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Results for “Functional Neuroimaging”

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PubMed1995

Coupling of brain activity and cerebral blood flow: basis of functional neuroimaging.

The coupling of brain cell function to the vascular system is the basis for a number of functional neuroimaging methods relevant for human studies. These include methods as diverse as functional magnetic resonance imaging, positron emission tomography, single photon emission tomography, optimal intrinsic signals, as well as near infrared spectroscopy, a method that may have imaging capabilities in the near future. These methods map a specific localized brain activation through a vascular response, such as an increase in cerebral blood flow or a change in blood oxygenation. To understand these direct maps to obtain high resolution maps of localized functional brain activity, a precise knowledge of the specific underlying physiological mechanisms and methodological properties and restrictions is essential. In this article, these fundamental physiological and methodological aspects will be discussed. After reviewing how the techniques cited obtain maps of functional activity, we will discuss our current knowledge of the physiology of coupling with particular reference to the functional imaging techniques. Specifically, we will consider the function, the mediators, and the hemodynamic mechanisms of coupling and point out potential interference by diet, and neurological disease.

Brain↗

PubMed2001

Exploring the neural bases of episodic and semantic memory: the role of structural and functional neuroimaging.

Exploration of the neural bases of episodic and semantic memory is best pursued through the combined examination of the effects of identified lesions on memory and functional neuroimaging of both normal people and patients when they engage in memory processing of various kinds. Both structural and functional neuroimaging acquisition and analysis techniques have developed rapidly and will continue to do so. This review briefly outlines the history of neuroimaging as it impacts on memory research. Next, what has been learned so far from lesion-based research is outlined with emphasis on areas of disagreement as well as agreement. What has been learned from functional neuroimaging, particularly emission tomography and functional magnetic resonance imaging, is then discussed, and some stress is placed on topics where the interpretation of imaging studies has so far been unclear. Finally, how functional and structural imaging techniques can be optimally used to help resolve three areas of disagreement in the lesion literature will be discussed. These disagreements concern what the hippocampus and perirhinal cortex contribute to memory; whether any form of priming depends on the medial temporal lobes; and whether remote episodic as well as semantic memories cease to depend on the medial temporal lobes. Although the discussion will show the value of imaging techniques, it will also emphasize some of the limitations of current neuroimaging studies.

Brain↗

PubMed2001

[Contribution of positron emission tomography to functional neuroimaging in Alzheimer's disease].

When combined with cognitive investigations, functional neuroimaging methods such as positron emission tomography allow to depict the neural substrates that underlie the neuropsychological alterations in Alzheimer's disease. Capitalising on the variance in both cognitive performances and resting cerebral metabolic rate of glucose (CMRGlc) in Alzheimer's disease, it is possible to correlate these two quantitative variables on a pixel-by-pixel basis and to generate maps showing the significant correlations in stereotaxic space. Some examples using this approach in the domain of memory disorders are presented in this brief review. We notably show that the localisation of the significant correlations differs from one memory system to another, as evaluated by clinical memory tasks. This approach also unravels the compensatory mechanisms that take place with evolution of the disease. Over and above its interest in clinical neuropsychology, this method constitutes a new source of inferences complementary to the classic activation paradigm in normal subjects, as the latter identifies the cerebral structures that are involved with, but not necessarily indispensable for, the normal execution of the task. This approach highlights the interest of combining functional neuroimaging and neuropsychology to better understand the neural substrates of cognitive deficits in both patients with memory disorders and elderly normal subjects.

Alzheimer Disease↗

PubMed2002

Nonparametric permutation tests for functional neuroimaging: a primer with examples.

Requiring only minimal assumptions for validity, nonparametric permutation testing provides a flexible and intuitive methodology for the statistical analysis of data from functional neuroimaging experiments, at some computational expense. Introduced into the functional neuroimaging literature by Holmes et al. ([1996]: J Cereb Blood Flow Metab 16:7-22), the permutation approach readily accounts for the multiple comparisons problem implicit in the standard voxel-by-voxel hypothesis testing framework. When the appropriate assumptions hold, the nonparametric permutation approach gives results similar to those obtained from a comparable Statistical Parametric Mapping approach using a general linear model with multiple comparisons corrections derived from random field theory. For analyses with low degrees of freedom, such as single subject PET/SPECT experiments or multi-subject PET/SPECT or fMRI designs assessed for population effects, the nonparametric approach employing a locally pooled (smoothed) variance estimate can outperform the comparable Statistical Parametric Mapping approach. Thus, these nonparametric techniques can be used to verify the validity of less computationally expensive parametric approaches. Although the theory and relative advantages of permutation approaches have been discussed by various authors, there has been no accessible explication of the method, and no freely distributed software implementing it. Consequently, there have been few practical applications of the technique. This article, and the accompanying MATLAB software, attempts to address these issues. The standard nonparametric randomization and permutation testing ideas are developed at an accessible level, using practical examples from functional neuroimaging, and the extensions for multiple comparisons described. Three worked examples from PET and fMRI are presented, with discussion, and comparisons with standard parametric approaches made where appropriate. Practical considerations are given throughout, and relevant statistical concepts are expounded in appendices.

Brain↗

PubMed1998

Neurobiology of cocaine-induced organic brain impairment: contributions from functional neuroimaging.

The present review is directed at imparting the current knowledge regarding functional neuroimaging as a tool for enhancing the understanding of cerebrophysiologic and neurobehavioral consequences of stimulant abuse. Stimulants like cocaine are capable of inducing clinically significant neurocognitive impairment through direct action on the brain, and indirectly through other organs that influence cerebral physiology. Neurochemical dysregulation including profound effects on the serotonergic and dopaminergic systems have substantial physiological and neurobehavioral consequences. Brain hemorrhages, transient ischemic attacks, strokes,and seizures frequently follow cocaine use. The residual cerebropathologic consequences of cocaine are seen only in significant or pronounced brain events when structural neuroimaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) are employed. However, recent research with newer functional neuroimaging techniques such as single photon emission, positron emission tomography, and quantitative electroencephalography have revealed high rates of significant alteration in brain function among cocaine users, with negative structural imaging studies. These findings are often associated with impairment on neuropsychological evaluation, also in the absence of positive findings on CT and MRI. Both cerebral metabolic and hypoperfusion anomalies are seen, especially in anterior and temporal brain regions. Observed changes can persist for months, and for some patients, may represent a permanent change in brain functioning.

Brain Ischemia↗

PubMed2001

Pharmacologic modulation of human cerebral activity: contribution of functional neuroimaging.

This article highlights the following: (1) How the tools of functional neuroimaging analyze the effect of drug therapy on the central nervous system; (2) how the interactions between the drugs and the cortical neuronal networks have illustrated new aspects of the concepts of cerebral neuroplasticity; and (3) how functional neuroimaging has proved to be a valuable tool in understanding the mechanisms that govern the therapeutic activity of experimental drugs.

Anticonvulsants↗

PubMed2004

Functional neuroimaging studies in restless legs syndrome.

Functional neuroimaging studies may contribute to elucidate pathophysiological mechanisms of the restless legs syndrome (RLS) which still remain unclear. Studies in patients with RLS have been performed using functional magnetic resonance imaging (fMRI), single photon emission computed tomography (SPECT) and, more recently, positron emission tomography (PET). SPECT and PET studies revealed some controversial results of the pre- and postsynaptic dopaminergic neurotransmission system and cerebral metabolism in RLS probably reflecting a dysfunction of the central dopaminergic system. However, it still has to be determined whether these alterations affect the nigrostriatal and/or other central dopaminergic systems like the diencephalospinal or mesolimbic pathway and whether they are the primary mechanisms or only secondary phenomena within the manifestation of RLS symptoms. A subtle receptor dysfunction or a synaptic dopaminergic deficit may play a major role. fMRI investigations of RLS patients revealed an activation in the red nuclei and brainstem close to the reticular formation during the symptomatic period, suggesting that subcortical cerebral generators are involved in the pathogenesis of RLS. However, both techniques are not yet clinically relevant methods to differentiate RLS from other movement disorders during sleep. Further investigations, especially at night when RLS symptoms are most pronounced, will lead to a better understanding of the mechanisms underlying RLS.

Brain↗

PubMed2006

Functional neuroimaging applications for assessment and rehabilitation planning in patients with disorders of consciousness.

OBJECTIVE: To describe the theoretic framework, design, and potential clinical applications of functional neuroimaging protocols in patients with disorders of consciousness. DATA SOURCES: Recent published literature and authors' own work. STUDY SELECTION: Studies using functional neuroimaging techniques to investigate cognitive processing in patients diagnosed with vegetative and minimally conscious state. DATA EXTRACTION: Not applicable. DATA SYNTHESIS: Positron-emission tomography activation studies suggest that the vegetative state represents a global disconnection syndrome in which higher order association cortices are functionally disconnected from primary cortical areas. In contrast, patterns of activation in functional magnetic resonance imaging studies of patients in the minimally conscious state show preservation of large-scale cortical networks associated with language and visual processing. CONCLUSIONS: Novel applications of functional neuroimaging in patients with disorders of consciousness may aid in differential diagnosis, prognostic assessment and identification of pathophysiologic mechanisms. Improvements in patient characterization may, in turn, provide new opportunities for restoration of function through interventional neuromodulation.

Auditory Perception↗

PubMed2003

Functional neuroimaging of malformations of cortical development.

Functional neuroimaging over the past 10 years has led to greater insights into the pathophysiology underlying symptomatic epilepsy. Such imaging has been used to localize cerebral dysfunction, predominantly through disturbances in metabolism or blood flow. Techniques available include single photon emission computed tomography (SPECT), positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). Although the use of these diagnostic techniques is widely reported for presurgical evaluation, there has been little work with specific reference to malformations of cortical development.

Adolescent↗

PubMed2002

MR atlas of the baboon brain for functional neuroimaging.

Mathematical co-registration of functional image data (e.g., positron emission tomography, PET) to anatomical magnetic resonance (MR) imaging data allows for objective associations between function and anatomy. Baboons are often used as non-human primate models for functional neuroimaging studies. In this work, a digital MR-based high-resolution atlas of the baboon brain was generated and evaluated for PET. The atlas was generated from six SPGR-MR datasets (centered at mid-sagittal line, AC-PC orientation) that were transformed into the space of one representative MR, averaged and resampled into PET space. The atlas was evaluated by comparing blood flow and dopamine receptor and serotonin transporter binding measures determined using regions-of-interest (ROIs) generated on each individual co-registered MR (ROI(i)) and the atlas-defined ROI template (ROI(ATLAS)). Common ROIs applied to all data included frontal cortex, temporal cortex, thalamus, caudate, putamen and cerebellum. High correlations (r(2)>0.87) were found between the ROI(i) and ROI(ATLAS) data for all radiotracers (linear regression across ROIs for each baboon). The average regression slope values ranged from 0.95 to 1.02 across radiotracers. Lastly, use of the atlas for statistical parametric mapping (SPM) of [15O]water data yielded good agreement with previous ROI(i) results. Overall, the digital MR-based atlas allowed for automatic co-registration, proved useful across a range of PET Studies, and is accessible electronically via the Internet.

Anatomy, Artistic↗

PubMed2000

[The pathophysiology of migraine: insights from functional neuroimaging].

Over the last 20 years, functional neuroimaging has led to major advances in the understanding of the pathophysiology of migraine. The migraine aura is characterized by the occurrence of an hypoperfusion of moderate intensity which is peculiar by its initial appearance in the posterior cortex and its anterior spread at a speed of about 2 to 3mm per minute, congruent with the migrainous march of neurologic deficit and reminiscent of the phenomenon of cortical spreading depression described in the laboratory animal after various neuronal aggressions. The hypoperfusion is followed by a phase of long-lasting hyperperfusion temporally dissociated from the headache, which seems rather to result from vasodilatation and inflammation of the extra-cerebral large vessels. Although this sequence of hypoperfusion followed by hyperperfusion would be consistent with an ischemic process, there is presently no formal argument in favour of such a process being operational in migraine aura. It is however possible that migrainous subjects are genetically susceptible to the development of some unknown process at the borderline between spreading depression and classic ischemia. In migraine without aura, the data indicate only rare and mild changes in brain perfusion, although there also exist isolated observations of pauci-symptomatic spreading bilateral hypoperfusion. Physiologic imaging has also documented the occurrence during migraine without aura of a dorsal mesencephalic activation in the vicinity of the raphé and the locus coeruleus, independent of the pain itself and which might represent the long sought-after "migraine generator". It remains unknown if this phenomenon is also present in migraine with aura. The main prevalent hypotheses attempting a synthesis of all the available data are briefly presented in the conclusion.

Brain↗

PubMed2006

Functional neuroimaging in the preoperative evaluation of children with drug-resistant epilepsy.

UNLABELLED: FUNCTIONAL NEUROIMAGING: Although the primary imaging modality in the management of epilepsy is magnetic resonance imaging MRI, functional neuroimaging with positron-emission tomography (PET) and single photon emission computed tomography (SPECT) often provides complementary information and, in a number of situations, provides unique information that cannot be obtained with MRI. The most commonly used PET tracers used for epilepsy evaluation are 2-deoxy-2-[(18)F]fluoro-D: -glucose (FDG) and [(11)C]flumazenil (FMZ). Recently, interictal PET with alpha-[(11)C]methyl-L: -tryptophan was found to be highly specific for the epileptic focus and can differentiate between epileptogenic and nonepileptogenic lesions in the same patient (e.g., in patients with tuberous sclerosis). DISCUSSION: In this review, we discuss clinical applications of these three PET tracers in drug-resistant temporal and extratemporal lobe epilepsy, selected epilepsy syndromes of childhood, lesional and nonlesional epilepsy, and the challenges of imaging secondary epileptic foci. A brief discussion of SPECT applications in epilepsy is also included. With further development of new tracers highly sensitive and specific for epileptogenic brain regions, the presurgical evaluation of refractory epilepsy will be greatly facilitated. Approximately 0.5 to 1.0% of the population suffer from epilepsy, of which 15-20% are intractable. Infants and children, whose seizures have a focal onset are refractory to anticonvulsants and are prolonged, tend to have the worst cognitive outcome [Meador KJ, Neurology 58 (Suppl 5):S21-S26, 2002]. Seizures themselves affect the developing brain and contribute to an adverse neurologic outcome (Holmes, Pediatric Neurology 33:1-110, 2005). CONCLUSION: Therefore, in treating children with intractable epilepsy, it is important to consider seizure control and to give allowance for normal cognitive development.

Brain Mapping↗

PubMed2001

Advances in functional neuroimaging methodology for the study of brain systems underlying human neuropsychological function and dysfunction.

Functional neuroimaging allows the non-invasive identification of distributed patterns of human brain activity associated with perceptual, congnitive, emotional and behavioral processes, in health and disease. Work in this field is methodologically intensive, requiring an interdisciplinary team of scientists to develop and apply rapidly advancing techniques. Here we focus upon the principles and methods of functional imaging, from hypothesis generation and study design, to subject recruitment and clinical characterization, neuropsychological paradigm development, image acquisition, image processing and statistical analysis, and data interpretation. The strengths and limitations of the various techniques are discussed, with an emphasis on positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), which have proven to be powerful tools for human brain mapping. The integration of these techniques with electroencephalography (EEG) and magnetoencephalography (MEG), which provide greater temporal information, is outlined. An understanding of such methodological issues is a necessary prerequisite to the development of new imaging methods with improved capabilities, to the careful application of existing methods to neuropsychological problems, and to the critical examination of planned or published studies.

Brain↗

PubMed2002

Functional neuroimaging studies of the amygdala in depression.

Here we review human functional neuroimaging studies suggesting that the amygdala may play a key role in depression. We begin by reviewing animal and human data concerning the function of the amygdala. We then compare these results with those of neuroimaging studies of normal human amygdala function. Finally, we discuss functional neuroimaging studies of the amygdala in depression in light of the animal and human data. We conclude that the initial studies of this disorder provide evidence of amygdala involvement. Furthermore, we suggest that the scope of the amygdala's involvement may go beyond its well-known role in fear to its more subtle and generalized role in modulating moment-to-moment vigilance levels.

Amygdala↗

PubMed2003

An expanded role for functional neuroimaging in schizophrenia.

Functional magnetic resonance imaging is a surprisingly versatile tool in the quest for disentangling the complexities of mental illnesses such as schizophrenia. Yet, the identification of pathognomonic physiological features of the illness or even a consensus regarding the interpretation of reported findings remain unfulfilled goals, in spite of the increasing sophistication of this technology. Nonetheless, by providing quantification of brain function during various cognitive challenges, functional MRI has been used to leap ahead of these quandaries to identify relationships between genetic variation and brain function. By examining recent findings and efforts to link these findings to genes, this article will review these exciting developments in schizophrenia research.

Brain Mapping↗

PubMedDate not supplied

[Functional neuroimaging of emotions and bipolar disorder].

In this review we comment the results of functional neuroimaging works of emotions on normal population and some parallelisms with the emotional changes of bipolar disorder correlated with their functional neuroimaging. Initially we refer the emotional ontogenetical development of human brain based on regional cerebral sanguineous flow evolution (FSC). Secondly we describe the differences of FSC between the externally generated emotions versus internally; between positive versus negative emotions and the correlation between FSC and some facial expressions. When FSC of bipolar disorder is compared with normal emotions on general population, we observe that temporal cortex, the prefrontal medial and insular anterior cortex, change their perfusion with the switch or the change of emotional expression. It is possible to determine if the findings obtained in samples of healthy subjects and bipolar patients converge in a dimensional model, or if on the contrary they support the categorical hypotheses, moving the emotional aspects to a second term on bipolar disorder.

Bipolar Disorder↗

PubMedDate not supplied

[Cognition and neural networks, a new perspective based on functional neuroimaging].

AIM: We went through a critical review of the current status of neuroimaging studies of cognition. Thus, we argue why the use of a neuronal network perspective could led us to a better understanding of cognition than a localizationism perspective. METHOD: The question about how cognitive functions are organized in the brain, comes from the very early lesions studies. Electrocortical stimulation and the intracorotid amytal procedure collaborate together with lesions studies to increase the knowledge about the organization of cognitive functions in the brain. Functional neuroimaging could help to this issue answering the following questions: where, when and how the activity is produced in the brain. Many of the functional neuroimaging studies have addressed the question of where the activity is located, but very few has been concentrated into describe the spatio temporal profiles of brain activity, and then how the neural networks which support cognition are organized. Taking into account just one of this perspectives (where or when) we could achieve a reductionism view of the problem. CONCLUSIONS: Executive function, memory or language are more distributed than located in just one area, even the different subprocesses that are included in each of this functions are supported by a network rather than a particular area. We analyze the current available functional neuroimaging techniques under this view and its possibilities to describe the neural networks which support cognition.

Brain↗

PubMed2006

Functional neuroimaging findings on the human perception of illusory contours.

Illusory contours (IC) have attracted a considerable interest in recent years to derive models of how sensory information is processed and integrated within the visual system. In addition to various findings from neuropsychology, neurophysiology, and psychophysics, several recent studies have used functional neuroimaging to identify the cerebral substrates underlying human perception of IC (in particular Kanizsa figures). In this paper, we review the results from more than 20 neuroimaging studies on IC perception and highlight the great diversity of findings across these studies. We then provide a detailed discussion about the localization ('where' debate) and the timing ('when' debate) of IC processing as suggested by functional neuroimaging. Cortical responses involving visual areas as early as V1/V2 and latencies as rapid as 100 ms have been reported in several studies. Particular issues concerning the role of the right hemisphere and the retinotopic encoding of IC are also discussed. These different findings are tentatively brought together to propose different hypothetical cortical mechanisms that might be responsible for the visual formation of IC. Several remaining questions on IC processing that could potentially be explored with functional neuroimaging techniques are finally emphasized.

Brain↗