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PubMed1982

Specificity of neural connections in the retinotectal system.

The existence of a retinotopic map raises the question of how such a map is formed during development. Since little is known about molecular mechanisms which may be involved in the formation of retinotopy, the structural aspects of this developmental process were studied to a greater detail in the chick. In the retina the following patterns of growth can be observed: (1) Ganglion cell formation starts in the centre and spreads towards the periphery. Thus, each cell is labelled by both its position and its time of origin. (2) Axons tend to grow towards the optic fissure by the shortest possible route, and more peripheral axons whose perikarya are born later than that of central ones tend to lie next to the inner limiting membrane. A regular change in the pattern of fibres, which we call transformation, occurs at the optic fissure. The incremental rings are transformed into crescents lying ventrally in the optic stalk at early stages of development. In the middle of the optic nerve retinotopy is re-established. Another transformation occurs shortly behind the chiasm. Except for these transformations, fibres run parallel to each other even across the chiasm. Thus, fibres arriving at the optic tectum are well organized. It is concluded that a multiplicity of factors contribute to the formation of the retinotectal map at any site of the visual pathway. The analysis of these factors may indicate how topographically organized projections develop.

Animals↗
PubMed2006

In vivo transcranial imaging of connections in mouse visual cortex.

From the moment the mouse model took center stage for studies of cortical arealization and map formation, there was an urgent need for methods to identify areal borders in the living animal. The need was met in part by intrinsic optical signal imaging, which has been successfully applied to map topographic representations in primary visual, auditory and somatosensory cortex. However, the challenge remains to register these maps to the underlying structure. This is especially important for studies of the mouse brain in which cortical areas are often only a few hundred microns across. Here, we show that in visual cortex neuronal tracing with fluororuby and fluoroemerald can be used for transcranial imaging through the intact skull of callosal connections from the opposite side of the brain, and for mapping of topographic striate-extrastriate cortical pathways in living mice. Because callosal connections are important landmarks for cortical areas, the new method will allow registration of functional maps to underlying structures and facilitate targeted single-unit recordings in identified cortical areas.

Animals↗
PubMed1993

Retinotopy of cortical connections between the striate cortex and extrastriate visual areas in the rat.

Previous studies have determined that the striate cortex of the rat is reciprocally connected with multiple extrastriate cortical areas that are retinotopically organized. The objective of this study was to investigate the retinotopy of the striate-extrastriate connections in the rat, by placing triple or double injections of fluorescent tracers (fluorogold, fast blue, rhodamine dextran, or rhodamine-labeled microspheres) in different regions of the striate cortex (Oc1) and mapping the distribution of cells and fibers labeled with the different tracers in the lateral (Oc2L) and medial (Oc2M) extrastriate cortex. The tracer injection sites were visualized in tangential sections of the flattened cortex and correlated with the myelin layout of the striate cortex and with an electrophysiological map from previous studies. The results showed retinotopically organized Oc1 connections with ten different extrastriate cortical areas. The location of these extrastriate areas and the retinotopy of their striate connections remained mostly invariant despite changes of the injection sites in Oc1. Thus, the quadrantic retinotopy was obtained for striate connections to areas posterior, posterolateral, lateromedial, laterointermediate, laterolateral, anterolateral and rostrolateral in Oc2L; and to areas posteromedial, anteromedial, and anterior in Oc2M. The present anatomical map correlates well with electrophysiological maps of the rat extrastriate cortex from previous studies. Furthermore, they provide a definition of the retinotopy of some areas that have not been completely mapped before. These results reaffirm the existence of multiple extrastriate visual areas in the rat.

Animals↗
PubMed1998

Environmental enrichment alters organizational features of the forepaw representation in the primary somatosensory cortex of adult rats.

The cortical forepaw area of young adult rats was mapped by recording the response properties of small clusters of neurons in layer IV of the primary somatosensory (SI) cortex. First we quantitatively analyzed the somatotopic organizational features of the cortical forepaw representation in terms of areal extent and topography, receptive field (RF) sensory modality, size, and location. We also assessed the influence of environmental enrichment, known to induce structural alterations in cortical connectivity, on the representational characteristics of the forepaw maps. Long-Evans rats were housed in environments (standard, SE; enriched, EE) promoting differential tactile experience for 71-113 days from weaning. Within the SI, we found a single and complete topographic map of the cutaneous surfaces of the forepaw consisting of a rostrolateral-caudomedial sequence of digit and pad representational zones. Small islets of noncutaneous responses (NCR; high-threshold, deep-receptor input) within the boundaries of the cutaneous maps were a conspicuous feature of the forepaw map for SE rats. These islets created discontinuities in the representation of contiguous skin territories. In the SE rats, about 79% of the cortical sites activated by light tactile stimulation had a single cutaneous RF, whereas about 21% exhibited multiple RFs. Most single-digit RFs we delineated in the SE rats extended across two or three phalanges. As a result, the representations of the phalangeal skin surfaces were not segregated but formed an overlapping continuum. Moreover, within these regions, as the electrode was displaced in regular steps across the mediolateral axis, RFs did not shift across the digit skin surface in an orderly manner, suggesting a lack of internal topography in the finger representation zones. Tactile experience promoted by environmental enrichment induced alterations in the representational features of the SI cutaneous map of the forepaw. In EE rats, the areal extent of the forepaw cutaneous representation was 1.5 times larger than in SE rats. Indeed, the cutaneous map extended into NCR cortical sectors along its external margins and also into NCR islets found in the forepaw area. Consequently, in EE rats there were fewer representational discontinuities. The areal enlargement was due to a selective increase in the areal extent of the glabrous but not the hairy skin surface representations. Furthermore, protuberant glabrous skin (digit tips, palmar pads) was represented over larger cortical regions than were other glabrous skin territories less likely to be stimulated during object palpation and manipulation. Maps from EE rats were also characterized by a larger proportion of sites with single RFs (88% compared with 79%). In addition, glabrous RFs from EE rats were smaller and more clustered on the digit tips and palmar pads than were RFs in SE rat maps. RF size on hairy skin surfaces remained unchanged. Because the RFs were smaller, the cutaneous maps of EE rats contained distinct representations of digit phalangeal glabrous skin. RFs tended to exhibit more orderliness in their progression across the digit glabrous skin of EE rats than they did in SE rats. The phalanges of EE rats were represented in distinct patches. Neurons in EE rats were more sensitive to light tactile stimulation than were neurons in SE rats. These alterations were presumably mediated by the selective potentiation of cutaneous over deep-receptor activation. More generally, the present study corroborates the view that cortical cutaneous maps are maintained in a permanent state of use-dependent fluctuation.

Animals↗
PubMed2001

Cardiovascular effects of verapamil and quinidine at normal and elevated ambient pressure.

Cardiovascular parameters were measured in rats before and after administration of verapamil and quinidine, a slow Ca2+ and fast Na+ channel blocker, respectively, at normal and elevated ambient pressure [5 bar (500 kPa)]. Left ventricular pressure (Pivt), maximal velocity of Plvt rise (+dP/dt) and fall (-dP/dt), and heart rate (HR), arterial systolic pressure (Pasys), and mean arterial pressure (MAP) were measured in all animals using catheters connected to pressure transducers. Cardiac output (Q), and myocardial blood flow (MBF) were detected by the microsphere technique. Total peripheral vascular resistance (TPVR), myocardial vascular resistance (MVR) and oxygen consumption of the heart (VO2) was calculated. In Groups 1a (control group; 1 bar) and 1b (test group; 1-5 bar), verapamil (1.5 mg x kg(-1)) caused a reduction in Plvt, +dP/dt, -dP/dt, Pasys, MAP, VO2, TPVR, and MVR in both groups at 1 bar (100 kPa), and these parameters remained depressed for at least 50 min in Group 1a. However, MBF increased after verapamil injection. After compression to 5 bar (500 kPa), Plvt, dP/dt, Pasys, VO2, and MBF were markedly elevated (Group 1b). No change in HR, SV, or Q was found in either of the groups. In Groups 2a (control group; 1 bar) and 2b (test group; 1-5 bar), quinidine (5 mg x kg(-1)), infused over a period of 10 min, reduced Plvt, +dP/dt, -dP/dt, MAP, Pasys, VO2, Q, stroke volume (SV), TPVR and MBF at 1 bar (100 kPa). These parameters remained depressed for almost the whole experimental period in Group 2a, while Plvt, +/-dP/dt, Pasys, MAP and VO2 were enhanced during exposure to 5 bar (500 kPa) in Group 2b. The HR was unchanged by quinidine in Group 2a, but was increased at elevated ambient pressure in Group 2b, whereas the MBF was unchanged in both groups. The present results show that verapamil and quinidine have a depressant effect on cardiac function, arterial pressure and VO2 at normal atmospheric pressure, whereas MBF was enhanced only in the verapamil group. During exposure to elevated ambient pressure, cardiac function, arterial pressure and VO2 increased despite adequate inhibition of slow Ca2+ and fast Na+ channels.

Air Pressure↗
PubMed1996

Anatomically based ablation of atrial flutter in an acute canine model of the modified Fontan operation.

BACKGROUND: Lateral tunnel total cavopulmonary connection, also called the modified Fontan operation, uses a baffle through the right atrium. We established, in an acute canine model, that atrial flutter after total cavopulmonary connection revolves around a line of conduction block imposed by the free wall lateral tunnel suture line. We hypothesized that a line of conduction block between the free wall total cavopulmonary connection suture line and the tricuspid anulus would interrupt atrial flutter in this model. OBJECTIVE: Our objective was to determine whether a cryolesion placed between the free wall total cavopulmonary connection suture line and the tricuspid anulus would terminate atrial flutter in an acute canine model. METHODS: Seven adult dogs underwent median sternotomy and institution of cardiopulmonary bypass. A suture line was placed through a right atriotomy to simulate total cavopulmonary connection lateral tunnel construction. Form-fitting 253-point biatrial endocardial mapping electrodes were placed via bilateral ventriculotomies. Atrial flutter was induced by atrial burst pacing. A cryothermal lesion was then placed between the free wall total cavopulmonary connection suture line and the tricuspid anulus in the low lateral right atrium (i.e., CRYO 1 procedure), and reinduction of atrial flutter was attempted. If atrial flutter was reinduced, the cryolesion was modified superiorly to include the caudal portion of the atriotomy (i.e., CRYO 2 procedure). Activation sequence maps were generated for sinus rhythms before and after the cryolesions were placed and for induced arrhythmias. RESULTS: In all seven cases, atrial flutter was inducible after suture line placement, before placement of a cryolesion. The reentrant circuit incorporated both caval orifices in five of seven cases and was successfully ablated by the CRYO 1 approach in each case. Atrial flutter was not inducible after placement of the CRYO 2 lesion in the remaining two cases, in which breakthrough of the wave front occurred across the lateral tunnel suture line in the intercaval region. Activation sequence maps of sinus rhythm after placement of the cryolesions demonstrated a conduction block at the site of the lesion. CONCLUSIONS: A linear cryothermal lesion placed between the free wall aspect of the total cavopulmonary connection suture line and the tricuspid anulus created a line of conduction block that successfully ablates atrial flutter in the canine model.

Acute Disease↗
PubMedDate not supplied

A small angle light scattering device for planar connective tissue microstructural analysis.

The planar fibrous connective tissues of the body are composed of a dense extracellular network of collagen and elastin fibers embedded in a ground matrix, and thus can be thought of as biocomposites. Thus, the quantification of fiber architecture is an important step in developing an understanding of the mechanics of planar tissues in health and disease. We have used small angle light scattering (SALS) to map the gross fiber orientation of several soft membrane connective tissues. However, the device and analysis methods used in these studies required extensive manual intervention and were unsuitable for large-scale fiber architectural mapping studies. We have developed an improved SALS device that allows for rapid data acquisition, automated high spatial resolution specimen positioning, and new analysis methods suitable for large-scale mapping studies. Extensive validation experiments revealed that the SALS device can accurately measure fiber orientation for up to a tissue thickness of at least 500 microns to an angular resolution of approximately 1 degree and a spatial resolution of +/-254 microns. To demonstrate the new device's capabilities, structural measurements from porcine aortic valve leaflets are presented. Results indicate that the new SALS device provides an accurate method for rapid quantification of the gross fiber structure of planar connective tissues.

Animals↗
PubMed1997

Model calculations of the effects of wide-band inhibitors in the dorsal cochlear nucleus.

In two previous papers [Reed and Blum, J. Acoust. Soc. Am. 97, 425-438 (1995), Blum et al., J. Acoust. Soc. Am. 98, 181-191 (1995)] a computational model for signal processing in the dorsal cochlear nucleus (DCN) was developed. In those modelling studies, stellate cells inhibited only type II cells. In this study, the effect of including wide-band inhibitory (WBI) connections from stellate cells to type IV cells, as proposed by Nelken and Young [J. Neurophysiol. 71, 2446-2462 (1994)], is examined. Inclusion of the WBI connections improves the fit to the experimental pure tone response maps for both the "standard" and "non-standard" cells examined by Spirou and Young [J. Neurophysiol. 66, 1750-1768 (1991)]. Thus, these modelling studies support the hypothesis of Nelken and Young [J. Neurophysiol. 71, 2446-2462 (1994)]. The degree of improvement is greatest for cells with prominent upper inhibitory sidebands. The qualitative features of the pure tone response map and the theoretical model allow one to deduce the probable frequency bias of the type II to type IV and stellate to type IV connections.

Acoustic Stimulation↗
PubMed2001

Solving the binding problem of the brain with bi-directional functional connectivity.

We propose a neural network model which gives one solution to the binding problem on the basis of 'functional connectivity' and bidirectional connections. Here, 'functional connectivity' is dynamic neuronal connectivity peculiar to temporal spike coding neural networks with coincidence detector neurons. The model consists of a single primary map and two higher modules which extract two different features shown on the primary map. There exist three layers in each higher module and the layers are connected bi-directionally. An object in the outer world is represented by a 'global dynamical cell assembly' which is organized across the primary map and the two higher modules. Detailed, but spatially localized, information is coded in the primary map, whereas coarse, but spatially extracted information or globally integrated information is coded in the higher modules. Computer simulations of the proposed model show that multiple cell assemblies sharing the same neurons partially can co-exist. Furthermore, we introduce a three-dimensional J-PSTH (Joint-Peri Stimulus Time Histogram) which is capable of tracking such cell assemblies, altering its constituent neurons as in our proposed model.

Action Potentials↗
PubMed1982

The afferent and efferent callosal connections of retinotopically defined areas in cat cortex.

We compared the callosal afferent and efferent connections of different retinotopic loci within a given visual cortical area as well as the connectivity patterns among similar retinotopic loci in different visual areas. Small injections (75 nl) of a mixture of horseradish peroxidase and [3H]leucine were made through a recording pipette at injection sites identified by retinotopic mapping. A small locus of cortex within a callosally connected region had precise reciprocal connections with the homotopic locus in the contralateral hemisphere. This small locus also was callosally connected with a variable number of heterotopic loci. Both reciprocal and nonreciprocal heterotopic callosal connections were found. Homotopic and heterotopic connections appeared to have a high degree of retinotopic fidelity. Precisely homotopic connections were present not only between locations on the vertical meridian representations at the left and right area 17/18 borders but also, for example, between mirror-symmetrical points on the peripheral horizontal meridian representation in the left and right posteromedial lateral suprasylvian areas. In several experiments, we found that both callosal neurons and terminals in the homotopic cortex were grouped into two to three distinct clusters ranging from 600 to 900 micrometers in width. Callosal neurons with homotopic connections were primarily pyramidal cells in lower layer III and upper layer IV. Outside of areas 17 and 18, there was a significant number of pyramidal and fusiform-shaped callosal neurons in layers V and VI. The majority of callosal terminals were located in layers II, III, and IV.

Afferent Pathways↗
PubMed1999

Positive effects on life skills motivation and self-efficacy: node-link maps in a modified therapeutic community.

In recent years, one response to drug abuse problems has been to provide treatment in prison and probation settings. Results are promising, although the need for improving mandated treatment has been expressed. The Cognitive Enhancements for Treatment of Probationers (CETOP) project is investigating cognitive enhancements in a modified therapeutic community (TC) setting. One enhancement is node-link mapping, a visual graphing strategy. Map "nodes" contain ideas, actions, and feelings; these are connected by links that illustrate meaningful relationships. Current findings indicate increases in group participation, ratings of session depth, and positive ratings of coresidents, counselors, and security staff. The present study extends this research by comparing mapping-enhanced counseling to standard counseling on self-efficacy and motivation for basic psychosocial skills (e.g., emotional control). Probationers (n = 381) in a 16-week residential program were assigned randomly to conditions in 12 TCs (n = 30-35). Motivation and self-efficacy were assessed by two self-report questionnaires, one midway and one at the end of treatment. A five-factor solution was produced from each questionnaire. With community as the unit of analysis, means of enhanced counseling were higher in all cases. Wilcoxen tests indicated four significant differences at midterm for mapping on motivation and self-efficacy of communication and emotional control (p < .05). At the end of treatment, mapping was higher for motivation of cognition and emotional control and self-efficacy was higher for communication. Discussing Bandura's model, these findings provide evidence that maps may enhance psychosocial skills, which have been associated with maintaining recovery.

Adolescent↗
PubMed1993

Organization of long-range inhibitory connections with rat visual cortex.

We have studied the laminar organization of local long-range inhibitory connections within rat primary visual cortex (area 17) by combining retrograde tracing of nerve cell bodies with glutamic acid decarboxylase immunocytochemistry. While most inhibitory connections are confined to within 0.4 mm of the injection site, a subset of neurons at the layer 5/6 border provide long-range (> 1 mm) inhibitory connections within area 17. However, other cell layers that contain similar local long-range horizontal connections, that is, lower layer 2/3, upper layer 5, and lower layer 6 (Burkhalter and Charles, 1990), show a much more restricted distribution of inhibitory connections. This suggests that cells at the layer 5/6 border play a role in the direct inhibition of neurons at a distant point of the topographic map. Similar double labeling studies reveal long-range inhibitory connections between visual areas. Following injections of fluorescent tracers into area 17, in horizontal sections inhibitory connections can be identified that are up to 8 mm long, linking the extrastriate subdivisions 18a and 18b with striate cortex. Conversely, injections of fluorescent tracers into the cytoarchitectonic subdivision 18a reveal local long-range inhibitory connections within 18a, long-range inhibitory connections between 18a and the cytoarchitectonic subdivision 18b, and inhibitory forward connections from area 17 to 18a. These results suggest that the communication between different cortical areas can be influenced by direct inhibitory connections.

Animals↗
PubMed1984

The possible role of "sibling neurite bias" in the coordination of neurite extension, branching, and survival.

In this review we consider a novel mechanism, "sibling neurite bias," which may explain aspects of the coordination of elongation, branching, and resorption among different neurites growing from the same neuronal cell body. In this model, growing neurites which incorporate structural precursors at higher rates would deplete the cellular pool of precursors available to their "sibling" neurites; neurites would compete for survival, but in addition they would bias each other's behavior during active growth. Evidence is reviewed that "sibling neurite bias" may contribute to the establishment and stabilization of specific neural connections. Specific examples examined include the loss of polyinnervation at the developing neuromuscular junction, contextual mapping in the retino-tectal system, and selective neurite growth patterns and synaptic connections in nerve tissue culture model systems.

Animals↗
PubMed2006

A sensorimotor map: modulating lateral interactions for anticipation and planning.

Experimental studies of reasoning and planned behavior have provided evidence that nervous systems use internal models to perform predictive motor control, imagery, inference, and planning. Classical (model-free) reinforcement learning approaches omit such a model; standard sensorimotor models account for forward and backward functions of sensorimotor dependencies but do not provide a proper neural representation on which to realize planning. We propose a sensorimotor map to represent such an internal model. The map learns a state representation similar to self-organizing maps but is inherently coupled to sensor and motor signals. Motor activations modulate the lateral connection strengths and thereby induce anticipatory shifts of the activity peak on the sensorimotor map. This mechanism encodes a model of the change of stimuli depending on the current motor activities. The activation dynamics on the map are derived from neural field models. An additional dynamic process on the sensorimotor map (derived from dynamic programming) realizes planning and emits corresponding goal-directed motor sequences, for instance, to navigate through a maze.

Action Potentials↗