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Results for “Functional Neuroimaging”

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PubMed2004

A functional neuroimaging study of motivation and executive function.

Executive functions, such as working memory, must intersect with functions that determine value for the organism. Functional imaging work in humans and single-unit recordings in non-human primates provide evidence that PFC might integrate motivational context with working memory. With functional magnetic resonance imaging (fMRI), we addressed the question of motivation and working memory, using a trial-related design in an object-working memory task. The design permitted the analysis of BOLD signal at separate stages, corresponding to encoding, maintenance, and retrieval. Subjects were motivated by a financial incentive during the task, such that they could gain a high or a low reward. The two different levels of reward also entailed greater or lesser risk of losing money for incorrect responses. In the high, relative to the low, reward condition, subjects shifted response bias, and showed a trend to greater sensitivity. We found main effects in fMRI BOLD signal for reward, which overlapped with BOLD effects for maintenance of information, in the right superior frontal sulcus and bilateral intraparietal sulcus. We also found an interaction between reward and retrieval from working memory in the right dorsolateral prefrontal cortex. Main effects of load and reward occurred in adjacent regions of the ventrolateral PFC during retrieval. The data demonstrate that when subjects perform a simple working memory task, financial incentives motivate performance and interact with some of the same neural networks that process various stages of working memory. Areas of overlap and interaction may integrate information about value, or they may represent a general effect of motivation increasing neural effort.

Adult↗

PubMed1998

A symbolic environment for visualizing activated foci in functional neuroimaging datasets.

This paper presents a symbolic visualization environment known as the Corner Cube environment, which was developed to facilitate rapid examination and comparison of activated foci defined by analyses of functional neuroimaging datasets. We have performed a comparative evaluation of this environment against maximum-intensity projection and 'gallery of slices' displays, and the results suggest that the Corner Cube environment has definite advantages over both conventional display techniques. We conclude that the Corner Cube is an effective tool for summarizing the spatial characteristics of activated foci within an easily understood visual context and is especially useful for displaying the similarities and differences in functional neuroimaging datasets.

Brain↗

PubMed2006

Forward inference using functional neuroimaging: dissociations versus associations.

Many people are excited by functional neuroimaging as a new tool for cognitive science; many others are sceptical. In this opinion article, I describe a 'forward inference' that one can make from patterns of brain activity to distinguish between cognitive theories. I give an example of forward inferences in research on recognition memory, and outline some statistical criteria for a 'qualitative difference' in brain activity. Forward inferences resemble the dissociation logic long-used in behavioural studies of healthy and brain-damaged people, although I argue that dissociations in neuroimaging data can go beyond behavioural dissociations. Nonetheless, forward inferences are only as good as the cognitive theories to which they pertain, and are most valuable in conjunction with other types of inference.

Association↗

PubMed2000

Functional neuroimaging and the neuroanatomy of obsessive-compulsive disorder.

Functional neuroimaging studies have advanced the understanding of the brain mediation of OCD by orbitofrontal-subcortical circuitry, but much is still unknown. Phenotypic heterogeneity could account for many of the inconsistencies among previous neuroimaging studies of OCD. Current studies are seeking to find the neurobiological basis of OCD symptom subtypes and predictors of treatment response. Future studies combining genetics and basic neuroanatomic research with neuroimaging may clarify the cause and pathophysiology of OCD. Although many lines of evidence point to dysfunction of orbitofrontal-subcortical circuitry in patients with OCD, many questions remain unanswered. Some have suggested that orbitofrontal-subcortical hyperactivity in OCD may be the result of abnormal neuroanatomic development of these structures or a failure of pruning of neuronal connections between them, as occurs in normal development, but no postmortem neuroanatomic studies of OCD exist to delineate its pathophysiology. Interventions that directly alter the indirect-direct pathway balance within frontal-subcortical circuits will allow for direct testing of the pathophysiologic hypotheses presented here. The roles of various neurochemical systems in OCD are similarly unclear. Although an abundance of indirect evidence suggests serotonergic abnormalities in patients with OCD, no direct evidence demonstrates what those abnormalities are or whether they are primary or secondary phenomena in patients with OCD. Ongoing studies of 5-HT synthesis in the brains of patients with OCD may shed light on this question.

Brain↗

PubMed2002

The neural basis of episodic memory: evidence from functional neuroimaging.

We review some of our recent research using functional neuroimaging to investigate neural activity supporting the encoding and retrieval of episodic memories, that is, memories for unique events. Findings from studies of encoding indicate that, at the cortical level, the regions responsible for the effective encoding of a stimulus event as an episodic memory include some of the regions that are also engaged to process the event 'online'. Thus, it appears that there is no single cortical site or circuit responsible for episodic encoding. The results of retrieval studies indicate that successful recollection of episodic information is associated with activation of lateral parietal cortex, along with more variable patterns of activity in dorsolateral and anterior prefrontal cortex. Whereas parietal regions may play a part in the representation of retrieved information, prefrontal areas appear to support processes that act on the products of retrieval to align behaviour with the demands of the retrieval task.

Brain Mapping↗

PubMed2001

[Functional neuroimaging in patients with rapid cycling bipolar depression].

Bipolar patients with a rapid cycling clinical course constitute an interesting sub-group for studies focused on the pathophysiology of the disorder, since several switches can be studied by the investigators in a short period of time. At present, functional neuroimaging techniques, as SPECT and PET, may be used for the neurobiological study of affective disorders. Few longitudinal functional neuroimaging studies assessing the different phases of bipolar disorder have been carried out. However, the published data suggest an asymmetrical temporal lobe dysfunction in depressive and manic phases of bipolar depression. Further studies with larger samples of patients are needed in order to improve our knowledge of the pathophysiology of bipolar disorder.

Bipolar Disorder↗

PubMed2004

Human functional neuroimaging in nicotine and tobacco research: basics, background, and beyond.

Modern functional neuroimaging techniques allow nicotine and tobacco researchers to investigate the neurobiological basis of addiction in humans. We introduce the methods and measures of the following neuroimaging techniques: Electroencephalography and event-related cortical potentials, positron emission tomography, and functional magnetic resonance imaging. We outline strengths and limitations across modalities and describe new and emerging technologies. We provide summaries of recent neuroimaging findings in the field of nicotine and tobacco research for neurochemistry, smoking and nicotine administration, craving and cue-reactivity, cognitive and affective information processing, and tobacco withdrawal. We address limitations of studies to date and identify opportunities for future research.

Affect↗

PubMed1999

[The contribution of functional neuroimaging to the understanding of schizophrenic psychosis].

Recent work on functional neuroimaging in schizophrenia is reviewed. The contribution of these studies is twofold: first, they help reintroducing some of the psychotic symptoms into the framework of well defined cognitive functions, such as representation of actions; second, they point to the implication of specific neural networks (including in the frontal and parietal lobes) in these dysfunctions.

Diagnostic Imaging↗

PubMed2003

Mapping form and function in the human brain: the emerging field of functional neuroimaging in cortical malformations.

Malformations of cortical development (MCDs) are increasingly being recognized as a common cause of epilepsy in cases previously felt to be cryptogenic. MCDs occur when the normal process of cerebral cortical development is disrupted, and include disorders of neuronal proliferation, migration, and organization. Many have a genetic basis and the genes responsible for some MCDs have been identified. MCDs represent a unique and valuable substrate in functional brain mapping studies, since as developmental lesions they provide complementary information to studies performed on patients with acquired brain lesions. In recent years an increasing number of functional neuroimaging methods, including positron emission tomography, single photon emission computed tomography, magnetic resonance spectroscopy, and functional magnetic resonance imaging, have been applied to patients with MCDs. In this review we highlight some of the prominent findings in this emerging field by presenting the functional neuroimaging characteristics of selected MCDs.

Brain Diseases↗

PubMed2026

Functional neuroimaging subtypes of obsessive-compulsive disorder: A systematic review and meta-analysis.

Obsessive-compulsive disorder (OCD) exhibits substantial clinical heterogeneity that may reflect underlying neurobiological diversity. Neuroimaging-based subtyping may advance precision psychiatry by identifying biologically distinct subgroups with differential treatment responses. This study systematically synthesized evidence from functional neuroimaging subtyping studies in OCD to identify reproducible neurobiological subtypes, characterize their clinical profiles, and establish a consensus-based classification framework. We reviewed 40 original studies employing machine learning, clustering, normative modeling, or classification approaches, encompassing approximately 8,150 patients. Consensus clustering identified three reproducible neurobiological subtypes. The Limbic-Hyperactive subtype, comprising approximately 40% of patients, exhibited amygdala and insula hyperconnectivity, elevated anxiety levels, predominant contamination and washing symptoms, and favorable response to cognitive-behavioral therapy. The Fronto-Striatal-Hypoconnected subtype, comprising approximately 35% of patients, demonstrated reduced orbitofrontal-striatal connectivity, cognitive inflexibility, predominant checking and ordering symptoms, and a favorable response to selective serotonin reuptake inhibitors. The Global-Disrupted subtype, comprising approximately 25% of patients, exhibited widespread connectivity disruption, greater symptom severity, and poor treatment response. Support vector machine classification achieved 81.5% accuracy for subtype assignment, though classification of OCD versus healthy controls showed limited generalizability in multisite settings (AUC 0.567-0.673). These findings support a neuroimaging-based framework for personalized treatment selection but require prospective validation.

Humans↗

PubMed2001

The contribution of functional neuroimaging to recovery after brain damage: a review.

The introduction of functional neuroimaging techniques has contributed to understanding the neural correlates of recovery of motor, sensory and cognitive functions after brain damage. In this paper, we review the literature of the past twenty years, with particular emphasis on quantitative studies of cerebral blood flow and metabolism. Studies are presented that examine recovery from hemiparesis, aphasia, spatial hemineglect and sensory disorders. The contribution of this research is critically discussed in a methodological perspective. A basic distinction is made between cerebral plasticity and recovery of functions. It is also argued that the most frequently used experimental designs do not permit directly relating changes in brain activity to functional recovery. The importance of accurate behavioural measures is underlined. Alternative experimental designs are proposed, based on correlations between behavioural performance and brain activations.

Brain↗

PubMed1999

Statistical limitations in functional neuroimaging. II. Signal detection and statistical inference.

The field of functional neuroimaging (FNI) methodology has developed into a mature but evolving area of knowledge and its applications have been extensive. A general problem in the analysis of FNI data is finding a signal embedded in noise. This is sometimes called signal detection. Signal detection theory focuses in general on issues relating to the optimization of conditions for separating the signal from noise. When methods from probability theory and mathematical statistics are directly applied in this procedure it is also called statistical inference. In this paper we briefly discuss some aspects of signal detection theory relevant to FNI and, in addition, some common approaches to statistical inference used in FNI. Low-pass filtering in relation to functional-anatomical variability and some effects of filtering on signal detection of interest to FNI are discussed. Also, some general aspects of hypothesis testing and statistical inference are discussed. This includes the need for characterizing the signal in data when the null hypothesis is rejected, the problem of multiple comparisons that is central to FNI data analysis, omnibus tests and some issues related to statistical power in the context of FNI. In turn, random field, scale space, non-parametric and Monte Carlo approaches are reviewed, representing the most common approaches to statistical inference used in FNI. Complementary to these issues an overview and discussion of non-inferential descriptive methods, common statistical models and the problem of model selection is given in a companion paper. In general, model selection is an important prelude to subsequent statistical inference. The emphasis in both papers is on the assumptions and inherent limitations of the methods presented. Most of the methods described here generally serve their purposes well when the inherent assumptions and limitations are taken into account. Significant differences in results between different methods are most apparent in extreme parameter ranges, for example at low effective degrees of freedom or at small spatial autocorrelation. In such situations or in situations when assumptions and approximations are seriously violated it is of central importance to choose the most suitable method in order to obtain valid results.

Biometry↗

PubMed2005

N-back working memory paradigm: a meta-analysis of normative functional neuroimaging studies.

One of the most popular experimental paradigms for functional neuroimaging studies of working memory has been the n-back task, in which subjects are asked to monitor the identity or location of a series of verbal or nonverbal stimuli and to indicate when the currently presented stimulus is the same as the one presented n trials previously. We conducted a quantitative meta-analysis of 668 sets of activation coordinates in Talairach space reported in 24 primary studies of n-back task variants manipulating process (location vs. identity monitoring) and content (verbal or nonverbal) of working memory. We found the following cortical regions were activated robustly (voxelwise false discovery rate = 1%): lateral premotor cortex; dorsal cingulate and medial premotor cortex; dorsolateral and ventrolateral prefrontal cortex; frontal poles; and medial and lateral posterior parietal cortex. Subsidiary meta-analyses based on appropriate subsets of the primary data demonstrated broadly similar activation patterns for identity monitoring of verbal stimuli and both location and identity monitoring of nonverbal stimuli. There was also some evidence for distinct frontoparietal activation patterns in response to different task variants. The functional specializations of each of the major cortical components in the generic large-scale frontoparietal system are discussed. We conclude that quantitative meta-analysis can be a powerful tool for combining results of multiple primary studies reported in Talairach space. Here, it provides evidence both for broadly consistent activation of frontal and parietal cortical regions by various versions of the n-back working memory paradigm, and for process- and content-specific frontoparietal activation by working memory.

Brain↗

PubMed2005

Functional neuroimaging during altered states of consciousness: how and what do we measure?

The emergence of functional neuroimaging has extended the doctrine of functional specificity of the brain beyond the primary stages of perception, language, and motor systems to high-level cognitive, personality, and affective systems. This chapter applies functional magnetic resonance imaging to another high-level realm of cognition and neurology to characterize cortical function in patients with disorders of consciousness. At first pass, this objective appears paradoxical because conventional investigations of a cognitive process require experimental manipulation. For example, to map the location of language-sensitive cortex, a language-related task is performed according to a temporal sequence that alternates the task with rest (no-task) periods. Application of this approach to the study of consciousness would require that levels of consciousness be similarly varied, this is an unlikely technique. Alternatively, another strategy is presented here where the focus is on functional brain activity elicited during various passive stimulations of patients who are minimally conscious. Comparisons between patients with altered states of consciousness due to brain injury and healthy subjects may be employed to infer readiness and potential to sustain awareness. As if a behavioral microscope, fMRI enables a view of occluded neural processes to inform medical practitioners about the health of the neurocircuity-mediating cognitive processes. An underlying point of view is that assessment of recovery potential can be enhanced by neuroimaging techniques that reveal the status of residual systems specialized for essential cognitive and volitional tasks for each patient. Thus, development of imaging techniques that assess the functional status of individual unresponsive patients is a primary goal. The structural integrity of injured brains is often compromised depending on the specific traumatic event, and, therefore, images cannot be grouped across patients, as is the standard practice for investigations of cognitive systems in healthy volunteers. This chapter addresses these challenges and discusses technique adaptations associated with passive stimulation, paradigm selection, and individual patient assessments, where there is "zero tolerance for error," and confidence in the results must meet the highest standards of care. Similar adaptations have been previously developed for the purpose of personalized planning for neurosurgical procedures by mapping the locations of essential functional systems such as language, perception, and sensory-motor functions for each individual patient. Rather than addressing the question of "how does the brain do consciousness" with these techniques, this chapter presents methods for assessment of neurocognitive health in specific patients with disorders of consciousness.

Attention↗

PubMed2003

Functional neuroimaging of genetic variation in serotonergic neurotransmission.

Serotonin (5-hydroxytryptamine; 5-HT) is a potent modulator of the physiology and behavior involved in generating appropriate responses to environmental cues such as danger or threat. Furthermore, genetic variation in 5-HT subsystem genes can impact upon several dimensions of emotional behavior including neuroticism and psychopathology, but especially anxiety traits. Recently, functional neuroimaging has provided a dramatic illustration of how a promoter polymorphism in the human 5-HT transporter (5-HTT) gene, which has been weakly related to these behaviors, is strongly related to the engagement of neural systems, namely the amygdala, subserving emotional processes. In this commentary, we discuss how functional neuroimaging can be used to characterize the effects of polymorphisms in 5-HT subsystem genes on the response of neural circuits underlying the generation and regulation of mood and temperament as well as susceptibility to affective illness. We argue that in time, such knowledge will allow us to not only transcend phenomenological diagnosis and represent mechanisms of disease, but also identify at-risk individuals and biological pathways for the development of new treatments.

Amygdala↗

PubMed1998

Physiologic aspects of event related paradigms in magnetic resonance functional neuroimaging.

In order to substantiate event related paradigms in magnetic resonance functional neuroimaging, we assessed the temporal and spatial characteristics of oxygenation-sensitive MRI responses to 1 s periods of visual activation in repetitive protocols. A main finding is a reduction of the functional contrast between conditions (reversing checkerboard vs. darkness) for decreasing interstimulus intervals yielding 4.5% signal change for 89 s, 4% for 9 s, 3% for 6 s, and 1% for 3 s, respectively. Although rapid repetitions of identical stimuli preclude the development of the full positive and negative MRI signal deflections, pertinent responses leave the spatial pattern of activated brain regions unaffected and result in identical maps. These findings suggest the use of interstimulus intervals of the order of the response time from stimulus onset to maximum signal strength (5-6 s in the visual system). The resulting distinction in time will allow for separate mapping of stimulus-related responses with spatially overlapping cortical representations.

Adult↗

PubMed1998

Neural correlates of attention and arousal: insights from electrophysiology, functional neuroimaging and psychopharmacology.

Attention and arousal are multi-dimensional psychological processes, which interact closely with one another. The neural substrates of attention, as well as the interaction between arousal and attention, are discussed in this review. After a brief discussion of psychological and neuropsychological theories of attention, event-related potential correlates of attention are discussed. Essentially, attention acts to modulate stimulus-induced electrical potentials (N100/P100, P300, N400), rather than generating any unique potentials of its own. Functional neuroimaging studies of attentional orienting, selective attention, divided attention and sustained attention (and its inter-dependence on underlying levels of arousal) are then reviewed. A distinction is drawn between the brain areas which are crucially involved in the top-down modulation of attention (the 'sources' of attention) and those sensory-association areas whose activity is modulated by attention (the 'sites' of attentional expression). Frontal and parietal (usually right-lateralised) cortices and thalamus are most often associated with the source of attentional modulation. Also, the use of functional neuroimaging to test explicit hypotheses about psychological theories of attention is emphasised. These experimental paradigms form the basis for a 'new generation' of functional imaging studies which exploit the dynamic aspect of imaging and demonstrate how it can be used as more than just a 'brain mapping' device. Finally, a review of psychopharmacological studies in healthy human volunteers outlines the contributions of the noradrenergic, cholinergic and dopaminergic neurotransmitter systems to the neurochemical modulation of human attention and arousal. While, noradrenergic and cholinergic systems are involved in 'low-level' aspects of attention (e.g. attentional orienting), the dopaminergic system is associated with more 'executive' aspects of attention such as attentional set-shifting or working memory.

Animals↗

PubMed2003

Comparative evaluation of concomitant structural and functional neuroimages in Rasmussen's encephalitis.

BACKGROUND AND PURPOSE: Rasmussen's encephalitis (RE) is a rare condition of unknown cause characterized by intractable seizures, progressive hemiparesis, mental impairment, and inflammatory histological findings in the cortex. The primary diagnosis is based on biopsy to confirm the typical clinical, electroencephalography, and brain imaging findings. The main objective of this study was to compare simultaneous structural and functional neuroimages in RE. METHODS: Concomitant magnetic resonance imaging and 2-deoxy-2-[18F]-fluoro-D-glucose positron emission tomography data from the authors' series of 5 children and 8 patients described in the literature were analyzed and compared. RESULTS: Typical early findings of RE include metabolic abnormalities (hypermetabolism and hypometabolism) starting in the frontal or temporal regions or, occasionally, involving the whole hemisphere. Focal abnormalities of cerebral glucose metabolism indicate lesions sooner and depict their extent better than concomitant magnetic resonance images. The major structural abnormality remains unilateral; however, contralateral frontal lobe hypometabolism or crossed cerebellar diaschisis can be a finding of this disease. Basal ganglia involvement and whole hemispheric metabolic abnormality appear typically only after several months of disease onset. CONCLUSION: Concomitant structural and functional neuroimaging provide possibly complementary information in the early noninvasive workup of RE and may facilitate the early diagnosis of this rare disorder.

Adolescent↗