Orientation column

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

Distribution of Cholecystokinin-containing Neurons in Cat Visual Cortex

Abstract: The visual cortex has been well studied anatomically and physiologically,’ but information on neurotransmitters used by cortical neurons, especially the interneurons, is still scarce. Up till now, only glutamic acid decarboxylase immunoreactivity (GAD-IR) has been demonstrated in the short-axon cells of cat visual cortex; 8-1 5% of these cells contain GAD-IR.’ As cholecystokinin (CCK) may play a role in the release of GABA,’ we have examined the laminar distribution of CCK in areas, 17, 18, and 19 of cat visual cortex. Four cats were injected with colchicine; two cats were untreated. CCK-immunoreactive nerve fibers and perikarya were found in both the untreated and colchicineinjected cats although the staining of the cells was more intense in the colchicinetreated animals. Immunoreactive cells were identified according to their dendritic pattern, as described by A. Peters and J. R e g i d ~ r . ~ All CCK-positive neurons were nonpyramidal cells, representing + 0.5-0.6% of the neuronal population of cat visual cortex. Cell bodies were spread throughout the cortex, but concentrated in the supragranular layers (FIG. l), where we also found an intrinsic plexus of CCKimmunoreactive nerve fibers. According to their dendritic pattern, the CCK-positive cells could be identified as multipolar or bitufted neurons. Only a few clear examples of bipolar neurons amongst the CCK-immunoreactive cells were found. The bitufted neurons can be classified into two groups: 1) the horizontally oriented neurons of layer I (width +15 pm, length k25 pm), with dendritic fields parallel to the pial surface (FIG. 2A). 2) the vertically oriented neurons of layers I1 and 111 (width k 13 pm, length k25 pm) most common at the border with layer I (FIG. 2B). Primary dendritic trunks arise from each pole of the perikaryon and divide into daughter branches which eventually pass into layer I. The remaining CCK-positive cells in layers I-VI are round or irregularly shaped (+20 pm) (FIG. 2C). Several dendritic trunks emanate nonpreferentially from the soma, especially in layer VI, where dendrites arise from the lateral portion of the horizontally oriented soma. The distribution pattern and the morphology of the different cell types was the same in the three visual areas examined. In all three areas about 92% of the CCK-positive neurons were found in the supragranular layers. As CCK may facilitate the release of GABA, and, as GABA has an important functional role in the visual cortex: CCK could be important in visual processing, especially in the supragranular layers.

A Ring Model for the Development of Simple Cells in the Visual Cortex

Abstract: A model was proposed for the development of simple receptive fields in the cat visual cortex, based on the empirical evidence that the development is due to dark or spontaneous activities in the lateral geniculate nucleus (LGN). We assumed that several cortical cells are arranged in a ring, with mutual excitatory and inhibitory connections of fixed weights; The cells also receive excitatory synapses from LGN cells, whose synaptic weights are initially set to be random and then modified according to the Hebb rule as well as to positive correlations among nearby LGN cells. Computer simulation showed that the cortical cells finally acquire two-dimensional simple receptive fields with their phases gradually varied along the ring.