Orientation column

About: Orientation column is a research topic. Over the lifetime, 1142 publications have been published within this topic receiving 130169 citations.

Intrinsic projections within visual cortex: evidence for orientation-specific local connections.

Abstract: The functional organization of intrinsic connections within area 18 of cat visual cortex was studied using combined electrophysiological and anatomical techniques. Physiological recordings were first used to map the distribution of orientation preference, ocular dominance, and receptive-field location relative to the cortical surface. Next, localized injections of lectin-conjugated horseradish peroxidase were made into physiologically identified regions within area 18. We found that (i) the local cortical interconnections are made preferentially between cell populations with orthogonal preferred orientations and are independent of the ocular dominance of the cortical cells, (ii) the map of visual space in the cortex is anisotropic with the magnification factor for vertical at least twice that for horizontal visual space, and (iii) the pattern of cortical projections compensates for the functional asymmetry so that a population of interconnected cells represents a roughly circular region of visual space.

Organization of sensory cortex in a Madagascan insectivore, the tenrec (Echinops telfairi).

Abstract: We identified subdivisions of somatosensory cortex, and the borders and extents of auditory and visual cortex in Madagascan tenrecs (Echinops telfairi) by using microelectrode recording techniques and cortical myeloarchitecture. There was evidence for three distinct somatosensory fields. The primary somatosensory area (S1) contained an orderly representation of the contralateral body surface that stained darkly for myelin. Neurons were activated by light touch, and receptive fields were often small, especially for the snout. Immediately rostral to S1, a lightly myelinated rostral field (R) also contained a representation of the contralateral body, although the internal topography was not fully determined. Neurons in R responded to manipulations of body parts and tissue displacements. A small, moderately myelinated area lateral to S1 was termed PV/S2 because it possessed features that were similar to both the parietal ventral area (PV) and the second somatosensory area (S2) in other mammals. Neurons in PV/S2 responded to light tactile stimulation. A densely myelinated oval of cortex caudal to PV/S2, the auditory area (A), contained neurons that responded to clicks, and the densely myelinated caudomedial visual area (V) contained neurons that were activated by stimulation of one or both eyes. Some characteristics of V were similar to the primary visual area (V1) described in other mammals. A visual area located in rostromedial cortex (RV) contained neurons that were highly responsive to visual stimulation. Area RV may be a specialization of tenrecs or an elaboration of a visuomotor field that has been retained in most extant mammals. The results support the view that most of the neocortex of primitive mammals was composed of a few sensory areas. J. Comp. Neurol. 379:399–414, 1997. © 1997 Wiley-Liss, Inc.

Faster Thalamocortical Processing for Dark than Light Visual Targets

Abstract: ON and OFF visual pathways originate in the retina at the synapse between photoreceptor and bipolar cells. OFF bipolar cells are shorter in length and use receptors with faster kinetics than ON bipolar cells and, therefore, process information faster. Here, we demonstrate that this temporal advantage is maintained through thalamocortical processing, with OFF visual responses reaching cortex ∼3–6 ms before ON visual responses. Faster OFF visual responses could be demonstrated in recordings from large populations of cat thalamic neurons representing the center of vision (both X and Y) and from subpopulations making connection with the same cortical orientation column. While the OFF temporal advantage diminished as visual responses reached their peak, the integral of the impulse response was greater in OFF than ON neurons. Given the stimulus preferences from OFF and ON channels, our results indicate that darks are processed faster than lights in the thalamocortical pathway.

Flexible retinotopy: Motion dependent position coding in visual cortex

Abstract: Although the visual cortex is organized retinotopically, it is not clear whether the cortical representation of position necessarily reflects perceived position. Using functional magnetic resonance imaging (fMRI), we show that the retinotopic representation of a stationary object in the cortex was systematically shifted when visual motion was present in the scene. Whereas the object could appear shifted in the direction of the visual motion, the representation of the object in the visual cortex was always shifted in the opposite direction. The results show that the representation of position in the primary visual cortex, as revealed by fMRI, can be dissociated from perceived location.

Thalamo-cortical projections in the tree shrew (Tupaia glis).

Abstract: Cortical lesions were placed in 18 hemispheres, and thalamic degeneration was studied after a survival period of at least six weeks. Very small lesions within the striate area produced complete degeneration of neurons in a column through the lateral geniculate, from medial to lateral borders and comprising all of the laminae. Lesions of various loci within the striate area reveal a precise topographic projection, with the rostral lateral geniculate sending fibers to the caudal extremity of the striate area and the caudal lateral geniculate projecting to the rostral extremity of the striate; further, the dorso-ventral dimension in the lateral geniculate projects to the medio-lateral dimension in the striate area. Finally, the evidence from striate area lesions suggests that the lateral geniculate projections are confined to the striate area as defined by cytoarchitecture, which in turn corresponds precisely with visual area I as defined by electrophysiological recording. This conclusion is supported by the failure to find retrograde degeneration after lesions of the belt of cortex adjacent to the striate area. The temporal area which occupies an extensive section from V II to the rhinal fissure and the auditory cortex and which has been shown to be a visual receiving area, is the target of essential projections from the pulvinar. The pulvinar also sends sustaining collaterals within the temporal area and probably outside as well, especially to V II. However, the very crude topographic organization apparent in the pulvinar projections does not seem to be sufficiently refined to account for the organization of V II. A suggestion was made in closing that V II may be the result of convergent evolution in different mammalian lines of descent.