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  • 1
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Topographical and functional aspects of neuronal plasticity were studied in the primary somatosensory cortex of adult rats in acute electrophysiological experiments. Under these experimental conditions, we observed short-term reversible reorganization induced by intracortical microstimulation or by an associative pairing of peripheral tactile stimulation. Both types of stimulation generate large-scale and reversible changes of the representational topography and of single cell functional properties. We present a model to simulate the spatial and functional reorganizational aspects of this type of short-term and reversible plasticity. The columnar structure of the network architecture is described and discussed from a biological point of view. The simulated architecture contains three main levels of information processing. The first one is a sensor array corresponding to the sensory surface of the hind paw. The second level, a pre-cortical relay cell array, represents the thalamo-cortical projection with different levels of excitatory and inhibitory relay cells and inhibitory nuclei. The array of cortical columns, the third level, represents stellate, double bouquet, basket and pyramidal cell interactions. The dynamics of the network are ruled by two integro-differential equations of the lateral-inhibition type. In order to implement neuronal plasticity, synaptic weight parameters in those equations are variables. The learning rules are motivated by the original concept of Hebb, but include a combination of both Hebbian and non-Hebbian rules, which modifies different intra- and inter-columnar interactions. We discuss the implications of neuronal plasticity from a behavioral point of view in terms of information processing and computational resources.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Area 19 ; Visual noise ; Detection performance ; Signal-to-noise thresholds ; S/N profiles ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The contribution of area 19 to pattern discrimination in the cat was studied by single cell recordings in this area and by behavioural experiments before and after bilateral lesions. In order to make quantitative comparisons between behavioural performance and that of cell systems, we introduced a new parameter that characterizes visual neurons by their signal-to-noise (S/N) thresholds. A structured visual background made up of Gaussian visual broadband noise which could be moved was superimposed on the signal (moving bars or outline patterns) and the S/N characteristics of the response were determined by varying the signal intensity. The detection performance of cats after bilateral lesion of area 19 showed no deficits. Only for slowly (11 deg/s) or quickly (110 deg/s) moving patterns, or when the background was moved relative to stationary patterns, did we find slight, but significant deficits in the low S/N range. However, when the S/N ratios were higher than 5, all cats achieved their full preoperative performances and no deficits remained. The S/N thresholds of neurons in area 19 were much higher than those found for neurons in areas 17 and 18. The lowest thresholds were found with a stationary background. Introduction of relative velocity between background and bar resulted in intermediate thresholds and the highest thresholds were observed for stimulus configurations lacking relative velocity. These effects correspond to the performance of the intact animal, in which introduction of relative motion increases the performance. The S/N thresholds did not correlate with levels of spike rate recorded at high S/N ratios, direction selectivity or speed preference, indicating that S/N threshold measurements provide a significant additional description of visual neurons. A limited number of area 19 cells recorded in area 17/18 lesioned animals showed very similar thresholds suggesting that this property may be independent of the intactness of areas 17 and 18. The residual performance by 17/18 lesioned cats in detecting small patterns corresponds well to the characteristics of the single cells of area 19. This suggests that area 19 might be able to make a considerable contribution to this task when areas 17/18 are eliminated, though by itself it seems not to be able to sustain the level of performance mediated by them. The contribution of area 19 is restricted to performances at high S/N ratios only. In contrast to what was found for areas 17 and 18, area 19 makes no essential contribution to lowering the S/N ratio at which the system is able to detect the presence of a pattern in a background of irrelevant detail.
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  • 3
    ISSN: 1432-1106
    Keywords: Detection performance ; Visual noise ; Pattern recognition ; Behavioural experiments ; Lesion of area 7 ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The contribution of the lateral suprasylvian cortex to pattern recognition was studied by behavioural detection experiments in combination with bilateral lesions of different parts of the lateral suprasylvian areas (LSA) and area 7 in seven cats. In a two-alternatives forced choice task the cats had to discriminate simple outline patterns which were additively superimposed on a structured visual background made up of broadband Gaussian noise. For various stimulus conditions (moving or stationary patterns and/or background) the detection probability (P D) of the cats was measured as a function of the signal to noise ratio (S/N). Each cat was tested before and after the lesion. Four different types of lesion could be distinguished depending on their extent: (1) lesion of parts of the (LSA); (2) lesion of parts of the LSA with undercutting of areas 17, 18 and 19; (3) lesion of area 7; (4) lesion of area 7 and parts of the LSA. 1. We found that a large bilateral lesion of the LSA led to significant deficits in all test situations which were dependent on the existence of relative velocity of moving patterns against a structured background. The ability of the cats to discriminate simple outline patterns which were kept stationary was not reduced. On the contrary, when they were tested with stationary and moving patterns on unfocused (empty) backgrounds, we found, to our great surprise, that the performance of the lesioned cats was significantly improved compared with intact animals. As these lesioned cats had no deficits with moving patterns on a uniformly grey background, we conclude that the deficits with the moving patterns must have been caused by interactions between patterns and background, and not by movement of a pattern per se. 2. As soon as the lesion of the LSA was extended by a bilateral undercutting of areas 17, 18 and 19 we found very severe deficits in all test situations, regardless of whether the patterns were moving or kept stationary, or whether they were superimposed on a background or not. The most substantial deficits occurred when the patterns were moving on a stationary background. In these situations the cats were no longer able to reach the 84% correct criterion. Again, the cats were able to reach criterion with moving patterns on a uniformly grey background indicating that this deficit is probably caused by the interaction of patterns and background and not by motion of the patterns per se. 3. A large lesion of area 7 led to modest but significant deficits of more or less the same degree in all test situations with the exception of quickly moving patterns on a structured background. In contrast, a much smaller lesion of area 7 yielded significant deficits only when the background was moved and there was a low relative velocity between the patterns and the background. 4. In brief, the combination of a lesion of area 7 with that of the LSA roughly provoked a combination of the effects of the two lesions (1 and 3) alone. We found significant deficits in all test situations. We did not find evidence for any type of functional recovery in any of the lesions described. All deficits were permanent. Our results support the idea of a functional segregation between the LSA and area 7. They confirm that the LSA are involved in pattern recognition whenever it is associated with motion in combination with object-background interactions. This suggests an involvement of the LSA in the analysis of object- and self-induced motion. An interpretation of the results of lesioning area 7 is based on the conjecture that the mechanism of vergence movements or of binocular fusion of both retina images might be impaired. Under this condition it seems conceivable to expect double images or a reduced visual acuity because the images are out of focus. This would have a similar effect on the detection performance in each stimulus configuration. In addition, the results of lesion 4 provide evidence that both functional subunits (LSA and area 7) are not able to compensate for one another. Finally, we conclude from the results after lesion 2 that the LSA is part of a system which is based on the cooperation with striate cortex and requires intact primary cortex for its full function.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 41 (1981), S. 47-57 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Proceeding from previous studies on cells in area 18, neurophysiological experiments were carried out using combinations of deterministic and statistical stimuli. The evaluation of the results on the space, time and amplitude characteristics of the cells show that for nearly all cells in this area, pattern distorition and shift due to motion are eliminated by spatial asymmetry of the coupling and specific combinations of on-off systems. So, the extraction of features despite pattern movement is possible in area 18. The features are extracted in the low spatial frequency range.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 41 (1981), S. 59-69 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract In addition to the asymmetry of the spatial coupling and of the specific temporal combination of excitation and inhibition, the non-linearity is very pronounced in area 18. Taking the sequence of a linear operation and a stationary nonlinear characteristic as a model, the experimental findings can be systematized and a cell classification specified which departs from the customary ones. The hypercomplex cell system probably originates in recurrent inhibition and leads to differentiation of the patterns along their contour line. Problems of cell classification and of the type of parallelism in the visual cortex are discussed.
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  • 6
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In respiratory modulated neurons of rabbits, vagally mediated inhibition is not bound to resting membrane potential oscillations. Latency of spinally evoked antidromical spike invasion, however, is shorter and threshold voltage is lower during the shift of membrane potential towards depolarization accompanying burst discharge.
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  • 7
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Behavioural impairments caused by brain lesions show a considerable, though often incomplete, recovery. It is hypothesized that cortical and subcortical plasticity of sensory representations contribute to this recovery. In the hindpaw representation of somatosensory cortex of adult rats we investigated the effects of focal unilateral cortical lesions on remote areas. Cortical lesions with a diameter of ≈ 2 mm were induced in the parietal cortex by photothrombosis with the photosensitive dye Rose Bengal. Subsequently, animals were kept in standard cages for 7 days. On day seven, animals were anaesthetized and cutaneous receptive fields in the cortical hindpaw representations ipsi- and contralateral to the lesion were constructed from extracellular recordings of neurons in layer IV using glass microelectrodes. Receptive fields in the lesioned animals were compared to receptive fields measured in nonlesioned animals serving as controls. Quantitative analysis of receptive fields revealed a significant increase in size in the lesioned animals. This doubling in receptive field size was observed equally in the hemispheres ipsi- and contralateral to the lesion. The results indicate that the functional consequences of restricted cortical lesions are not limited to the area surrounding the lesion, but affect the cortical maps on the contralateral, nonlesioned hemisphere.
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  • 8
    ISSN: 1432-2013
    Keywords: Bulbar respiratory centre ; Inspiratory neurons ; Respiratory movements ; Neuronal classification ; Metabolic modifiers of neuronal activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The property of the neuronal membrane to be permeable to metabolic modifiers of two regulatory enzymes has been utilized to manipulate the spike activity of inspiratory (I) and expiratory-inspiratory (EI) neurons of the bulbar respiratory centre. The neurons have been classified according to their response to lung distension or collapse (α- or β-type) and to hyperventilation (tonic firing denoted by “+”, cessation of activity by “−”). Using extracellular microelectrodes for single unit recording, the medulla oblongata was superfused with a metabolite-containing CSF. The various neuronal sub-types exhibited a differential activating or inhibitory response to one or several metabolic effectors. For example I α + units were activated by 5 mM glucose-6-phosphate (G-6-P) and 3.5 mM 3-phosphoglycerate (3-PGA), which both inhibited I β + neurons, while 5 mM AMP inhibited I α + much more strongly than I β + cells. The spike density of I α − and I β − neurons was increased in the presence of 2.5 mM fructose-6-phosphate and 3.5–5 mM AMP, but became reduced by G-6-P. In contrast, 3 mM fructose-1,6-diphosphate and 5 mM 3-PGA activated the I α − but inhibited the I β − neurons. The EIβ units were characteristically activated by 10 mM citrate, which inhibited all I-type neurons. Activations of the Iα and Iβ neurons led to an accelerated respiratory rate and a higher tidal volume, while the opposite was true for EIβ neurons. Intravenous injection of metabolites could not duplicate the striking effects under local applications.
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  • 9
    ISSN: 1432-2013
    Keywords: Respiratory neurons ; Neuronal discharge pattern ; Lung volume changes ; Hyperventilation ; Metabolic modifiers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Phase shifts between inspiratory-related and expiratory-related discharge patterns can be reversibly induced in respiratory neurons following volume changes of the lung, hypocapnic apnea as a result of hyperventilation, or supefusion with certain metabolic modifiers. Phase-spanning expiratory-inspiratory or inspiratory-expiratory discharges are frequently induced in those neurons which are activated either by pulmonary stretch receptors or collapse afferents. The same is true for regulatory effects which activate key steps of the neuronal metabolism such as ADP, 3-phosphoglycerate,l-glutamine, fructose-6-phosphate and fructose-1,6-diphosphate. In contrast, inhibitory vagal inputs or superfusion with citrate, an inhibitory metabolic modifier, revert preexisting expiratory-inspiratory discharges into a phase-coupled inspiratory pattern. It is postulated that the respiratory neuronal network represents a time-optimal control system which strives to adjust to a new equilibrium value in a minimum of time, following a given mechanical or chemical perturbation. Following the hypothesis advanced by Cohen (1974) that the phase-spanning units modulate the activity of the inphase neurons, it is suggested that the additional recruitment of expiratory-inspiratory and inspiratory-expiratory units provides a measure of the quality of time-optimal control and hence a performance index of the system.
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