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At least 847 records · Page 47Linked to original sources

PubMed1992

Cortical mechanisms mediating asterixis.

We describe a patient with chronic renal failure who suffered multifocal action-induced jerks. Electromyography (EMG) recorded the typical silence of asterixis. Back-averaging the EEG activity preceding the EMG silent periods in the forearm showed a biphasic wave antedating the asterixis by 23 ms. Somatosensory evoked potentials (SEPs) after median nerve stimulation were pathologically enlarged on both hemispheres. Brain-mapping of the biphasic wave preceding asterixis and the giant SEPs indicated a common origin in the sensorimotor cortex. This observation provides further documentation of a cortical origin for some types of asterixis in humans.

Brain Mapping↗

PubMed2004

Evaluation of a pneumatically driven tactile stimulator device for vision substitution during fMRI studies.

Functional magnetic resonance imaging (fMRI) experiments on tactile perception are difficult to perform because the special characteristics of an MRI environment restrict the experimental setup. Although recently developed actuators have made it possible to apply vibrotactile stimuli to the skin during an fMRI experiment, the projection of spatially extended patterns is still precluded. In order to examine the processing of tactile perception, a new pneumatically-driven tactile device (PTD) has been built. This device is capable of stimulating the skin, using arbitrary time sequences that consist of 2D tactile images up to 64 pixels. It is shown how the device is implemented in a 2 T fMRI environment, and show that it operates without generating artifacts. Dedicated software allows the generation of complex paradigms and provides a user-friendly interface to other brain mapping systems, as well as automated operation. This paper describes the PTD elucidates its features, and demonstrate its reliability by reporting results from an fMRI study based on an event-related protocol involving six subjects.

Adult↗

PubMed1999

Conduction aphasia elicited by stimulation of the left posterior superior temporal gyrus.

OBJECTIVE: Disruption of fascicular tracts that connect Wernicke's to Broca's areas is the classic mechanism of conduction aphasia. Later work has emphasised cortical mechanisms. METHODS: To determine the distribution of language on dominant cortex, electrical cortical stimulation was performed using implanted subdural electrodes during brain mapping before epilepsy surgery. RESULTS: A transient, isolated deficit in repetition was elicited with stimulation of the posterior portion of the dominant superior temporal gyrus. CONCLUSION: This finding suggests that cortical dysfunction, not just white matter disruption, can induce conduction aphasia.

Adult↗

PubMed1996

Alterations in functional neuroanatomical connectivity in Alzheimer's disease. Positron emission tomography of auditory verbal short-term memory.

Conscious recall of past events which have specific temporal and spatial contexts, termed episodic memory, is mediated by a system of interrelated brain regions. In Alzheimer's disease (AD) this system breaks down, resulting in an inability to recall events from the immediate past. Studies of normal human auditory-verbal short-term memory suggest that the brain system underlying these processes has distinct components, and the present study utilized the methods of functional brain mapping to determine the nature and extent of the breakdown that occurs in AD. Using subtraction techniques of PET-acquired images of regional cerebral blood flow we demonstrate that AD patients show a compensatory hyperactivation of various regions of cerebral cortex normally involved in these tasks, as well as activation of cortical areas not activated by normal elderly subjects. These results provide clear evidence of functional plasticity in the AD patient's brain even if those changes do not result in normal memory function.

Aged↗

PubMed2001

Stereopsis-processing regions in the human parieto-occipital cortex.

We performed fMRI on the human parieto-occipital cortex in order to identify the neural processing regions of stereopsis. Visual stimulation for stereopsis was performed with a random-dot stereogram displayed in the image guides of a new binocular visual stimulation device that we developed. Interestingly, regions from the dorsal portion of the occipital lobe to the superior parietal lobule were activated by binocular disparity, while the inferior parietal lobule was not activated. Moreover, these regions were shown as dominant in the right hemisphere. Functional brain mapping revealed that the processing regions of stereopsis were dorsally located in parieto-occipital cortex, and that the superior parietal lobule is an important region for neural processing of human stereopsis.

Adult↗

PubMed1998

Spatial and temporal resolution of functional magnetic resonance imaging.

Functional magnetic resonance imaging has become an invaluable tool for cognitive neuroscience, despite the fact that many of the physiological mechanisms giving rise to the effect are not well understood. We review the known biochemical and physiological basis of the technique and discuss how, within the noted limits, one might fully exploit the spatial and temporal resolution that is intrinsic to the very high magnetic fields that we use for human studies. This noninvasive brain mapping technique relies on the changes in blood oxygenation, blood volume, and blood flow, and we discuss some of the issues influencing the effects of these hemodynamic parameters on image intensity.

Anaerobiosis↗

PubMed1999

Determination of cognitive hemispheric lateralization by "functional" transcranial Doppler cross-validated by functional MRI.

BACKGROUND AND PURPOSE: Changes of blood flow velocity in the right and left middle cerebral artery (MCA) induced by cognitive demands are detectable by means of "functional" transcranial Doppler sonography (fTCD). Functional MRI (fMRI) is an alternative method for mapping brain activity. The purpose of this study was to determine whether fTCD can detect hemispheric lateralization and to cross-validate fTCD with fMRI. METHODS: Bilateral continuous MCA monitoring of 14 healthy, right-handed subjects with TCD was performed while the subjects underwent a visuospatial task, and the hemispheric blood flow velocity shift was calculated. Identical stimulus and response patterns were used in fMRI. Blood oxygenation level-dependent fMRI was performed with the use of a gradient-echo echo-planar sequence on a 1.5-T scanner. Statistical maps were computed on a voxel-by-voxel basis, hemispheric ratios for activated pixels were computed, and a group study was performed separately for the male and female subgroups. RESULTS: Statistical analyses (t test) showed a significantly higher mean peak blood flow velocity increase (P<0.05) of the right MCA (111.3+/-7.0%) compared with the left MCA (107.1+/-6.1%). fMRI demonstrated bilateral activation in the superior parietal lobulus (Brodmann area 7) with a right/left ratio of 1.95. Concordant differences between the female and male subgroups could be visualized with both methods. CONCLUSIONS: Both methods succeeded in discriminating a blood flow shift to the right hemisphere induced by a complex cognitive visuospatial task. fMRI cross-validates the findings of fTCD. Our study suggests that fTCD can investigate the close relationship between brain activity and blood flow and lateralize higher cognitive functions reliably.

Adult↗

PubMed1994

Pharmacokinetic and -dynamic studies with a new anxiolytic, suriclone, utilizing EEG mapping and psychometry.

1. In a double-blind, placebo-controlled, cross-over study, acute pharmacokinetic, neurophysiological and psychotropic effects of suriclone, a new cyclopyrrolone derivative, were investigated and compared with alprazolam. 2. Fifteen normal young volunteers received randomized oral single doses of placebo, 0.1, 0.2 and 0.4 mg suriclone as well as 1 mg alprazolam as reference compound. Investigations were carried out before and 1, 2, 4, 6 and 8 h after drug administration. 3. Pharmacokinetic investigations by radioimmunoassay showed a dose-dependent fast rise of plasma concentrations with a peak at 1 h and a rapid decline thereafter. Both the Cmax and the AUC values exhibited a linear relationship to dose. 4. EEG brain mapping demonstrated significant CNS effects of both compounds, characteristic for tranquillizers (increase of beta, decrease of alpha and increase of delta activity; attenuation of total power and acceleration of the centroid, i.e. centre of gravity frequency). When compared with alprazolam, suriclone exerted less sedative effects. 5. Time-efficacy calculations showed the pharmacodynamic peak effect of suriclone from the 2nd to the 4th hour, and of alprazolam in the 1st hour. Dose-efficacy calculations showed that the most pronounced CNS changes occurred after 1 mg alprazolam, followed by 0.4, 0.2 and 0.1 mg suriclone. 6. Psychometric investigations demonstrated no significant effects after the two lower doses of suriclone, while 0.4 mg and 1 mg alprazolam induced a decrement both in noopsychic and thymopsychic variables seen after higher doses of anxiolytic sedatives. Psychophysiology (critical flicker fusion, pupillometry, and skin conductance measures) pulse rate, systolic and diastolic blood pressure remained unchanged. 7. Psychophysiology (critical flicker fusion, pupillometry and skin conductance measures) showed differential dose-dependent effects. Pulse rate, systolic and diastolic blood pressure remained unchanged. Anxiolytic-characteristic side-effects (tiredness, drowsiness, etc.) occurred predominantly after the highest doses 0.4 mg suriclone and 1 mg alprazolam.

Administration, Oral↗

PubMedDate not supplied

[Creutzfeldt-Jakob disease. Clinical, electrophysiological and histopathological correlations].

Creutzfeldt-Jakob disease (CJD) is one of a small group of the so-called spongiform encephalopathies. It is a rare transmissible disorder which is characterized by progressive and irreversible neurological damage. There are few reports where clinical manifestations are correlated with neurophysiologic and histopathologic findings. The present paper includes three cases of CJD where alterations in evoked potentials and brain mapping studies gave valuable information, especially in those where the clinical picture and the electroencephalogram were non-specific, we conclude that these alterations suggest that the classic histopathological changes in C-J disease involves both cortical and subcortical structures.

Biopsy↗

PubMed1992

Use of moclobemide in children with attention deficit hyperactivity disorder.

A monoamine oxidase hypothesis for the cause of attention deficit hyperactivity disorder has recently been established (Shekim et al. 1986). To test this, moclobemide, a new and reversible inhibitor of monoamine oxidase-A, was administered to 12 children between the ages of 6 and 13 years, diagnosed as attention deficit hyperactive according to DSM III-R, in a 4-week study. All had previously discontinued treatment with methylphenidate due to side-effects. A 40% improvement in parental assessment of children's behaviour occurred among those who received moclobemide as outpatients, and a 31% improvement among the five in-patients. There was a general increase in concentration and attention span at the end of the trial, but mood changes and explosive behaviour continued to be present at a low level. Brain mapping after moclobemide treatment showed an overall reduction in frontal lobe delta activity. Moclobemide was well tolerated by these patients, although two complained of mild gastrointestinal disturbances during the first week of therapy.

Adolescent↗

PubMed2004

Comparison of TCA and ICA techniques in fMRI data processing.

PURPOSE: To make a quantitative comparison of temporal cluster analysis (TCA) and independent component analysis (ICA) techniques in detecting brain activation by using simulated data and in vivo event-related functional MRI (fMRI) experiments. MATERIALS AND METHODS: A single-slice MRI image was replicated 150 times to simulate an fMRI time series. An event-related brain activation pattern with five different levels of intensity and Gaussian noise was superimposed on these images. Maximum contrast-to-noise ratio (CNR) of the signal change ranged from 1.0 to 2.0 by 0.25 increments. In vivo visual stimulation fMRI experiments were performed on a 1.9 T magnet. Six human volunteers participated in this study. All imaging data were analyzed using both TCA and ICA methods. RESULTS: Both simulated and in vivo data have shown that no statistically significant difference exists in the activation areas detected by both ICA and TCA techniques when CNR of fMRI signal is larger than 1.75. CONCLUSION: TCA and ICA techniques are comparable in generating functional brain maps in event-related fMRI experiments. Although ICA has richer features in exploring the spatial and temporal information of the functional images, the TCA method has advantages in its computational efficiency, repeatability, and readiness to average data from group subjects

Brain Mapping↗

PubMedDate not supplied

Diffusion tensor MR imaging of the brain: effect of diffusion weighting on trace and anisotropy measurements.

BACKGROUND AND PURPOSE: In human brain, the relationship between MR signal and b value is complicated by cerebral perfusion, restricted diffusion, anisotropy, cellular membrane permeability, and active cellular transport of water molecules. Our purpose was to evaluate the effect of the number and strength of diffusion-sensitizing gradients on measured isotropic apparent diffusion coefficients (ADCi), fractional anisotropy (FA), and their respective SD in different anatomic locations of the brain. METHODS: Quantitative apparent diffusion coefficients and diffusion anisotropy brain maps were obtained from 10 healthy volunteers by using six different levels of diffusion weighting (b0 = 0, bl = 160, b2 = 320, b3 = 480, b4 = 640, and b5 = 800 s/mm2), applied sequentially in six different directions (Gxx, Gyy, Gzz, Gxy, Gxz, Gyz) and coupled to a single-shot spin-echo echo-planar (2,045/115 [TR/TE]) MR imaging technique. ADCi, FA, eigenvalues (lambda1, lambda2, lamdba3)1 of the principal eigenvectors, and their respective SD were measured from seven different anatomic locations in the brain. Repeated measures analysis of variance was used to evaluate for the existence of significant differences in the average and SD of the calculated ADCi and FA as a function of the number and strength of b values. When a difference existed, the Bonferroni t method was used for paired comparisons of the groups. RESULTS: The measured ADCi was affected by the number and strength of b values (P < .05). The SD of the ADCi was affected by the strength (P < .05) but not the number of b values (P > .05). The measured FA was unaffected by the number and strength of b values (P > .05). The SD was affected by the number and strength of b values (P < .05). CONCLUSION: The number and strength of b values do influence measures of diffusion and anisotropy. Attention to the choice of diffusion sensitization parameters is important in decisions regarding clinical feasibility (acquisition time) and normative measures.

Adult↗

PubMed2001

Neuroimaging databases.

These are comments written by the Governing Council of the Organization for Human Brain Mapping (OHBM), the primary international organization dedicated to neuroimaging research. The purpose of these comments is to identify and frame issues concerning data sharing within the neuroimaging community. Data sharing has become an important issue in most fields of science. The neuroimaging community is no exception, and it clearly perceives potential benefits in such efforts, as have been realized in other fields such as genomics. At the same time, such efforts can be costly (both in time and expense), and there are important factors that differentiate brain imaging from other fields and that pose specific challenges to the generation of useful neuroimaging databases. These include the rapid pace of change in brain imaging technologies; the complexity of the variables that must be specified to meaningfully interpret the results (such as the method of image acquisition, behavioral design, and subject characteristics); and concerns about participant confidentiality. These issues are outlined with the goal of framing and promoting a public discussion of the benefits and risks of data sharing, which can inform the field of neuroimaging as well as others that face similar challenges.

Brain↗

PubMed2002

Cortical deactivation induced by visual stimulation in human slow-wave sleep.

It has previously been demonstrated that sleeping and sedated young children respond with a paradoxical decrease in the blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal in the rostro-medial occipital visual cortex during visual stimulation. It is unresolved whether this negative BOLD response pattern is of developmental neurobiological origin particular to a given age or to a general effect of sleep or sedative drugs. To further elucidate this issue, we used fMRI and positron emission tomography (PET) to study the brain activation pattern during visual stimulation in spontaneously sleeping adult volunteers. In five sleeping volunteers fMRI studies confirmed a robust signal decrease during stimulation in the rostro-medial occipital cortex. A similar relative decrease at the same location was found during visual stimulation and polysomnographically verified slow-wave sleep in a separate group of six subjects using H(2)(15)O PET measures of the regional cerebral blood flow (rCBF). This decrease was more rostro-dorsal compared to the relative rCBF increase along the calcarine sulcus found during visual stimulation in the awake state. This study reconfirms the previously described paradoxical stimulation-correlated negative BOLD signal change in the rostro-medial occipital cortex, expanding this response mode to an age spectrum ranging from the newborn to the adult. Further, the use of complementary brain mapping techniques suggests that this decrease was secondary to a relative rCBF decrease. Possible mechanisms for the paradoxical response pattern during sleep include an active inhibition of the visual cortex or a disruption of an energy-consuming process.

Adult↗

PubMed2004

[Visualisation of phantom- and backpain using imaging techniques. Implication for treatment].

If patients with chronic low back pain are stimulated in the painful region, an expanded representation of the back in the primary somatosensory cortex becomes visible that increases with chronicity. This "pain memory" might play an important role in the chronicity process. In patients with phantom limb pain, e.g. subsequent to the amputation of an arm or leg, a shift in the representation of neighboring areas into the deafferented area in primary somatosensory cortex has been observed. This reorganization of functional brain maps is not present in congenital amputees or amputees without phantom limb pain. The magnitude of such pain is positively correlated with this reorganization. We present a model of phantom limb pain that assigns an important role to pre-existing chronic pain. The modulation of plasticity and phantom limb pain by anesthesiological manipulation, the use of NMDA receptor antagonists and opioids is presented. Behaviorally relevant stimulation, e.g. by the use of a myoelectric prosthesis or sensory discrimination training can also influence the cortical somatosensory pain memory. More recent studies focus also on brain areas such as the cingulate gyrus believed to be involved in the affective processing of pain.

Back Pain↗

PubMed1988

Characterization of the microtubule-activated ATPase of brain cytoplasmic dynein (MAP 1C).

We recently found that the brain cytosolic microtubule-associated protein 1C (MAP 1C) is a microtubule-activated ATPase, capable of translocating microtubules in vitro in the direction corresponding to retrograde transport. (Paschal, B. M., H. S. Shpetner, and R. B. Vallee. 1987b. J. Cell Biol. 105:1273-1282; Paschal, B. M., and R. B. Vallee. 1987. Nature [Lond.]. 330:181-183.). Biochemical analysis of this protein (op. cit.) as well as scanning transmission electron microscopy revealed that MAP 1C is a brain cytoplasmic form of the ciliary and flagellar ATPase dynein (Vallee, R. B., J. S. Wall, B. M. Paschal, and H. S. Shpetner. 1988. Nature [Lond.]. 332:561-563). We have now characterized the ATPase activity of the brain enzyme in detail. We found that microtubule activation required polymeric tubulin and saturated with increasing tubulin concentration. The maximum activity at saturating tubulin (Vmax) varied from 186 to 239 nmol/min per mg. At low ionic strength, the Km for microtubules was 0.16 mg/ml tubulin, substantially lower than that previously reported for axonemal dynein. The microtubule-stimulated activity was extremely sensitive to changes in ionic strength and sulfhydryl oxidation state, both of which primarily affected the microtubule concentrations required for half-maximal activation. In a number of respects the brain dynein was enzymatically similar to both axonemal and egg dyneins. Thus, the ATPase required divalent cations, calcium stimulating activity less effectively than magnesium. The MgATPase was inhibited by metavandate (Ki = 5-10 microM for the microtubule-stimulated activity), 1 mM NEM, and 1 mM EHNA. In contrast to other dyneins, the brain enzyme hydrolyzed CTP, TTP, and GTP at higher rates than ATP. Thus, the enzymological properties of the brain cytoplasmic dynein are clearly related to those of other dyneins, though the brain enzyme is unique in its substrate specificity and in its high sensitivity to stimulation by microtubules.

Adenosine Triphosphatases↗

PubMed1999

Neuropsychiatric dynamics: the study of mental illness using functional magnetic resonance imaging.

Functional magnetic resonance imaging (fMRI) is poised to make significant contributions to the study of neuropsychiatric illnesses. Whatever neural pathology attends such illnesses has proven subtle at best. By identifying predictable, regionally specific deficits in brain function, fMRI can suggest brain regions for detailed cellular analyses, provide valuable in vivo data regarding effective connectivity, provide a means to model the effects of various drug challenge paradigms, and characterize intermediate phenotypes in the search for the genes underlying mental illness. Nonetheless, as promising as fMRI appears to be in terms of its relative safety, repeatability, ability to generate individual brain maps and widespread availability, it is still subject to a number of unresolved conceptual conundrums inherited from earlier neuroimaging work. For example, functional neuroimaging has not generated any pathognomic findings in mental illness, has not established a clear link between neurophysiology and observable behavior, and has not resolved the potential confounds of medication. In this article, we will review the relevant historical background preceding fMRI, address methodological considerations in fMRI, and summarize recent fMRI findings in psychiatry. Finally, fMRI is being used to simplify the complex genetics of neuropsychiatric illness by generating quantitative and qualitative brain phenotypes.

Brain↗

PubMed2006

A preliminary fluorodeoxyglucose positron emission tomography study in healthy adults reporting dream-enactment behavior.

STUDY OBJECTIVES: To test the hypothesis that healthy adults reporting dream-enactment behavior (DEB+) have reduced cerebral metabolic rate for glucose (CMRgl) in regions preferentially affected in patients with dementia with Lewy bodies (DLB). DESIGN: Automated brain-mapping algorithms were used to compare regional fluorodeoxyglucose (FDG) positron emission tomography (PET) measurements from previously evaluated DEB cases and controls. SETTING: Tertiary-care academic medical centers. PARTICIPANTS: Seventeen cognitively normal patients with DEB+ and 17 control subjects (DEB-) who were individually matched for age (59 +/- 11 years), education level (16 +/- 4 years), sex (67% women), body mass index (26 +/- 4.8 kg/m2), first-degree relative with dementia (85%), and proportion of apolipoprotein E (APOE) e4 carriers (13 e4 carriers, 4 noncarriers). INTERVENTIONS: FDG-PET. MEASUREMENTS AND RESULTS: DEB was associated with significantly lower CMRgl in several brain regions known to be preferentially affected in both DLB and Alzheimer disease (parietal, temporal, and posterior cingulate cortexes) and in several other regions, including the anterior cingulate cortex (p < .001, uncorrected for multiple comparisons). The DEB-associated CMRgl reductions were significantly greater in the APOE e4 noncarriers than in the carriers. CONCLUSIONS: These preliminary findings suggest that cognitively normal persons with DEB have reduced CMRgl in brain regions known to be metabolically affected by DLB, supporting further study of DEB as a possible risk factor for the development of DLB.

Adult↗