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Results for “Functional Neuroimaging”

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At least 19 recordsLinked to original sources

PubMed2005

Renewal of the neurophysiology of language: functional neuroimaging.

Functional neuroimaging methods have reached maturity. It is now possible to start to build the foundations of a physiology of language. The remarkable number of neuroimaging studies performed so far illustrates the potential of this approach, which complements the classical knowledge accumulated on aphasia. Here we attempt to characterize the impact of the functional neuroimaging revolution on our understanding of language. Although today considered as neuroimaging techniques, we refer less to electroencephalography and magnetoencephalography studies than to positron emission tomography and functional magnetic resonance imaging studies, which deal more directly with the question of localization and functional neuroanatomy. This review is structured in three parts. 1) Because of their rapid evolution, we address technical and methodological issues to provide an overview of current procedures and sketch out future perspectives. 2) We review a set of significant results acquired in normal adults (the core of functional imaging studies) to provide an overview of language mechanisms in the "standard" brain. Single-word processing is considered in relation to input modalities (visual and auditory input), output modalities (speech and written output), and the involvement of "central" semantic processes before sentence processing and nonstandard language (illiteracy, multilingualism, and sensory deficits) are addressed. 3) We address the influence of plasticity on physiological functions in relation to its main contexts of appearance, i.e., development and brain lesions, to show how functional imaging can allow fine-grained approaches to adaptation, the fundamental property of the brain. In closing, we consider future developments for language research using functional imaging.

Aphasia↗

PubMed1999

Functional neuroimaging.

Functional neuroimaging represents an area of brain imaging that has undergone tremendous advancements in the last decade. It is now possible to design experiments that elucidate the functional interplay between brain regions that give rise to specific human cognitive processes. Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) form the core technologies that have allowed such studies. This article reviews the basis of these techniques, their strengths and limitations, the underlying neurophysiology, and the future of functional neuroimaging.

Brain↗

PubMedDate not supplied

[Schizophrenia: a brain disease. II. Functional neuroimaging].

Functional neuroimaging techniques constitute formidable tools to investigate the human brain in vivo. This possibility has led to a growing interest in these techniques in psychiatric research, particularly in the study of neural mechanism involved in schizophrenia. Three main lines of research have been developed in this field: 1. Patterns of brain activity in a rest condition or during cognitive task performance, 2. correlations between psychopathology and brain activity, and 3. investigations of neurochemical characteristics (neurotransmitters and neuroreceptors) of schizophrenic patients. However, despite of the great effort developed lately these studies have yielded little in the way of coherent pathophysiologic theories of schizophrenia. Future studies combining molecular biology and genetic techniques with structural and functional neuroimaging studies are needed in our purpose to explore the neural mechanisms involved in schizophrenia.

Brain↗

PubMedDate not supplied

Functional neuroimaging correlates of functional amnesia.

Especially in the field of memory encoding and retrieval, the results of functional neuroimaging have provided new insights in anatomico-functional interactions. In particular this holds true for the role of the prefrontal cortex in mnestic information processing, for the contribution and participation of the two hemispheres in various processes of information transmission, and for views on disturbed information processing after organically obvious and so-called psychogenic forms of memory impairments. This report particularly stresses the insights obtained by functional neuroimaging for probably environmentally triggered deficiencies in memory processing and discusses possible subtle neuroanatomical correlates of functional amnesias. It is especially emphasised that stress conditions and depressive states may modify the release of steroids (glucocorticoids) and transmitter agonists at the brain level with the consequence of selective memory disturbances which may manifest as a "mnestic block syndrome".

Amnesia↗

PubMed1997

The functional organization of working memory processes within human lateral frontal cortex: the contribution of functional neuroimaging.

Recent functional neuroimaging studies have provided a wealth of new information about the likely organization of working memory processes within the human lateral frontal cortex. This article seeks to evaluate the results of these studies in the context of two contrasting theoretical models of lateral frontal-lobe function, developed through lesion and electrophysiological recording work in non-human primates (Goldman-Rakic, 1994, 1995; Petrides, 1994, 1995). Both models focus on a broadly similar distinction between anatomically and cytoarchitectonically distinct dorsolateral and ventrolateral frontal cortical areas, but differ in the precise functions ascribed to those regions. Following a review of the relevant anatomical data, the origins of these two theoretical positions are considered in some detail and the main predictions arising from each are identified. Recent functional neuroimaging studies of working memory processes are then critically reviewed in order to assess the extent to which they support either, or both, sets of predictions. The results of this meta-analysis suggest that lateral regions of the frontal lobe are not functionally organized according to stimulus modality, as has been widely assumed, but that specific regions within the dorsolateral or ventrolateral frontal cortex make identical functional contributions to both spatial and non-spatial working memory.

Animals↗

PubMed2002

Hypotheses from functional neuroimaging studies.

Functional neuroimaging, especially positron emission tomography (PET) using various tracers, provided new insights into the pathophysiology of West syndrome in the past decade. Glucose PET studies revealed a unique corticosubcortical circuitry assumed to be involved in the age-dependent generalization of seizure activity leading to symmetric spasms. The findings strongly suggested that cortical abnormalities, mostly consistent with dysplastic lesions or diffuse cortical dysfunction due to an underlying systemic disorder, trigger brain stem nuclei and activate basal ganglia bilaterally. PET is also able to investigate developmental abnormalities of serotonergic and GABAergic neurotransmitter systems in vivo. Involvement of these systems in the pathophysiology of infantile spasms is strongly supported by animal data and can be further elucidated by future PET studies. In addition, the development of new PET tracers (such as neurotracers for imaging NMDA receptors) could help further clarify the role of altered neurotransmission in generation of spasms. This review of the most important functional neuroimaging findings illustrates how human PET and single photon emission computed tomography data help answer basic questions regarding the pathomechanisms involved in this often devastating condition and how these findings might facilitate development of a useful animal model of West syndrome.

Brain Diseases↗

PubMed2005

Defining the neurocircuitry of borderline personality disorder: functional neuroimaging approaches.

Functional neuroimaging recently has been used to localize brain dysfunction in borderline personality disorder (BPD). Initial studies have examined baseline activity or emotional reactivity, and our group has investigated what we consider to be a crucial interaction between negative emotion and behavioral (dys)control. This research is beginning to identify abnormal frontolimbic circuitry likely underlying core clinical features of this condition. We review the evidence for dysfunction in specific frontolimbic regions, leading to a mechanistic model of symptom formation in BPD. In addition, we offer an integration of these neuroimaging findings with developmental perspectives on the emergence of borderline psychopathology, focusing on the ways in which early psychosocial experience may interact with developing brain systems. We also consider possible mechanisms of psychotherapeutic change at the neural systems level in BPD. Finally, we propose that future neuroimaging studies of BPD should integrate multiple levels of observation (structural, functional, neurochemical, genetic, and clinical) in a model-driven fashion to further understand the dynamic relationship between biological and psychological factors in the development and treatment of this difficult condition.

Adolescent↗

PubMed1998

Brain activations in schizophrenia during a graded memory task studied with functional neuroimaging.

BACKGROUND: Functional neuroimaging experiments have implicated prefrontal cortex (PFC) in memory processes. Several studies of schizophrenic patients have shown failure of activation in the dorsolateral region of PFC (DLPFC). We used a graded memory challenge to characterize functional neuroanatomical differences between schizophrenic and control subjects. The graded manipulation of task demands enabled us to assess group differences in the context of normal and abnormal psychological task performance. METHODS: Memory-related activity was assessed using positron emission tomography in schizophrenic patients and age-matched controls during performance of a graded memory task. Subjects underwent scanning while learning and recalling word lists of variable length. RESULTS: We used a model that assessed linear and nonlinear effects of memory load. Nonlinear group differences in DLPFC activation were observed. Controls showed a steepening slope of DLPFC increase as task demands increased. By contrast, schizophrenic subjects showed initial DLPFC increases that fell away with increasing memory load. The DLPFC response in schizophrenic subjects was closely related to measured task performance. In addition, schizophrenic subjects failed to show task-related decreases in activity in the left superior temporal and inferior parietal gyrus. CONCLUSIONS: Patients with schizophrenia showed a failure in DLPFC activation only in the face of diminished performance measures, suggesting that a full characterization of task-related changes in DLPFC activation must consider performance levels. However, striking failures of deactivation in superior temporal and inferior parietal regions were independent of task performance, possibly reflecting a core abnormality of the condition.

Adult↗

PubMed2004

Lateralization of amygdala activation: a systematic review of functional neuroimaging studies.

Functional neuroimaging studies of emotion processing consistently report amygdala activation. Most of these studies observed lateralized amygdala activity, indicative of a clear hemisphere-specific processing difference between the left and right amygdalae. Because individual studies use varying paradigms and are limited by statistical power and sensitivity, it has remained unclear whether the left or the right amygdala is more consistently involved in emotional processing. By combining results across 54 fMRI and PET studies in a metaanalysis, we sought to establish if a common pattern of lateralized amygdala activation exists. Our findings indicate that across studies, the left amygdala is more often activated than the right amygdala, suggesting different roles for the left and right amygdalae in emotional processing. Further analysis showed that this predominant left amygdala activation is not significantly related to stimulus type, task instructions, differential habituation rates of the left and right amygdalae or elaborate processing. The results are discussed in relation to methodological and theoretical issues regarding functional brain asymmetry.

Amygdala↗

PubMed2000

Neurophysiologic basis of functional neuroimaging: animal studies.

Functional neuroimaging adds metabolic or biochemical information to that obtained with anatomic imaging, allowing localization of a neural function. Positron emission tomography and single photon emission tomography make use of radioactive tracers tagged to a molecule which can indicate glucose metabolism, oxygen consumption, or blood flow. Functional magnetic resonance imaging uses the different magnetic properties of oxyhemoglobin and deoxyhemoglobin to identify areas of increased blood flow, which, in turn, reflects neuronal activation. Magnetic resonance spectroscopic imaging, with magnetically labeled molecules, can be used to follow biochemical pathways. Functional neuroimaging is based on the experimental data that neuronal activation leads to increased metabolism. Uptake of glucose and oxygen increases to meet increased energy needs. The fractionally increased glucose appears to be taken up mostly by glia, which metabolize it through glycolysis. The end product, lactate, is released for neuronal uptake and subsequent oxidative phosphorylation. To meet these metabolic needs, blood flow increases to such an extent that overall capillary oxyhemoglobin concentration increases. This changes the magnetic signal in the region and permits functional magnetic resonance imaging studies. Recent data suggest that there is an initial decrease in the concentration of oxyhemoglobin which may be more spatially specific to the area of neuronal activation. Further refinements in functional neuroimaging will lead to improved understanding of the normal functional anatomy of the brain and will shed further light on the pathophysiology of many neurologic disorders.

Animals↗

PubMed1999

Functional neuroimaging in psychiatry.

Functional neuroimaging is one of the most powerful means available for investigating the pathophysiology of psychiatric disorders. In this review, we shall focus on the different ways that it can be employed to this end, describing the major findings in the field in the context of different methodological approaches. We will also discuss practical issues that are particular to studying psychiatric disorders and the potential contribution of functional neuroimaging to future psychiatric research.

Brain↗

PubMed2001

Frontal lobes and human memory: insights from functional neuroimaging.

The new functional neuroimaging techniques, PET and functional MRI (fMRI), offer sufficient experimental flexibility and spatial resolution to explore the functional neuroanatomical bases of different memory stages and processes. They have had a particular impact on our understanding of the role of the frontal cortex in memory processing. We review the insights that have been gained, and attempt a synthesis of the findings from functional imaging studies of working memory, encoding in episodic memory and retrieval from episodic memory. Though these different aspects of memory have usually been studied in isolation, we suggest that there is sufficient convergence with respect to frontal activations to make such a synthesis worthwhile. We concentrate in particular on three regions of the lateral frontal cortex--ventrolateral, dorsolateral and anterior--that are consistently activated in these studies, and attribute these activations to the updating/maintenance of information, the selection/manipulation/monitoring of that information, and the selection of processes/subgoals, respectively. We also acknowledge a number of empirical inconsistencies associated with this synthesis, and suggest possible reasons for these. More generally, we predict that the resolution of questions concerning the functional neuroanatomical subdivisions of the frontal cortex will ultimately depend on a fuller cognitive psychological fractionation of memory control processes, an enterprise that will be guided and tested by experimentation. We expect that the neuroimaging techniques will provide an important part of this enterprise.

Animals↗

PubMed2004

Functional neuroimaging of headaches.

Functional neuroimaging, mainly PET and functional MRI, is the main tool that allows the capturing of neurovascular events during a headache attack. In migraine, functional imaging has clarified the underlying pathophysiology of the visual aura, whereas in migraine without aura, brainstem findings suggest a dysfunctional pain system. In cluster headache, the activation and morphological changes seen in a region posterior and inferior to the hypothalamus has provided a useful therapeutic target using deep-brain stimulation. We will discuss the main neuroimaging findings pertaining to the pathophysiology of these two common headache disorders, migraine and cluster headache.

Headache Disorders↗

PubMed2000

Locating and fractionating working memory using functional neuroimaging: storage, maintenance, and executive functions.

Working memory encompasses the short-term store of information and operations on that information. We review functional neuroimaging studies that have attempted to determine cortical areas involved in working memory functions. Current research suggests distinct systems for verbal information, visual objects, and spatial locations. Passive storage buffers appear to be located in posterior brain areas, whereas active maintenance of the information involves ventrolateral prefrontal areas. More complex, executive operations appear to recruit dorsolateral prefrontal cortex and anterior cingulate cortex. The possible involvement of reciprocal circuits including frontal cortex, basal ganglia, and thalamus is also discussed.

Brain↗

PubMed2002

Functional neuroimaging in neurology and psychiatry.

How can functional neuroimaging be applied to clinical neurology and psychiatry? This article reviews selected contributions of functional neuroimaging to the clinical neurosciences. We review selected technical aspects of positron emission tomography, single photon emission tomography, and functional magnetic resonance imaging with a focus on the relative strengths and weaknesses of these techniques. Consumers of functional neuroimaging research are encouraged to consider the limitations of imaging techniques and theoretical pitfalls of cognitive task design when interpreting results of functional imaging studies. Then, we selectively review the contributions of functional neuroimaging to neurology and psychiatry, including the areas of epilepsy, stroke, chronic pain, schizophrenia, depression, and obsessive-compulsive disorder. Future directions of functional neuroimaging research are offered, with the emphasis that the best conclusions are informed by a convergence of research from functional neuroimaging, neurophysiological, and lesion studies.

Journal Article↗

PubMed2003

Controlling the familywise error rate in functional neuroimaging: a comparative review.

Functional neuroimaging data embodies a massive multiple testing problem, where 100,000 correlated test statistics must be assessed. The familywise error rate, the chance of any false positives is the standard measure of Type I errors in multiple testing. In this paper we review and evaluate three approaches to thresholding images of test statistics: Bonferroni, random field and the permutation test. Owing to recent developments, improved Bonferroni procedures, such as Hochberg's methods, are now applicable to dependent data. Continuous random field methods use the smoothness of the image to adapt to the severity of the multiple testing problem. Also, increased computing power has made both permutation and bootstrap methods applicable to functional neuroimaging. We evaluate these approaches on t images using simulations and a collection of real datasets. We find that Bonferroni-related tests offer little improvement over Bonferroni, while the permutation method offers substantial improvement over the random field method for low smoothness and low degrees of freedom. We also show the limitations of trying to find an equivalent number of independent tests for an image of correlated test statistics.

Brain↗

PubMed1999

Recent advances in functional neuroimaging.

New functional imaging techniques, including positron emission tomography, transcranial magnetic stimulation and functional magnetic resonance imaging, promise to allow the noninvasive study of haemodynamic, metabolic and activation parameters during acute migraine attacks in humans. These techniques are currently being applied to the study of the transient neurologic symptoms of the aura, as well as the painful headache phase of migraine. This review summarizes the most recent of these studies and discusses how they relate to the prevailing theories of migraine pathophysiology.

Humans↗

PubMed1997

Understanding functional neuroimaging methods based on neurovascular coupling.

Functional neuroimaging techniques are usually grouped according to the employed apparatus into functional magnetic resonance imaging techniques (fMRI), nuclear medicine approaches such as single photon emission tomography (SPET) or positron emission tomography (PET), and optical approaches (measurement of intrinsic signals, near infrared spectroscopy (NIRS)). However, the physiological parameters that are measured with these methods do not necessarily follow this technical classification. On the one hand, using different imaging modalities the same physiological parameters are measured and on the other hand, using the same imaging devices completely different physiological parameters can be assessed. The present article covers those functional neuroimaging methods which measure the vascular response to functional brain activation (PET, SPET, fMRI and NIRS). First, starting with the traditional grouping of these methods, it is outlined how the specific methods assess vascular changes associated with brain activation in order to localize brain function. Based on the understanding of the underlying physiological events, subsequently, a new classification of functional neuroimaging methods is proposed.

Animals↗