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At least 379 records · Page 21Linked to original sources

PubMed2000

In search of the language switch: An fMRI study of picture naming in Spanish-English bilinguals.

For many years, researchers investigating the brain bases of bilingualism have concentrated on two basic questions. The first concerns the nature of language representation. That is, are a bilinguals' two languages represented in distinct or overlapping areas of the brain. The second basic question in the neuropsychology of bilingualism concerns the neural correlates of language switching, that is, the areas that are active when bilinguals switch from one language to the other. Performance between single-language and dual-language picture naming was compared in a group of six Spanish-English bilinguals using behavioral measures and functional magnetic resonance imaging. Participants showed slower reaction times and increased activation in the dorsolateral prefrontal cortex in the mixed language condition relative to single language condition. There was no evidence that each language was represented in different areas of the brain. Results are consistent with the view that language switching is a part of a general executive attentional system and that languages are represented in overlapping areas of the brain in early bilinguals.

Adult↗

PubMed1999

Words in the brain's language.

If the cortex is an associative memory, strongly connected cell assemblies will form when neurons in different cortical areas are frequently active at the same time. The cortical distributions of these assemblies must be a consequence of where in the cortex correlated neuronal activity occurred during learning. An assembly can be considered a functional unit exhibiting activity states such as full activation ("ignition") after appropriate sensory stimulation (possibly related to perception) and continuous reverberation of excitation within the assembly (a putative memory process). This has implications for cortical topographies and activity dynamics of cell assemblies forming during language acquisition, in particular for those representing words. Cortical topographies of assemblies should be related to aspects of the meaning of the words they represent, and physiological signs of cell assembly ignition should be followed by possible indicators of reverberation. The following postulates are discussed in detail: (1) assemblies representing phonological word forms are strongly lateralized and distributed over perisylvian cortices; (2) assemblies representing highly abstract words such as grammatical function words are also strongly lateralized and restricted to these perisylvian regions; (3) assemblies representing concrete content words include additional neurons in both hemispheres; (4) assemblies representing words referring to visual stimuli include neurons in visual cortices; and (5) assemblies representing words referring to actions include neurons in motor cortices. Two main sources of evidence are used to evaluate these proposals: (a) imaging studies focusing on localizing word processing in the brain, based on stimulus-triggered event-related potentials (ERPs), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI), and (b) studies of the temporal dynamics of fast activity changes in the brain, as revealed by high-frequency responses recorded in the electroencephalogram (EEG) and magnetoencephalogram (MEG). These data provide evidence for processing differences between words and matched meaningless pseudowords, and between word classes, such as concrete content and abstract function words, and words evoking visual or motor associations. There is evidence for early word class-specific spreading of neuronal activity and for equally specific high-frequency responses occurring later. These results support a neurobiological model of language in the Hebbian tradition. Competing large-scale neuronal theories of language are discussed in light of the data summarized. Neurobiological perspectives on the problem of serial order of words in syntactic strings are considered in closing.

Association Learning↗

PubMed2005

The effects of prenatal social stress on behaviour: mechanisms and function.

In this review, we summarise experimental animal studies on the effects of the social environment during pregnancy on the offsprings' behaviour, brain, and neuroendocrine function. We show that in non-human mammals the stability of the social environment in which the pregnant females live is critical for the offsprings' social and sexual behaviour later in life as well as for reproductive functioning, endocrine state and androgen and estrogen receptor distribution in specific parts of the brain. Based on these findings, we discuss different neuroendocrine mechanisms mediating the influence of the social environment during pregnancy on the offsprings' behaviour. We conclude that maternal steroids play a decisive role in shaping foetal brain development. However, a pituitary adrenocortical pathway need not always be involved. At least in some cases an involvement of the sympathetic adrenomedullary system seems to be possible. Concerning function, we favour the hypothesis that the behavioural effects of prenatal social stress are not necessarily the 'pathological' consequences of adverse social conditions (non-adaptive explanation). Contrarily, mothers could be adjusting their offspring to the environment in which they live during pregnancy in an efficient way (adaptive explanation).

Animals↗

PubMedDate not supplied

Graphical analysis of MR feature space for measurement of CSF, gray-matter, and white-matter volumes.

The problem of volume averaging in quantitating CSF, gray-matter, and white-matter fractions in the brain is solved using a three-compartment model and a simple graphical analysis of a multispectral MR feature space. Compartmentalization is achieved without the ambiguities of thresholding techniques or the need to assume that the underlying pixel probability distributions have a particular form. A 2D feature space is formed by double SE (proton density- and T2-weighted) MR data with image nonuniformity removed by a novel technique in which the brain itself serves as a uniformity reference. Compartments other than the basic three were rejected by the tailoring of limits in feature space. Phantom scans substantiate this approach, and the importance of the careful selection and standardization of pure tissue reference signals is demonstrated. Compartmental profiles from standardized subvolumes of three normal brains, based on a 3D (Talairach) coordinate system, demonstrate slice-by-slice detail; longitudinal studies confirm reproducibility. Compartmentalization may be described graphically and algebraically, complementing data displays in feature space and images of compartmentalized brain scans. These studies anticipate the application of our compartmentalization technique to patients with neurological disorders.

Adult↗

PubMed1980

Physical attributes of single-photon tomography.

Physical properties important for assessment of the potentials of emission computed tomography implemented by collimated detector systems include sensitivity, statistical and angular sampling requirements, attenuation compensation, resolution uniformity, and multisection design constraints. The limited angular range and sampling interval of coded aperture methods for longitudinal tomography impose severe limitations on quantitative imaging capabilities. These methods are discussed. Disadvantages of limited angular range are avoided by transverse section devices that have lower sensitivity than comparable positron devices. It is shown here, however, that the sensitivity for a single section device for head transverse section 2 cm thick can be congruent to 200 events sec-1 microCi-1 per axial cm for 2 x 2 cm resolution. This is 40% of that for a well-designed positron system of similar resolution. The problem of attenuation compensation for constant attenuation, as in brain imaging, is well understood and a fast algorithm of the convolution type gives excellent results if angular sampling is over 360 degrees. Though there is a need to move the single-photon detector array over wide angular distances for adequate sampling, dynamic ECT is possible for the measurement of biological washout kinetics of clinical importance, such as clearance studies in brain. Based on physical principles, experiences with low sensitivity devices, and the prospects for devices with sensitivity comparable to positron tomographs, single photon tomography has sound potentials for research and clinical studies of the adult brain and whole body in small subjects. Practical whole-body tomography in adults is limited to nonquantitative lesion detection.

Tomography, Emission-Computed↗

PubMed1997

Continuous monitoring and regulating of brain temperature in the conscious and freely moving ischemic gerbil: effect of MK-801 on delayed neuronal death in hippocampal CA1.

Many glutamate antagonists have been reported to have a neuroprotective effect against ischemic brain damage; however, some of them have been also reported to induce hypothermia that confers remarkable neuroprotection against the damage. In order to avoid the confounding effects of hypothermia, we assembled a telemeter-based brain temperature control system that allows continuous monitoring and regulating of brain temperature during an ischemic insult and in the post-ischemic period in conscious and freely moving animals. Experiments were performed in gerbils that were subjected to administration of MK-801 (3, 5, and 10 mg/kg) and/or to 5-min ischemia. The system monitored continuous changes in brain temperature and regulated brain temperature at normothermic levels, revealing that a neuroprotective effect of 3 mg/kg MK-801 against ischemia-induced delayed hippocampal CA1 neuronal death was mainly due to hypothermia, whereas a high dose of MK-801 (5 and 10 mg/kg) produced a neuroprotective effect even when the brain temperature was maintained at normothermic levels. These results indicate that this system is very useful to test potential antiischemic agents, especially when the agents have hypothermic side effects.

Animals↗

PubMed1997

Is the alpha rhythm a control parameter for brain responses?

The main goal of the present study is to develop a conceptual analysis of alpha response in the brain based on single sweep evaluation. A new method was employed to estimate a set of single-sweep parameters and quantify the oscillatory behaviour of single, electroencephalograph (EEG) sweeps. It was aimed to demonstrate that brain alpha responses are governed by spontaneous alpha activity and to validate the principle of brain response excitability. Because the spontaneous alpha activity depends on both the topology of recording and the subject's age, topology and age models were used. Spontaneous and evoked alpha activity were recorded at frontal and occipital sites in three groups of subjects: 3-year-old children, young adults and middle-aged subjects. Amplitude, enhancement and phase-locking of single alpha responses to visual stimuli were analysed. Major results showed that; (1) visual alpha responses could be recorded only if the alpha rhythm was developed in the spontaneous EEG independent of electrode location; (2) middle-aged adults showed more expressed frontal spontaneous alpha activity in comparison with young adults; (3) accordingly, alpha responses with higher amplitude and stronger phase-locking were produced over the frontal brain area in middle-aged than young adults. These results validate the principle of brain response excitability and demonstrate that a shift towards frontal brain areas for both the spontaneous and evoked alpha activity occurs with increasing age in adults. The results are discussed in the context of the diffuse and distributed alpha system of the brain. Age-dependent changes in frontal alpha activity are suggested to be related to frontal brain functioning during aging.

Adult↗

PubMedDate not supplied

[The structure of the arteries of the base of the brain in saccular aneurysms].

In 100 autopsy observations with saccular aneurysms of diverse localization the structure of arteries at the base of the brain was studied. In 26 per cent of the cases this structure was of the normal or "classic" type. In some instances there could be detected deviations from the "classic" type, with a tendency in certain localization of the aneurysm towards hypoplasia of the proximal length of the anterior cerebral artery. Frequently encountered divergences from the "classic" type of the structure come as a result of a delayed development of the vessels at the base of the brain during early stages of ontogenesis.

Cerebral Arteries↗

PubMed2001

Diffusion tensor imaging of the developing mouse brain.

It is shown that diffusion tensor MR imaging (DTI) can discretely delineate the microstructure of white matter and gray matter in embryonic and early postnatal mouse brains based on the existence and orientation of ordered structures. This order was found not only in white matter but also in the cortical plate and the periventricular zone, which are precursors of the cerebral cortex. This DTI-based information could be used to accomplish the automated spatial definition of the cortical plate and various axonal tracts. The DTI studies also revealed a characteristic evolution of diffusion anisotropy in the cortex of the developing brain. This ability to detect changes in the organization of the brain during development will greatly enhance morphological studies of transgenic and knockout models of cortical dysfunction. Magn Reson Med 46:18-23, 2001.

Animals↗

PubMed1987

[Effect of clorgyline on the intensity of lipid peroxidation and on erythrocyte membrane stability in hyperoxia].

Administration of monoamine oxidase type A inhibitor clorgyline to rats before hyperoxia prevented oxygen-induced increase in diene conjugate and Shiff's base brain and plasma levels in hyperoxia. This was due to antioxidative effect of clorgyline which resulted in stabilization of blood cellular membranes. Clorgyline had a normalizing effect on extraerythrocyte hemoglobin level, total peroxidase activity and glucose-6-phosphate dehydrogenase activity in the serum.

Animals↗

PubMed2005

Seladin-1 as a target of estrogen receptor activation in the brain: a new gene for a rather old story?

Experimental evidence indicates that estrogen exerts neuroprotective effects. According to the fact that Alzheimer's disease (AD) is more common in post-menopausal women, estrogen treatment has been proposed. However, the beneficial effect of estrogen or selective estrogen receptor modulators (SERMs) in preventing or treating AD is a controversial issue, which will be summarized in this review. Recently, a novel gene, named selective AD indicator-1 (seladin-1), has been isolated and found to be down-regulated in brain regions affected by AD. Seladin-1, which is considered the human homolog of the plant protein DIMINUTO/DWARF1, confers protection against beta-amyloid-mediated toxicity and from oxidative stress and is an effective inhibitor of caspase 3 activity, a key mediator of apoptosis. This review will present the up-to-date findings regarding seladin-1 and DIMINUTO/DWARF1. In addition, the possibility that seladin-1 may be a downstream effector of estrogen receptor activation in the brain, based on our recent experimental findings using a human fetal neuronal model, will be addressed.

Alzheimer Disease↗

PubMed1992

Iodine-125 and fluorine-18 labeled aryl-1,4-dialkylpiperazines: potential radiopharmaceuticals for in vivo study of the dopamine uptake system.

A series of fluorine-18 and iodine-125 labeled aryl-1,4-dialkylpiperazine analogs, derivatives of GBR 12935, were synthesized as radiotracers for positron emission tomography or single photon emission computerized tomography imaging of the brain based on their affinity for the presynaptic dopamine reuptake system. High specific activity fluorine-18 tracers were prepared by nucleophilic aromatic substitution reactions; iodine-125 tracers were prepared by isotopic exchange reactions. In vitro competitive binding studies demonstrated that iodine substitution is tolerated in the 4-position of the phenyl ring of the phenalkylpiperazine group. In vivo regional brain biodistribution studies in mice indicated no selectivity of the radioiodinated ligands for the dopamine reuptake site, with striatum/cerebellum concentration ratios of 1. Similar negative results with the new fluorine-18 derivatives demonstrated that in vivo selectivity for the dopamine reuptake site appears to be critically dependent on the carbon chain length between the piperazine ring and the solitary aromatic ring. These studies suggest that development of new radiopharmaceuticals based on the GBR 12935 structure cannot be based solely on considerations of in vitro binding affinities.

Animals↗

PubMed2006

Effect of GDNF-releasing biodegradable microspheres on the function and the survival of intrastriatal fetal ventral mesencephalic cell grafts.

The transplantation of fetal ventral mesencephalic (FVM) cell suspensions into the brain striatal system is an alternative approach for the treatment of Parkinson's disease (PD). However, one objection to this procedure is the relatively poor survival of implanted cells. Attempts have been made to improve the survival of grafted dopaminergic neurons using glial cell line-derived neurotrophic factor (GDNF). Nevertheless, the clinical application of GDNF is limited, due to the difficulties in administering a protein to the brain tissue and due to the ubiquity of its receptor, thus leading to neurological side effects. A strategy to deliver GDNF in the brain based on the intracerebral implantation of biodegradable poly(D,L-lactic acid-co-glycolic acid) sustained release microspheres has been developed. Such microparticles can be easily implanted by sterotaxy in precise and functional areas of the brain without causing damage to the surrounding tissue. Moreover, the release profile of the GDNF-loaded microspheres showed a sustained release over 56 days of biologically active GDNF at clinically relevant doses. The present study shows that the implantation of GDNF-loaded microspheres at a distance to the site of FVM cells in the 6-hydroxydopamine-lesioned rat model of PD improves dopaminergic graft survival and function. Furthermore, the unloaded and the GDNF-loaded microspheres, when they are mixed with FVM cells, may provide a mechanical support and a 3D environment inducing differentiation and increased function of dopaminergic neurons. Taken together, these results show that GDNF microspheres represent an efficient delivery system for cell transplantation studies.

Animals↗

PubMedDate not supplied

Behavior adjustments in traumatic brain injury. A case study.

A traumatic assault to the brain often leaves significant residual effects, including severe behavioral dyscontrol. The person may demonstrate unwanted behaviors, such as physical aggression or verbal abuse, and lack motivation or the skills to engage in desirable behavior. ReMed, a community-based brain injury program, specializes in using a behavior analytic approach to address unwanted behaviors while understanding and developing strategies to further recovery from the brain injury.

Activities of Daily Living↗

PubMedDate not supplied

Synergistic effects of neurons and astrocytes on the differentiation of brain capillary endothelial cells in culture.

Brain capillary endothelial cells form a functional barrier between blood and brain, based on the existence of tight junctions that limit paracellular permeability. Occludin is one of the major transmembrane proteins of tight junctions and its peripheral localization gives indication of tight junction formation. We previously reported that RBE4.B cells (brain capillary endothelial cells), cultured on collagen IV, synthesize occludin and correctly localize it at the cell periphery only when cocultured with neurons. In the present study, we describe a three-cell type-culture system that allowed us to analyze the combined effects of neurons and astrocytes on differentiation of brain capillary endothelial cells in culture. In particular, we found that, in the presence of astrocytes, the neuron-induced synthesis and localization of occludin is precocious as compared to cells cocultured with neurons only.

Animals↗

PubMed1993

The neuropathology of schizophrenia. A focus on the subcortex.

Investigations into the neuropathology of schizophrenia have increasingly altered the perception of the illness. Early studies focused on finding consistent and discrete areas of cortical pathology in the brain material of schizophrenic patients. After nearly a half century of study, little evidence emerged from a great body of data suggesting any consistent, discrete neuropathologic finding associated with this illness. This lack of evidence led to obvious frustration on the part of researchers and movement within the psychiatric community towards significantly less brain-based theories of the genesis of schizophrenia. With the advent of new technologies such as enhanced structural imaging (CT, MRI), functional imaging (PET, SPECT), and better neuropathologic methods, the focus of schizophrenia research has again turned towards the brain. Ultimately, hypotheses regarding the cause of schizophrenia will be proved or disproved on neuropathologic evidence. Few, if any, modern schizophrenia researchers would make the argument that there is a single, consistent neuropathologic lesion that is responsible for the entire illness of schizophrenia. Current theories tend to interpret the wide variety of neuropathologic changes in this illness as evidence of disturbed nervous system maturation--either acquired or inherent--or perhaps as a response to damage with aberrant neuronal regeneration. Evidence for a neurodegenerative disorder has not proved to be compelling. Furthermore, these theories emphasize dysfunction of elements of distributed neuronal systems, including subcortical systems, not discrete "lesions." The danger with the theoretic approach of distributed systems is, as Steriade and McCarley noted so well, that the flexibility of this idea can "mean a retreat into vagueness so that hypotheses concerning the role of multiple interrelated structures in the genesis of a given behavioral state cannot be proved wrong." (p 23). Despite the risks, this approach to investigation promises to offer more than just information pertinent to schizophrenia research; it offers insights into the mechanisms of behavior as a product of integrated brain function.

Brain↗

PubMed1991

Neurobehavioral organization of the newborn: opportunity for assessment and intervention.

A functional model has been formulated that attempts to specify the behavioral subsystems of functioning that exemplify in their respective interplay an infant's individuality of behavioral functioning in the manner in which they move from stable to disorganized functioning and in the flexibility with which they maintain organized functioning in the face of varied exogenous and endogenous events. Based on this model, Als and colleagues have attempted to develop systematic assessments, the APIB and the K-Box Paradigm, to quantify the degree of differentiation and modulation of these behaviorally defined subsystems of functioning. It is hypothesized that the differences documented via these assessments are brain based (i.e., part of the child's biological makeup, which is influenced by the intrauterine and extrauterine environment, be it sensory and/or drug exposure, and which shows a recognizable pattern along a definable trajectory).

Behavior↗

PubMed2006

Regional protein levels of cytosolic phospholipase A2 and cyclooxygenase-2 in Rhesus monkey brain as a function of age.

Limited evidence suggests that brain cytosolic phospholipase A(2) (cPLA(2)), which selectively releases arachidonic acid (AA) from membrane phospholipids, and cyclooxygenase-2 (COX-2), the rate-limiting enzyme for AA metabolism to prostanoids, change as a function of normal aging. In this study, we examined the protein levels of cPLA(2) and COX-2 enzymes in hippocampus, frontal pole and cerebellum from young (2-5 years old), middle-aged (8-11 years old) and old (23 years old) male and female Rhesus monkeys. In the cerebellum, cPLA(2) protein level was higher in the young brain as compared to levels seen at both middle-aged and old. Similarly, in the frontal pole, the young brain showed a higher level of COX-2 protein as compared to the levels seen at both older ages. For both, once an animal reached 8-11 years of age the levels appeared to remain relatively constant over the next decade. Immunohistochemistry of COX-2 protein within the brain demonstrated no significant change in the localization to neurons within the frontal pole. Qualitatively, a greater number of neurons were positively stained for COX-2 in the young brain than in the aged brain. Based on the previous reports of localization of cPLA(2) and COX-2 at post-synaptic sites in neurons results from the current study suggest that the elevated protein levels of the two enzymes seen in the younger brain is related to the greater potential for synaptic plasticity across multiple neurons as a function of age and that cPLA(2) and COX-2 may be considered as post-synaptic markers.

Aging↗