Organization Of Corticocortical Connections Research Articles

Functional Split between Parietal and Entorhinal Cortices in the Rat

Posterior parietal cortex (PPC) and medial entorhinal cortex (MEC) are important elements of the neural circuit for space, but whether representations in these areas are controlled by the same factors is unknown. We recorded single units simultaneously in PPC and MEC of freely foraging rats and found that a subset of PPC cells are tuned to specific modes of movement irrespective of the animals' location or heading, whereas grid cells in MEC expressed static spatial maps. The behavioral correlates of PPC cells switched completely when the same animals ran in a spatially structured maze or when they ran similar stereotypic sequences in an open arena. Representations in PPC were similar in identical mazes in different rooms where grid cells completely realigned their firing fields. The data suggest that representations in PPC are determined by the organization of actions while cells in MEC are driven by spatial inputs.

Development of the Ordered Organization of Corticocortical Connections between Field 17 and the Posteromedial Wall of the Lateral Suprasylvian Sulcus in Early Postnatal Ontogeny in Cats

The development of the clustered organization of corticocortical connections between visual field 17 and the posteromedial wall of the lateral suprasylvian sulcus (field PMLS) was studied in cats. The retrograde axonal marker horseradish peroxidase was microinjected into the PMLS region. The distribution of labeled initial neurons was analyzed in field 17 in kittens aged five and 12 weeks. A significant increase in the area of cortex containing labeled neurons and a decrease in their distribution density were seen between week 5 and week 12. Analysis of Fourier amplitude and phase spectra demonstrated differences in the distributions of labeled neurons in kittens of different ages and provided evidence of the incomplete formation of the clustered organization of connections in these animals. The temporal morphofunctional characteristics of the development of intercortical connections of the PMLS zone as compared with other visual areas of the cortex are discussed.

Ontogenetic Characteristics of the Organization of Corticocortical Connections between the Primary Visual Cortex and the Lateral Suprasylvian Area of the Cat Brain

Studies on 10 cats aged five and 12 weeks included qualitative and quantitative analyses of the distribution in field 17 of initial neurons organizing corticocortical connections with the posteromedial lateral suprasylvian gyrus (PMLS) of the brain using retrograde labeling with horseradish peroxidase. The PMLS area is a higher center for processing information relating to the movement of visual stimuli. Ontogenetic characteristics of the formation of the ordered (clustered) organization of initial neurons in field 17 were identified. An age-related decrease in the density of initial neurons in field 17 was found, from 125.2 ± 69.8 cells/mm 2 in kittens aged five weeks to 34.7 ± 17.4 cells/mm 2 in 12-week-old kittens (p = 0.05). During the period between postnatal weeks 5 and 12, there was an increase in the size of the labeled area containing the majority of initial neurons. The morphofunctional aspects of the formation of the ordered structure of corticocortical connections between field 17 and the PMLS during postnatal ontogenesis and its possible relationship with the development of the function of the visual perception of moving objects are discussed.

Corticocortical connections of cat primary somatosensory cortex.

The organization of corticocortical connections in the representation of the forepaw in cat primary somatosensory cortex (SI) was studied following injections of various tracers into different cortical cytoarchitectonic areas. Small injections of horseradish peroxidase, wheat germ agglutinin-conjugated HRP, Phaseolus vulgaris leukoagglutinin, or fast blue were placed into the representation of the forepaw in areas 3b, 1, or 2. The positions of labeled neurons in SI and the surrounding cortical areas were plotted on flattened surface reconstructions to determine the organization of the corticocortical connections within SI. A strong, reciprocal projection linked the two forepaw representations which have been described in area 3b and the part of area 2 which lies in the anterior bank of the lateral ansate sulcus (see Iwamura and Tanaka 1978a, b). Dense projections also linked these areas with SII, as previously reported (Burton and Kopf 1984a). Additional projections to area 3b arose primarily from areas 3a and 1. Projections to area 2 were more widespread than those to area 3b, and arose from all other areas of SI as well as from areas 4 and 5a. All injections into SI tended to label groups of neurons which lay in mediolateral strips. Corticocortical projection neurons which were most heavily labeled by SI injections were pyramidal cells in layer III. Additional projections from area 2 to 3b, area 5a to 2, and SII to areas 2 and 3b arose from layer VI as well. Although neurons of layers III and VI were always the most densely labeled, large injections into SI labeled neurons in layers II and V as well.

Organization of corticocortical connections in human visual cortex.

Clinical and psychophysical observations indicate that the visual cortex is critical for the perception of color, form, depth, and movement. Little, however, is known about the cortical circuitry that underlies these functions in humans. In an attempt to learn more about these connections, we have traced projections of primary (V1) and secondary (V2) visual cortex in the postmortem, fixed human brain, using the fluorescent dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate as an axonal marker. The results show that V1 makes a forward projection to layers 3 and 4 of V2, and V2 projects back to layers 1, 2, 3, 5, and 6 of V1. Some V2 injections also show an input to layer 4B of V1. Projections to 4B probably originate from cytochrome oxidase (CO)-reactive stripes that we have identified in V2. Differential connections between CO-rich (blobs) and CO-poor regions (interblobs) also exist within V1; blobs are connected to blobs and interblobs are connected to interblobs. The results show that the connections in human visual cortex are similar to those of nonhuman primates and that their organization is consistent with the concept of multiple processing streams in the visual system.

Organization of corticocortical connections in the parietal cortex of the rat.

An analysis based on Nissl, anterograde degeneration, and succinic dehydrogenase histochemical techniques reveals that there are two distinct regions of parietal cortex which are characterized by different cytoarchitectonic features and anatomical connections. The "granular" cortical zone possesses a well-defined fourth layer composed of small, densely-packed cells, receives dense projections from the ventral posterior nucleus of the thalamus, and is essentially free of callosal inputs. "Agranular" cortical areas which surround or lie embedded within the granular zone lack a well-defined fourth layer, receive sparse projection from the ventral posterior nucleus, but send and receive extensive callosal projections. These findings suggest that thalamic and callosal projections to the parietal cortex maintain a pattern of areal segregation. The granular cortical zone, which apparently corresponds to SmI, projects ipsilaterally to motor cortex, SmII, and adjacent agranular areas. The superficial layers of the granular cortex also project heavily upon the underlying layer V. This intracortical projection is not organized in discrete clusters within the "barrel field" cortex. This suggests that the specialized organization of thalamic afferents and granule cells within the "barrel field" is not maintained in the intracortical circuitry of this region.