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PubMed1980

The basic uniformity in structure of the neocortex.

The number of neuronal cell bodies has been counted in a narrow strip (30 micrometers) through the depth of the neocortex in several different functional areas (motor, somatic sensory, area 17, frontal, parietal and temporal and in many species (mouse, rat, cat, monkey and man). With the exception of area 17 of the visual cortex in a number of primates the same absolute number (congruent to 110) of neurons has been found in all areas and in all species. In the binocular part of area 17 of the primates there are approximately 2.5 times more neurons. Thus in mammalian evolution the area of the neocortex increases in larger brains but the number of neurons through the depth remains constant, except in area 17 of primates. From these and other findings it is suggested that the intrinsic structure of the neocortex is basically more uniform than has been thought and that differences in cytoarchitecture and function reflect differences in connections.

Adult↗
PubMed1997

The columnar organization of the neocortex.

The modular organization of nervous systems is a widely documented principle of design for both vertebrate and invertebrate brains of which the columnar organization of the neocortex is an example. The classical cytoarchitectural areas of the neocortex are composed of smaller units, local neural circuits repeated iteratively within each area. Modules may vary in cell type and number, in internal and external connectivity, and in mode of neuronal processing between different large entities; within any single large entity they have a basic similarity of internal design and operation. Modules are most commonly grouped into entities by sets of dominating external connections. This unifying factor is most obvious for the heterotypical sensory and motor areas of the neocortex. Columnar defining factors in homotypical areas are generated, in part, within the cortex itself. The set of all modules composing such an entity may be fractionated into different modular subsets by different extrinsic connections. Linkages between them and subsets in other large entities form distributed systems. The neighborhood relations between connected subsets of modules in different entities result in nested distributed systems that serve distributed functions. A cortical area defined in classical cytoarchitectural terms may belong to more than one and sometimes to several distributed systems. Columns in cytoarchitectural areas located at some distance from one another, but with some common properties, may be linked by long-range, intracortical connections.

Animals↗
PubMedDate not supplied

Gap junctional communication and the development of local circuits in neocortex.

In the neocortex, as well as in many other brain regions, neurons responding to similar stimulus features are usually found close to one another. Here we examine the possible role of gap junctional communication in forming and defining these local neuronal groupings, examples of which may be the columns found in the neocortex of virtually all mammalian species. We have approached this question experimentally in cortical brain slices using calcium imaging to visualize multicellular activity patterns, and tracer injections to identify the anatomical pattern of gap junction coupling in the developing neocortex. Our results suggest that dendrodendritic gap junctional communication may be involved in the formation of local connectivity, most likely by synchronizing electrical or biochemical activity among neighboring neurons.

Animals↗
PubMed1994

NADPH diaphorase neurones are evenly distributed throughout cat neocortex irrespective of functional specialization of each region.

Using NADPH diaphorase histochemistry as a marker for nitric oxide synthase we investigated the possible sites of nitric oxide synthesis in cat cerebral neocortex. Intensely stained neurones were found mainly in the deep layers of the neocortex and underlying medulla. Virtually all neurones in the cerebral medulla were NADPH diaphorase positive. The density of diaphorase neurones was estimated in the cortex/medulla border zones of each neocortical gyrus. Diaphorase neurones were evenly distributed throughout the neocortex and no significant statistical difference between gyri was observed. These findings indicate that the density of diaphorase neurones is irrespective of functional specialization of each region and are more in line with the hypothesis that NADPH diaphorase neurones are involved in the control of local cortical blood flow.

Amino Acid Oxidoreductases↗
PubMed1990

The total number of neurons in the human neocortex unbiasedly estimated using optical disectors.

An efficient method is presented for obtaining, in under 4 h, an unbiased estimate of the total number of neurons in the human neocortex, with a coefficient of error on the estimate of approximately 5%. The novel sampling scheme used in this study is unbiased and was designed so that only a small amount of neocortical grey matter had to be removed. Hence, the majority of the cerebral grey matter and all the internal grey matter was left intact for further resampling and analysis. Each cerebral hemisphere was subdivided into the four major neocortical regions, sliced coronally at 7-mm intervals and the volume of the neocortex determined using Cavalieri's principle. Uniform sampling of neocortex was performed in the hemisphere followed by regional subsampling with a varying sampling fraction being taken from each region. Neuronal density estimates were made in thick plastic sections using optical disectors. Shrinkage estimates were made in parallel with the number estimates and found to be negligible. The total number of neocortical neurons in the right hemisphere of five normal 80-year-old men was found to be 13.7 x 10(9) with an inter-individual coefficient of variation of 12%.

Aged↗
PubMed1985

Cyclic AMP concentrations in rat neocortex and hippocampus during and following incomplete ischemia: effects of central noradrenergic neurons, prostaglandins, and adenosine.

The concentrations of cyclic AMP, noradrenaline, glycogen, glucose, lactate, pyruvate, labile phosphate compounds, and free fatty acids were investigated in the rat neocortex and hippocampus during and following cerebral ischemia. An incomplete ischemia of 5 and 15 min duration was induced by bilateral carotid clamping combined with hypotension. The postischemic events were studied after 5, 15, and 60 min of recirculation. Five minutes of ischemia did not significantly alter the neocortical or hippocampal concentrations of cyclic AMP. After 15 min of ischemia the neocortical levels decreased significantly below control values. In the recirculation period following ischemia a significant elevation of the cyclic AMP concentrations was observed. Following 5 min of recirculation after 5 min of ischemia the levels increased from 2.53 +/- 0.21 nmol X g-1 to 5.18 +/- 0.09 nmol X g-1 in the neocortex and from 2.14 +/- 0.16 nmol X g-1 to 3.52 +/- 0.35 nmol X g-1 in the hippocampus. Five minutes of recirculation following 15 min of ischemia led to a significant increase in the levels of cyclic AMP, to 12.86 +/- 1.43 nmol X g-1 in the neocortex to 5.58 +/- 0.57 nmol X g-1 in the hippocampus. With longer recirculation periods the cyclic AMP levels progressively decreased and were similar to control values after 60 min. Depletion of cortical noradrenaline by at least 95% was performed by injections of 6-hydroxydopamine into the ascending axon bundles from the locus ceruleus. The lesion did not significantly change the ischemic or post-ischemic neocortical and hippocampal levels of cyclic AMP, glycogen, or free fatty acids including arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1989

Noradrenaline metabolism in neocortex and hippocampus following transient forebrain ischemia in rats: relation to development of selective neuronal necrosis.

Noradrenaline (NA) metabolism in the neocortex and hippocampus was examined in rats at 1, 24, and 48 h following 15 min of reversible forebrain ischemia. As assessed by the ratio of accumulated 3,4-dihydroxyphenylalanine (DOPA) to the tissue NA level after inhibition of DOPA decarboxylase, the NA turnover rates were markedly increased (120-148% above the control) at 1 h postischemia in both the neocortex and hippocampal formation (CA1 and CA3 plus dentate gyrus). The DOPA:NA ratio went back to control levels after longer postischemic survival times. The ratio between levels of the deaminated NA metabolite, 3,4-dihydroxyphenylethyleneglycol (DOPEG), and NA, which gives another measure of NA turnover rate, showed similar changes. In the neocortex and the CA3 plus dentate gyrus, the DOPEG:NA ratio was markedly increased (89-118%) 1 h after the ischemia, but this change had disappeared at 24 and 48 h. Thus, both the DOPA accumulation experiments and the NA and DOPEG measurements indicate that following transient forebrain ischemia, there is an increased NA turnover in the hippocampus and cortex only in the early recirculation period and not after longer postischemic survival times. The degree of neuronal necrosis in the CA1 region was examined light microscopically on celestine blue-acid fuchsin-stained sections at 24, 48, and 96 h following the ischemic insult. The neuronal damage in CA1 was sparse after 24 h of recovery, had increased markedly after 48 h, and was very pronounced at 96 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Coevolution of the mammalian middle ear and neocortex.

Phylogenetic analysis with x-ray computed tomography of fossilized and recent crania implicates differential growth of the neocortex in the evolution and development of the mammalian middle ear. In premammalian tetrapods, the middle ear evolved as a chain of bones attached to the mandible and cranium, but in adult mammals the chain is detached from the mandible and lies behind it. The neocortex evolved concurrently with detachment of the chain. In mammalian development the auditory chain arises connected to the mandible but later detaches, recapitulating the phylogenetic transformation. In modern didelphid development, the auditory chain reaches mature size by the third week after birth and is then separated from the jaw and displaced caudally as the neocortex grows for another 9 weeks.

Animals↗
PubMedDate not supplied

Intracortical dentate fascia grafts: mossy fiber synapses in the host neocortex.

Embryonic dentate fascia was grafted into a cavity in the area of the adult rat neocortex which represents the vibrissae (barrel field). We wished to test the possibility of development of connections between the two brain areas which do not have synaptic or tissue contacts in situ. The unique characteristics of the giant synaptic boutons of the dentate mossy fibers were used for detection of the dentate synaptic contacts with neocortical neurons at the electron microscopic level. Ultrastructural analysis nine months postgrafting has shown that the bundles of mossy axons enter the host neocortex and develop multiple terminal and en passant contacts with typical characteristics. Neuronal perikarya, large dendritic trunks and fine caliber terminal dendritic branches were used by the mossy fibers as postsynaptic targets, as well as spines of various complexity and configurations. The subsynaptic dendrites seemed to be modified by synapsing giant boutons. Accumulation of cytoplasmic organelles was observed at these sites. Various bumps and protuberances were formed by the subsynaptic dendrite surface. The contents of these appendages were variable; some of them contained organelles typical of dendroplasm, while others were more spine-like, often with inclusion of ribosomes. It is concluded that mossy fibers growing into the host neocortex can develop typical contacts with inappropriate targets with all the ultrastructural features of functional synapses.

Animals↗
PubMed1981

An analysis of some thalamic projections to parietofrontal neocortex in the marsupial native cat, Dasyurus viverrinus (Dasyuridae).

Thalamocortical projections to parietofrontal neocortex in the marsupial native cat, Dasyurus viverrinus, were examined using the retrograde transport of horseradish peroxidase. The results show that the organisation in Dasyurus is similar to that reported in another Australian marsupial, the brush-tailed possum, Trichosurus vulpecula, and is different to that found in the primitive American form, Didelphis virginiana. In Daysurus, as in Trichosurus, the areas of neocortex receiving projections from the trigeminothalamic system do not appreciably coincide with those areas receiving input from the cerebellothalamic system. In Didelphis there appears to be complete overlap of these areas of motor and somaesthetic neocortex. These results suggest that the motor--somaesthetic organisation in Australian marsupials is divergent from the presumed stem pattern seen in the American forms. If the Australian marsupials, as is now believed, were isolated from the stem Polyprotodonta in the upper Cretaceous, it would appear that the Australian marsupials may have begun to develop certain aspects of their characteristic CNS configuration very early, as the oldest known marsupial fossils are not much older than this.

Animals↗
PubMed1989

Comparative distribution of acid phosphatase and simple esterase in the mouse neocortex and hippocampal formation.

The present study deals with the detailed distribution of acid phosphatase (AcP) and simple esterase (SE) in different layers of the neocortex and hippocampal formation of the mouse brain. The neurons, in general, had moderate to intense enzyme activity for AcP and mild to moderate activity for SE. The AcP activity dominated in the neuronal population as compared to the neuropil; the neuropil stained mildly for SE. The large pyramidal cells in the neocortex and cornu ammonis, and the granular cell layer of the gyrus dentatus, demonstrated strong enzyme activity both in AcP and SE preparations. The role of AcP and SE has been discussed in relation to various structures of the neocortex and hippocampal formation.

Acid Phosphatase↗
PubMed1997

Marr's theory of the neocortex as a self-organizing neural network.

Marr's proposal for the functioning of the neocortex (Marr, 1970) is the least known of his various theories for specific neural circuitries. He suggested that the neocortex learns by self-organization to extract the structure from the patterns of activity incident upon it. He proposed a feedforward neural network in which the connections to the output cells (identified with the pyramidal cells of the neocortex) are modified by a mechanism of competitive learning. It was intended that each output cell comes to be selective for the input patterns from a different class and is able to respond to new patterns from the same class that have not been seen before. The learning rule that Marr proposed was underspecified, but a logical extension of the basic idea results in a synaptic learning rule in which the total amount of synaptic strength of the connections from each input ("presynaptic") cell is kept at a constant level. In contrast, conventional competitive learning involves rules of the "postsynaptic" type. The network learns by exploiting the structure that Marr assumed to exist within the ensemble of input patterns. For this case, analysis is possible that extends that carried out by Marr, which was restricted to the binary classification task. This analysis is presented here, together with results from computer simulations of different types of competitive learning mechanisms. The presynaptic mechanism is best known in the computational neuroscience literature. In neural network applications, it may be a more suitable mechanism of competitive learning than those normally considered.

Algorithms↗
PubMed1990

3 beta-hydroxysteroid dehydrogenase/isomerase in the fetal zone and neocortex of the human fetal adrenal gland.

The fetal zone of the human fetal adrenal (HFA) gland is established to have decreased 3 beta-hydroxysteroid dehydrogenase/delta 4-5 isomerase (3 beta HSD) activity compared to the neocortex or definitive zone. 3 beta HSD activity, however, can be induced in primary cell culture through treatment with ACTH. Therefore, the HFA with two distinct steroidogenic zones with differences in 3 beta HSD activity as well as the capacity to increase 3 beta HSD activity in response to ACTH provides an excellent model to study the regulation of this enzyme. The presence of 3 beta HSD in the fetal and neocortex zones of the HFA was examined using a polyclonal antibody raised against purified human placental microsomal 3 beta HSD. After homogenates of the fetal and neocortical zones of the HFA were electrophoresed on a sodium dodecyl sulfate-polyacrylamide gel and immunoblotted, the presence of the 3 beta HSD protein with a molecular size of 45 kDa could be demonstrated only in the neocortical zone. ACTH treatment (greater than 2 days) of fetal and neocortical zone explant cultures produced increases in cortisol secretion associated with the respective levels of immunodetectable 3 beta HSD protein. Cortisol and dehydroepiandrosterone sulfate were the respective principal steroid products of neocortical and fetal zone explants. After ACTH treatment, immunodetectable 3 beta HSD was induced to a greater magnitude in the neocortex. These findings provide evidence that the lack of 3 beta HSD activity in the fetal zone, previously considered to be the result of the presence of an endogenous inhibitor, is due to an absence of the protein in this portion of the gland. The lack or minimal expression of 3 beta HSD in the fetal zone of HFA may be due to the action (or lack thereof) of a tissue-specific factor regulating the synthesis of 3 beta HSD.

3-Hydroxysteroid Dehydrogenases↗
PubMed1994

Left temporal neocortex mediation of verbal memory: evidence from functional mapping with cortical stimulation.

We examined the contribution of the temporal neocortex to short-term memory (STM) in 15 patients with left hemisphere language dominance during intraoperative or extraoperative cortical mapping prior to left anterior temporal lobectomy. Recall errors were examined following stimulation during the acquisition, consolidation, and retrieval stages of a verbal STM task. Ten patients showed stimulation-induced recall errors, and five patients showed no significant memory errors. More patients showed errors following stimulation during consolidation than during acquisition or retrieval, possibly because of disrupted transfer of information from the temporal neocortex to the hippocampus. Patients with stimulation-induced recall errors did not differ significantly from patients without memory errors in terms of seizure, demographic, or neuropsychological variables. Patients with resection of sites showing stimulation-induced recall errors had greater postoperative decline in verbal memory than did patients with resection sparing these sites. We suggest that the left temporal neocortex contributes to verbal memory consolidation in patients with chronic epilepsy.

Adult↗
PubMed1990

Long-term potentiation and depression in the cerebral neocortex.

Long-term potentiation of synaptic efficacy following tetanic synaptic inputs was described originally in the hippocampus, and it has been studied extensively based on the hypothesis that it represents a synaptic model of learning and memory in the brain. In the cerebral neocortex, studies on LTP have burgeoned later, and have progressed less rapidly than those in the hippocampus. Recently, however, experimental data describing the phenomenology and the mechanisms underlying LTP have accumulated in the neocortex, particularly in the visual, somatosensory, and motor cortices. In the developing visual cortex, LTP has been induced by afferent tetanic stimulation at relatively low frequencies, for long duration. Thus, particular attention has been given to parameters of the tetanus optimal for the induction of cortical LTP, and the differences between these and those effective in inducing hippocampal LTP have been reviewed. In the motor cortex, the associative LTP following combined activation of separate sites as well as homosynaptic LTP following activation of single pathways have been reported and these types of synaptic plasticity have been suggested as being a basis for a certain type of motor learning. Long-lasting depression (LTD) of synaptic efficacy also has been reported in the developing visual cortex and suggested as a neural basis for experience-dependent modifications of visual cortical neurons. LTD has been found in other areas of the neocortex as well, although the probability of its induction is relatively low and its functional significance is not yet clear. Among the possible mechanisms for the induction of LTP and LTD, those including the involvement of NMDA receptors, protein kinase C, Ca2+/calmodulin-dependent kinase II, and membrane-associated cytoskeletal proteins have been reviewed, although the results obtained so far are only fragmentary and are premature for definitive conclusions to be drawn.

Animals↗
PubMedDate not supplied

[The effect of cryogenic exclusion of the neocortex on preservation of the functioning of its temporal regions].

In chronic experiments on nine cats a study was made of different forms of their behavior in conditions of cold elimination of the cerebral cortex with the exception of the temporal areas. The first sessions of cooling produced a diminution of alimentary excitability, enhanced motor activity, loss of the reaction of mouse chasing and of a defensive reaction against the dog, and a disappearance of previously elaborated conditioned runnings to the feeding trough, etc. In the course of subsequent experiments with the neocortex cooling, the disturbed forms of behavior were restored. In the second and third sessions alimentary excitation was considerably restored; by the sixth and seventh sessions motor activity became normal, while the 20th to 25th sessions exhibited a protective reaction against the dog. Conditioned runnings restored in the seventinth session were manifest in the 20th to 25th sessions in 80% of cases. It is assumed that the temporal areas of the neocortex while playing a considerable part in integrating the activity of the whole brain, including the formation and manifestation of conditioned reflexes, under normal conditions, to a large extent lose their integrative role when the rest of the neocortex is elimated.

Agonistic Behavior↗
PubMed1976

[The role of several brain stem structures in activation of the neocortex and motor reflexes in chronically premesencephalic cats].

Chronic experiments were carried out in 18 cats. After premesencephalic section of the brain-stem, the neocortex can be activated both spontaneously and in response to the posterior hypothalamus or the forepaw skin stimulation. After bilateral lesions in the posterior hypothalamus, neither spontaneous nor the forepaw-skin stimulation-produced activation of the neocortex, was observed. Excitation of the mesencephalic RF is accompanied by activation of motor reflexes. A conclusion was made that the posterior hypothalamus, independently of the mesencephalic RF, is capable of activating the neocortex, while the mesencephalic RF, independently of the rostral structures, is responsible for the motor reflex activation.

Animals↗
PubMed1992

The size of the neocortex in relation to ecology and social structure in monkeys and apes.

In an attempt to reveal factors associated with neocortical development in monkeys and apes (anthropoids), relationships between the relative size of the neocortex and differences in ecology and social structure were examined for 24 genera of 11 subfamilies. Relative sizes of the neocortex (RSNs) in a given group were assessed as the difference between actual neocortical volume and the volume expected from an allometric relationship between neocortical volume and the volume of the rest of the brain. We found that RSNs are related to diet and social structure: frugivorous anthropoids had higher values of RSNs than folivorous anthropoids, and polygynous anthropoids had significantly higher values of RSNs than monogynous anthropoids. Furthermore, RSNs were positively correlated with the size of the troop. These results suggest that development of the neocortex is associated with both diet and social structure in anthropoids.

Animals↗