Functional MRI studies in disruptive behaviour disorders

Aggressive or antisocial behaviours with violations of social rules are the main features of disruptive behaviour disorders (DBDs), which are developmental diseases and include conduct disorder and oppositional defiant disorder. In the last decade, several efforts have been made to shed light on the biological underpinnings of DBDs. In this context, the main findings of functional magnetic resonance imaging studies in DBD are reported here. There are indications of neural dysfunctions in response to affective stimuli, especially regarding medial and orbitofrontal prefrontal cortex and connected subcortical structures.     

Functional MRI studies of auditory comprehension

The location of brain regions essential for auditory language comprehension is an important consideration in the planning of neurosurgical procedures that involve resections within the dominant temporal lobe. Language testing during intraoperative and extraoperative cortical stimulation has been the primary method for localizing these regions; however, noninvasive alternatives using functional neuroimaging have been sought. Here we report on a study of 14 subjects who listened passively to alternating sentences spoken in their native English language and in unfamiliar Turkish while functional magnetic resonance images were acquired. The English sentences produced strong activation within the left superior temporal sulcus in all subjects. Lesser activation was seen in homotopic right hemisphere locations in several subjects. In addition to these posterior temporal activations, 8 subjects also showed activation to English sentences in the left inferior frontal gyrus. Turkish sentences evoked no coherent region of activation in any subject. As both the Turkish and English sentences were read by the same speaker, and were matched for length, volume, and intonation, we conclude that the activation pattern evoked by the English sentences reflects auditory comprehension. This conclusion is further supported by additional control studies that have shown a markedly different pattern of activation by pure tone frequency glides. Hum. Brain Mapping 6:1–13, 1998. © 1998 Wiley-Liss, Inc.     

Diffusion tensor MRI of chemotherapy-induced cognitive impairment in non-CNS cancer patients: a review

Patients with non-central nervous system cancers often experience subtle cognitive deficits after treatment with cytotoxic agents. Therapy-induced structural changes to the brain could be one of the possible causes underlying these reported cognitive deficits. In this review, we evaluate the use of diffusion tensor imaging (DTI) for assessing possible therapy-induced changes in the microstructure of the cerebral white matter (WM) and provide a critical overview of the published DTI research on therapy-induced cognitive impairment. Both cross-sectional and longitudinal DTI studies have demonstrated abnormal microstructural properties in WM regions involved in cognition. These findings correlated with cognitive performance, suggesting that there is a link between reduced “WM integrity” and chemotherapy-induced impaired cognition. In this paper, we will also introduce the basics of diffusion tensor imaging and how it can be applied to evaluate effects of therapy on structural changes in cerebral WM. The review concludes with considerations and discussion regarding DTI data interpretation and possible future directions for investigating therapy-induced WM changes in cancer patients. This review article is part of a Special Issue entitled: Neuroimaging Studies of Cancer and Cancer Treatment.     

Functional MRI studies in awake rhesus monkeys: methodological and analytical strategies

The technical advances in hardware and software for multiunit recordings have made it easier to gather data from a large number of neurons for behavioral correlations. This paper discusses several such advances in implantable hardware, magnetic resonance imaging of electrodes in situ, and data analysis software for multiple simultaneous signals.     

Functional MRI and Wada studies in patients with interhemispheric dissociation of language functions

Rare patients with chronic epilepsy show interhemispheric dissociation of language functions on intracarotid amobarbital (Wada) testing. We encountered four patients with interhemispheric dissociation in 490 consecutive Wada language tests. In all cases, performance on overt speech production tasks was supported by the hemisphere contralateral to the seizure focus, whereas performance on comprehension tasks was served by the hemisphere with the seizure focus. These data suggest that speech production capacity is more likely to shift hemispheres than is language comprehension. Wada and fMRI language lateralization scores were discordant in three of the four patients. However, the two methods aligned more closely when Wada measures loading on comprehension were used to calculate lateralization scores. Thus, interhemispheric dissociation of language functions could explain some cases of discordance on Wada/fMRI language comparisons, particularly when the fMRI measure used is not sensitive to speech production processes.     

Functional MRI applications in epilepsy surgery

Functional magnetic resonance imaging (fMRI) is a non-invasive neuroimaging technique that has grown rapidly in popularity over the past decade. It is already prevalent in psychology, cognitive and basic neuroscience research and is being used increasingly as a tool for clinical decision-making in epilepsy. It has been used to determine language location and laterality in patients, sometimes eliminating the need for invasive tests. fMRI can been used pre-surgically to guide resection margins, preserving eloquent cortex. Other fMRI paradigms assessing memory, visual and somatosensory systems have limited clinical applications currently, but show great promise. Simultaneous recording of electroencephalogram (EEG) and fMRI has also provided insights into the networks underlying seizure generation and is increasingly being used in epilepsy centres. In this review, we present some of the current clinical applications for fMRI in the pre-surgical assessment of epilepsy patients, and examine a number of new techniques that may soon become clinically relevant.     

Functional MRI in children with epilepsy

Advances in brain mapping with functional magnetic resonance imaging (fMRI) have opened an important window into understanding how language is organized in the developing brain. Children with epilepsy, particularly those anticipating surgical intervention, may benefit from preoperative language localization with fMRI, thus minimizing the risk of incurring new deficits. Clinical applications of fMRI, however, await more information on how different linguistic skills are represented in the developing brain and how epileptic lesions impact on this organization at different stages of cognitive development. This article presents some of the current methods for brain mapping in children as well as early results using fMRI for language mapping in pediatric epilepsy. Copyright Copyright 1999 S. Karger AG, Basel     

Utility of Functional MRI in Pediatric Neurology

Functional MRI (fMRI), a tool increasingly used to study cognitive function, is also an important tool for understanding not only normal development in healthy children, but also abnormal development, as seen in children with epilepsy, attention-deficit/hyperactivity disorder, and autism. Since its inception almost 15 years ago, fMRI has seen an explosion in its use and applications in the adult literature. However, only recently has it found a home in pediatric neurology. New adaptations in study design and technologic advances, especially the study of resting state functional connectivity as well as the use of passive task design in sedated children, have increased the utility of functional imaging in pediatrics to help us gain understanding into the developing brain at work. This article reviews the background of fMRI in pediatrics and highlights the most recent literature and clinical applications.     

Functional MRI and Outcome in Traumatic Coma

Advances in task-based functional MRI (fMRI), resting-state fMRI (rs-fMRI), and arterial spin labeling (ASL) perfusion MRI have occurred at a rapid pace in recent years. These techniques for measuring brain function have great potential to improve the accuracy of prognostication for civilian and military patients with traumatic coma. In addition, fMRI, rs-fMRI, and ASL perfusion MRI have provided novel insights into the pathophysiology of traumatic disorders of consciousness, as well as the mechanisms of recovery from coma. However, functional neuroimaging techniques have yet to achieve widespread clinical use as prognostic tests for patients with traumatic coma. Rather, a broad spectrum of methodological hurdles currently limits the feasibility of clinical implementation. In this review, we discuss the basic principles of fMRI, rs-fMRI, and ASL perfusion MRI and their potential applications as prognostic tools for patients with traumatic coma. We also discuss future strategies for overcoming the current barriers to clinical implementation.     

Functional MRI using molecular imaging agents

Contrast agents for magnetic resonance imaging (MRI) have recently been used as cellular-level probes of neural function. New in vivo labeling strategies now enable researchers to follow plasticity of brain activation patterns and cellular structure over time. On the horizon is the prospect that molecular imaging agents specifically designed for functional imaging (fMRI) on a relatively fast timescale could offer an alternative to conventional hemodynamics-based approaches. Development of several MRI sensors has defined principles by which imaging agents for "molecular fMRI" can be constructed; application of engineered sensors for cellular-level correlates of neuronal activity would allow researchers to combine the noninvasiveness of MRI with spatial resolution of tens of microns and temporal resolution of 100ms or less. Facilitated by advances in imaging-agent delivery methods and model systems appropriate for high-resolution neuroimaging, novel molecular imaging strategies continue to potentiate MRI as a tool for mechanistic investigation of neural systems.     

Functional MRI Studies of Animal Models in Epilepsy

Summary:  Functional magnetic resonance imaging (fMRI) has become a widely used imaging modality in the past decade in both human studies and animal models. Epilepsy presents unique challenges for neuroimaging due to subject movement during seizures, and the need to correlate the timing of often unpredictable seizure events with fMRI data acquisition. These challenges can readily be overcome in animal models of epilepsy. Animal models also provide an opportunity to investigate the fundamental relationships between fMRI signals and brain electrical activity through invasive studies not possible in humans. fMRI studies in animal models of epilepsy can enable us to correctly interpret fMRI signal increases and decreases in human studies, ultimately elucidating specific networks that will be targeted for improved treatment of epilepsy.     

Functional MRI of sustained attention in bipolar mania

We examined sustained attention deficits in bipolar disorder and associated changes in brain activation assessed by functional magnetic resonance imaging (fMRI). We hypothesized that relative to healthy participants, those with mania or mixed mania would (1) exhibit incremental decrements in sustained attention over time, (2) overactivate brain regions required for emotional processing and (3) progressively underactivate attentional regions of prefrontal cortex. Fifty participants with manic/mixed bipolar disorder (BP group) and 34 healthy comparison subjects (HC group) received an fMRI scan while performing a 15-min continuous performance task (CPT). The data were divided into three consecutive 5-min vigilance periods to analyze sustained attention. Composite brain activation maps indicated that both groups activated dorsal and ventral regions of an anterior-limbic network, but the BP group exhibited less activation over time relative to baseline. Consistent with hypotheses 1 and 2, the BP group showed a marginally greater behavioral CPT sustained attention decrement and more bilateral amygdala activation than the HC group, respectively. Instead of differential activation in prefrontal cortex over time, as predicted in hypothesis 3, the BP group progressively decreased activation in subcortical regions of striatum and thalamus relative to the HC group. These results suggest that regional activation decrements in dorsolateral prefrontal cortex accompany sustained attention decrements in both bipolar and healthy individuals. Stable amygdala overactivation across prolonged vigils may interfere with sustained attention and exacerbate attentional deficits in bipolar disorder. Differential striatal and thalamic deactivation in bipolar disorder is interpreted as a loss of amygdala (emotional brain) modulation by the ventrolateral prefrontal-subcortical circuit, which interferes with attentional maintenance.     

Functional MRI in the early detection of dementias

Functional MRI is a non-invasive imaging technology that can illuminate regional brain activity during the performance of a task, such as a memory paradigm, or at rest. fMRI data can be acquired during a session in which MRI data is also acquired to measure grey and white matter regional brain structure, and these measures can be analyzed together to investigate the relationships between altered regional brain function, structure, and cognitive task performance in neurologic illness. Data will be reviewed on the application of fMRI to the early detection of physiologic abnormalities associated with neurodegenerative diseases that cause dementia, and to differential diagnosis of dementias. Recent fMRI work will also be reviewed on the identification of abnormalities in regional brain function prior to dementia, the use of these measures to predict cognitive decline, and their application in investigations of alterations in regional brain networks that subserve cognitive function. Finally, the use of fMRI as a biomarker in clinical trials of putative neurotherapeutics for dementias will be discussed.