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PubMed1984

Interhemispheric connections of visual cortex of owl monkeys (Aotus trivirgatus), marmosets (Callithrix jacchus), and galagos (Galago crassicaudatus).

Interhemispheric connections of visual cortex were studied in owl monkeys, marmosets, and galagos after multiple injections of horseradish peroxidase into one cerebral hemisphere. Areal patterns of connections were revealed in sections of cortex that was flattened and cut parallel to the surface. Results were related to the locations of known visual areas, especially in owl monkeys, in which more visual areas have been established. The connection patterns in owl monkeys and marmosets are very similar, suggesting that the organization of visual cortex differs little in these two New World simians. Galagos have a basically similar pattern, but the connections are more widespread. In all three primates, connections are not restricted to cortex representing the line of decussation of the retina, and even striate cortex has connections displaced from the border. These connections extend up to 2 mm into area 17 in owl monkeys, and they are most extensive in galagos, where they form foci that are coextensive with regions of high cytochrome oxidase activity. Connections are concentrated in the caudal half of area 18, but protrusions of connections cross of the width of the field. The middle temporal visual area (MT) has unevenly distributed connections throughout, with some increase in density along the border. The dorsomedial visual area (DM) of owl monkeys has connections restricted to the rostral border, and a similar region of sparse connections identifies the probable location of DM in marmosets and galagos. Caudal parts of the dorsolateral visual area (DL) of owl monkeys have dense interhemispheric connections. Other visual areas are characterized by unevenly distributed clumps of connections, suggesting that functions are not uniformly distributed, and that semiregular processing modules exist. The results indicate that most extrastriate visual neurons are subject to interhemispheric influences and support the conclusion that callosal connections are functionally heterogeneous.

Animals↗

PubMed1993

Connections of somatosensory cortex in megachiropteran bats: the evolution of cortical fields in mammals.

The cortical connections of the primary somatosensory area (SI or 3b), a caudal somatosensory field (area 1/2), the second somatosensory area (SII), the parietal ventral area (PV), the ventral somatosensory area (VS), and the lateral parietal area (LP) were investigated in grey headed flying foxes by injecting anatomical tracers into electrophysiologically identified locations in these fields. The receptive fields for clusters of neurons were mapped with sufficient density for injection sites to be related to the boundaries of fields, and to representations of specific body parts within the fields. In all cases, cortex was flattened and sectioned parallel to the cortical surface. Sections were stained for myelin and architectonic features of cortex were related to physiological mapping and connection patterns. We found patterns of topographic and nontopographic connections between 3b and adjacent anterior parietal fields 3a and 1/2, and fields caudolateral to 3b (SII and PV). Area 1/2 had both topographic and nontopographic connections with 3b, PP, and SII. Connections of SII and PV with areas 3b, 3a, and 1/2 were roughly topographic, although there was clear evidence for nontopographic connections between these fields. SII was most densely connected with area 1/2, while PV was most densely connected with 3b. SII had additional connections with fields in lateral parietal cortex and with subdivisions of motor cortex. Other connections of PV were with subdivisions of motor cortex and pyriform cortex. Laminar differences in connection patterns of SII and PV with surrounding cortex were also observed. Injections in the ventral somatosensory area revealed connections with SII, PV, area 1/2, auditory cortex, entorhinal cortex, and pyriform cortex. Finally, the lateral parietal field had very dense connections with posterior parietal cortex, caudal temporal cortex, and with subdivisions of motor cortex. Our results indicate that the 3b region is not homogeneous, but is composed of myelin dense and light regions, associated with 3b proper and invaginations of area 1/2, respectively. Connections of myelin dense 3b were different from invaginating portions of myelin light area 1/2. Our findings that 3b is densely interconnected with PV and moderately to lightly interconnected with SII supports the notion that SII and PV have been confused across mammals and across studies. Our connectional evidence provides further support for our hypothesis that area 1/2 is partially incorporated in 3b and has led to theories of the evolution of cortical fields in mammals.

Animals↗

PubMed1988

Reciprocal connections of the insular and piriform claustrum with limbic cortex: an anatomical study in the cat.

The connections of the claustrum with non-isocortical limbic and paralimbic cortex in the cat are described, using the anterograde transport of tritiated amino acids and the retrograde transport of various fluorescent tracers and of horseradish peroxidase conjugated to the lectin wheatgerm agglutinin. It could be demonstrated that the claustrum, in addition to its connections with sensory-related areas, is reciprocally and bilaterally connected with widespread limbic and paralimbic cortical regions. These connections are organized such that the area of origin of claustral efferents to a certain cortical region coincides with the area of termination in the claustrum of afferents from that same cortical region. A rostrocaudal topographical organization of the limbic-related connections of the claustrum is not very apparent. However, the results clearly demonstrate a dorsoventral topographical organization in the connections between the claustrum and the cortex. The ventral part of the claustrum has reciprocal connections predominantly with the entorhinal cortex, and possibly with the anterior olfactory nucleus and the prepiriform cortex. A more dorsally located part of the claustrum is preferentially connected with the orbitofrontal, the insular, the perirhinal, the anterior limbic, and the cingular cortices, and with parts of the subicular complex. The most dorsal portion of the claustrum is more heavily connected with parasensory and sensory cortices. It is concluded that the traditional subdivision of the claustrum into two discrete nuclei, i.e. the insular claustrum connected with the isocortex, and the piriform claustrum or endopiriform nucleus connected with the allocortex, does not reflect the actual organization of the cortical connections of the claustrum. The present data provide a more differentiated view, such that the ventral portion of the claustrum is reciprocally connected mainly with the olfactory-related cortices and the entorhinal cortex, whereas the cortical connections of progressively more dorsal parts of the claustrum gradually shift from limbic and paralimbic towards parasensory and sensory cortical connections. The significance of these findings is discussed in the light of a possible function of the claustrum in relation to corticocortical integration and memory processing.

Amino Acids↗

PubMed1992

Electrogram criteria for identification of appropriate target sites for radiofrequency catheter ablation of accessory atrioventricular connections.

BACKGROUND: Catheter ablation of accessory atrioventricular (AV) connections using radiofrequency current has been demonstrated to be effective in the majority of patients with the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardia involving a concealed accessory AV connection. However, electrogram criteria have not been established to guide attempts at radiofrequency catheter ablation. METHODS AND RESULTS: The characteristics of local electrograms recorded at successful and unsuccessful sites of radiofrequency catheter ablation were determined in 132 patients. Electrograms recorded at a total of 438 sites were analyzed: 338 recorded during ablation of 90 manifest accessory AV connections and 100 recorded during ablation of 44 concealed accessory AV connections. During ablation of manifest accessory AV connections, the independent predictors of outcome were electrogram stability (p less than 0.001), the interval between activation of the ventricular electrogram and onset of the QRS complex (p less than 0.001), and the presence of an accessory AV connection potential (p less than 0.001). Radiofrequency energy delivery at sites demonstrating stable electrograms, a probable or possible accessory AV connection potential, and activation of the local ventrical electrogram before the onset of the QRS complex had a 57% probability of success compared with a 3% probability of success at sites without these features. During ablation of concealed accessory AV connections, the independent predictors of outcome were electrogram stability (p = 0.02), the presence of an accessory AV connection potential (p = 0.05), and the presence of retrograde continuous electrical activity (p = 0.04). Sites demonstrating a stable local electrogram, an accessory AV connection potential, and retrograde continuous electrical activity had an 82% probability of success compared with only a 5% probability of success at sites demonstrating none of these features. CONCLUSIONS: The local electrogram parameters of greatest importance in predicting the success or failure of radiofrequency catheter ablation of accessory AV connections are electrogram stability, the presence of an accessory AV connection potential, and the timing of ventricular activation relative to the QRS complex (for manifest accessory AV connections) or retrograde continuous electrical activity (for concealed accessory AV connections). Awareness of these variables during attempts at radiofrequency catheter ablation of accessory AV connections may minimize the number of unnecessary applications of radiofrequency energy.

Adult↗

PubMed1995

Breast implants, rheumatoid arthritis, and connective tissue diseases in a clinical practice.

This study was designed to assess the relationship between breast implants and certain rheumatologic diseases (rheumatoid arthritis and diffuse connective tissue diseases). The study base was a rheumatological practice in Atlanta, Georgia that started in 1982 and began computerizing its records in 1985. The computerized records through May 1992 included 4229 women patients, 150 with breast implants and 721 with a diagnosis of rheumatoid arthritis (RA) and/or one of the connective tissue diseases (CTDs). Of the 721 patients who had been diagnosed as having rheumatoid arthritis (RA) and/or one of the connective tissue diseases (CTDs), 392 had rheumatoid arthritis, 344 had connective tissue disease, 15 had both rheumatoid arthritis and a connective tissue disease, and 33 had more than one connective tissue disease. Of the patients with connective tissue disease, 179 had systemic lupus erythematosus, 64 had scleroderma, 49 had Sjögren's syndrome, 36 had dermatomyositis or polymyositis, and 49 had mixed connective tissue disease. Data were analyzed by univariate and multivariate techniques including logistic regression. Significant variables included age at first visit, income strata, and period of first visit. Analyses were performed for each clinical diagnosis, for all connective tissue diseases together (CTDs), and for those with rheumatoid arthritis and/or connective tissue disease (RA/CTD). Analyses were performed on the total data base and on the records of new patients (1986-1992). The adjusted odds ratio for breast implants among women who entered the practice in 1986-1992 and were diagnosed as having rheumatoid arthritis and/or one of the connective tissue diseases (RA/CTDs) was 0.45 (0.22-0.90), for those with rheumatoid arthritis was 0.61 (0.28-1.49), for those with any of these specific diffuse connective tissue diseases was 0.34 (0.11-1.06) compared to those without the disease. For systemic lupus erythematosus, the odds ratio of 0.24 (0.03-1.75) was based on a single case who had the disease 5 yr before the implant. For Sjögren's syndrome, the odds ratio was 1.67 (0.39-7.13) based on two cases, one of whom had the disease 5 yr before the implant. The calculated odds ratios for scleroderma, dermatomyositis/polymyositis, and mixed connective tissue disease were zero since no cases were diagnosed among the patients with breast implants. This study found no evidence that women with breast implants are at an increased risk for having rheumatoid arthritis or other diffuse connective tissue disease.

Adult↗

PubMed1987

Development of the connective tissue in the digestive tract of the larval and metamorphosing Xenopus laevis.

Developmental changes, until the completion of metamorphosis, of the connective tissue of the digestive tract in the South African clawed frog Xenopus laevis were examined by light and scanning electron microscopy. During the pre- and prometamorphosis (stages 50 through 59) the layer of connective tissue was prominent in the typhlosole, while that in the rest of the intestine and stomach remained very thin. Most of the connective tissue cells were fibroblasts and were concentrated mainly in the typhlosole, the boundaries of which were distinct. In the anterior part of the typhlosole just behind the stomach, the layers of connective tissue and muscle were the thickest and the boundary between these 2 layers was obscure. Although the mitotic cells of the connective tissue were rare, if any, and no migrating cells were observed on the surface of the connective tissue, the connective tissue of the intestine gradually increased in cell number during the pre- and prometamorphosis. In the stomach, on the other hand, there was no such increase. At the beginning of the metamorphic climax (stages 60 and/or 61), the layer of connective tissue suddenly became thick in both the stomach and the intestine. The boundaries of the typhlosole became less distinct. Mitotic index of the connective tissue became high, and its cells dramatically increased in number and contained many undifferentiated mesenchyme-like cells. In the stomach, these connective tissue cells invaded the glands of the larval epithelium into just below the surface epithelium and mitotic index of the entire stomach epithelium increased. In the intestine, in contrast, mitotic epithelial cells were localized in the islets which invaginated into the connective tissue and later formed the adult epithelium. With the growth of islets, the intestinal folds were formed as straight rows and, after stage 63, were modified into a zigzag pattern and had mitotic cells localized in the troughs of folds. The present results indicate that dramatic changes of the connective tissue of both the stomach and the intestine occur at the beginning of the metamorphic climax, concomitantly with those of the epithelium. Moreover, the results also show that, before the climax, even when there were no indications of metamorphic changes in the epithelium, cells of the connective tissue gradually increased in number in the intestine (but not in the stomach). It is also suggested that the muscle cells of the typhlosole just behind the stomach may participate in this gradual increase of connective tissue cells.

Animals↗

PubMed1982

[Age-dependent changes in connective tissue].

Alterations of the various connective tissues with aging are investigated by combined morphological and biochemical methods. The aging of connective tissues depends on aging of informational- and structural-macromolecules. Aging-dependent alterations of proteoglycans/GAG and collagen can be caused by changes in genetic information or in the cellular information-coded synthesis, but also by changes in the controls of the various metabolic processes of connective tissue cells. The activities of enzymes involved in the anabolism and the catabolism of proteoglycans/GAG and collagen show reductions with aging, but do not show age-specific variations. The aging of connective tissues is rather a dynamic process (with measurable metabolic parameters of the various connective tissue cells and their products) than a passive or so-called degenerative connective tissue process. The bradytrophy concept of connective tissue cannot be accepted any longer, because connective tissue cells partly have metabolic rates at the same level as parenchymal cells. Furthermore, parenchymal cells can synthesize and degrade mesenchymal structural macromolecules. Connective tissue aging is demonstrated on 3 organ groups: 1. on typical mesenchymal organs: aorta, cartilage and skin, 2. on organs, which are mainly composed by connective tissue: heart and lung, 3. on connective tissues of parenchymal organs: liver and kidney. These various organs exhibit some common basic processes but also differences in connective tissue aging, which are due to the different composition of proteoglycans/GAG and collagen types, and on structure and function. The aging of connective tissues is of special importance for the aging of organs. Besides alterations of cells and GAG, the very important aging fibrosis in several mesenchymal and parenchymal organs is demonstrated and discussed. The connective tissue aging of organs is one of the reasons why the frequency of diseases increases with aging and diseases are grafted more strongly on aging cells, tissues, organs and organisms.

Aging↗

PubMed1994

Thalamic connections of the primary motor cortex (M1) of owl monkeys.

To determine the relative contributions of transthalamic cerebellar and pallidal projections to the primary motor cortex (M1) of owl monkeys, we examined the thalamic labeling resulting from injections of fluorescent tracers and wheatgerm agglutinin/horseradish peroxidase conjugate (WGA-HRP) into regions of M1 identified by intracortical microstimulation. Injections were placed in the major somatotopic divisions of M1 (the hindlimb, trunk, forelimb, and face representations) and in the caudal and rostral M1 subareas. In most cases, we injected several differentiable tracers into different parts of M1. Our results indicate that the strongest connections of M1 are with subdivisions of the ventral lateral thalamus (VL); other connections are mainly with intralaminar nuclei (the central lateral, paracentral, and center median nuclei) and the reticular nucleus. Most projections are reciprocal and topographically organized. M1 is strongly connected with the principal (VLp), medial (VLx), and anterior (VLa) subdivisions of the VL complex but has at most weak connections with the dorsal division (VLd). Each of the major somatotopic divisions of M1 is connected with an anteroposteriorly elongated territory within the VL complex. The connections are somatotopically organized such that the M1 hindlimb representation is connected with a band of cells in the lateral and anterior portions of the VL complex (spanning VLa and VLp), whereas the trunk, forelimb, and face representations are connected with successively more medially and posteriorly situated cell bands (spanning VLa, VLp, and VLx). There is some degree of overlap between the somatotopic territories within VL, although the absence of double-labeled cells in cases with injections of adjacent somatotopic divisions of M1 suggests that individual thalamic neurons project to single somatotopic regions. In addition to somatotopic differences, the connections of the caudal and rostral subdivisions of M1 differ to some extent. Caudal M1 is connected most strongly with VLp, a target of cerebellar projections, but it is also connected with VLa, which receives pallidal inputs. In complementary fashion, rostral M1 is most strongly connected with VLa, but it is also connected with VLp. VLx, a target of cerebellar projections, has significant connections with both caudal and rostral M1. These results indicate that all parts of M1 are influenced by both the cerebellum and globus pallidus in owl monkeys, as has been suggested in some recent studies of macaque monkeys.

Afferent Pathways↗

PubMed2005

Pre-strained epimuscular connections cause muscular myofascial force transmission to affect properties of synergistic EHL and EDL muscles of the rat.

BACKGROUND: Myofascial force transmission occurs between muscles (intermuscular myofascial force transmission) and from muscles to surrounding nonmuscular structures such as neurovascular tracts and bone (extramuscular myofascial force transmission). The purpose was to investigate the mechanical role of the epimuscular connections (the integral system of inter- and extramuscular connections) as well as the isolated role of extramuscular connections on myofascial force transmission and to test the hypothesis, if such connections are prestrained. METHOD OF APPROACH: Length-force characteristics of extensor hallucis longus (EHL) muscle of the rat were measured in two conditions: (I) with the neighboring EDL muscle and epimuscular connections of the muscles intact: EDL was kept at a constant muscle tendon complex length. (II) After removing EDL, leaving EHL with intact extramuscular connections exclusively. RESULTS: (I) Epimuscular connections of the tested muscles proved to be prestrained significantly. (1) Passive EHL force was nonzero for all isometric EHL lengths including very low lengths, increasing with length to approximately 13% of optimum force at high length. (2) Significant proximodistal EDL force differences were found at all EHL lengths: Initially, proximal EDL force = 1.18 +/- 0.11 N, where as distal EDL force = 1.50 +/- 0.08 N (mean +/- SE). EHL lengthening decreased the proximo-distal EDL force difference significantly (by 18.4%) but the dominance of EDL distal force remained. This shows that EHL lengthening reduces the prestrain on epimuscular connections via intermuscular connections; however; the prestrain on the extramuscular connections of EDL remains effective. (II) Removing EDL muscle affected EHL forces significantly. (1) Passive EHL forces decreased at all muscle lengths by approximately 17%. However, EHL passive force was still non-zero for the entire isometric EHL length range, indicating pre-strain of extramuscular connections of EHL. This indicates that a substantial part of the effects originates solely from the extramuscular connections of EHL. However, a role for intermuscular connections between EHL and EDL, when present, cannot be excluded. (2) Total EHL forces included significant shape changes in the length-force curve (e.g., optimal EHL force decreased significantly by 6%) showing that due to myofascial force transmission muscle length-force characteristics are not specific properties of individual muscles. CONCLUSIONS: The pre-strain in the epimuscular connections of EDL and EHL indicate that these myofascial pathways are sufficiently stiff to transmit force even after small changes in relative position of a muscle with respect to its neighboring muscular and nonmuscular tissues. This suggests the likelihood of such effects also in vivo.

Animals↗

PubMed1991

Electrocardiographic body surface potential mapping in the Wolff-Parkinson-White syndrome. Noninvasive determination of the ventricular insertion sites of accessory atrioventricular connections.

BACKGROUND: A reliable, noninvasive procedure to determine the location of accessory atrioventricular connections in patients with Wolff-Parkinson-White syndrome would add an important diagnostic tool to the clinical armamentarium. METHODS AND RESULTS: Body surface potential mapping (BSPM) using 180 electrodes in various-sized vests and displayed as a calibrated color map was used to determine the ventricular insertion site of the accessory atrioventricular (AV) connections in 34 patients with Wolff-Parkinson-White syndrome. Attempts were made to determine the 17 ventricular insertion sites described by Guiraudon et al. All 34 patients had an electrophysiologic study (EPS) at cardiac catheterization, and 18 had surgery so the ventricular insertion sites could be accurately located using EPS at surgery. A number of physiologic observations were also made with BSPM. CONCLUSIONS: The following conclusions were drawn: 1) BSPM using QRS analysis accurately predicts the ventricular insertion site of accessory AV connections in the presence of a delta wave in the electrocardiogram; 2) the ventricular insertion sites of accessory AV connections determined by BSPM and by EPS at surgery were identical or within one mapping site (1.5 cm or less) in all but four of 18 cases; three of the four exceptions had more than one accessory AV connection, and the other had a very broad ventricular insertion; 3) BSPM and EPS locations of the accessory AV connections correlated very well in the 34 cases despite the fact that BSPM determines the ventricular insertion site and EPS determines the atrial insertion site of the accessory AV connection; 4) as suggested by the three cases of multiple accessory AV connections, EPS and BSPM may be complementary since BSPM identified one pathway and EPS identified the other (in the case with a broad ventricular insertion, BSPM and EPS demonstrated different proportions of that insertion); 5) BSPM using ST-T analysis is very much less accurate in predicting the ventricular insertion site of accessory AV connections unless there is marked preexcitation; 6) standard electrocardiography using the Gallagher grid methodology (but with no attempt at stimulating maximal preexcitation) was not as accurate as QRS analysis of BSPM in predicting the ventricular insertion site of the accessory AV connection; however, exact comparison is hampered by the different number and size of the Gallagher and Guiraudon insertion sites; 7) BSPM using QRS analysis appears to be very accurate in predicting right ventricular versus left ventricular posteroseptal accessory AV connections; 8) typical epicardial right ventricular breakthrough, indicative of conduction via the specialized AV conduction system, occurs in all patients with left ventricular free wall accessory AV connections; 9) epicardial right ventricular breakthrough was not observed in cases with right ventricular free wall or anteroseptal accessory AV connections; 10) epicardial right ventricular breakthrough can occur in the presence of posteroseptal accessory AV connections, whether right or left ventricular; and 11) the delay in epicardial right ventricular breakthrough in cases with left ventricular insertion may provide a marker to estimate the degree of ventricular preexcitation.

Adult↗

PubMed1990

Input and output connections of an anteromedial group of spiking local interneurons in the metathoracic ganglion of the locust.

Intracellular recordings were made from an anteromedial group of spiking local interneurons in the metathoracic ganglion of the locust to determine the input connections that shape their mechanoreceptive fields on a hindleg and the output connections that define their effects on hindleg motor neurons. The receptive fields of these interneurons may contain excitatory and inhibitory regions. An excitatory region on the ipsilateral hind leg is formed by direct excitatory connections of the afferents from exteroceptors. Afferent spikes consistently evoke EPSPs in interneurons with a central synaptic latency of 1.2-1.5 msec. The connections appear to be direct and chemically mediated. An inhibitory region of a receptive field is not formed by direct afferent connections. Instead, spiking local interneurons of a midline group, which also receive direct excitatory inputs from the afferents, make direct inhibitory connections with anteromedial interneurons. Spikes in particular midline interneurons consistently evoke IPSPs in anteromedial interneurons with a central synaptic latency of about 1.0 msec. The connections appear to be direct and chemically mediated. By contrast, spikes in anteromedial interneurons could not be linked to any synaptic potentials in midline interneurons, so that direct connections are unidirectional and inhibitory. The large inhibitory regions to the receptive fields of anteromedial interneurons result from convergent inhibitory inputs of several midline interneurons. Each midline interneuron may make inhibitory output connections with several anteromedial interneurons, but there is a high degree of specificity in these divergent connections. Anteromedial interneurons make excitatory output connections with specific hind leg motor neurons. EPSPs in motor neurons follow spikes in the interneurons with short and consistent synaptic latencies of about 1.0 msec. The connections appear to be direct and chemically mediated. Two or more anteromedial interneurons with overlapping receptive fields may converge onto one motor neuron, and, in turn, one interneuron may make divergent connections with several motor neurons of the same pool. This pattern of connections suggests that these interneurons are essential elements in the local circuitry responsible for the expression of local reflexes of a leg. They provide an excitatory drive to the motor neurons in parallel to that from nonspiking local interneurons when particular arrays of exteroceptors are stimulated.

Action Potentials↗

PubMed1995

Analysis of connectivity in the cat cerebral cortex.

The mammalian cerebral cortex is innervated by a large number of corticocortical connections. The number of connections makes it difficult to understand the organization of the cortical network. Nonetheless, conclusions about the organization of cortical systems drawn from examining connectional data have often been made in a speculative and informal manner, unsupported by any analytic treatment. Recently, progress has been made toward more systematic ways of extracting organizing principles from data on the network of connections between cortical areas of the monkey. In this article, we extend these approaches to the cortical systems of the cat. We collated information from the neuroanatomical literature about the corticocortical connections of the cat. This collation incorporated 1139 reported corticocortical connections between 65 cortical areas. We have previously used an optimization technique (Scannell and Young, 1993) to analyze this database in order to represent the connectional organization of cortical systems in the cat. Here, we report the connectional database and analyze it in a number of further ways. First, we employed rules from Felleman and Van Essen (1991) to investigate hierarchical relations among the areas. Second, we compared quantitatively the results of the optimization method with the results of the hierarchical method. Third, we examined quantitatively whether simple connection rules, which may reflect the development and evolution of the cortex, can account for the experimentally identified corticocortical connections in the database. The results showed, first, that hierarchical rules, when applied to the cat visual system, define a largely consistent hierarchy. Second, in both auditory and visual systems, the ordering of areas by hierarchical analysis and by optimization analysis was statistically significantly related. Hence, independent analyzes concur broadly in their ordering of areas in the cortical hierarchies. Third, the majority of corticocortical connections, and much of the pattern of connectivity, were accounted for by a simple "nearest-neighbor-or-next-door-but-one" connection rule, which may suggest one of the mechanisms by which the development of cortical connectivity is controlled.

Animals↗

PubMed2004

Cytoarchitecture and cortical connections of the posterior cingulate and adjacent somatosensory fields in the rhesus monkey.

The cytoarchitecture and connections of the caudal cingulate and medial somatosensory areas were investigated in the rhesus monkey. There is a stepwise laminar differentiation starting from retrosplenial area 30 towards the isocortical regions of the medial parietal cortex. This includes a gradational emphasis on supragranular laminar organization and general reduction of the infragranular neurons as one proceeds from area 30 toward the medial parietal regions, including areas 3, 1, 2, 5, 31, and the supplementary sensory area (SSA). This trend includes a progressive increase in layer IV neurons. Area 23c in the lower bank and transitional somatosensory area (TSA) in the upper bank of the cingulate sulcus appear as nodal points. From area 23c and TSA the architectonic progression can be traced in three directions: one culminates in areas 3a and 3b (core line), the second in areas 1, 2, and 5 (belt line), and the third in areas 31 and SSA (root line). These architectonic gradients are reflected in the connections of these regions. Thus, cingulate areas (30, 23a, and 23b) are connected with area 23c and TSA on the one hand and have widespread connections with parieto-temporal, frontal, and parahippocampal (limbic) regions on the other. Area 23c has connections with areas 30, 23a and b, and TSA as well as with medial somatosensory areas 3, 1, 2, 5, and SSA. Area 23c also has connections with parietotemporal, frontal, and limbic areas similar to areas 30, 23a, and 23b. Area TSA, like area 23c, has connections with areas 3, 1, 2, 5, and SSA. However, it has only limited connections with the parietotemporal and frontal regions and none with the parahippocampal gyrus. Medial area 3 is mainly connected to medial and dorsal sensory areas 3, 1, 2, 5, and SSA and to areas 4 and 6 as well as to supplementary (M2 or area 6m), rostral cingulate (M3 or areas 24c and d), and caudal cingulate (M4 or areas 23c and d) motor cortices. Thus, in parallel with the architectonic gradient of laminar differentiation, there is also a progressive shift in the pattern of corticocortical connections. Cingulate areas have widespread connections with limbic, parietotemporal, and frontal association areas, whereas parietal area 3 has more restricted connections with adjacent somatosensory and motor cortices. TSA is primarily related to the somatosensory-motor areas and has limited connections with the parietotemporal and frontal association cortices.

Animals↗

PubMed1995

Ipsilateral intracortical connections of physiologically defined cutaneous representations in areas 3b and 1 of macaque monkeys: projections in the vicinity of the central sulcus.

This study examined cortical connections of areas 3b and 1 in 17 macaque monkeys in reference to regional somatotopography. The fluorescent retrograde tracers Fast Blue and Diamidino Yellow and the anterograde tracer Rhodamine Dextran were injected into closely related cutaneously responsive sites in primary somatosensory cortex, e.g., adjacent digits. Supra- and infragranular layers in nearly all studied areas contained labeled pyramidal cells. Labeled infragranular cells predominated at the fringes of a distribution where cells labeled from different tracer injections in the same brain intermixed more. All topographical regions across area 1 have reciprocal connections with areas 4, 3a, 3b, 1, 2, and 5. Intrinsic connections within area 1 and between it and area 2 are greatest; those with area 3b are less. Intrinsic connections within area 3b exceed all other nearby projections from this area which reciprocally connects with areas 3a, 1 and 2. Connections appear topographically organized, including those with poorly mapped regions, like area 5. These connections link representations of neighboring skin and skip map regions that include disjoint dermatomal areas. Connections from adjacent digit representations overlap; however, double-labeled cells were not found. Distal and proximal digit zones mostly interconnect within an area. Intrinsic connections spread further in area 1 than in area 3b, thereby joining more disparate topographical zones than interareal connections, which project more homotopically. The domain over which the map in somatosensory cortical area I (SI) dynamically changes following intracortical microstimulation (Recanzone, Merzenich and Dinse, Cerebral Cortex 2:181-196, 1992) may depend on the range of intrinsic connections observed in this study. The extent of connections between cortical areas was less than expected and this challenges the hypothesis that these connections directly create receptive field enlargements.

Animals↗

PubMed1987

Coexistent Mahaim and Kent accessory connections: diagnostic and therapeutic implications.

Six patients with coexistent Mahaim and Kent accessory connections are described. Two had left nodoventricular Mahaim connections, the first reported cases demonstrating these findings. In neither were the left-sided Mahaim connections components of a tachycardia and their presence was incidental. In two of four with nodoventricular connections, associated atrioventricular (AV) node conduction and coexistent posteroseptal accessory pathways were found. One of these had the unusual finding of a right-sided Mahaim connection arising from a "fast" AV node pathway. In only one patient did the tachycardia incorporate the Mahaim connection. In this patient, anterograde conduction during tachycardia occurred over a right nodoventricular connection whereas retrograde conduction occurred through a concealed right free wall Kent connection. Two patients had fasciculoventricular connections that were associated with either septal (one patient) or left free wall (one patient) Kent connections. The latter also had evidence of enhanced AV node conduction. This report is unique in that it describes in detail two patients with left nodoventricular connections (Mahaim) inserting in or near the left posterior fascicle. Combined Kent and Mahaim connections, present in the six patients, appear to occur in approximately 5% of patients with the Wolff-Parkinson-White syndrome. Precise identification of bypass connections critical for reentrant circuits is essential for intelligent application of treatment options.

Adult↗

PubMedDate not supplied

Development of forward and feedback connections between areas V1 and V2 of human visual cortex.

We have determined the sequence in which forward connections between visual cortical areas V1 and V2, and feedback connections between V2 and V1 develop in humans. For this purpose Dil was injected into V1 and V2 of postmortem brains of different pre- and postnatal ages. The laminar distribution of labeled fibers and cell bodies in V1 and V2 indicates that forward and feedback connections emerge shortly before birth. The development of both pathways proceeds over several postnatal months such that the laminar termination pattern of forward connections appears relatively mature before feedback connections reach their mature form. At 37 weeks of gestation both forward and feedback connections originate exclusively from deep-layer neurons, which extend axons in deep layers only. By 9 d postnatal, forward connections from V1 to V2, in addition to layers 5 and 6, also arise from neurons in layer 4B of V1. At this stage for the first time forward fibers enter layer 4 at the topographically appropriate location of V2. At 9 d postnatal most feedback fibers from V2 still occupy deep layers of V1 but many, through interstitial growth, elaborate vertical sprouts at regular intervals along the length of horizontal axons. As feedback connections mature, distal segments of horizontal axons are pruned back to branch points and fibers assume L-shaped configurations. By 7 weeks of age forward fibers from V1 enter V2 through deep and superficial layers and provide input to layers 3 and 4. At this stage feedback fibers from V2 have entered layer 4B of V1. By 4 months of age forward connections have assumed all the laminar characteristics of mature connections; that is, they arise from layers 2/3, 4B, 5, and 6 of V1, and terminate in layers 3 and 4 of V2. In sharp contrast, at 4 months of age feedback connections to V1 are still immature, showing terminations in layers 4B, 5, and 6 but no input to layer 2/3. The protracted postnatal emergence of feedback connections is similar to that of local long-range connections within layer 2/3 of V1 (Burkhalter et al., 1993). Since both of these circuits are thought to provide information about the context in which objects are seen, it is interesting to speculate that the late onset of texture segmentation in infants (Atkinson and Braddick, 1992; Sireteanu and Rieth, 1992) may be related to the postnatal maturation of specific intracortical circuits.

Carbocyanines↗

PubMed2026

Childhood Trauma and Frontoparietal Network Connectivity During Working Memory Task Performance in Individuals With Schizophrenia and Healthy Participants.

Schizophrenia is associated with altered frontoparietal connectivity, which supports higher-order cognition, including working memory. Childhood trauma has been linked to altered functional connectivity and reduced cognitive performance in individuals with schizophrenia and controls. Prior evidence suggests that trauma-related default mode dysconnectivity mediates the association between trauma and cognition. We hypothesised that childhood trauma would be associated with altered frontoparietal connectivity during a working memory task and that such connectivity changes would mediate the relationship between trauma and working memory. Childhood trauma, working memory and fMRI data were collected from individuals with schizophrenia or schizoaffective disorder (n = 38) and controls (n = 128). fMRI data were preprocessed in CONN, and seed-based connectivity analyses were performed for four frontoparietal seeds (bilateral dorsolateral prefrontal and posterior parietal cortices). Connectivity was contrasted across (a) diagnosis and (b) trauma severity. Moderated mediation analyses tested the associations between trauma, connectivity and working memory, with diagnosis as a moderator. Across all participants, higher physical neglect severity predicted poorer working memory performance. Stronger inverse connectivity between left dorsolateral prefrontal and frontal medial cortices predicted better working memory performance. As expected, patients showed widespread frontoparietal dysconnectivity relative to controls, but no differences in frontoparietal connectivity were observed across trauma severity groups. Frontoparietal connectivity did not mediate the association between trauma and working memory, although diagnosis moderated both the trauma-connectivity and connectivity-cognition associations. We conclude that, unlike previous evidence suggesting a mediating role for the default mode network, frontoparietal connectivity did not mediate the trauma-cognition association, possibly suggesting the unique significance of default mode network dysconnectivity in linking trauma to cognition in psychosis.

Humans↗

PubMed2006

Connectivity in an agricultural landscape as reflected by interpond movements of a freshwater turtle.

Connectivity is a measure of how landscape features facilitate movement and thus is an important factor in species persistence in a fragmented landscape. The scarcity of empirical studies that directly quantify species movement and determine subsequent effects on population density have, however, limited the utility of connectivity measures in conservation planning. We undertook a 4-year study to calculate connectivity based on observed movement rates and movement probabilities for five age-sex classes of painted turtles (Chrysemys picta) inhabiting a pond complex in an agricultural landscape in northern Virginia (U.S.A.). We determined which variables influenced connectivity and the relationship between connectivity and subpopulation density. Interpatch distance and quality of habitat patches influenced connectivity but characteristics of the intervening matrix did not. Adult female turtles were more influenced by the habitat quality of recipient ponds than other age-sex classes. The importance of connectivity on spatial population dynamics was most apparent during a drought. Population density and connectivity were low for one pond in a wet year but dramatically increased as other ponds dried. Connectivity is an important component of species persistence in a heterogeneous landscape and is strongly dependent on the movement behavior of the species. Connectivity may reflect active selection or avoidance of particular habitat patches. The influence of habitat quality on connectivity has often been ignored, but our findings highlight its importance. Conservation planners seeking to incorporate connectivity measures into reserve design should not ignore behavior in favor of purely structural estimates of connectivity.

Agriculture↗