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At least 271 records · Page 15Linked to original sources
PubMed1993

Examining the volume efficiency of the cortical architecture in a multi-processor network model.

The convoluted form of the sheet-like mammalian cortex naturally raises the question whether there is a simple geometrical reason for the prevalence of cortical architecture in the brains of higher vertebrates. Addressing this question, we present a formal analysis of the volume occupied by a massively connected network or processors (neurons) and then consider the pertaining cortical data. Three gross macroscopic features of cortical organization are examined: the segregation of white and gray matter, the circumferential organization of the gray matter around the white matter, and the folded cortical structure. Our results testify to the efficiency of cortical architecture.

Animals↗
PubMed1994

Whole-head mapping of middle-latency auditory evoked magnetic fields.

We recorded middle-latency auditory evoked magnetic fields from 9 healthy subjects with a 122-channel whole-head SQUID gradiometer. The stimuli were click triplets, 2.5 msec in total duration, delivered alternately to the two ears once every 333 msec. Contralateral clicks elicited P30m responses in 16 and P50m responses in 12 out of 18 hemispheres studied; ipsilateral clicks did so in 7 and 13 hemispheres, respectively. The field patterns were satisfactorily explained by current dipoles in 16 and 4 hemispheres for contra- and ipsilateral P30m, and in 4 and 10 hemispheres for contra- and ipsilateral P50m. The peak latencies of P30m and P50m were not affected by stimulation side. The results show that middle-latency auditory evoked responses receive a strong contribution from auditory cortical structures, and that differences of input latency to cortical auditory areas, evaluated from MLAEF latencies, do not explain the latency differences seen in late auditory evoked fields to contralateral vs. ipsilateral stimulation.

Adult↗
PubMed2006

[Early changes in rats cervical lymph nodes after pinealectomy].

OBJECTIVES: Pineal gland acts as a reley where an anabolic activity be replaced to catabolic and conversely, to adapt a biological rhythm according to the organisme requirement. It is established that pineal extracts stimulate lymphopoiesis in the lymph node and had a radioprotective effects in lymph tissues. Lymph nodes reaction was investigated four weeks after pinealectomy, using qualitative and stereological. METHODS: One group of animals ( Wistar rats of both sex) was shame-pinealectomized (chirurgic treatment without pineal extirpation/control) and the other was submitted to surgical ablation of pineal gland.(experimental group). The animals were kept under the same ecologic conditions and they had free access to water supplies. Animals of the same group sacrificed at the same day between 10/14 hour to equal the effects of hormonal rhythm. The paraffin section died with HE (haematoxillin-eosin), PAS/alcian blue and impregnated by Bielschowsky method. For stereological analysis multipurpose M/42 test system was applied. Volume density of nodal structure and relative cellular distribution was evaluated. RESULTS: Cortical tissue of lymph nodes of pinealectomized rats was reduced, particularly the paracotical regions. Only in the female rats, decreased number of lymphocytes was observed in the cortex and modularly cords. Stereological analysis confirmed that increased volume density of the medulla is the result of medullar sinus dilatation. Under regressive changes of the cortical structures can be considered the involutary processes in germinal centers and reduction of the younger lymphocyte forms. Macrophage was activated and increased PAS + an inclusion was observed on the cortico/medullary junction and in the modularly cords. Reticular stroma was intensively impregnated and fibrils more coarsed and fragmented. DISCUSSION: Established changes in the lymph nodes of pinealectomized a rat was analogous with that observed after treatment with the pineal extracts but in the reverse means. It was evident that the structural dissociation of the reactivity had been established. Really, at one side we have involutive changes in lymphoid population and plasma cells but progressive in phagocytes and reticular cells. It is probably that increased concentration of corticosteroides and gonadal hormones after pinealectomy is responsible for these changes. CONCLUSION: Pineal gland-lymph nodes correlations established possibly via hypophyso-adreno-genital axis.

Animals↗
PubMedDate not supplied

[Glutamate decarboxylase activity in subcellular fractions of tissues of brain visual analyzer in dogs during postnatal ontogenesis].

Fractions of mitochondria, synaptosomes and fragments of membranes isolated from structures of dog brain visual analyzer in the postnatal ontogenesis period differs in the glutamate decarboxylase activity. Till the 45th day of development it rises, as a rule, in all the fractions under study and then it lowers. An increase in the activity in most cases is more pronounced in subfractions of heavy synaptosomes and fragments membrane. The enzyme activity in the visual cortex (field 17), anterior corpora bigemina and external geniculate body rises differently. In one-day animals GABA is formed in the fraction of heavy synaptosomes of anterior corpora bigemina and external geniculate body with a higher intensity than in the visual cortex area (field 17) that may be associated with earlier GABA accumulation in GABA-ergic neurons of subcortical structures of the visual analyzer than in its cortical structures.

Aging↗
PubMed2002

Temporal structure in neuronal activity during working memory in macaque parietal cortex.

Many cortical structures have elevated firing rates during working memory, but it is not known how the activity is maintained. To investigate whether reverberating activity is important, we studied the temporal structure of local field potential (LFP) activity and spiking from area LIP in two awake macaques during a memory-saccade task. Using spectral analysis, we found spatially tuned elevated power in the gamma band (25-90 Hz) in LFP and spiking activity during the memory period. Spiking and LFP activity were also coherent in the gamma band but not at lower frequencies. Finally, we decoded LFP activity on a single-trial basis and found that LFP activity in parietal cortex discriminated between preferred and anti-preferred direction with approximately the same accuracy as the spike rate and predicted the time of a planned movement with better accuracy than the spike rate. This finding could accelerate the development of a cortical neural prosthesis.

Action Potentials↗
PubMed1982

Correlation between ventral surface structures and local degeneration of cilia during conjugation in Paramecium.

Correlation between cortical structures, such as the suture lines and the oral apparatus, and local degeneration of cilia during conjugation was investigated using aberrantly shaped cells which were produced by treating normal cells with 2 mM adenine for 24 h. Three types of aberrantly shaped cells were obtained: (1) proters, in which the oral apparatus is located at or near the posterior end of the cell and the preoral suture is much longer than that of a normally shaped cell' (2) opisthes, in which the oral apparatus is located extremely anteriorly, the preoral suture is very short and bent to the left, and the postoral suture and cytoproct are much longer than those of normally shaped cells; and (3) L-shaped cells, which are cells that have not separated at division and contain two buccal openings. The anterior member of the L-shaped cells (AML) has a long preoral suture and the posterior member of the L-shaped cell (PML) has a long postoral suture and cytoproct. The postoral field of AML and the preoral field of PML are missing. When these cells were mixed with normally shaped cells of the opposite mating type, the mating reaction took place between them. Scanning electron microscopic observation showed that, in all abnormally shaped cells, the degeneration of cilia always occurred along the full length of the preoral suture, regardless of its total length, and along the posterior right field of the buccal vestibulum, regardless of its location in the cell cortex. The localization of the degeneration of cilia, therefore, coincided with the position of the preoral suture and the buccal opening.

Adenine↗
PubMed1996

Ischemia and lesion induced imbalances in cortical function.

Cortical structures are often critically affected by ischemic and traumatic lesions which may cause transient or permanent functional disturbances. These disorders consist of changes in the membrane properties of single cells and alterations in synaptic network interactions within and between cortical areas including large-scale reorganizations in the representation of the peripheral input. Prominent functional modifications consisting of massive membrane depolarizations, suppression of intracortical inhibitory synaptic mechanisms and enhancement of excitatory synaptic transmission can be observed within a few minutes following the onset of cortical hypoxia or ischemia and probably represent the trigger signals for the induction of neuronal hyperexcitability, irreversible cellular dysfunction and cell death. Pharmacological manipulation of these early events may therefore be the most effective approach to control ischemia and lesion induced disturbances and to attenuate long-term neurological deficits. The complexity of secondary structural and functional alterations in cortical and subcortical structures demands an early and powerful intervention before neuronal damage expands to intact regions. The unsatisfactory clinical experience with calcium and N-methyl-D-aspartate antagonists suggests that this result might be achieved with compounds that show a broad spectrum of actions at different ligand-activated receptors, voltage-dependent channels and that also act at the vascular system. Whether the same therapy strategies developed for the treatment of ischemic injury in the adult brain may be applied for the immature cortex is questionable, since young cortical networks with a high degree of synaptic plasticity reveal a different response pattern to hypoxic and ischemic insults. Age-dependent molecular biological, morphological and physiological parameters contribute to an enhanced susceptibility of the immature brain to these noxae during early ontogenesis and have to be investigated in more detail for the development of adequate clinical therapy.

Adult↗
PubMed2000

Expression of a novel neuropeptide Y receptor subtype involved in food intake: an in situ hybridization study of Y5 mRNA distribution in rat brain.

Our group has reported on the cloning of a novel rat neuropeptide Y (NPY) receptor involved in NPY-induced food intake, the Y5 receptor. The distribution in rat brain of the mRNA encoding this receptor has been determined by in situ hybridization histochemistry, using radiolabeled oligonucleotide probes. Control experiments were carried out in cell lines transfected with either rat Y1 or rat Y5 cDNAs. With the exception of the cerebellum, only the antisense probes yielded hybridization signal in rat brain tissue sections. A number of brain regions contained hybridization signals indicative of Y5 mRNA localization. Chief among these were various hypothalamic nuclei, including the medial preoptic nucleus, the supraoptic nucleus, the paraventricular nucleus, and the lateral hypothalamus. Other regions with substantial hybridization signals included the midline thalamus, parts of the amygdala and hippocampus, and some midbrain and brain-stem nuclei. In general a low density of Y5 mRNA was observed in most cortical structures, with the exception of the cingulate and retrosplenial cortices, each of which contained a moderate abundance of Y5 hybridization signal. The distribution of this receptor mRNA is consistent with a role for the Y5 receptor in food intake and also suggests involvement in other processes mediated by NPY.

Animals↗
PubMedDate not supplied

3D reconstructions of neurofunctional structures for neuroimaging.

An improved method for computer-aided 3D reconstruction of neuroanatomical structures derived from intracranially fixed human brains is demonstrated. The embedded brains are cut into slices. The sliced surfaces are photographed. The outlines of the neuroanatomical structures are drawn onto transparencies which are scanned. The surfaces of the structures are 3D reconstructed with the triangulation method. The cortical structures of the human brain are complex, resulting in possible ambiguities for triangulation which must be solved interactively. These surface reconstructions allow for 3D visualization of the brain and its components comparable with intravital conditions found in clinical neuroimaging.

Algorithms↗
PubMed2005

SPECT findings in children with specific language impairment.

Findings from 99mTc-HMPAO SPECT measurements at rest in a group of 19 school-age children with specific language impairment (SLI) were compared to a group of 12 children with attention-deficit hyperactivity disorder (ADHD). The regional cerebral blood flow (CBF) distributions were different in the two groups. Children with SLI showed significantly lower CBF values in the right parietal region and in the subcortical region compared to the ADHD group. In addition, the SLI group had symmetric CBF distributions in the left and right temporal regions, whereas the ADHD group showed the usual asymmetry with left-sided hemispheric predominance in the temporal regions. The findings give further evidence for anomalous neurodevelopment with deviant hemispheric lateralization as an important factor in the aetiology of SLI. They also point to the role of subcortical structures in language impairment in childhood. Earlier focus on cortical structures in SLI research needs to be widened to include subcortical regions as well.

Adolescent↗
PubMed1992

["Glare vision". II. Study of visual acuity of glare sensitive patients in increasing test field luminance].

Sensitivity to glare is an unspecific ophthalmological symptom that can be caused by different anatomical structures; it can be related to optical and to cortical structures, it also can be due to defects in the neuronal mechanisms of the retina that control adaptation processes. In many cases the exact mechanisms are still unknown. Tests of visual acuity in glare sensitive patients with increasing test field luminance reveal-depending on the underlying disease-several types of variations from the normal visual-acuity-function that was determined over a wide range of light intensity from 0.1 to 30,000 cd/m2. Marked changes in the visual acuity-luminance-function at high test field intensities were found primarily in patients with retinal diseases, particularly in disturbances of the cone system. These visual acuity losses at high test field luminances can be explained by major functional impediments of the neuronal adaptive mechanisms at the retinal level. Less apparent were the changes in visual acuity-luminance-function in cases of optic nerve diseases. According to our studies changes in the visual acuity-luminance-function accompanied with high glare sensitivity are most often due to pathological changes in neuronal circuitry of the retina, less often to the effects of stray light. This test therefore can provide an important criterion for establishing the correct diagnosis.

Adolescent↗
PubMed2001

Brain images of pain.

Combined magneto- and encephalography proves the sequential involvement of multiple cortical structures in pain processing. Bilateral activity in secondary somatosensory cortices reflects the sensory-discriminative component and is reduced in states of unconsciousness. Later activity in the posterior cingulum reflects the emotional-aversive component, which is blocked by narcoanalgesics.

Brain↗
PubMed1998

Abnormalities of neural circuitry in Alzheimer's disease: hippocampus and cortical cholinergic innervation.

Severe pathology in Alzheimer's disease (AD) results in marked disruption of cortical circuitry. Formation of neurofibrillary tangles, neuronal loss, decrease in dendritic extent, and synaptic depletion combine to halt communication among various cortical areas, resulting in anatomic isolation and fragmentation of many cortical zones. The clinical manifestation of this disruption is severe and debilitating cognitive dysfunction, often accompanied by psychiatric and behavioral disturbances and a diminished ability to perform activities of daily living. However, different cortical circuits are not equally vulnerable to AD pathology. In particular, two cortical systems that appear to be involved in the neural processing of memory are selectively vulnerable to degeneration in AD. One consists of connections between the hippocampus and its neighboring cortical structures within the temporal lobe. The second is the cortical cholinergic system that originates in neurons within the basal forebrain and innervates the entire cortical mantle. The circuitry in these systems shows early and severe degenerative changes in the course of AD. The selective vulnerability of these circuits is the probable reason for the early and marked loss of memory observed in these patients. This review presents current knowledge of the general pattern of cortical circuitry, followed by a summary of abnormalities of this circuitry in AD. The cortical circuits that exhibit selective pathology in AD are described in greater detail. Therapeutic implications of the abnormal circuitry in AD are also discussed. For therapies to be effective, early diagnosis of AD is necessary. Future efforts at AD therapy must be combined with an equally intense effort to develop tools capable of early diagnosis of AD, preferably at a preclinical stage before the onset of cognitive symptoms.

Alzheimer Disease↗
PubMed1999

Patterning events and specification signals in the developing hippocampus.

The mouse hippocampus is an attractive model system in which to study patterning of a cortical structure. Ongoing studies indicate that hippocampal areas or fields are specified many days before birth -- possibly involving signals from within the cortical mantle. Although the hippocampal CA fields are distinguished by cytoarchitecture only after birth, molecular differences between fields appear by late gestation. Moreover, these embryonic fields are already specified to develop additional features that characterize the mature fields. The basic division of the hippocampus into fields may be specified still earlier. Thus, if medial cortical neuroepithelium is isolated in vitro early in hippocampal neurogenesis, it can autonomously generate features of a patterned hippocampus. In vivo, the spatial progression of initial field differentiation suggests that signals regulating growth and patterning could arise from sources close to the hippocampal poles. Observations of mouse mutants indicate that the cortical hem, an embryonic structure close to one pole of the hippocampus, is a source of such regulatory signals.

Age Factors↗
PubMedDate not supplied

[Progress in research on etiopathogenesis of schizophrenia in recent decades].

In this paper, a progress in research on etiopathogenesis of schizophrenia made in the recent decade was presented. Two main etiopathogenetic factors in this illness include genetic predisposition and brain damage in early period of life, leading to a disorder of brain development and lateralization, and to an increased susceptibility to stress. The use of new methods of genetic studies brought about a significant progress as to identification of relationship between schizophrenia and various changes within genotype. In the 1990s, many data have been obtained concerning possible brain damaging factors as well as the existence of structural and functional brain abnormalities in this illness. Impaired brain development in schizophrenia results in disturbances of neuronal connection in the cortical structures and in cortical-limbic transmission, what may underlie the appearance of psychopathological symptoms. New neuroleptic drugs introduced in the recent years show more complete therapeutic action against schizophrenic symptoms compared with drugs used so far. This may result from their broader influence on the pathogenetic processes of schizophrenia, which may be due, apart from their effect on dopaminergic system, also to their action on some elements of serotonergic neurotransmission.

Antipsychotic Agents↗
PubMed2000

Parallel information processing in motor systems: intracerebral recordings of readiness potential and CNV in human subjects.

We performed intracerebral recordings of Readiness Potential (RP) and Contingent Negative Variation (CNV) with simple repetitive distal limb movement in candidates for epilepsy surgery. In 26 patients (in Paris), depth electrodes were located in various cortical structures; in eight patients (in Brno), in the basal ganglia and the cortex. RPs were displayed in the contralateral primary motor cortex, contralateral somato-sensory cortex, and bilaterally in the SMA and the caudal part of the anterior cingulate cortices. CNVs were recorded in the same cortical regions as the RP, as well as in the ipsilateral primary motor cortex, and bilaterally in the premotor fronto-lateral, parietal superior, and middle temporal regions. In the basal ganglia, the RP was recorded in the putamen in six of seven patients, and in the head of the caudate nucleus and the pallidum in the only patient with electrodes in these recording sites. We suggest that our results are consistent with a long-lasting, simultaneous activation of cortical and subcortical structures, before and during self-paced and stimulus-triggered movements. The particular regions that are simultaneously active may be determined by the task context.

Brain↗
PubMed2003

Maternal mRNAs of PEM and macho 1, the ascidian muscle determinant, associate and move with a rough endoplasmic reticulum network in the egg cortex.

Localization of maternal mRNAs in the egg cortex is an essential feature of polarity in embryos of Drosophila, Xenopus and ascidians. In ascidians, maternal mRNAs such as macho 1, a determinant of primary muscle-cell fate, belong to a class of postplasmic RNAs that are located along the animal-vegetal gradient in the egg cortex. Between fertilization and cleavage, these postplasmic RNAs relocate in two main phases. They further concentrate and segregate in small posterior blastomeres into a cortical structure, the centrosome-attracting body (CAB), which is responsible for unequal cleavages. By using high-resolution, fluorescent, in situ hybridization in eggs, zygotes and embryos of Halocynthia roretzi, we showed that macho 1 and HrPEM are localized on a reticulated structure situated within 2 mum of the surface of the unfertilized egg, and within 8 mum of the surface the vegetal region and then posterior region of the zygote. By isolating cortices from eggs and zygotes we demonstrated that this reticulated structure is a network of cortical rough endoplasmic reticulum (cER) that is tethered to the plasma membrane. The postplasmic RNAs macho 1 and HrPEM were located on the cER network and could be detached from it. We also show that macho 1 and HrPEM accumulated in the CAB and the cER network. We propose that these postplasmic RNAs relocalized after fertilization by following the microfilament- and microtubule-driven translocations of the cER network to the poles of the zygote. We also suggest that the RNAs segregate and concentrate in posterior blastomeres through compaction of the cER to form the CAB. A multimedia BioClip 'Polarity inside the egg cortex' tells the story and can be downloaded at www.bioclips.com/bioclip.html

Animals↗