Orientation column

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

Functional anatomy of macaque striate cortex. IV. Contrast and magno- parvo streams

Abstract: Macaque monkeys were shown achromatic gratings of various contrasts during 14C-2-deoxy-d-glucose (DG) infusion in order to measure the contrast sensitivity of different subdivisions of primary visual cortex. DG uptake is essentially saturated at stimulus contrasts of 50% and above, although the saturation contrast varies with layer and with different criteria. Following visual stimulation with gratings of 8% contrast, stimulus-driven uptake was relatively high in striate layer 4Ca (which receives primary input from the magnocellular LGN layers), but was absent in layer 4Cb (which receives primary input from the parvocellular layers). In this same (magnocellular-specific) stimulation condition, striate layers 4B, 4Ca, and 6 showed strong stimulus-induced DG uptake, and layers 2, 3, 4A, and 5 showed only light or negligible uptake. By comparison to other cases that were shown stimuli of systematically higher contrast, and to a wide variety of DG cases shown very different stimuli, it is evident that information derived from the magnocellular and parvocellular layers in the LGN remains partially, or largely, segregated in its passage through striate cortex, and projects in a still somewhat segregated fashion to different extrastriate areas. The sum of all available evidence suggests that the magnocellular information projects strongly through striate layers 4Ca, 4B, and 6, with moderate input into the blobs in layers 2 + 3, and to blob-aligned portions of layer 4A. Parvocellular-dominated regions of striate cortex include both the blob and interblob portions of layers 2 + 3, 4A, 4Cb, and 5. Because the major striate input to V2 arrives from striate layers 2 + 3, and because the major striate input to MT originates in layer 4B and 6, it appears that area V2 receives information derived largely from the parvocellular LGN layers, and that area MT receives information derived mainly from the magnocellular layers.

Microcolumns in the cerebral cortex

Abstract: Neuroanatomists from Cajal on (1) have searched in the cerebral cortex for units of structural organization that transcend the laminar pattern visible even to the untutored eye in Nissl-stained preparations. Many have commented on the vertical column-like arrays of cell bodies running orthogonal to the horizontal laminae that are particularly conspicuous in the temporal cortex of humans and other primates (Fig. 1). These columns have been promoted in the past as the morphological correlates of the functional columnarity of the cortex, known from physiological studies (2). The hypothesis of the column as the fundamental processing unit of the cerebral cortex was formulated by Mountcastle (3) from studies of cells responding to tactile stimuli in the somatosensory cortex of the cat. The hypothesis requires that nerve cells in middle layers of the cortex, in which thalamic afferents terminate, should be joined by narrow vertical connections to cells in layers lying superficial and deep to them, so that all cells in the column are excited by incoming stimuli with only small latency differences. The columns form a series of repeating units across the horizontal extent of the cortex. Figure 1 Nissl-stained section of the upper bank of the superior temporal sulcus from a human brain, showing microcolumns of nerve cells (×40). The verticality of cell–cell connections in the cortex has never been in doubt, but determining the minimal unit of such connectivity and the extent to which it is based on morphologically definable arrays of cells continues to exercise investigators. One problem inherent in the different experimental models customarily invoked as demonstrative of cortical columns is that they differ in scale. A column defined by neurons responding to peripheral stimulation as a vertically oriented microelectrode descends through the cortical layers, is narrower than the layer IV barrels of the rodent somatosensory cortex, and the …

Asymmetric Suppression Outside the Classical Receptive Field of the Visual Cortex

Abstract: Areas beyond the classical receptive field (CRF) can modulate responses of the majority of cells in the primary visual cortex of the cat (). Although general characteristics of this phenomenon have been reported previously, little is known about the detailed spatial organization of the surrounds. Previous work suggests that the surrounds may be uniform regions that encircle the CRF or may be limited to the "ends" of the CRF. We have examined the spatial organization of surrounds of single-cell receptive fields in the primary visual cortex of anesthetized, paralyzed cats. The CRF was stimulated with an optimal drifting grating, whereas the surround was probed with a second small grating patch placed at discrete locations around the CRF. For most cells that exhibit suppression, the surrounds are spatially asymmetric, such that the suppression originates from a localized region. We find a variety of suppressive zone locations, but there is a slight bias for suppression to occur at the end zones of the CRF. The spatial pattern of suppression is independent of the parameters of the suppressive stimulus used, although the effect is clearest with iso-oriented surround stimuli. A subset of cells exhibit axially symmetric or uniform surround fields. These results demonstrate that the surrounds are more specific than previously realized, and this specialization has implications for the processing of visual information in the primary visual cortex. One possibility is that these localized surrounds may provide a substrate for figure-ground segmentation of visual scenes.

An intracellular study of neuronal organization in the visual cortex.

Abstract: Neuronal connections in the visual cortex of cat (areas 17 and 18) were studied with intracellular recording and electrical stimulation techniques under Nembutal anaesthesia. Four types of axonal projection were seen; 1. association efferent cells projecting to adjacent cerebral cortex on the ipsilateral side, 2. commissural efferent cells to visual cortex on the contralateral side, 3. corticofugal efferent cells to the ipsilateral lateral geniculate body and superior colliculus, and 4. non-efferent cells whose projection is confined within the visual cortex. Both association and commissural efferent cells were located in layer III, corticofugal efferent cells in layer V and non-efferent cells in layers II–VI. Upon these cells two types of synaptic actions were exerted by the specific visual afferents that originate from the lateral geniculate body; 1. type I, monosynaptic excitation plus disynaptic inhibition and 2. type II, disynaptic excitation plus trisynaptic inhibition. Type I effects were found in layers III–V, and type II in layers II and VI. In the border region between areas 17 and 18 monosynaptic excitation and disynaptic inhibition were produced also by the commissural efferents originating from the contralateral visual cortex. On the basis of these results, a possible neuronal circuitry in the visual cortex is postulated.