in selecting a spatial locus for attention and/or eye-movements

Sur un cas d’infestation du Copépode

La présence de Metschnikowia sp., levure ascosporée, est signalée comme parasite du Copépode Eurytemora velox en Camargue (France). Des observations sont faites sur les stades végétatifs, les asques fusiformes allongés ne contenant qu’une seule spore effilée aux deux extrémités. Le champignon envahit le corps du Crustacé entraînant sa mort

Enantiomeric separation using a L-RNA aptamer as chiral additive in partial-filling capillary electrophoresis.

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A L-RNA aptamer chiral stationary phase for the resolution of target and related compounds

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