Distant Connections Research Articles

Cortical connections of the frontoparietal opercular areas in the Rhesus monkey

The connections of the frontoparietal opercular areas were studied in rhesus monkeys by using antero- and retrograde tracer techniques. The rostral opercular cortex including the gustatory and proisocortical motor (ProM) areas is connected with precentral areas 3, 1, and 2 as well as with the rostral portion of the opercular area which resembles the second somatosensory type of cortex (area SII) and the ventral portion of area 6. Its distant connections are with the ventral portion of prefrontal areas 46, 11, 12, and 13 as well as with the rostral insula and cingulate motor area (CMAr). The mid opercular region (areas 1 and 2) is connected with pre- and postcentral areas 3, 1, and 2 as well as SII. Additionally, it is connected with the ventral portion of area 6, area 44, area ProM, the gustatory area, and the rostral insula. Its distant connections are with area 4, the ventral portion of area 46, area 7b, and area POa in the intraparietal sulcus (IPS). The rostral parietal opercular region is connected with the postcentral portions of areas 3, 1, and 2; areas 5, 7, and SII; the gustatory area; and the vestibular area. Its other connections are with area 4, area 44, the ventral portion of area 46, area ProM, CMAr, and the supplementary motor area (SMA). The caudal opercular region is connected with the dorsal portion of area 3; areas 2, 5, and 7a; and areas PEa as well as IPd of IPS. It is also connected with area SII, insula, and the superior temporal sulcus. Its distant connections are with area 44; the dorsal portion of area 8 and the ventral portion of area 46; as well as CMAr, SMA, and the supplementary sensory area. This connectivity suggests that the ventral somatosensory areas are involved in sensorimotor activities mainly related to head, neck, and face structures as well as to taste. Additionally, these areas may have a role in frontal (working) and temporal (tactile) memory systems.

The role of axonal delay in the synchronization of networks of coupled cortical oscillators.

Coupled oscillator models use a single phase variable to approximate the voltage oscillation of each neuron during repetitive firing where the behavior of the model depends on the connectivity and the interaction function chosen to describe the coupling. We introduce a network model consisting of a continuum of these oscillators that includes the effects of spatially decaying coupling and axonal delay. We derive equations for determining the stability of solutions and analyze the network behavior for two different interaction functions. The first is a sine function, and the second is derived from a compartmental model of a pyramidal cell. In both cases, the system of coupled neural oscillators can undergo a bifurcation from synchronous oscillations to waves. The change in qualitative behavior is due to the axonal delay, which causes distant connections to encourage a phase shift between cells. We suggest that this mechanism could contribute to the behavior observed in several neurobiological systems.

Synaptic organizations and dynamical properties of weakly connected neural oscillators. II. Learning phase information.

This is the second of two articles devoted to analyzing the relationship between synaptic organizations (anatomy) and dynamical properties (function) of networks of neural oscillators near multiple supercritical Andronov-Hopf bifurcation points. Here we analyze learning processes in such networks. Regarding learning dynamics, we assume (1) learning is local (i.e. synaptic modification depends on pre- and postsynaptic neurons but not on others), (2) synapses modify slowly relative to characteristic neuron response times, (3) in the absence of either pre- or postsynaptic activity, the synapse weakens (forgets). Our major goal is to analyze all synaptic organizations of oscillatory neural networks that can memorize and retrieve phase information or time delays. We show that such network have the following attributes: (1) the rate of synaptic plasticity connected with learning is determined locally by the presynaptic neurons, (2) the excitatory neurons must be long-axon relay neurons capable of forming distant connections with other excitatory and inhibitory neurons, (3) if inhibitory neurons have long axons, then the network can learn, passively forget and actively unlearn information by adjusting synaptic plasticity rates.

Cerebellorubral degeneration after resection of cerebellar dentate nucleus neoplasms: evaluation with MR imaging.

The authors describe the magnetic resonance (MR) findings in seven patients who developed severe cerebellar symptoms and atrophy of the contralateral red nucleus following removal of unilateral neoplasms in the deep nuclei of the cerebellum. For most patients, pre- and postoperative spin-echo MR images were obtained with long repetition times (TRs) at 1.5 T. The long TR images obtained before surgery demonstrated unilateral masses involving the dentate nucleus. Long TR images obtained after surgical resection of the dentate nucleus showed increased signal intensity in all of seven contralateral red nuclei, three of seven ipsilateral superior cerebellar peduncles, and two of seven contralateral inferior olivary nuclei. Three other patients who underwent surgery for cerebellar neoplasms without resection of the dentate nuclei showed no postoperative brain stem changes on MR images. The authors speculate that the changes in the contralateral red nuclei are due to cerebellorubral degeneration (since well-described neural tracts interconnect the dentate nucleus and the contralateral red nucleus). Injury of the dentate nucleus may result in degeneration of distant neural connections.

Conditioned states of cortical cells

Experimental data are presented on reorganizations of intra- and interanalyzer functional connections of neurones in the course of conditioning, by interval cross-histograms of two impulse series, and notions on neuronal organization of local and spread conditioned states are formulated. Numerous varieties of the analysis of systemic, interconnected activity of cortical neurones in the process of learning convince of the fact that individual and integrative neuronal functions characterize different qualitative levels of their activity. The integrative function of neurones shows various degrees of complicacy and specialization. The local conditioned state is considered to represent functional integration of neurones in cortical microregions, and the spread conditioned state--as neuronal integration between cortical projection zones. The interaction of neurones in the cortical projection of conditioned stimulus is more multiform and complex than that in the motor cortex. During the elaboration of inhibitory conditioned reflex there occurs a reorganization of the cortical systemic activity in the projection zone of the conditioned stimulus and a decrease of intensity of distant connections.

Distant Connections

The four years of the Carter administration saw both the United States and the Soviet Union fully engaged in intense efforts at what might be termed from the strategist's point of view geopolitical position building. Triggered by an imminent shift in the strategic weapons balance, position building occurred across the entire landscape in both the eastern and western hemispheres and was accompanied by military conflicts as the process reached flashpoints in Central America, Southeast Asia, Southwest Asia, the Middle East, and the Horn of Africa. This essay will focus on two of these areas, the Middle East and Southeast Asia, with particular emphasis on the interrelationship of events in early 1979 when the position-building process reached a point of intensity and there occurred virtually simultaneously the Sino-Vietnamese war, the VietnameseCambodian conflict, South Yemen's attack on North Yemen, the culmination of the Camp David peace treaty, the fall of the Shah in Iran, and the early stages of the crisis in Nicaragua.

Temporal pattern of HRP spread from an iontophoretic deposit site and description of a new HRP-gel implant method.

In the course of examining afferents to ventromedial hypothalamic (VMH) neurons using horseradish peroxidase (HRP), we needed to know how close to an iontophoretic deposit site neurons could be proved to be retrogradely labeled. In evaluating cells near but clearly outside HRP deposit sites visualized after a 24-hour survival period, for example, neurons which had been filled with HRP by somal or dendritic uptake could not be treated as retrogradely labeled and thus would not add to studies of intrahypothalamic connections. Rats were given standardized iontophoretic applications of HRP into VMH (continuous positive current 0.25 mu amp for 1 minute) and sacrificed after 5 or 15 minutes, 1, 4, 8, 12, or 24 hours in order to examine the pattern of HRP spread. The chromogen was tetramethylbenzidine. The volume of the application site visualized at 24 hours was less than 10% of maximum site size, which occurred at 1 hour. Since the cells located within the maximal spread boundary are candidates for nonretrograde labeling, HRP data on local connections obtained even from small iontophoretic deposits must be evaluated in the light of the demonstrated expansion and subsequent contraction of the application site. These results may also hold implications for the precision with which distant connections can be examined using the HRP retrograde method, as sites that appear discrete when visualized after 24-hour survival may have overlapped at shorter times post-iontophoresis. Incorporation of retrograde tracers into polyacrylamide gels provides an effective alternative to pressure injection or iontophoresis of aqueous tracer solutions. We describe a method for filling micropipettes with HRP-polyacrylamide gel. The pipettes are then implanted into brain sites to provide a confined pool of HRP. With postimplantation survival of 24 hour or longer, this method produces sites comparable in size to iontophoretic sites examined at 24 hours and results in improved retrograde labeling. Some results obtained with this method concerning the afferent connections of the dorsomedial hypothalamus are described.

Clustered intrinsic connections in cat visual cortex

The intrinsic connections of the cortex have long been known to run vertically, across the cortical layers. In the present study we have found that individual neurons in the cat primary visual cortex can communicate over suprisingly long distances horizontally (up to 4 mm), in directions parallel to the cortical surface. For all of the cells having widespread projections, the collaterals within their axonal fields were distributed in repeating clusters, with an average periodicity of 1 mm. This pattern of extensive clustered projections has been revealed by combining the techniques of intracellular recording and injection of horseradish peroxidase with three-dimensional computer graphic reconstructions. The clustering pattern was most apparent when the cells were rotated to present a view parallel to the cortical surface. The pattern was observed in more than half of the pyramidal and spiny stellate cells in the cortex and was seen in all cortical layers. In our sample, cells made distant connections within their own layer and/or within another layer. The axon of one cell had clusters covering the same area in two layers, and the clusters in the deeper layer were located under those in the upper layer, suggesting a relationship between the clustering phenomenon and columnar cortical architecture. Some pyramidal cells did not project into the white matter, forming intrinsic connections exclusively. Finally, the axonal fields of all our injected cells were asymmetric, extending for greater distances along one cortical axis than along the orthogonal axis. The axons appeared to cover areas of cortex representing a larger part of the visual field than that covered by the excitatory portion of the cell's own receptive field. These connections may be used to generate larger receptive fields or to produce the inhibitory flanks in other cells' receptive fields.

The power of local information

The author argues that telecommunications efforts too often tend to stress distant connections. The local informative contacts are important, and should be given a chance in future systems. The argument presented to support this view includes the specific example of the TERESE project (Telecommunications and Rural Development in Sweden). This publically funded project uses narrowband communication, including computer conferencing, to stress economic and social identity in a region in the far north of Sweden. Details of continuing regional efforts are given.

Isrecessionen inom Uppsalaområdet

Abstract Ice recession in the Uppsala region. In connection with mapping for the Geological Survey of Sweden in the Uppsala region drillings were carried out at 17 localities (Fig. 1) through the glacial varved clay in order to discover the ice recession in this area. The device used for drilling was a soil sampler with metal foils, constructed by the Swedish Geotechnical Institute (W. Kjellman and co-workers 1950) and able to take undisturbed samples of lengths up to 11 m. Varve measurements were carried out at all localities and used for connections with each other and with earlier measurements from here by Gerard De Geer (1940). The results are given in the graphs of Plate 3 and 4 and the table of Plate 5. Between all localities, situated in the Uppsala plain and the vallies associated with it, it is possible to find varve connections, but it is nearly impossible to do so in the area W of the town, probably owing to topographical conditions influencing the silty bottom streams of melt water from the ice front. Also in about 40 proximal varves, deposited in front of the ice tunnel opening, great irregularities in thickness are observed, owing to the same fact as mentioned above. In the author's opinion it is not possible to make far distant connections of varve series. The map of Plate 2 shows the ice recession in the region with ice margins for every 10 years. During a period of about 90 years — between the years −900—−810 according to the timescale of Gerard de Geer—the ice front retreated from the Uppsala region. From the ice margins it is clear that the ice tunnel, now indicated of the immense glacifluvial deposits of the Uppsala esker, must have debouched into an ice ravine, a fact earlier stated by G. Lundqvist (1955). As it appears from the map the youngest glacial striae W of the esker have a NNW direction, but E of it a NNE direction, indicating an activity of the local ice fronts, formed by the ravine. Glacial striae and end moraines of the region (quoted from G. Lundqvist 1956) correspond very well with the ice margins found in this investigation. In the upper part of the glacial clay of the Uppsala region about 20 to 30 cm above the last discernible microvarve, there is a zone maximally some 10 cm thick — the spotted zone — dotted with sand and gravel particles, mostly calcareous (Fig. 4). The problem of its origin has also been dealt with. According to J. P. Gustafsson (1905) the calcareous material in the spotted zone was once deposited in the sea or lake by ice bergs from the Bay of Gävle, a region where the land ice was rich in such fragments. But the zone is not distributed at random as it would, naturally, be if the material was transported by floating ice, and it is found in every locality where the original strata is preserved, but not in glacial clay, deposited from ice rivers W of the Uppsala region. Its thickness also gradually diminishes with increasing distance from the esker (Table 1), and we never find the spotted zone together with ice floated, large till material which now and then occurs in the glacial clay. The facts above suggest that the spotted zone is a synchronized phenomenon and limited to the sedimentation region of the Uppsala esker. As calculated in Fig. 5, it must have been deposited when the ice front was situated in the southern part of the Bay of Gävle, and the melt water from the ice river carried enormous quantities of calcareous fragments from the Silurian area in the bay. Further investigation of the sediment series N of the Uppsala region will probably provide a definite solution to the problem about the origin of the spotted zone.

CARBON DIOXIDE FROM THE UNSEVERED VAGUS NERVE OF THE SNAKE

1. The vagus nerve of the gopher-snake, Drymarchon corais couperi (Holbrook), discharges carbon dioxide at an average rate of 0.00234 mgm. of gas per gram of nerve per minute. The extremes were 0.0032 mgm. and 0.0017 mgm. 2. These rates were maintained as well when the nerve was separated from its central and its peripheral connections as when these connections were intact showing that the resting metabolism of nerve is a local operation and is not immediately dependent upon distant connections. 3. These observations also point to the conclusion that the passage of normal impulses over a nerve call for an increase of activity that is unobservable by the method employed and that must be small in amount compared with that produced by artificial stimulation.