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At least 757 records · Page 42Linked to original sources
PubMed2000

The peak CT number of profiles perpendicular to the vertebral cortical shell may be a useful indicator of the integrity of the cortical shell.

Limited spatial resolution affects the ability of clinical CT systems to directly measure the thickness and density of the vertebral cortical shell. In such cases the peak CT number (CTp) of a profile through the cortical shell is approximately proportional to the product of thickness and density and hence an average of several of these values (CTp) may be useful as an indicator of the integrity of the cortical shell. Values of CTp were determined around the anterior two-thirds of the cortical shell of the L3 and L4 lumbar vertebrae of 96 Kuwaiti women (mean age+/-SD=50.0+/-8.5). There was no significant difference between the two vertebrae in terms of CTp and trabecular BMD values. There was a significant correlation between CTp and trabecular BMD for each vertebra (r=0.597, p<0.0001), and between CTp and patient age (r=0.624, p<0.001), suggesting that both cortical and trabecular bone may be subject to similar thinning mechanisms during ageing and osteoporosis. The variation of CTp around the cortical shell, represented by the standard deviation of nine CTp measurements, was significantly correlated with the mean value (r=0.503, p<0.0001) and may be useful as a descriptor of cortical structure.

Adult↗
PubMed2002

Serial registration of intraoperative MR images of the brain.

The increased use of image-guided surgery systems during neurosurgery has brought to prominence the inaccuracies of conventional intraoperative navigation systems caused by shape changes such as those due to brain shift. We propose a method to track the deformation of the brain and update preoperative images using intraoperative MR images acquired at different crucial time points during surgery. We use a deformable surface matching algorithm to capture the deformation of boundaries of key structures (cortical surface, ventricles and tumor) throughout the neurosurgical procedure, and a linear finite element elastic model to infer a volumetric deformation. The boundary data are extracted from intraoperative MR images using a real-time intraoperative segmentation algorithm. The algorithm has been applied to a sequence of intraoperative MR images of the brain exhibiting brain shift and tumor resection. Our results characterize the brain shift after opening of the dura and at the different stages of tumor resection, and brain swelling afterwards. Analysis of the average deformation capture was assessed by comparing landmarks identified manually and the results indicate an accuracy of 0.7+/-0.6 mm (mean+/-S.D.) for boundary surface landmarks, of 0.9+/-0.6 mm for landmarks inside the boundary surfaces, and 1.6+/-0.9 mm for landmarks in the vicinity of the tumor.

Algorithms↗
PubMed2000

Cognitive and emotional influences in anterior cingulate cortex.

Anterior cingulate cortex (ACC) is a part of the brain's limbic system. Classically, this region has been related to affect, on the basis of lesion studies in humans and in animals. In the late 1980s, neuroimaging research indicated that ACC was active in many studies of cognition. The findings from EEG studies of a focal area of negativity in scalp electrodes following an error response led to the idea that ACC might be the brain's error detection and correction device. In this article, these various findings are reviewed in relation to the idea that ACC is a part of a circuit involved in a form of attention that serves to regulate both cognitive and emotional processing. Neuroimaging studies showing that separate areas of ACC are involved in cognition and emotion are discussed and related to results showing that the error negativity is influenced by affect and motivation. In addition, the development of the emotional and cognitive roles of ACC are discussed, and how the success of this regulation in controlling responses might be correlated with cingulate size. Finally, some theories are considered about how the different subdivisions of ACC might interact with other cortical structures as a part of the circuits involved in the regulation of mental and emotional activity.

Journal Article↗
PubMed2001

Shedding light on brain function: the event-related optical signal.

One of the basic goals of cognitive psychology is the analysis of the covert processes that occur between stimulus and response. In the past 20-30 years, the tools available to cognitive psychologists have been augmented by a number of imaging techniques for studying the 'brain in action' in a non-invasive manner. These techniques have their strength in either temporal or spatial information, but not both. We review here recent advances of a new approach, the event-related optical signal (EROS). This method allows measurements of the time course of neural activity in specific cortical structures, thus combining good spatial and temporal specificity. As an example, we show how EROS can be used to distinguish between serial and parallel models of information processing.

Journal Article↗
PubMed1999

Selective visual-spatial attention alters induced gamma band responses in the human EEG.

OBJECTIVES: The present study was designed to investigate the attentional modulation of gamma band responses in a visual spatial attention task using a 128-channel-EEG-montage. METHODS: Colored rectangles were presented on a screen. After 500 ms an arrow indicated whether subjects had to shift their attention to the left or right half of the screen to detect target stimuli. During the task, either the attended half of the screen rotated horizontally while the unattended part remained motionless, or vice versa. RESULTS: When subjects attended the rotating stimulus, we found significantly higher power in a specific gamma band from 35-51 Hz on parieto-occipital electrode sites contralateral to the stimulation side. In addition, after the onset of the arrow which indicated what side subjects should direct their attention to, the 35-51 Hz response shifted from a broad posterior distribution to an increase of power at parieto-occipital sites contralateral to the to-be-attended side. Furthermore, the rotating stimulus elicited higher gamma band power as compared to the standing stimulus at electrode locations, which may be related to the activity of underlying cortical structures specialized for motion processing. CONCLUSIONS: The present results replicate important parts of previous findings of enhanced gamma power when a moving stimulus was attended.

Adult↗
PubMed2004

Central mechanisms of pain perception.

Mechanisms of human nociception can be studied by the use of CO2 laser stimulation, which selectively activates nociceptive receptors, and by the use of various noninvasive techniques. In addition to the contralateral thalamus, at least several cortical areas including the contralateral SI, bilateral SII, anterior cingulated cortex, and insular cortices are involved in the pain sensation/perception. Pain perception (Fig. 8) is unique because these cortical structures seem to be activated in parallel at nearly the same latency after the stimulus presentation. SI seems to play a role in basic pain processing while SII and insula are involved in higher functions of pain perception. Emotional aspects of pain perception are mediated by anterior cingulate cortex and posterior insula/parietal operculum.

Brain Mapping↗
PubMed2001

Changes in osteocalcin response to 1,25-dihydroxyvitamin D(3) stimulation and basal vitamin D receptor expression in human osteoblastic cells according to donor age and skeletal origin.

Age-related osteopenia is known to occur differently throughout the skeleton. In the present study, we examine the influence of donor age (<50 and >50 years), and bone structure (cortical vs. trabecular) on osteocalcin and vitamin D receptor (VDR) expression in primary cultures of human osteoblastic cells (hOB) cells. Cells were isolated from trabecular bone samples obtained from donors undergoing either knee (mainly trabecular) (n = 22; 4 <50 years, 18 >50 years) or hip (mainly cortical) (n = 16; 6 <50 years, 10 >50 years) arthroplasty. Pooling the results from knee and hip hOB cell cultures, we found that secreted osteocalcin was higher in hOB cells from the younger donors, compared with that in older donors, and peaked after stimulation with 10(-6)--10(-8) mol/L 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. In cells from the latter donors, this secretion was maximal after 10(-6) mol/L 1,25(OH)(2)D(3) treatment. On the other hand, using reverse transcription followed by polymerase chain reaction, baseline osteocalcin mRNA was found to be lower in hOB cells from the older donors than in those from younger donors. After treatment with 10(-6)--10(-8) mol/L 1,25(OH)(2)D(3), osteocalcin mRNA increased over baseline in all groups of hOB cells studied. In age-matched cultures, both basal and 10(-6)--10(-8) mol/L 1,25(OH)(2)D(3)-stimulated osteocalcin mRNA showed similar values in hOB cells from both skeletal sites in younger donors. However, in the older donors, baseline as well as 10(-8) mol/L 1,25(OH)(2)D(3)-stimulated osteocalcin mRNA were higher in knee hOB cells than in hip hOB cells. Furthermore, baseline VDR mRNA expression was also higher in the former cells than in the latter cells in the older group. Considering the influence of donor age at each skeletal site of origin, we found lower baseline osteocalcin and VDR mRNA levels in hip hOB cells in the older group than in the younger group. Our findings indicate that the response of osteocalcin secretion and its mRNA to physiological doses of 1,25(OH)(2)D(3) decreases with aging and is associated with decreased VDR mRNA expression in hOB cells from mainly cortical bone.

Adult↗
PubMed2002

Aversive Pavlovian conditioning in psychopaths: peripheral and central correlates.

Differential aversive Pavlovian conditioning with a foul odor as unconditioned stimulus (US) and neutral faces as conditioned stimuli (CS) was compared between 9 noncriminal psychopaths as defined by the Hare Psychopathy Checklist Revised and 12 healthy controls. Event-related potentials (ERP), heart rate, skin conductance response, corrugator EMG, and startle response potentiation as well as valence, arousal, and contingency of the CS were assessed. Whereas the healthy controls (HC) showed significant CS +/CS- differentiation, the psychopaths (PP) failed to exhibit a conditioned response although unconditioned responses were comparable between the groups. N100, P200, and P300 to the CSs revealed that psychopaths were not deficient in information processing and showed even better anticipatory responding than the HC group indicated by the terminal contingent negative variation (tCNV), that lacked, however, CS+ and CS- differentiation. These data indicate a deficit in association formation in psychopaths that may be related to deficient interaction of limbic-subcortical and cortical structures.

Adult↗
PubMed1998

Dissociation of brain ERP topographies for tonal and phonetic oddball tasks.

ERP topographies for 30 scalp electrodes were examined in 26 healthy right-handed volunteers during oddball tasks (20% targets) using binaurally presented consonant-vowel syllables or complex tones. Response hand was counterbalanced across participants. Both window averages and a principal components analysis (PCA) with Varimax rotation revealed task-related (tonal/phonetic) hemispheric asymmetries for N2, early P3, and particularly for N2-P3 amplitude. In the tonal task, N2 was maximal over right lateral-temporal regions, and early P3 over right medial-parietal regions. For the phonetic task, N2 was maximal over the left lateral-parietal regions, and late P3/N3 over left medial-parietal regions. A response-related frontal negativity (N3) interacted with task-related asymmetries in an unbalanced fashion. The distinct, asymmetric N2 and P3 topographies for tonal and phonetic tasks presumably reflect differential involvement of cortical structures in pitch (right frontotemporal) and phoneme (left parietotemporal) discrimination.

Acoustic Stimulation↗
PubMed1998

A role for ovarian hormones in sexual differentiation of the brain.

Historically, studies of the role of endogenous hormones in developmental differentiation of the sexes have suggested that mammalian sexual differentiation is mediated primarily by testicular androgens, and that exposure to androgens in early life leads to a male brain as defined by neuroanatomy and behavior. The female brain has been assumed to develop via a hormonal default mechanism, in the absence of androgen or other hormones. Ovarian hormones have significant effects on the development of a sexually dimorphic cortical structure, the corpus callosum, which is larger in male than in female rats. In the females, removal of the ovaries as late as Day 16 increases the cross-sectional area of the adult corpus callosum. Treatment with low-dose estradiol starting on Day 25 inhibits this effect. Female callosa are also enlarged by a combination of daily postnatal handling and exogenous testosterone administered prior to Day 8. The effects of androgen treatment are expressed early in development, with males and testosterone-treated females having larger callosa than control females as early as Day 30. The effects of ovariectomy do not appear until after Day 55. These findings are more consistent with other evidence of a later sensitive period for ovarian feminization as compared to androgenic masculinization.

Adult↗
PubMedDate not supplied

The effects of lateral geniculate nucleus, area V4, and middle temporal (MT) lesions on visually guided eye movements.

Visually guided saccadic eye movements to singly presented stationary targets form a bimodal distribution. After superior colliculus lesions, the so called "express saccades" that form the first mode of the distribution are no longer obtained. The aim of this study was to determine what role several other neural systems play in the generation of express and regular saccades, with the latter being those that form the second mode in the bimodal distribution. Lesions were made in the parvocellular and magnocellular portions of the lateral geniculate nucleus to disrupt either the midget system or the parasol system that originates in the retina and areas V4 and MT. The effects of the lesions were examined on the accuracy and latency of saccadic eye movements made to stationary and to moving visual targets. Following magnocellular and MT lesions deficits were observed in smooth pursuit and in the amplitude of saccades made to moving targets. However, none of the lesions produced significant changes in the bimodal distribution of saccadic latencies to stationary targets. The results suggest that express saccades and regular saccades are not selectively mediated by either the midget or the parasol systems or by areas V4 and MT. Neither are the frontal eye fields involved as had previously been shown. We suggest that the superior colliculus plays a central role in producing both express and regular saccades by virtue of highly convergent input from numerous cortical structures.

Animals↗
PubMed2003

New developments in electroconvulsive therapy and magnetic seizure therapy.

New findings regarding the mechanisms of action of electro-convulsive therapy (ECT) have led to novel developments in treatment technique to further improve this highly effective treatment for major depression. These new approaches include novel placements, optimization of electrical stimulus parameters, and new methods for inducing more targeted seizures(eg, magnetic seizure therapy [MST]). MST is the use of transcranial magnetic stimulation to induce a seizure. Magnetic fields pass through tissue unimpeded, providing more control over the site and extent of stimulation than can be achieved with ECT. This enhanced control represents a means of focusing the treatment on target cortical structures thought to be essential to antidepressant response and reducing spread to medial temporal regions implicated in the cognitive side effects of ECT. MST is at an early stage of development. Preliminary results suggest that MST may have some advantages over ECT in terms of subjective side effects and acute cognitive functioning. Studies designed to address the antidepressant efficacy of MST are underway. As with all attempts to improve convulsive therapy technique, the clinical value of MST will need to be established through controlled clinical trials. This article reviews the experience to date with MST, and places this work in the broader context of other means of optimizing convulsive therapy in the treatment of depression.

Animals↗
PubMedDate not supplied

Use of green fluorescent protein-conjugated beta-actin as a novel molecular marker for in vitro tumor cell chemotaxis assay.

To study the dynamics of actin cytoskeleton rearrangement in living cells, an eukaryotic expression vector expressing a beta-actin-GFP fusion protein was generated. The expression construct when transfected into NIH3T3 fibroblast, A2058 human melanoma and 293T human embryonic kidney carcinoma cell lines expressed beta-actin-GFP fusion protein, which colocalized with endogenous cellular actin as determined by histoimmunofluorescence staining. The beta-actin-GFP was also observed to be reorganized in response to treatments with the chemoattractant type IV collagen. Cells extended pseudopodial protrusions and altered the morphology of their cortical structure in response to type IV collagen stimulation. More importantly, beta-actin-GFP accumulated in areas undergoing these dynamic cytoskeleton changes, indicating that beta-actin-GFP could participate in actin polymerization. Although ectopic expression of beta-actin-GFP lead to minor side effects on cell proliferation, these studies suggest that this strategy provides an alternative to the invasive techniques currently used to study actin dynamics and permits real-time visualization of actin rearrangements in response to environmental cues.

3T3 Cells↗
PubMedDate not supplied

Speech and motor disturbances in Rett syndrome.

Rett syndrome is a severe, genetically determined disease of early childhood which produces a defined clinical phenotype in girls. The main clinical manifestations include lesions affecting speech functions, involving both expressive and receptive speech, as well as motor functions, producing apraxia of the arms and profound abnormalities of gait in the form of ataxia-apraxia. Most investigators note that patients have variability in the severity of derangement to large motor acts and in the damage to fine hand movements and speech functions. The aims of the present work were to study disturbances of speech and motor functions over 2-5 years in 50 girls aged 12 months to 14 years with Rett syndrome and to analyze the correlations between these disturbances. The results of comparing clinical data and EEG traces supported the stepwise involvement of frontal and parietal-temporal cortical structures in the pathological process. The ability to organize speech and motor activity is affected first, with subsequent development of lesions to gnostic functions, which are in turn followed by derangement of subcortical structures and the cerebellum and later by damage to structures in the spinal cord. A clear correlation was found between the severity of lesions to motor and speech functions and neurophysiological data: the higher the level of preservation of elements of speech and motor functions, the smaller were the contributions of theta activity and the greater the contributions of alpha and beta activities to the EEG. The possible pathogenetic mechanisms underlying the motor and speech disturbances in Rett syndrome are discussed.

Adolescent↗
PubMedDate not supplied

Somatosensory evoked potentials during natural and learning rearrangements of posture accompanied by limb elevation in dogs.

Changes in the functional state of the sensorimotor cortex associated with reorganization of the natural pattern of postural rearrangement before limb elevation (the "diagonal" patten and of an artificial rearrangement (the "unilateral" pattern) were studied in dogs. The state of cortical structures on postural rearrangement was assessed in terms of the pattern of somatosensory evoked potentials produced in response to stimulation of the forelimb during postural preparation of the animal for elevating the hindlimb (acquired avoidance response to a sound signal). Evoked potentials during the natural postural preparation (the "diagonal" pattern) were compared with those during the altered pattern of postural preparation (the "unilateral" pattern), this preparation taking place prior to elevation of the limb. Controls consisted of evoked potentials in the resting state. Decreases were seen in the latencies and amplitudes of most components of evoked potentials during postural rearrangement. In general, changes in evoked potentials were less marked in the "unilateral" pattern than in the "diagonal" pattern, though the differences were significant only for the amplitude of the first negative component. Changes in evoked potentials were similar regardless of whether the supporting forces of the limb to which the test stimulus was applied increased or decreased during postural rearrangement. It is suggested that differences in evoked potentials may reflect changes in the interaction between neuronal populations within the sensorimotor cortex during reorganization of the pattern of postural rearrangement associated with learning.

Animals↗
PubMed2001

Effects of grating spatial orientation on visual evoked potentials and contrast sensitivity in multiple sclerosis.

Previous studies suggest a delay of pattern visual evoked potentials (PVEPs) in multiple sclerosis (MS) depending on grating orientation. We examined a group of 14 patients with definite MS recording PVEPs to vertical and horizontal grating and analysing latency and amplitude of P60, N70 and P100 waves. We evaluated contrast sensitivity (CS) to dark and bright bars of several spatial frequencies (SF). The aim was to evaluate the diagnostic value of evoked responses and CS in revealing involvement of cortical structures. PVEPs to 1 degrees cycle/degree (c/d) vertical bars were abnormal in 25% for P60, in 32% for N70 and in 36%, for P100; in 25%, 36% and 42% respectively at 4 c/d; as regards horizontal bars at 1 c/d we found alterations of P60, N70 and P100 in 11%, 19% and 27% respectively; at 4 c/d in 19%, 27%) and 35%. CS resulted more abnormal for vertical grating, with a maximum impairment for 3.7 c/d SF. We may conclude that the use of vertical grating in clinical routine is more reliable both for PVEPs and CS testing; in addition CS can be abnormal even with normal PVEPs: this could mean an early impairment of CS and provide useful indications about a subclinical involvement of visual cortex.

Adult↗
PubMed2001

Complement deposition in renal allografts with early malfunction.

Among patients with early severe impairment of renal allograft function we have previously identified a group displaying isolated deposition of complement factor C3 in glomeruli. Here we studied the pattern of complement deposition more extensively in allograft biopsies from five patients using an immunofluorescence technique. We found a prominent deposition of C3c, C3d and C4d antigens in the glomerular capillary walls, and a positive reaction to vitronectin (S-protein), but only trace amounts of the complement factor C9 neoepitope. Clq, C4c, C3a, iC3b, factor B, properdin, immunoglobulins IgG, IgA or IgM were not found in glomeruli or in any other cortical structure. These findings indicate that most of the demonstrated glomerular C3 consists of C3b and/or C3c/C3d molecules. By immunoelectron microscopy the C3 antigen was found within the glomerular basement membrane. Our findings indicate that there is a mechanism of complement activation involving the early steps of the classical pathway, despite the lack of demonstrable immunoglobulins in the tissue. In analogy with similar reactions described recently in heart allografts, we suggest that this may be a manifestation of a humoral rejection, possibly mediated by a low titer of circulating antibodies directed against endothelial surface antigens, presumed to be the initial step leading to complement activation.

Adult↗
PubMed2003

Effects of alcohol on person perception: a social cognitive neuroscience approach.

The acute effects of alcohol on cognitive processing of expectancy violations were investigated using event-related brain potentials and a cued recall task to index attentional and working memory processes associated with inconsistency resolution. As predicted, expectancy-violating behaviors elicited larger late positive potentials (LPP) and were recalled better than expectancy-consistent behaviors. These effects were moderated by alcohol and the valence of initial expectancies. For placebo group participants, positive targets performing negative behaviors elicited the largest LPP responses and were recalled best. For those in the alcohol groups, negative targets behaving positively elicited the largest LPP and recall responses. These findings suggest that alcohol does not globally impair working memory processes in person perception but instead changes the nature of valenced information processing. Findings are discussed in the context of alcohol's effects on working memory processes, reward sensitivity, and the prefrontal cortical structures thought to mediate them.

Adult↗