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  • 1
    Electronic Resource
    Electronic Resource
    Changes in volume, surface estimate, three-dimensional shape and total number of neurons of the human primary visual cortex from midgestation until old age (1994)
    Springer
    Anatomy and embryology 190 (1994), S. 351-366 
    Details
    ISSN: 1432-0568
    Keywords: Development ; Aging ; Visual cortex ; Volume ; Surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Macroscopic features such as volume, surface estimate, thickness and caudorostral length of the human primary visual cortex (Brodman's area 17) of 46 human brains between midgestation and 93 years were studied by means of camera lucida drawings from serial frontal sections. Individual values were best fitted by a logistic function from midgestation to adulthood and by a regression line between adulthood and old age. Allometric functions were calculated to study developmental relationships between all the features. The three-dimensional shape of area 17 was also reconstructed from the serial sections in 15 cases and correlated with the sequence of morphological events. The sulcal pattern of area 17 begins to develop around 21 weeks of gestation but remains rather simple until birth, while it becomes more convoluted, particularly in the caudal part, during the postnatal period. Until birth, a large increase in cortical thickness (about 83% of its mean adult value) and caudorostral length (69%) produces a moderate increase in cortical volume (31%) and surface estimate (40%) of area 17. After birth, the cortical volume and surface undergo their maximum growth rate, in spite of a rather small increase in cortical thickness and caudorostral length. This is due to the development of the pattern of gyrification within and around the calcarine fissure. All macroscopic features have reached the mean adult value by the end of the first postnatal year. With aging, the only features to undergo significant regression are the cortical surface estimate and the caudorostral length. The total number of neurons in area 17 shows great interindividual variability at all ages. No decrease in the postnatal period or in aging could be demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00187293
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  • 2
    Electronic Resource
    Electronic Resource
    The Mode of Activation of a Barrel Column: Response Properties of Single Units in the Somatosensory Cortex of the Mouse upon Whisker Deflection (1993)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 5 (1993), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Response properties of single units in the mouse barrel cortex were studied to determine the sequence in which the neurons that form a cortical column become activated by a single‘natural’stimulus. Mice (n= 11) were anaesthetized with urethane. For a total of 153 cells, grouped by cortical layer, responses to a standardized deflection of a single whisker were characterized using poststimulus time and latency histograms. Usually, for each unit, data were collected for stimulation of its principal whisker (PW; the whiskers corresponding to the barrel column in which the cell was located) and of the four whiskers surrounding the PW. In all layers, PW stimulation evoked responses at shorter latency than surround whisker stimulation. In layers II – III and IV a bimodal distribution of cells according to latency to PW stimulation was found. Statistical analysis indicated the presence of two classes of cells in each of these layers:‘fast’units (latency 〈 15 ms) and 'slow’units (latency 〉15 ms). The great majority of cells in layers I, V and VI fired at latencies of 〉20 ms to PW stimulation. In general, stimulation of surround whiskers evoked a smaller response than PW stimulation. The fast cells of layer IV showed the greatest response to PW stimulation (mean = 1.78 spikes/100 ms poststimulus). Their firing was maximal during the 10–20 ms poststimulus epoch, while the slow layer IV cells fired maximally during the 20 – 30 ms poststimulus epoch. Surround inhibition occurred in all layers within the first 10 ms after stimulus onset, during which period the fast cells are the most active ones, and are thus likely to be responsible for the surround inhibition. This notion is supported by an analysis of spike duration that showed that eight of the ten cells with a thin spike (supposed to be GABAergic; McCormick et al., J. Neurophysiol., 54, 782 – 806, 1985), had PW latencies of 〈15 ms. We conclude that the activation of a barrel column is initially inhibitory in nature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1993.tb00534.x
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  • 3
    Electronic Resource
    Electronic Resource
    Topography of cortico-striatal connections in man: anatomical evidence for parallel organization (2004)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 20 (2004), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Tracing studies in non-human primates support the existence of several parallel neuronal circuits involving cerebral cortex, basal ganglia and thalamus. Distinct functional loops were proposed to underlie multiple aspects of normal and pathological behaviour in man. We present here the first anatomical evidence for separate corticostriatal systems in humans. Neural connections of the sensorimotor and prefrontal cortex to the striatum were studied in one human brain using the Nauta method for anterogradely degenerating axons. Axons originating from a lesion in the left sensorimotor cortex, including the face area, were found to terminate in the superolateral part of the ipsilateral putamen, forming a narrow band in its posterior part. Inside the band, the distribution of degenerating axons was inhomogeneous; high-density clusters of approximately 2.5 mm in diameter were separated by regions with less dense cortical projections. Axons originating from a small lesion in the fundus of the right superior frontal sulcus were found in the upper part of the ipsilateral caudate nucleus. The existence of discrete and anatomically segregated terminal patches originating from distinct cortical regions suggests parallel organization of cortico-striatal connections in man.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.2004.03640.x
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  • 4
    Electronic Resource
    Electronic Resource
    Distal dendrites of frog motor neurons: a computer-aided electron microscopic study of cobalt-filled cells (1986)
    Springer
    Journal of neurocytology 15 (1986), S. 303-310 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary With the aid of the cobalt labelling technique, frog spinal cord motor neuron dendrites of the subpial dendritic plexus have been identified in serial electron micrographs. Computer reconstructions of various lengths (2.5–9.8 μm) of dendritic segments showed the contours of these dendrites to be highly irregular, and to present many thorn-like projections 0.4–1.8 μm long. Number, size and distribution of synaptic contacts were also determined. Almost half of the synapses occurred at the origins of the thorns and these synapses had the largest contact areas. Only 8 out of 54 synapses analysed were found on thorns and these were the smallest. For the total length of reconstructed dendrites there was, on average, one synapse per 1.2 μm, while 4.4% of the total dendritic surface was covered with synaptic contacts. The functional significance of these distal dendrites and their capacity to influence the soma membrane potential is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01611433
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  • 5
    Electronic Resource
    Electronic Resource
    Synapses on motoneuron dendrites in the brachial section of the frog spinal cord: a computer-aided electron microscopic study of cobalt-filled cells (1992)
    Springer
    Journal of neurocytology 21 (1992), S. 34-49 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Cobalt-labelled motoneuron dendrites of the frog spinal cord at the level of the second spinal nerve were photographed in the electron microscope from long series of ultrathin sections. Three-dimensional computer reconstructions of 120 dendrite segments were analysed. The samples were taken from two locations: proximal to cell body and distal, as defined in a transverse plane of the spinal cord. The dendrites showed highly irregular outlines with many 1–2 μm-long ‘thorns’ (on average 8.5 thorns per 100 μm2 of dendritic area). Taken together, the reconstructed dendrite segments from the proximal sites had a total length of about 250 μm; those from the distal locations, 180 μm. On all segments together there were 699 synapses. Nine percent of the synapses were on thorns, and many more close to their base on the dendritic shaft. The synapses were classified in four groups. One third of the synapses were asymmetric with spherical vesicles; one half were symmetric with spherical vesicles; and one tenth were symmetric with flattened vesicles. A fourth, small class of asymmetric synapses had dense-core vesicles. The area of the active zones was large for the asymmetric synapses (median value 0.20 μm2), and small for the symmetric ones (median value 0.10 μm2), and the difference was significant. On average, the areas of the active zones of the synapses on thin dendrites were larger than those of synapses on large calibre dendrites. About every 4 μm2 of dendritic area received one contact. There was a significant difference between the areas of the active zones of the synapses at the two locations. Moreover, the number per unit dendritic length was correlated with dendrite calibre. On average, the active zones covered more than 4% of the dendritic area; this value for thin dendrites was about twice as large as that of large calibre dendrites. We suggest that the larger active zones and the larger synaptic coverage of the thin dendrites compensate for the longer electrotonic distance of these synapses from the soma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01206896
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