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At least 487 records · Page 27Linked to original sources
PubMed1987

A sequential double-label 14C- and 3H-2-DG technique: validation by double-dissociation of functional states.

We investigated a double-label 2-DG protocol and method of analysis in which sequential injections of 3H- and 14C-2-DG were used to map brain metabolism during two distinct experimental treatments in the same animal. In initial studies, brain sections from rats given only 3H-2-DG or only 14C-2-DG were exposed on Ultrofilm and on X-ray film with an interposed sheet of mylar (X-ray/mylar). These studies were needed to determine whether, at the 50:1 3H:14C dose ratio used, 3H-2-DG uptake would be revealed only in Ultrofilm images and 14C-2-DG uptake only in X-ray/mylar images. We found that X-ray/mylar images indeed showed only 14C-2-DG uptake as 3H emissions were blocked by the protective coating of the film and the mylar. By contrast, Ultrofilm autoradiograms showed the 2-DG uptake pattern for both the 14C-2-DG and 3H-2-DG cases. We then examined autoradiograms from double-label cases in which 14C-2-DG and 3H-2-DG were sequentially given using a 100:1 3H:14C dose ratio, with a different treatment following each injection. As predicted from the single-label cases, activity in the X-ray/mylar images corresponded to the treatment that followed the 14C-2-DG injection, while the Ultrofilm images reflected both treatments and thus were not veridical representations of 3H label. This paper provides a solution to the contamination of Ultrofilm by 14C label in that we devised a subtraction algorithm using a computerized imaging system which removes the contaminating 14C from the Ultrofilm image, leaving a 'Difference' image of 3H-2-DG uptake. Difference images revealed activity consistent with the treatment that followed the 3H-2-DG injection. Thus, the X-ray/mylar and difference images separately indexed metabolic activity for two different functional states in the same subject. By allowing a subject to serve as its own control, this double-label method greatly increases the applicability and power of the 2-DG method.

Algorithms↗
PubMed2001

Functional magnetic resonance imaging during pantomiming tool-use gestures.

The purpose of this study was to identify the functional fields activated in relation to gestural movements. Using functional magnetic resonance imaging (fMRI), we mapped brain activity in ten right-handed, normal volunteers during activation and control tasks. The activation condition consisted of pantomiming tool-use gestures with either the left hand or right hand, whereas the control condition comprised repetitive, oppositional movements between thumb and index finger. Activated cortical regions were highly lateralized to the left hemisphere during pantomiming of tool use regardless of hand used. Praxis with either hand commonly activated the superior parietal lobule, supplementary motor area, premotor area of the left hemisphere, and cerebellar vermis. However, minimal activation occurred in the inferior parietal lobule, which has been known to be a critical area for praxis generation. Compared with left-hand praxis, right-hand praxis exhibited additional activation in the left putamen and posterior part of the left inferior temporal region. Our findings concur with neuropsychological observations that the left hemisphere in right-handers mediates programming and executing skilled movements and that, within the left hemisphere, praxis is predominantly subserved by the parietal lobe, supplementary motor area, and premotor area. However, unlike previous lesion studies, the results of our fMRI study suggested that the superior parietal lobule more likely than the inferior parietal lobule play an important role in gesture production.

Adult↗
PubMed2003

The functional neuroanatomy of visual conjunction search: a parametric fMRI study.

Visual conjunction search is proposed to be a multicomponent process which involves scaling and successive shifts of attention in space as well as object identification. Here, we first mapped brain areas sustaining the proposed attentional subprocesses and then tested whether their activity was modulated by search load, i.e., the number of shifts, as predicted by serial search models. Search load was manipulated indirectly by precueing a varying number of locations at which relevant objects were shown. Multiple subregions within the intraparietal sulcus (IPS) and the prefrontal cortex were activated after cueing. Activity in the right posterior IPS was modulated by the distance of attention shifts and in the left posterior IPS by "zooming out" to cover a large region of the visual field. More anterior subregions of the left IPS responded to object identification irrespective of the need for serial scanning. Corresponding regions in the right IPS were modulated parametrically with respect to search load, along with the right temporoparietal junction. These results support a functional segregation of subregions of the IPS. The posterior regions participate in large-scale shifts and scaling of the attentional focus and the anterior regions in object identification and rapid serial shifts during search. The sustained activation in the frontal eye fields after cueing suggests a role in maintaining attention in the periphery. Together with the findings in early visual areas from this experiment (Müller et al., 2003) the current observations are best accounted for by hybrid models of visual conjunction search, where parallel processing in visual and temporoparietal regions and serial scanning controlled by the right IPS cooperate.

Adult↗
PubMed1995

Use of implicit motor imagery for visual shape discrimination as revealed by PET.

Positron emission tomography (PET) can be used to map brain regions that are active when a visual object (for example, a hand) is discriminated from its mirror form. Chronometric studies suggest that viewers 'solve' this visual shape task by mentally modelling it as a reaching task, implicitly moving their left hand into the orientation of any left-hand stimulus (and conversely for a right-hand stimulus). Here we describe an experiment in which visual and somatic processing are dissociated by presenting right hands to the left visual field and vice versa. Frontal (motor), parietal (somatosensory) and cerebellar (sensorimotor) regions similar to those activated by actual and imagined movement are strongly activated, whereas primary somatosensory and motor cortices are not. We conclude that mental imagery is realized at intermediate-to-high order, modality-specific cortical systems, but does not require primary cortex and is not constrained to the perceptual systems of the presented stimuli.

Adult↗
PubMed2007

Serial vagus nerve stimulation functional MRI in treatment-resistant depression.

Vagus nerve stimulation (VNS) therapy has shown antidepressant effects in open acute and long-term studies of treatment-resistant major depression. Mechanisms of action are not fully understood, although clinical data suggest slower onset therapeutic benefit than conventional psychotropic interventions. We set out to map brain systems activated by VNS and to identify serial brain functional correlates of antidepressant treatment and symptomatic response. Nine adults, satisfying DSM-IV criteria for unipolar or bipolar disorder, severe depressed type, were implanted with adjunctive VNS therapy (MRI-compatible technique) and enrolled in a 3-month, double-blind, placebo-controlled, serial-interleaved VNS/functional MRI (fMRI) study and open 20-month follow-up. A multiple regression mixed model with blood oxygenation level dependent (BOLD) signal as the dependent variable revealed that over time, VNS therapy was associated with ventro-medial prefrontal cortex deactivation. Controlling for other variables, acute VNS produced greater right insula activation among the participants with a greater degree of depression. These results suggest that similar to other antidepressant treatments, BOLD deactivation in the ventro-medial prefrontal cortex correlates with the antidepressant response to VNS therapy. The increased acute VNS insula effects among actively depressed participants may also account for the lower dosing observed in VNS clinical trials of depression compared with epilepsy. Future interleaved VNS/fMRI studies to confirm these findings and further clarify the regional neurobiological effects of VNS.

Adult↗
PubMed2001

Dissociating neural correlates of cognitive components in mental calculation.

Mental calculation is a complex cognitive operation that is composed of a set of distinct functional processes. Using functional magnetic resonance imaging (fMRI), we mapped brain activity in healthy subjects performing arithmetical tasks and control tasks evoking a comparable load on visuo-constructive, linguistic, attentional and mnemonic functions. During calculation, as well as non-mathematical tasks, similar cortical networks consisting of bilateral prefrontal, premotor and parietal regions were activated, suggesting that most of these cortical areas do not exclusively represent modules for calculation but support more general cognitive operations that are instrumental but not specific to mental arithmetic. Significant differences between calculation and the non-mathematical tasks were found in parietal sub-regions, where non-arithmetic number or letter substitution tasks preferentially activated the superior parietal lobules whereas calculation predominantly elicited activation of the left dorsal angular gyrus and the medial parietal cortices. We interpret the latter activations to reflect sub-processes of mental calculation that are related to the processing of numerical representations during exact calculation and to arithmetical fact retrieval. Finally, we found that more complex calculation tasks involving the application of calculation rules increased activity in left inferior frontal areas that are known to subserve linguistic and working memory functions. Taken together, these findings help to embed the specific cognitive operation of calculation into a neural framework that provides the required set of instrumental components. This result may further inform the cognitive modeling of calculation and adds to the understanding of neuropsychological deficit patterns in patients.

Adult↗
PubMed1995

Different neural systems for the recognition of animals and man-made tools.

Using positron emission tomography, we mapped brain activity in normal volunteers during the recognition of visual stimuli representing living (animals) and non-living (artefacts) entities. The subjects had to decide whether pairs of visual stimuli were different representations of the same object, or different objects. Animal recognition was associated with activations in the inferior temporo-occipital areas, bilaterally, whereas artefact recognition engaged a predominantly left hemispheric network, involving the left dorsolateral frontal cortex. These findings, which concur with clinical observations in neurological patients, provide in vivo evidence for a fractionation of the neural substrates of semantic knowledge in man.

Adult↗
PubMedDate not supplied

Susceptibility induced MR line broadening: applications to brain iron mapping.

Magnetic susceptibility variations due to the presence of iron in neural tissue can result in a shift of local resonance frequency, decreased T2 resulting from water diffusion through local field gradients, and line broadening due to field inhomogeneity within a voxel. In this study, modified spin echo phase contrast pulse sequences were used to map proton resonance line widths in phantoms and in vivo. In agar gels containing varying concentrations of Fe3O4 (magnetite), line broadening mechanisms permitted accurate spatial localization of iron deposits from measurement of local resonance line widths. Furthermore, line widths estimated from the data were strongly correlated with iron concentrations, indicating the potential quantitative applications of the method. The technique was applied clinically to map iron in subacute brain hemorrhages. These data suggest that resonance line widths may be a useful measure of brain iron content.

Adult↗
PubMed2006

Event-related fMRI of myoclonic jerks arising from dysplastic cortex.

BACKGROUND: Malformations of cortical development can cause epileptiform activity and myoclonic jerks, yet EEG correlates of jerks can be difficult to obtain. METHODS: We studied a woman who had frequent episodes of persistent right-foot jerking since childhood. Ictal and interictal EEG had shown no localizing epileptiform activity. Functional imaging experiments were performed with concurrent video monitoring to document the timing of foot jerks. These studies mapped brain regions controlling voluntary right- and left-foot movements, and spontaneous right-foot jerks. RESULTS: High-resolution structural MR imaging revealed a dysplastic gyrus extending anteriorly off the left central sulcus. Event-related analysis of spontaneous jerks revealed prominent activation of the left precentral gyrus (right-foot motor area), bilateral medial frontal regions (supplementary motor area), and the dysplastic gyrus. Hemodynamic response modeling to foot jerks revealed the hemodynamic response peaked earlier in the dysplastic cortex and SMA regions than in the foot area. DISCUSSION: Event-related fMRI in a patient with spontaneous and induced epileptic foot jerks revealed brain regions active during jerks. The results of this analysis allowed us to tailor subsequent intracerebral recordings. Analysis of the timing of the hemodynamic response showed certain brain regions with an earlier rise in BOLD signal, suggesting a possible initiating role, or different hemodynamic response functions. Hemodynamic response timing should be considered carefully when interpreting event-related studies of epileptiform activity.

Adult↗
PubMed2002

Covert auditory attention generates activation in the rostral/dorsal anterior cingulate cortex.

The anterior cingulate cortex (ACC) is believed to mediate conscious information processing or high-capacity attention. However, previous functional imaging studies have largely relied on tasks that involve motor function as well as attention. The work from our group utilizing an auditory continuous performance task demonstrated increased activity in a caudal division of the ACC that borders the supplementary motor area (SMA). Activity in this region was attributed to motor responding as well as attention. In the present study, we used (15)O H(2)O positron emission tomography (PET) to map brain activation during nonmotor, covert auditory attention. Our hypothesis was that a different region within the ACC, anterior to the SMA, would be active during covert attention (CA). Six men and six women were asked to monitor aurally presented syllables presented at a 1-sec interstimulus interval. During the CA condition, subjects were asked to continuously discriminate target (.19 probability) from nontarget stimuli. Simultaneous recording of event-related potentials (ERPs) confirmed the discrimination of target and nontarget stimuli and the allocation of attention capacity. Comparison of the monitored versus nonmonitored presentation of stimuli demonstrated significant activity in a rostral/dorsal division of the right ACC, anterior to SMA. Other regions of activation included the lateral prefrontal cortex and posterior superior temporal gyrus in the left hemisphere, consistent with neurocognitive models of language and vigilance. We conclude that a rostral/dorsal subdivision of the right ACC is specific for conscious attention during auditory processing, in contrast to premotor response formation.

Adult↗
PubMed1998

The functional neuroanatomy of tinnitus: evidence for limbic system links and neural plasticity.

We used PET to map brain regions responding to changes in tinnitus loudness in four patients who could alter tinnitus loudness by performing voluntary oral facial movements (OFMs). Cerebral blood flow was measured in four patients and six controls at rest, during the OFM, and during stimulation with pure tones. OFM-induced loudness changes affected the auditory cortex contralateral to the ear in which tinnitus was perceived, whereas unilateral cochlear stimulation caused bilateral effects, suggesting a retrocochlear origin for their tinnitus. Patients, compared with controls, showed evidence for more widespread activation by the tones and aberrant links between the limbic and auditory systems. These abnormal patterns provide evidence for cortical plasticity that may account for tinnitus and associated symptoms. Although audiologic symptoms and examinations of these patients were typical, the unusual ability to modulate tinnitus loudness with an OFM suggests some caution may be warranted in generalizing these findings.

Acoustic Stimulation↗
PubMed2005

Pup suckling is more rewarding than cocaine: evidence from functional magnetic resonance imaging and three-dimensional computational analysis.

Nursing has reciprocal benefits for both mother and infant, helping to promote maternal behavior and bonding. To test the "rewarding" nature of nursing, functional magnetic resonance imaging was used to map brain activity in lactating dams exposed to their suckling pups versus cocaine. Suckling stimulation in lactating dams and cocaine exposure in virgin females activated the dopamine reward system. In contrast, lactating dams exposed to cocaine instead of pups showed a suppression of brain activity in the reward system. These data support the notion that pup stimulation is more reinforcing than cocaine, underscoring the importance of pup seeking over other rewarding stimuli during lactation.

Animals↗
PubMed1997

[Functional MRI in search of basal ganglia].

We investigated activation of the globus pallidus using conventional gradient echo sequence with a 1.5 tesla equipment. In accordance with complex finger tapping in the left hand, an increase in signal intensity from bilateral globus pallidus was attained, being grossly predominated on right side. On the other hand, activations in primary motor cortex were elicited mainly on right side, thereby being correctly accorded in attitude of on-off changes in signal intensity. fMRI in basal ganglia faces severer condition in detecting real activation, owing to influences to signal recording by ventricular pulsation, accumulation of iron by age, and differences in activation by the tasks applied. This study, however, suggests that fMRI of basal ganglia is a promising technique for mapping brain function in regard to correlations between cerebral cortex and deep structures.

Adolescent↗
PubMed1998

Localisation and characterisation of auditory perception through Functional Magnetic Resonance Imaging.

In the last few years, Functional Magnetic Resonance Imaging (fMRI) has been widely accepted as an effective tool for mapping brain activities in both the neurosensorial and the cognitive field. The present work aims to assess the possibility of using fMRI methods to perform a non-invasive evaluation of the human auditory function. To this end the cortical response to different non speech stimuli (pure tones, pulsed tones) was examined for ten subjects with no audiological impairment. Our findings point out some remarkable differences in both the spatial and the temporal features of the primary auditory cortex response to pulsed tones and to pure tones.

Adult↗
PubMed1998

Some relationships between skills in word-category recall and factors in adults' aphasia.

It has long been recognized that a basic dimension to the lexical organization of the brain is semantic, and some brain mapping studies have indicated that the brain fields are distinctly different from some grammatical classes. Findings from the present investigation showed consistent relationships between 29 aphasic adults' performances on tasks involving graphic and gestural skills and those involving sequential recall of spoken words from different word categories. Each adult received the Porch Index of Communication Abilities which relies upon the physical manipulation of objects to assess verbal, gestural, and graphic abilities. Scores on a test requiring recall of word strings of nouns, verbs, adverbs, adjectives, or prepositions were used to predict the subscale scores from the Graphic and Gestural factors of the index. Recall scores for verb and preposition were predictive of the aphasic subjects' performances on the Graphic subscale, and noun and preposition scores were predictors of subjects' scores on the Gestural subscale. The results are related to other research showing that verb and preposition skills are predictive of fine motor abilities of children with communication disorders and brain-mapping studies. Some discussion centers on possible overlapping functions of brain activity involving word categories, language, and fine motor skills.

Adult↗
PubMed2005

Brain structural mapping using a novel hybrid implicit/explicit framework based on the level-set method.

This paper presents a novel approach to feature-based brain image warping, by using a hybrid implicit/explicit framework, which unifies many prior approaches in a common framework. In the first step, we develop links between image warping and the level-set method, and we formulate the fundamental mathematics required for this hybrid implicit/explicit approach. In the second step, we incorporate the large-deformation models into these formulations, leading to a complete and elegant treatment of anatomical structure matching. In this latest approach, exact matching of anatomy is achieved by comparing the target to the warped source structure under the forward mapping and the source to the warped target structure under the backward mapping. Because anatomy is represented nonparametrically, a path is constructed linking the source to the target structure without prior knowledge of their point correspondence. The final point correspondence is constructed based on the linking path with the minimal energy. Intensity-similarity measures can be naturally incorporated in the same framework as landmark constraints by combining them in the gradient descent body forces. We illustrate the approach with two applications: (1) tensor-based morphometry of the corpus callosum in autistic children; and (2) matching cortical surfaces to measure the profile of cortical anatomic variation. In summary, the new mathematical techniques introduced here contribute fundamentally to the mapping of brain structure and its variation and provide a framework that unites feature and intensity-based image registration techniques.

Algorithms↗