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At least 199 records · Page 11Linked to original sources

PubMed1991

Contribution of striate cortex and the superior colliculus to visual function in area MT, the superior temporal polysensory area and the inferior temporal cortex.

We studied the visual responses of single neurons in three extra-striate visual areas of the macaque following lesions of striate cortex, lesions of the tecto-pulvinar system or both. After striate lesions, there was (a) considerable specific activity remaining in area MT including direction selectivity, (b) only non-specific activity in the superior temporal polysensory area (STP), and (c) no visual responsiveness at all in inferior temporal cortex (IT). In animals with striate lesions, interruption of the tecto-pulvinar pathway eliminated the residual visual activity in MT and STP that survived the striate lesions. Interruption of the tecto-pulvinar pathway alone had little or no effect on visual evoked activity in any of the three areas. These results are related to the relative dependence of visual responsiveness in MT, STP and IT on striate cortex and the superior colliculus, to differences between the dorsal and ventral cortical processing streams, and to neural mechanisms underlying blind sight.

Animals↗

PubMed1979

Loss of hybridizable ribosomal DNA from human post-mitotic tissues during aging: II. Age-dependent loss in human cerebral cortex--hippocampal and somatosensory cortex comparison.

DNA was isolated from the hippocampal and from the somatosensory cortex of 13 humans (at autopsy). In both the cortex and hippocampus, the loss of ribosomal DNA (rDNA), as measured through hybridization in the liquid phase, approximates about 0.9% per year. The r value for somatosensory cortex was about -0.7 and that for the hippocampus was about -0.91. The correlation coefficient between the sets of two samples derived from the same individual (two different areas) in +0.945. These results are consistent with those reported concurrently for human myocardium and with earlier studies conducted with beagle dogs, in which only post-mitotic tissues (brain, heart and skeletal muscle) showed measurable decrements in these key genes. To the degree that the synthesis of new proteins is essential for sustained mental activity, these results are consistent with the observations that Nissl substance is more slowly replenished, following exhaustive work by motor cortical cells, and the fact that many older persons experience mental fatigue during continuous mental work at earlier times than do younger persons. The mechanism of loss is not certain, but may well be related to inadequacies in DNA repair systems, thereby allowing deletion of tandemly duplicated genes through cross-over "episome" formation, followed by degradation of the excised DNA segments. The ratio of loss of rDNA hybridizability in human and dogs in about 1 to 7, which approximates the relative ratios of their lifespans (reciprocals).

Adolescent↗

PubMed1993

Comparisons of hemi-inattention produced by unilateral lesions of the posterior parietal cortex or medial agranular prefrontal cortex in rats: neglect, extinction, and the role of stimulus distance.

Neglect in human and non-human primates has been demonstrated following unilateral lesions of both posterior parietal and prefrontal areas. While it has now been well established that a unilateral lesion of the rodent analog of dorsolateral prefrontal cortex, medial agranular cortex (AGm), results in neglect, the effects of unilateral damage restricted to rodent posterior parietal cortex (PPC) have not been examined in detail. The current study assessed rats with unilateral lesions of PPC or AGm on their ability to orient to unilateral and bilateral stimulation. Since it has been proposed in both the primate and rodent literatures that frontal areas may be responsible for the perception of near space while parietal areas may be responsible for far space, stimuli were presented at two different distances. Lesions of PPC and AGm resulted in severe neglect relative to control operates, with both PPC and AGm operates manifesting severe hemi-inattention and allesthesia relative to control operates. After behavioral recovery from neglect there was no evidence of extinction to bilateral simultaneous stimulation. While neglect to visual stimuli predominated in unilateral PPC operates, unilateral AGm operates had severe neglect in all modalities. In addition, while both left and right PPC operates showed contralesional neglect, AGm operates demonstrated the lateralized differences in neglect reported in previous studies. All groups demonstrated an approximately equivalent level of neglect to stimuli presented at the two different distances, and thus failed to support the suggestion of a peripersonal-extrapersonal dichotomy between frontal and parietal areas in rodents.

Animals↗

PubMed1994

Lack of effect of lesions in the anterior cingulate cortex and retrosplenial cortex on certain tests of spatial memory in the rat.

The effects of cytotoxic lesions in either the anterior cingulate cortex or the retrosplenial cortex were compared with those of fornix lesions on three tests of spatial memory. Two of the tasks, delayed nonmatching-to-position and spatial reversal learning, were tested in an automated apparatus. The third task, forced alternation, was tested in a T-maze. Neither anterior cingulate nor retrosplenial cortex damage produced any significant impairment on the three tasks. In contrast, rats with fornix lesions (hippocampal system damage) were markedly impaired on all three tasks. The results, which were considered in the light of proposals for a hippocampal--anterior thalamic--cingulate system that is important for spatial memory, suggest that neither of the cingulate regions involved in this study form a critical subcomponent of this proposed system. It is therefore assumed that the cingulate cortices are only critical for certain classes of spatial problem. It is also suggested that in some previous studies the effects of inadvertent damage to the cingulum bundle may have contributed to the apparent effects of cingulate lesions.

Animals↗

PubMed1994

Efferents of frontal or occipital cortex grafted into adult rat's motor cortex.

Phaseolus vulgaris leucoagglutinin (PHA-L) was used to examine the efferent connectivity of embryonic (E16) frontal (homotopic) or occipital (heterotopic) neocortical transplants placed into--or in the vicinity of--lesion cavities made in the frontal cortex of adult recipients. Homotopic transplants projected towards the host sensorimotor cortex and, in most cases, into the lateral caudate-putamen (CPu). Heterotopic transplants projected into the anterior cingulate cortex and, in most cases, distributed terminals into the medial CPu. It is suggested that embryonic neocortical tissue placed into a damaged cortical site of an adult recipient develops a pattern of efferents corresponding to its cortical origin.

Animals↗

PubMed1987

Dopaminergic innervation of the primary visual cortex in the rat, and some correlations with human cortex.

Dopaminergic terminals have been identified in the primary visual cortex with three techniques; immunocytochemistry with an anti-dopamine antiserum, retrograde axonal transport techniques using unconjugated wheat germ agglutinin and HPLC determination of catecholamines and metabolites in microdissected sub-regions of occipital cortex in the rat. The results demonstrate a specific dopaminergic innervation, arising from the ventral tegmental area, which is found mainly in laminae VI and V, but with minor innervation also in lamina I. Dopaminergic innervation to adjacent cortical regions is also described. Neurochemical data from post-mortem human material suggests that a similar innervation exists in man. An analysis of the distribution of dopaminergic fibres in relation to the known connections and possible functions of the deep laminae of visual cortex suggests that dopaminergic axons may participate in the corticofugal control of visual afferent pathways.

Aged↗

PubMed1988

Layer V in rat auditory cortex: projections to the inferior colliculus and contralateral cortex.

This study compares the form and distribution within layer V of cells projecting to the inferior colliculus with that of commissural cells of origin in adult rat auditory cortex after horseradish peroxidase injections in the ipsilateral inferior colliculus or auditory cortex. The goal of this work was to determine whether every part of layer V participates equally in both projections, and if the cortical neurons in each pathway were similar. The types of neurons were defined in Golgi-Cox preparations and matched with the profiles of retrogradely labeled cells from architectonically defined cortical area 41. Inferior colliculus and commissural neurons form two populations that differ in their distribution in layer V, in somatic area, and in the form of their apical dendritic arbors. Corticocollicular neurons include the largest pyramidal cells, whose robustly filled apical dendrites ascend into layer II or farther. Commissural cells are smaller and have a more heterogeneous form. Their apical dendrites do not usually extend above layer IV, and a few of these cells may be non-pyramidal. Small pyramidal cells and inverted pyramidal cells project to the opposite cortex, but not to the inferior colliculus. Medium-sized pyramidal cells project in both systems. In addition, certain callosal cells of origin in layers V and III were morphologically similar. More than one-third of the commissural cells originate in the superficial part of layer V, where only 7% of the inferior colliculus projection neurons arise. Most corticocollicular cells lie deeper in layer V, where there are fewer commissural neurons. These findings suggest that the efferent systems projecting to telencephalic and mesencephalic targets are morphologically distinct and spatially segregated in layer V. However, the commissural projection includes similar cells in different cortical layers. The types of these efferent neurons may be more closely related to their target than to their laminar origin.

Animals↗

PubMed2004

A role for right medial prefontal cortex in accurate feeling-of-knowing judgements: evidence from patients with lesions to frontal cortex.

The hypothesis that prefrontal cortex plays a critical role in accurate predictions of episodic memory performance was tested using the feeling-of-knowing (FOK) paradigm. Fourteen patients with a broad spectrum of damage to the frontal cortex and matched controls read sentences and later were tested for recall memory, confidence judgments, and FOK accuracy using as cues the sentences with the final word missing. While frontal patients were impaired at recall and recognition memory, they were able to make accurate confidence judgments about their recall attempts. By contrast, as a group, the patients were markedly impaired in the accuracy of their prospective FOK judgments. Lesion analysis of frontal patients with clear FOK impairment revealed an overlapping region of damage in right medial prefrontal cortex. These findings provide functional and anatomical evidence for a dissociation between recall confidence and prospective memory monitoring and are discussed in terms of familiarity and access theories of FOK predictions.

Adult↗

PubMed2000

Functional plasticity in extrastriate visual cortex following neonatal visual cortex damage and monocular enucleation.

Neonatal lesions of primary visual cortex (areas 17, 18 and 19; VC) in cats lead to significant changes in the organization of visual pathways, including severe retrograde degeneration of retinal ganglion cells of the X/beta class. Cells in posteromedial lateral suprasylvian (PMLS) cortex display plasticity in that they develop normal receptive-field properties despite these changes, but they do not acquire the response properties of striate neurons that were damaged (e.g., high spatial-frequency tuning, low contrast threshold). One possibility is that the loss of X-pathway information, which is thought to underlie striate cortical properties in normal animals, precludes the acquisition of these responses by cells in remaining brain areas following neonatal VC damage. Previously, we have shown that monocular enucleation at the time of VC lesion prevents the X-/beta-cell loss in the remaining eye. The purpose of the present study was to determine whether this sparing of retinal X-cells leads to the development of striate-like response properties in PMLS cortex. We recorded the responses of PMLS neurons to visual stimuli to assess spatial-frequency tuning, spatial resolution, and contrast threshold. Results indicated that some PMLS cells in animals with a neonatal VC lesion and monocular enucleation displayed a preference for higher spatial frequencies, had higher spatial resolution, and had lower contrast thresholds than PMLS cells in cats with VC lesion alone. Taken together, these results suggest that preserving X-pathway input during this critical period leads to the addition of some X-like properties to PMLS visual responses.

Animals↗

PubMed1999

Frontal midline theta rhythms reflect alternative activation of prefrontal cortex and anterior cingulate cortex in humans.

Frontal midline theta rhythm (Fm theta) often appears on electroencephalogram (EEG) during consecutive mental tasks. To clarify the source of rhythmic activity, magnetoencephalogram (MEG) and EEG were simultaneously measured in six healthy volunteers during different mental tasks using whole head MEG system. MEG records were averaged every one cycle of Fm theta rhythms using individual positive peaks of Fm theta waves in Fz EEG as a trigger. Averaged theta components of MEG signals were analyzed with a multi-dipole model. Two sources were estimated to the regions both of the prefrontal-medial superficial cortex and anterior cingulate cortex (ACC). These regions were alternatively activated in about 40 to 120 degrees phase shift during one Fm theta cycle. From above results, we hypothesize that appearance of Fm theta during consecutive mental tasks reflects alternative activities of the medial prefrontal cortex and ACC.

Adult↗

PubMed1983

Neonatal hemidecortication or frontal cortex ablation produces similar behavioral sparing but opposite effects on morphogenesis of remaining cortex.

Rats with complete removal of the neocortex of one hemisphere (hemidecorticate) or of the cortex anterior to bregma in both hemispheres (frontal cortex) in adulthood were compared behaviorally and neuroanatomically with rats with similar removals at 7 days of age. Neonatal ablation of the frontal cortex produced partial sparing of performance on the Morris water task and reduced the thickness of the remaining neocortex. Neonatal hemidecortication produced similar sparing of function on the water task but increased the thickness of the contralateral neocortex. These results imply that behavioral sparing following neonatal cortical lesions is independent of the gross morphogenesis of the remaining neocortex.

Age Factors↗

PubMed1992

[Morphologic aspects of the maturation of the sensory areas of the cerebral cortex exemplified by the visual cortex of the rabbit].

When the cerebral cortex commences its earliest functional tasks, the cellular layers and the basic organisation pattern of cell processes have already developed. In the rabbit visual cortex it could be shown that the functional differentiation runs parallel to an increase in number and growth of cell processes. Those tissue compartments where the newly formed branches of the dendritic trees of cortical neurons come into contact with the axons arising from other cerebral regions, grow between two and six times larger depending on the cortical layer where their volume fractions are measured. Cell processes grow and increase in number most rapidly between the second and the fourth postnatal weeks. Myelination of fast conducting axons takes longer and attains an adult level about three month after birth. Then the visual cortex of the rabbit may be regarded as mature with regard to both structure and function.

Animals↗

PubMedDate not supplied

Cadmium in kidney cortex, liver, and pancreas from Swedish autopsies. Estimation of biological half time in kidney cortex, considering calorie intake and smoking habits.

Cadmium and zinc have been analyzed in tissues from 292 persons autopsied in Stockholm. In kidney cortex, liver, and pancreas the individual cadmium levels are distributed in a lognormal way. In kidney cortex there is a continuous accumulation of cadmium with age up to 50 years, followed by a decrease. Smokers show a higher cadmium accumulation. For nonsmokers, the biological half time of cadmium in kidney cortex is estimated at 30 years, with an average concentration at age 50 of 11 mug/g wet weight. When smokers are included, the average cadmium concentration at age 50 is 22 mug/g wet weight. Based on the more pronounced cadmium accumulation among smokers than nonsmokers, the respiratory absorption rate of cadmium from tobacco smoke is estimated to be approximately 50%.

Adolescent↗

PubMed2002

Involvement of reelin and Cajal-Retzius cells in the developmental formation of vertical columnar structures in the cerebral cortex: evidence from the study of mouse presubicular cortex.

The mammalian cerebral cortex is organized into horizontal and vertical arrays of neurons and their fiber connections that form anatomically and physiologically distinct laminar and columnar compartments. However, the developmental mechanism(s) underlying this dichotomous pattern remains a mystery. We provide anatomical evidence suggesting that reelin, a diffusible protein produced and secreted by Cajal-Retzius cells, is involved in the developmental formation of the vertical cell structures in the mouse presubicular cortex, the unique site where the vertical columnar arrays of cortical plate neurons and their dendritic branches are clearly identified during the early postnatal period. Our results also suggest that reelin plays a role in the formation of these vertical structures by acting as an inhibitory or stop signal for cortical plate neurons and their dendritic extensions. In addition to having perturbed horizontal laminae, reeler mutant mice, lacking reelin, display disruption of these vertical structures. Based on the present findings, we hypothesize that reelin and Cajal-Retzius cells regulate the developmental formation of not only horizontal laminations, but also vertical columnar structures in the cerebral cortex.

Animals↗

PubMed2004

Localization of the glutamine transporter SNAT1 in rat cerebral cortex and neighboring structures, with a note on its localization in human cortex.

SNAT1 mediates glutamine (Gln) influx into neurons and is believed to replenish the transmitters pools of glutamate (Glu) and gamma-aminobutyric acid (GABA). We investigated its distribution and cellular localization in the cerebral cortex and neighboring regions of rats and humans using light and electron microscopic immunocytochemical methods with specific antibodies. In the first somatic sensory cortex of rats and in areas 9, 10, 21 and 46 of the human cortex, numerous SNAT1-positive (+) cells were present in the cortical parenchyma and in the white matter; >95% of SNAT1+ cells were neurons, but some were astrocytes. Most SNAT1+ cells were pyramidal neurons, but numerous non-pyramidal neurons were also observed: SNAT1/GABA double-labeling studies showed that SNAT1 is expressed in all GABA+ neurons. SNAT1/synaptophysin studies showed that <0.1% of all synaptophysin+ puncta coexpressed SNAT1. SNAT1 immunoreactivity (ir) was also in leptomeninges, ependymal cells and choroid plexus. Electron microscopic studies showed that neuronal SNAT1 ir was almost exclusively observed in perikarya and dendritic profiles. SNAT1 ir was also in distal astrocytic processes, including end feet profiles, and in leptomeninges. These findings suggest that the major function of SNAT1 is not to replenish the transmitter pools of Glu and GABA.

Amino Acid Transport System X-AG↗

PubMed2003

The eloquence of silent cortex: analysis of afferent input to deafferented cortex in arm amputees.

Cortical reorganisation after limb amputation includes topographic displacements of body representation areas and changes of areal extent. Remarkably, truncated nerves, which had innervated amputated limb parts and remained in the residual limbs, can retain access to the deafferented somatosensory cortex. Using somatosensory evoked potentials (SEP) we characterized afferences from electrically stimulated truncated nerves to the brachial plexus and cortex in 12 arm amputees. While peripheral responses were highly variable, thalamocortical input to S-1, as reflected by the primary cortical SEP component, was present in 11 of 12 patients. Despite long-term deafferentation, macroscopic phenomena of inhibition/refractoriness, as assessed by stimulus rate variations, appeared to be changed only marginally. Thus, deafferented cortex remains responsive when given artificial phantom input and could provide a neuronal substrate for spontaneous phantom limb sensations, including phantom pain.

Adult↗

PubMed1991

Acute effects of alcohol on unit activity in the motor cortex of freely moving rabbits: comparison with the limbic cortex.

Unit activity was recorded from the motor cortex of eight freely moving rabbits in order to examine the acute effect of ethanol (1 g kg-1) on organization of unit activity and to compare it with our earlier results from the limbic cortex. The rabbits performed a food-acquisition task in the experimental cage. Unit activity was recorded during behaviour in the control experiment followed by the alcohol experiment on the next day. After ethanol, behavioural mistakes and the duration of the behavioural cycle significantly increased. In the control experiments activation of 58% of the units had no constant relation to the phases of the behavioural cycle (non-involved units), whereas 42% of the units were constantly activated during certain phases (involved units). Two per cent of the latter units were activated in relation to newly learned behavioural acts (e.g. pedal pressing; L units), 28% in relation to food seizure and/or grinding (S units) and 12% in relation to certain movements during different behavioural acts (M units). Ethanol had no effect on the number of active units and the same relation between the number of non-involved and involved units or between the number of different types of involved units was found. However, the number of involved units decreased in the upper and increased in the lower cortical layers. Also the number of units with low background frequency increased, although the frequency within activations did not change. In our earlier study the number of active units in the limbic cortex decreased after ethanol by one third and the relation between the number of L and M units was reversed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1999

Organization of somatosensory areas I and II in marsupial cerebral cortex: parallel processing in the possum sensory cortex.

Organization of somatosensory areas I and II in marsupial cerebral cortex: parallel processing in the possum sensory cortex. Controversy exists over the organization of mammalian thalamocortical somatosensory networks. An issue of particular contention is whether the primary and secondary somatosensory areas of cortex (SI and SII) are organized in a parallel or serial scheme for processing tactile information. The current experiments were conducted in the anesthetized brush-tail possum (Trichosurus vulpecula) to determine which organizational scheme operates in marsupials, which have taken a quite different evolutionary path from the placental species studied in this respect. The effect of rapid reversible inactivation of SI, achieved by localized cortical cooling, was examined on both evoked potential and single neuron responses in SII. SI inactivation was without effect on the amplitude, latency, and time course of SII-evoked potentials, indicating that the transient inputs responsible for the SII-evoked potential reach SII directly from the thalamus rather than traversing an indirect serial route via SI. Tactile responsiveness was examined quantitatively before, during, and after SI inactivation in 16 SII neurons. Fourteen were unchanged in their responsiveness, and two showed some reduction, an effect probably attributable to the loss of a facilitatory influence exerted by SI on a small proportion of SII neurons. The temporal precision and pattern of SII responses to dynamic forms of mechanical stimuli were unaffected, and temporal dispersion in the SII response bursts was unchanged in association with SI inactivation. In conclusion, the results establish that, within this marsupial species, tactile inputs can reach SII directly from the thalamus and are not dependent on a serially organized path through SI. A predominantly parallel organizational scheme for SI and SII operates in this representative of the marsupial order, as it does in a range of placental mammals including the cat and rabbit, the tree shrew and prosimian galago, and at least one primate representative, the marmoset monkey.

Animals↗