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Functional MRI (functional + mri)
Selected AbstractsThe heterogeneity of causes and courses of attention-deficit/hyperactivity disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 5 2009H-C. Steinhausen Objective:, Attention-deficit / Hyperactivity Disorder (ADHD) is a frequent mental disorder with onset in childhood and persistence into adulthood in a sizeable number of people. Despite a rather simple clinical definition, ADHD has many facets because of frequent co-morbid disorders and varying impact on psychosocial functioning. Thus, there is considerable heterogeneity in various domains. Method:, A review of recent research findings in: i) selected domains of aetiology reflecting the role of genes, brain structures and functioning and the interplay of causal factors and ii) clinical heterogeneity in terms of co-morbidities, gender effects, courses and outcomes. Results:, Molecular genetic studies have identified a number of candidate genes which have a small effect on behavioural variation in ADHD. In the most recent Genome Scan Meta Analysis of seven ADHD linkage studies, genome-wide significant linkage was identified on chromosome 16. The volume of both the total brain and various regions including the prefrontal cortex, the caudate nucleus and the vermis of the cerebellum is smaller in ADHD. Functional MRI has documented a specific deficit of frontostriatal networks in ADHD. Integrative aetiological models have to take the interaction of gene and environment on various dysfunctions into account. Clinical heterogeneity results from frequent associations with various co-morbidities, the impact of the disorder on psychosocial functioning, and gender effects. Partly, these effects are evident also in the course and outcome of ADHD. Conclusion:, ADHD is a chronic mental disorder with a complex aetiology. So far, various neurobiological factors have been identified that need to be studied further to better understand their interaction with environmental factors. The clinical presentation and the long-term course of ADHD are manifold. [source] Functional MRI of visual cortex in sedated 18 month-old infants with or without periventricular leukomalaciaDEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 7 2001L T L Sie MD Functional MRI (fMRI) of the visual cortex was evaluated in 42 sedated 18-month-old infants (mean corrected age; 31 males, 11 females) with or without periventricular leukomalacia (PVL). Data from 14 infants could not be evaluated because of movement artefacts. Ten of the remaining 28 infants showed no significant fMRI response upon visual stimulation. In 18 infants, a significant signal change upon stimulation was found in the visual cortex: in 17 a signal decrease and in one a signal increase. Functional changes were located mainly in the anterior part of the visual cortex. Seven of the 28 infants had normal MRI and 21 showed variable occipital PVL. An fMRI response was equally frequent in infants without PVL (4 of 7 infants) and with PVL (14 of 21 infants). In conclusion, fMRI was shown to be feasible in sedated infants. No correlation was found between functional activation and the presence or absence of occipital PVL. Type of fMRI response (signal decrease) and localization (anterior part of the visual cortex) are different from those seen in adults, probably reflecting a combination of sedation effects and immaturity of the visual system. At present, fMRI is a highly promising research tool; its clinical relevance still has to be established. [source] Functional MRI Predicts Memory Performance after Right Mesiotemporal Epilepsy SurgeryEPILEPSIA, Issue 2 2005Jozsef Janszky Summary:,Purpose: Anterior temporal lobe resection (ATR) is a treatment option in drug-resistant epilepsy. An important risk of ATR is loss of memory because mesiotemporal structures contribute substantially to memory function. We investigated whether memory-activated functional MRI (fMRI) can predict postoperative memory loss after anterior temporal lobectomy in right-sided medial temporal lobe epilepsy (MTLE). Methods: We included 16 patients (10 women) aged 16,54 years. The mean age at epilepsy onset was 12.5 years (range, 1,26 years). The patients' mean Wechsler IQ score was 95.2 (range, 62,125). The activation condition of fMRI consisted of retrieval from long-term memory induced by self-paced performance of an imaginative walk. All but one patient had left-sided speech dominance according to speech-activated fMRI. Outside the scanner, we evaluated the pre- and postoperative visual memory retention by using Rey Visual Design Learning Test. Results: We found a correlation between the preoperative asymmetry index of memory- fMRI and the change between pre- and postsurgical measures of memory retention. Reduced activation of the mesiotemporal region ipsilateral to the epileptogenic region correlated with a favorable memory outcome after right-sided ATR. Conclusions: In light of the postoperative results, the theoretical implication of our study is that fMRI based on a simple introspective retrieval task measures memory functions. The main clinical implication of our study is that memory- fMRI might replace the invasive Wada test in MTLE by using a simple fMRI paradigm. Predictive power, however, will be studied in larger patient samples. Other studies are required for left-sided MTLE and neocortical epilepsies to assess the clinical usefulness of memory- fMRI. [source] A Sheep Model for the Study of Focal Epilepsy with Concurrent Intracranial EEG and Functional MRIEPILEPSIA, Issue 8 2002Helen I. Opdam Summary: ,Purpose: We describe a sheep model of penicillin-induced seizure activity using electroencephalography (EEG) and functional MRI (fMRI). Methods: Ten adult sheep were used. Spikes and seizures were generated by instillation of 8,000,10,000 IU of penicillin into the right prefrontal cortex via a specially designed port. Bilateral intracranial EEG was acquired by using carbon fiber electrodes. Animals had behavioral characterization of their seizures and were then anesthetized for fMRI studies. Functional MRI was performed at 1.5 and 3 Tesla by measuring blood oxygen level,dependent (BOLD) weighted signal intensity at different times during the evolution of seizures. Results: Behavioral seizures were associated with electrographic seizures. Intracranial EEG obtained in the MR scanner was of high quality. Focal spiking and seizures were seen in all animals and developed 11.3 ± 11.2 s and 17.3 ± 12.1 min after penicillin administration, respectively. An average of 13 ± 4.8 seizures were seen per animal, each lasting 27.3 ± 12.3 s. Functional MR images with little parenchymal artefact were obtained. Regional BOLD signal-intensity changes were observed during seizures at the seizure focus and ipsilateral amygdala. Conclusions: We have developed an animal model of partial epilepsy in which seizures can be reliably elicited with concurrent fMRI and intracranial EEG. During unilateral electrographic seizures, focal BOLD signal changes occurred at the seizure focus and ipsilateral amygdala, suggesting the presence of a cortico,subcortical loop. This observation illustrates the potential of the model for understanding seizure generation, spread, and possibly the consequences of repeated seizures on the brain. [source] Functional MRI of the visual cortex and visual testing in patients with previous optic neuritisEUROPEAN JOURNAL OF NEUROLOGY, Issue 3 2002A. R. Langkilde The volume of cortical activation as detected by functional magnetic resonance imaging (fMRI) in the visual cortex has previously been shown to be reduced following optic neuritis (ON). In order to understand the cause of this change, we studied the cortical activation, both the size of the activated area and the signal change following ON, and compared the results with results of neuroophthalmological testing. We studied nine patients with previous acute ON and 10 healthy persons served as controls using fMRI with visual stimulation. In addition to a reduced activated volume, patients showed a reduced blood oxygenation level dependent (BOLD) signal increase and a greater asymmetry in the visual cortex, compared with controls. The volume of visual cortical activation was significantly correlated to the result of the contrast sensitivity test. The BOLD signal increase correlated significantly to both the results of the contrast sensitivity test and to the Snellen visual acuity. Our results indicate that fMRI is a useful method for the study of ON, even in cases where the visual acuity is severely impaired. The reduction in activated volume could be explained as a reduced neuronal input; however, the greater asymmetry might point to a cortical reorganization as a consequence of neuronal damage. Future fMRI studies in ON will add to the understanding of the neural adaptive behaviour following ON. [source] Linking structural, metabolic and functional changes in multiple sclerosisEUROPEAN JOURNAL OF NEUROLOGY, Issue 4 2001Massimo Filippi In patients with multiple sclerosis (MS), conventional magnetic resonance imaging (MRI) has markedly improved our ability to detect the macroscopic abnormalities of the brain and spinal cord. New quantitative magnetic resonance (MR) approaches with increased sensitivity to subtle normal-appearing white matter (NAWM) and grey matter changes and increased specificity to the heterogeneous pathological substrates of MS may give information complementary to conventional MRI. Magnetization transfer imaging (MTI) and diffusion-weighted imaging (DWI) have the potential to provide important information on the structural changes occurring within and outside T2-visible lesions. Magnetic resonance spectroscopy (MRS) adds information on the biochemical nature of such changes. Functional MRI might quantify the efficiency of brain plasticity in response to MS injury and improve our understanding of the link between structural damage and clinical manifestations. The present review summarizes how the application of these MR techniques to the study of MS is dramatically changing our understanding of how MS causes irreversible neurological deficits. [source] Task-relevance and temporal synchrony between tactile and visual stimuli modulates cortical activity and motor performance during sensory-guided movementHUMAN BRAIN MAPPING, Issue 2 2009Sean K. Meehan Abstract Sensory-guided movements require the analysis and integration of task-relevant sensory inputs from multiple modalities. This article sought to: (1) assess effects of intermodal temporal synchrony upon modulation of primary somatosensory cortex (S1) during continuous sensorimotor transformations, (2) identify cortical areas sensitive to temporal synchrony, and (3) provide further insight into the reduction of S1 activity during continuous vibrotactile tracking previously observed by our group (Meehan and Staines 2007: Brain Res 1138:148,158). Functional MRI was acquired while participants received simultaneous bimodal (visuospatial/vibrotactile) stimulation and continuously tracked random changes in one modality, by applying graded force to a force-sensing resistor. Effects of intermodal synchrony were investigated, unbeknownst to the participants, by varying temporal synchrony so that sensorimotor transformations dictated by the distracter modality either conflicted (low synchrony) or supplemented (high synchrony) those of the target modality. Temporal synchrony differentially influenced tracking performance dependent upon tracking modality. Physiologically, synchrony did not influence S1 activation; however, the insula and superior temporal gyrus were influenced regardless of tracking modality. The left temporal-parietal junction demonstrated increased activation during high synchrony specific to vibrotactile tracking. The superior parietal lobe and superior temporal gyrus demonstrated increased activation during low synchrony specific to visuospatial tracking. As previously reported, vibrotactile tracking resulted in decreased S1 activation relative to when it was task-irrelevant. We conclude that while temporal synchrony is represented at higher levels than S1, interactions between inter- and intramodal mechanisms determines sensory processing at the level of S1. Hum Brain Mapp, 2009. © 2007 Wiley-Liss, Inc. [source] Imaging brain activity during natural vision using CASL perfusion fMRIHUMAN BRAIN MAPPING, Issue 7 2007Hengyi Rao Abstract Functional MRI (fMRI) has begun to be used to explore human brain activity during ecological and natural conditions. Arterial spin labeling (ASL) perfusion fMRI provides an appealing approach for imaging sustained brain activity during natural conditions because of its long-term temporal stability and ability to noninvasively quantify absolute cerebral blood flow (CBF). The present study used ASL perfusion fMRI to measure brain activation patterns associated with natural vision by concurrently recording CBF and blood oxygen level-dependent (BOLD) contrasts while subjects were freely viewing a cartoon movie. Reliable quantitative whole-brain CBF values (,60 mL/100g/min) as well as regional CBF values (45,80 mL/100g/min) were measured during movie viewing and resting states. The perfusion contrast revealed CBF increases in multiple visual pathway areas and frontal areas, and CBF decreases in ventromedial frontal cortex and superior temporal cortex during movie viewing compared to resting states. Concurrent BOLD contrast revealed similar but weaker activation and deactivation patterns. Regression analyses of both CBF data and BOLD data showed significant associations between activation in the middle temporal (MT) region and subjects' perception of motion. Region of interest analysis based on a priori literature-defined MT demonstrated significant monotonic stepwise associations between the intensity of motion perception and the CBF and BOLD signal changes. These results demonstrate the feasibility of using ASL perfusion fMRI for imaging both sustained and dynamic effects in neural activation during natural and ecologically valid situations, and support the notion of maintained functional segregation and specialization during natural vision. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source] A developmental fMRI study of self-regulatory controlHUMAN BRAIN MAPPING, Issue 11 2006Rachel Marsh Abstract We used functional magnetic resonance imaging (fMRI) to investigate the neural correlates of self-regulatory control across development in healthy individuals performing the Stroop interference task. Proper performance of the task requires the engagement of self-regulatory control to inhibit an automatized response (reading) in favor of another, less automatic response (color naming). Functional MRI scans were acquired from a sample of 70 healthy individuals ranging in age from 7 to 57 years. We measured task-related regional signal changes across the entire cerebrum and conducted correlation analyses to assess the associations of signal activation with age and with behavioral performance. The magnitude of fMRI signal change increased with age in the right inferolateral prefrontal cortex (Brodmann area [BA] 44/45) and right lenticular nucleus. Greater activation of the right inferolateral prefrontal cortex also accompanied better performance. Activity in the right frontostriatal systems increased with age and with better response inhibition, consistent with the known functions of frontostriatal circuits in self-regulatory control. Age-related deactivations in the mesial prefrontal cortex (BA 10), subgenual anterior cingulate cortex (BA 24), and posterior cingulate cortex (BA 31) likely represented the greater engagement of adults in self-monitoring and free associative thought processes during the easier baseline task, consistent with the improved performance on this task in adults compared with children. Although we cannot exclude the possibility that age-related changes in reading ability or in the strategies used to optimize task performance were responsible for our findings, the correlations of brain activation with performance suggest that changes in frontostriatal activity with age underlie the improvement in self-regulatory control that characterizes normal human development. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source] Functional MRI: An introduction to methodsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2003Jonathan S. Lewin M.D. [source] Evidence for enhanced functional activity of cervical cord in relapsing multiple sclerosisMAGNETIC RESONANCE IN MEDICINE, Issue 5 2008F. Agosta Abstract Functional MRI (fMRI) was used to assess proprioceptive-associated cervical cord activity in 24 relapsing multiple sclerosis (MS) patients and 10 controls. Cord and brain conventional and diffusion tensor (DT) MRI were also acquired. fMRI was performed using a block design during a proprioceptive stimulation consisting of a passive flexion-extension of the right upper limb. Cord lesion number, cross-sectional area, mean diffusivity (MD) and fractional anisotropy (FA), whole brain and left corticospinal tract lesion volume (LV), gray matter (GM) MD, and normal-appearing white matter (NAWM) MD and FA were calculated. MS patients had higher average cord fMRI signal changes than controls (3.4% vs. 2.7%, P = 0.03). Compared to controls, MS patients also had a higher average signal change in the anterior section of the right cord at C5 (P = 0.005) and left cord at C5,C6 (P = 0.03), whereas no difference was found in the other cord sections. Cord average signal change correlated significantly with cord FA and brain left corticospinal tract LV, GM-MD, and NAWM-FA. This study shows an abnormal pattern of activations in the cervical cord of MS patients following proprioceptive stimulation. Cord fMRI changes might have a role in limiting the clinical consequences of MS associated with irreversible tissue damage. Magn Reson Med 59:1035,1042, 2008. © 2008 Wiley-Liss, Inc. [source] BOLD contrast sensitivity enhancement and artifact reduction with multiecho EPI: Parallel-acquired inhomogeneity-desensitized fMRIMAGNETIC RESONANCE IN MEDICINE, Issue 6 2006Benedikt A. Poser Abstract Functional MRI (fMRI) generally employs gradient-echo echo-planar imaging (GE-EPI) to measure blood oxygen level-dependent (BOLD) signal changes that result from changes in tissue relaxation time T between activation and rest. Since T strongly varies across the brain and BOLD contrast is maximal only where the echo time (TE) equals the local T, imaging at a single TE is a compromise in terms of overall sensitivity. Furthermore, the long echo train makes EPI very sensitive to main field inhomogeneities, causing strong image distortion. A method is presented that uses accelerated parallel imaging to reduce image artifacts and acquire images at multiple TEs following a single excitation, with no need to increase TR. Sensitivity gains from the broadened T coverage are optimized by pixelwise weighted echo summation based on local T or contrast-to-noise ratio (CNR) measurements. The method was evaluated using an approach that allows differential BOLD CNR to be calculated without stimulation, as well as with a Stroop experiment. Results obtained at 3 T showed that BOLD sensitivity improved by 11% or more in all brain regions, with larger gains in areas typically affected by strong susceptibility artifacts. The use of parallel imaging markedly reduces image distortion, and hence the method should find widespread application in functional brain imaging. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Functional MRI of the rodent somatosensory pathway using multislice echo planar imaging,MAGNETIC RESONANCE IN MEDICINE, Issue 1 2004Shella D. Keilholz Abstract A multislice EPI sequence was used to obtain functional MR images of the entire rat brain with BOLD contrast at 11.7 T. Ten to 11 slices covering the rat brain, with an in-plane resolution of 300 ,m, provided enough sensitivity to detect activation in brain regions known to be involved in the somatosensory pathway during stimulation of the forelimbs. These regions were identified by warping a digitized rat brain atlas to each set of images. Data analysis was constrained to four major areas of the somatosensory pathway: primary and secondary somatosensory cortices, thalamus, and cerebellum. Incidence maps were generated. Electrical stimulation at 3 Hz led to significant activation in the primary sensory cortex in all rats. Activation in the secondary sensory cortex and cerebellum was observed in 70% of the studies, while thalamic activation was observed in 40%. The amplitude of activation was measured for each area, and average response time courses were calculated. Finally, the frequency dependence of the response to forepaw stimulation was measured in each of the activated areas. Optimal activation occurred in all areas at 3 Hz. These results demonstrate that whole-brain fMRI can be performed on rodents at 11.7 T to probe a well-defined neural network. Magn Reson Med 52:89,99, 2004. Published 2004 Wiley-Liss, Inc. [source] Regional activation in the rat brain during visceral stimulation detected by c- fos expression and fMRINEUROGASTROENTEROLOGY & MOTILITY, Issue 4 2005J. Lazovic Abstract, Aim:, The aim of the study was to determine and compare the areas of brain activated in response to colorectal distention (CRD) using functional magnetic resonance imaging (fMRI) and c- fos protein expression. Methods:, For fMRI study (3.0 T magnet), anaesthetized rats underwent phasic CRD, synchronized with fMRI acquisition. Stimulation consisted of eight cycles of balloon deflation (90 s) and inflation (30 s), at 40, 60 or 80 mmHg of pressure. For c- fos study two sets of experiments were performed on anaesthetized rats: comparing (A) brain activation in rats with the inserted colorectal balloon (n = 5), to the rats without the balloon (n = 5); and (B) rats with inserted balloon (n = 10), to the rats with inserted and distended balloon (n = 10). The pressure of 80 mmHg was applied for 2 h of 30 s inflation and 90 s deflation, alternating cycles. Results:, Functional MRI revealed significant activation in the amygdala, hypothalamus, thalamus, cerebellum and hippocampus. Significant increase in c- fos expression was observed in amygdala and thalamus in the first set of experiments, and hypothalamus and parabrachial nuclei in the second. Conclusion:, The two methods are not interchangeable but appeared to be complementary: fMRI was more sensitive, whereas c- fos had much greater resolution. [source] Endogenous functional CBV contrast revealed by diffusion weightingNMR IN BIOMEDICINE, Issue 8 2006Todd B. Harshbarger Abstract Functional MRI (fMRI) based on the blood oxygenation level dependent (BOLD) contrast often suffers from a lack of specificity because of the vascular spread of oxygenation changes. It is suggested from the optical imaging and animal fMRI literature that cerebral blood volume (CBV) changes are more closely tied to the smaller vessels. As such, fMRI contrast based on CBV changes will have improved spatial specificity to the neuronal activities as they are immediately adjacent to the smaller vessels. In this paper, an endogenous contrast mechanism based on a diffusion weighting strategy that could detect functional CBV changes is presented. Initially, a theoretical framework is presented to model the functional signal changes as a function of CBV under diffusion weighting, which predicts peak CBV sensitivity at various vessel,tissue mixtures. It was found that a b factor over 1500,s/mm2 would be necessary to achieve dominant CBV contrast. Further, two sets of experimental results are also presented. In the first experiment, diffusion weighting at a set of b factors ranging from 300 to 600,s/mm2 was used. The results indicated that while the positive activation (predominantly BOLD signal) continued to reduce in magnitude and spatial extent, the negative activation (predominantly CBV signal) remained virtually constant with increasing b factors. The second experiment used a b factor of 1600,s/mm2 and showed extensive negative activation in the visual cortex and greatly reduced positive activations compared with images with no diffusion weighting. The time course of negative activation showed a faster time to peak and return to baseline than the positive BOLD activity, consistent with the small vessel origin of the signal changes. These results suggest that appropriate diffusion weighting could be used to measure activation related CBV changes. Copyright © 2006 John Wiley & Sons, Ltd. [source] Stimulation of the rat somatosensory cortex at different frequencies and pulse widthsNMR IN BIOMEDICINE, Issue 1 2006N. Van Camp Abstract Functional MRI (fMRI) during electrical somatosensory stimulation of the rat forepaw is a widely used model to investigate the functional organization of the somatosensory cortex or to study the underlying mechanisms of the blood oxygen level-dependent (BOLD) response. In reality, somatosensory stimuli have complex timing relationships and are of long duration. However, by default electrical sensory stimulation seems to be performed at an extremely short pulse width (0.3,ms). As the pulse duration may alter the neuronal response, our aim was to investigate the influence of a much longer stimulus pulse width (10,ms) using BOLD fMRI during electrical forepaw stimulation. The optimal neuronal response was investigated by varying the stimulus frequency at a fixed pulse duration (10,ms) and amplitude (1,mA). In a parallel experiment we measured the neuronal response directly by recording the somatosensory evoked potentials (SEPs). Quantification of the BOLD data revealed a shift in the optimal response frequencies to 8,10,Hz compared with 1,Hz at 0.3,ms. The amplitude of the recorded SEPs decreased with increasing stimulation frequency and did not display any correlation with the BOLD data. Nevertheless, the summated SEPs, which are a measure of the integrated neuronal activity as a function of time, displayed a similar response profile, with a similar maximum as observed by relative BOLD changes. This shift in optimal excitation frequencies might be related to the fact that an increased pulse width of an electrical stimulus alters the nature of the stimulation, generating also sensorimotor instead of merely somatosensory input. This may influence or alter the activated pathways, resulting in a shift in the optimal response profile. Copyright © 2006 John Wiley & Sons, Ltd. [source] DICHOTOMY OF CORTICAL PAIN PROCESSINGPAIN MEDICINE, Issue 2 2002Article first published online: 4 JUL 200 Jahangir Maleki, Rollin M. Gallagher, Pain Medicine and Rehabilitation Center, MCP/Hahnemann School of Medicine Introduction: Functional MRI and PET studies of cortical pain processing indicate segregated pain pathways above the thalamus. Although experimental pain may result in multiple areas of altered cortical activity, it is postulated that thalamic pain fibers known as the lateral system, projecting to sensory cortex, serve to localize pain, whereas medial pathways projecting to limbic cortex, process affective aspects of pain. Case Study: A 27 y/o female, with left upper extremity pain and severe allodynia from Complex Regional Pain Syndrome, Type I (CRPS I / RSD), after receiving intra-pleural bupivacaine blocks developed an ipsilateral focal-onset secondary generalized tonic clonic seizure. This was followed by one hour of post-ictal confusion. Simultaneously she developed a dense left-sided motor and sensory deficit (Todd's palsy) with a motor deficit resolving in one day whereas a sensory deficit lasted 2 days. Throughout the duration of the sensory deficit she denied any left arm pain, although she continued to report the same intensity of pain, but now localized to her epigastric region. Interestingly, despite the lack of sensory perception on the left side, palpation of her left arm resulted in increased epigastric pain and suffering. Discussion: This case indicates a bifurcation of the pain pathway between the thalamus and cortex. Due to focal seizure activity, the sensory cortex (i.e. lateral system) was transiently rendered dysfunctional, during which time the continued presence of pain and allodynia without appropriate localization likely resulted from pain conduction, from the thalamus to functional limbic structures such as Cingulum (i.e. via the medial fibre system). Conclusion: This case report strongly supports the hypothesis of medial and lateral pain conducting fibers branching at the level of thalamus with medial sub-serving the emotional aspects of pain by projection to limbic cortex, whereas lateral fibres project to sensory cortex, primarily serving a localizing function. [source] Perfusion-based functional magnetic resonance imaging,CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003Afonso C. Silva Abstract The measurement of cerebral blood flow (CBF) is a very important way of assessing tissue viability, metabolism, and function. CBF can be measured noninvasively with magnetic resonance imaging (MRI) by using arterial water as a perfusion tracer. Because of the tight coupling between neural activity and CBF, functional MRI (fMRI) techniques are having a large impact in defining regions of the brain that are activated due to specific stimuli. Among the different fMRI techniques, CBF-based fMRI has the advantages of being specific to tissue signal change, a critical feature for quantitative measurements within and across subjects, and for high-resolution functional mapping. Unlike the conventional blood oxygenation level dependent (BOLD) technique, the CBF change is an excellent index of the magnitude of neural activity change. Thus, CBF-based fMRI is the tool of choice for longitudinal functional imaging studies. A review of the principles and theoretical backgrounds of both continuous and pulsed arterial spin labeling methods for measuring CBF is presented, and a general overview of their current applications in the field of functional brain mapping is provided. In particular, examples of the use of CBF-based fMRI to investigate the fundamental hemodynamic responses induced by neural activity and to determine the signal source of the most commonly used BOLD functional imaging are reviewed. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 16A: 16,27, 2003 [source] Neural correlates of movement generation in the ,at-risk mental state'ACTA PSYCHIATRICA SCANDINAVICA, Issue 4 2010M. R. Broome Broome MR, Matthiasson P, Fusar-Poli P, Woolley JB, Johns LC, Tabraham P, Bramon E, Valmaggia L, Williams SCR, Brammer MJ, Chitnis X, McGuire PK. Neural correlates of movement generation in the ,at-risk mental state'. Objective:, People with ,prodromal' symptoms have a very high risk of developing psychosis. We examined the neurocognitive basis of this vulnerability by using functional MRI to study subjects with an at-risk mental state (ARMS) while they performed a random movement generation task. Method:, Cross-sectional comparison of individuals with an ARMS (n = 17), patients with first episode schizophreniform psychosis (n = 10) and healthy volunteers (n = 15). Subjects were studied using functional MRI while they performed a random movement generation paradigm. Results:, During random movement generation, the ARMS group showed less activation in the left inferior parietal cortex than controls, but greater activation than in the first episode group. Conclusion:, The ARMS is associated with abnormalities of regional brain function that are qualitatively similar to those in patients who have recently presented with psychosis but less severe. [source] A shift from diffuse to focal cortical activity with developmentDEVELOPMENTAL SCIENCE, Issue 1 2006Sarah Durston Recent imaging studies have suggested that developmental changes may parallel aspects of adult learning in cortical activation becoming less diffuse and more focal over time. However, while adult learning studies examine changes within subjects, developmental findings have been based on cross-sectional samples and even comparisons across studies. Here, we used functional MRI in children to test directly for shifts in cortical activity during performance of a cognitive control task, in a combined longitudinal and cross-sectional study. Our longitudinal findings, relative to our cross-sectional ones, show attenuated activation in dorsolateral prefrontal cortical areas, paralleled by increased focal activation in ventral prefrontal regions related to task performance. [source] Language lateralization in temporal lobe epilepsy using functional MRI and probabilistic tractographyEPILEPSIA, Issue 8 2008Sebastian Rodrigo Summary Purpose: Language functional magnetic resonance imaging (fMRI) is used to noninvasively assess hemispheric language specialization as part of the presurgical work-up in temporal lobe epilepsy (TLE). White matter asymmetries on diffusion tensor imaging (DTI) may be related to language specialization as shown in controls and TLE. To refine our understanding of the effect of epilepsy on the structure,function relationships, we focused on the arcuate fasciculus (ArcF) and the inferior occipitofrontal fasciculus (IOF) and tested the relationship between DTI- and fMRI-based lateralization indices in TLE. Methods: fMRI with three language tasks and DTI were obtained in 20 patients (12 right and 8 left TLE). The ArcF, a major language-related tract, and the IOF were segmented bilaterally using probabilistic tractography to obtain fractional anisotropy (FA) lateralization indices. These were correlated with fMRI-based lateralization indices computed in the inferior frontal gyrus (Pearson's correlation coefficient). Results: fMRI indices were left-lateralized in 16 patients and bilateral or right-lateralized in four. In the ArcF, FA was higher on the left than on the right side, reaching significance in right but not in left TLE. We found a positive correlation between ArcF anisotropy and fMRI-based lateralization indices in right TLE (p < 0.009), but not in left TLE patients. No correlation was observed for the IOF. Conclusions: Right TLE patients with more left-lateralized functional activations also showed a leftward-lateralized arcuate fasciculus. The decoupling between the functional and structural indices of the ArcF underlines the complexity of the language network in left TLE patients. [source] Functional MRI Predicts Memory Performance after Right Mesiotemporal Epilepsy SurgeryEPILEPSIA, Issue 2 2005Jozsef Janszky Summary:,Purpose: Anterior temporal lobe resection (ATR) is a treatment option in drug-resistant epilepsy. An important risk of ATR is loss of memory because mesiotemporal structures contribute substantially to memory function. We investigated whether memory-activated functional MRI (fMRI) can predict postoperative memory loss after anterior temporal lobectomy in right-sided medial temporal lobe epilepsy (MTLE). Methods: We included 16 patients (10 women) aged 16,54 years. The mean age at epilepsy onset was 12.5 years (range, 1,26 years). The patients' mean Wechsler IQ score was 95.2 (range, 62,125). The activation condition of fMRI consisted of retrieval from long-term memory induced by self-paced performance of an imaginative walk. All but one patient had left-sided speech dominance according to speech-activated fMRI. Outside the scanner, we evaluated the pre- and postoperative visual memory retention by using Rey Visual Design Learning Test. Results: We found a correlation between the preoperative asymmetry index of memory- fMRI and the change between pre- and postsurgical measures of memory retention. Reduced activation of the mesiotemporal region ipsilateral to the epileptogenic region correlated with a favorable memory outcome after right-sided ATR. Conclusions: In light of the postoperative results, the theoretical implication of our study is that fMRI based on a simple introspective retrieval task measures memory functions. The main clinical implication of our study is that memory- fMRI might replace the invasive Wada test in MTLE by using a simple fMRI paradigm. Predictive power, however, will be studied in larger patient samples. Other studies are required for left-sided MTLE and neocortical epilepsies to assess the clinical usefulness of memory- fMRI. [source] A Sheep Model for the Study of Focal Epilepsy with Concurrent Intracranial EEG and Functional MRIEPILEPSIA, Issue 8 2002Helen I. Opdam Summary: ,Purpose: We describe a sheep model of penicillin-induced seizure activity using electroencephalography (EEG) and functional MRI (fMRI). Methods: Ten adult sheep were used. Spikes and seizures were generated by instillation of 8,000,10,000 IU of penicillin into the right prefrontal cortex via a specially designed port. Bilateral intracranial EEG was acquired by using carbon fiber electrodes. Animals had behavioral characterization of their seizures and were then anesthetized for fMRI studies. Functional MRI was performed at 1.5 and 3 Tesla by measuring blood oxygen level,dependent (BOLD) weighted signal intensity at different times during the evolution of seizures. Results: Behavioral seizures were associated with electrographic seizures. Intracranial EEG obtained in the MR scanner was of high quality. Focal spiking and seizures were seen in all animals and developed 11.3 ± 11.2 s and 17.3 ± 12.1 min after penicillin administration, respectively. An average of 13 ± 4.8 seizures were seen per animal, each lasting 27.3 ± 12.3 s. Functional MR images with little parenchymal artefact were obtained. Regional BOLD signal-intensity changes were observed during seizures at the seizure focus and ipsilateral amygdala. Conclusions: We have developed an animal model of partial epilepsy in which seizures can be reliably elicited with concurrent fMRI and intracranial EEG. During unilateral electrographic seizures, focal BOLD signal changes occurred at the seizure focus and ipsilateral amygdala, suggesting the presence of a cortico,subcortical loop. This observation illustrates the potential of the model for understanding seizure generation, spread, and possibly the consequences of repeated seizures on the brain. [source] Dopamine gene predicts the brain's response to dopaminergic drugEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007Michael X Cohen Abstract Dopamine is critical for reward-based decision making, yet dopaminergic drugs can have opposite effects in different individuals. This apparent discrepancy can be accounted for by hypothesizing an ,inverted-U' relationship, whereby the effect of dopamine agents depends on baseline dopamine system functioning. Here, we used functional MRI to test the hypothesis that genetic variation in the expression of dopamine D2 receptors in the human brain predicts opposing dopaminergic drug effects during reversal learning. We scanned 22 subjects while they engaged in a feedback-based reversal learning task. Ten subjects had an allele on the Taq1A DRD2 gene, which is associated with reduced dopamine receptor concentration and decreased neural responses to rewards (A1+ subjects). Subjects were scanned twice, once on placebo and once on cabergoline, a D2 receptor agonist. Consistent with an inverted-U relationship between the DRD2 polymorphism and drug effects, cabergoline increased neural reward responses in the medial orbitofrontal cortex, cingulate cortex and striatum for A1+ subjects but decreased reward responses in these regions for A1, subjects. In contrast, cabergoline decreased task performance and fronto-striatal connectivity in A1+ subjects but had the opposite effect in A1, subjects. Further, the drug effect on functional connectivity predicted the drug effect on feedback-guided learning. Thus, individual variability in how dopaminergic drugs affect the brain reflects genetic disposition. These findings may help to explain the link between genetic disposition and risk for addictive disorders. [source] Correction for pulse height variability reduces physiological noise in functional MRI when studying spontaneous brain activityHUMAN BRAIN MAPPING, Issue 2 2010Petra J. van Houdt Abstract EEG correlated functional MRI (EEG-fMRI) allows the delineation of the areas corresponding to spontaneous brain activity, such as epileptiform spikes or alpha rhythm. A major problem of fMRI analysis in general is that spurious correlations may occur because fMRI signals are not only correlated with the phenomena of interest, but also with physiological processes, like cardiac and respiratory functions. The aim of this study was to reduce the number of falsely detected activated areas by taking the variation in physiological functioning into account in the general linear model (GLM). We used the photoplethysmogram (PPG), since this signal is based on a linear combination of oxy- and deoxyhemoglobin in the arterial blood, which is also the basis of fMRI. We derived a regressor from the variation in pulse height (VIPH) of PPG and added this regressor to the GLM. When this regressor was used as predictor it appeared that VIPH explained a large part of the variance of fMRI signals acquired from five epilepsy patients and thirteen healthy volunteers. As a confounder VIPH reduced the number of activated voxels by 30% for the healthy volunteers, when studying the generators of the alpha rhythm. Although for the patients the number of activated voxels either decreased or increased, the identification of the epileptogenic zone was substantially enhanced in one out of five patients, whereas for the other patients the effects were smaller. In conclusion, applying VIPH as a confounder diminishes physiological noise and allows a more reliable interpretation of fMRI results. Hum Brain Mapp, 2010. © 2009 Wiley-Liss, Inc. [source] Noninvasive dynamic imaging of seizures in epileptic patientsHUMAN BRAIN MAPPING, Issue 12 2009Louise Tyvaert Abstract Epileptic seizures are due to abnormal synchronized neuronal discharges. Techniques measuring electrical changes are commonly used to analyze seizures. Neuronal activity can be also defined by concomitant hemodynamic and metabolic changes. Simultaneous electroencephalogram (EEG)-functional MRI (fMRI) measures noninvasively with a high-spatial resolution BOLD changes during seizures in the whole brain. Until now, only a static image representing the whole seizure was provided. We report in 10 focal epilepsy patients a new approach to dynamic imaging of seizures including the BOLD time course of seizures and the identification of brain structures involved in seizure onset and discharge propagation. The first activation was observed in agreement with the expected location of the focus based on clinical and EEG data (three intracranial recordings), thus providing validity to this approach. The BOLD signal preceded ictal EEG changes in two cases. EEG-fMRI may detect changes in smaller and deeper structures than scalp EEG, which can only record activity form superficial cortical areas. This method allowed us to demonstrate that seizure onset zone was limited to one structure, thus supporting the concept of epileptic focus, but that a complex neuronal network was involved during propagation. Deactivations were also found during seizures, usually appearing after the first activation in areas close or distant to the activated regions. Deactivations may correspond to actively inhibited regions or to functional disconnection from normally active regions. This new noninvasive approach should open the study of seizure generation and propagation mechanisms in the whole brain to groups of patients with focal epilepsies. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] Superior temporal lobe dysfunction and frontotemporal dysconnectivity in subjects at risk of psychosis and in first-episode psychosisHUMAN BRAIN MAPPING, Issue 12 2009Nicolas A. Crossley Abstract Background: Superior temporal lobe dysfunction is a robust finding in functional neuroimaging studies of schizophrenia and is thought to be related to a disruption of fronto-temporal functional connectivity. However, the stage of the disorder at which these functional alterations occur is unclear. We addressed this issue by using functional MRI (fMRI) to study subjects in the prodromal and first episode phases of schizophrenia. Methods: Subjects with an at risk mental state (ARMS) for psychosis, a first psychotic episode (FEP), and controls were studied using fMRI while performing a working memory task. Activation in the superior temporal gyrus (STG) was assessed using statistical parametric mapping, and its relationship to frontal activation was examined using dynamic causal modeling. Results: The STG was differentially engaged across the three groups. There was deactivation of this region during the task in controls, whereas subjects with FEP showed activation and the response in subjects with ARMS was intermediately relative to the two other groups. There were corresponding differences in the effective connectivity between the STG and the middle frontal gyrus across the three groups, with a negative coupling between these areas in controls, a positive coupling in the FEP group, and an intermediate value in the ARMS group. Conclusions: A failure to deactivate the superior temporal lobe during tasks that engage prefrontal cortex is evident at the onset of schizophrenia and may reflect a disruption of fronto-temporal connectivity. Qualitatively similar alterations are evident in people with prodromal symptoms of the disorder. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] A comparison of Granger causality and coherency in fMRI-based analysis of the motor systemHUMAN BRAIN MAPPING, Issue 11 2009Andrew S. Kayser Abstract The ability of functional MRI to acquire data from multiple brain areas has spurred developments not only in voxel-by-voxel analyses, but also in multivariate techniques critical to quantifying the interactions between brain areas. As the number of multivariate techniques multiplies, however, few studies in any modality have directly compared different connectivity measures, and fewer still have done so in the context of well-characterized neural systems. To focus specifically on the temporal dimension of interactions between brain regions, we compared Granger causality and coherency (Sun et al., 2004, 2005: Neuroimage 21:647,658, Neuroimage 28:227,237) in a well-studied motor system (1) to gain further insight into the convergent and divergent results expected from each technique, and (2) to investigate the leading and lagging influences between motor areas as subjects performed a motor task in which they produced different learned series of eight button presses. We found that these analyses gave convergent but not identical results: both techniques, for example, suggested an anterior-to-posterior temporal gradient of activity from supplemental motor area through premotor and motor cortices to the posterior parietal cortex, but the techniques were differentially sensitive to the coupling strength between areas. We also found practical reasons that might argue for the use of one technique over another in different experimental situations. Ultimately, the ideal approach to fMRI data analysis is likely to involve a complementary combination of methods, possibly including both Granger causality and coherency. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] fMRI evidence for multisensory recruitment associated with rapid eye movements during sleepHUMAN BRAIN MAPPING, Issue 5 2009Charles Chong-Hwa Hong Abstract We studied the neural correlates of rapid eye movement during sleep (REM) by timing REMs from video recording and using rapid event-related functional MRI. Consistent with the hypothesis that REMs share the brain systems and mechanisms with waking eye movements and are visually-targeted saccades, we found REM-locked activation in the primary visual cortex, thalamic reticular nucleus (TRN), ,visual claustrum', retrosplenial cortex (RSC, only on the right hemisphere), fusiform gyrus, anterior cingulate cortex, and the oculomotor circuit that controls awake saccadic eye movements (and subserves awake visuospatial attention). Unexpectedly, robust activation also occurred in non-visual sensory cortices, motor cortex, language areas, and the ascending reticular activating system, including basal forebrain, the major source of cholinergic input to the entire cortex. REM-associated activation of these areas, especially non-visual primary sensory cortices, TRN and claustrum, parallels findings from waking studies on the interactions between multiple sensory data, and their ,binding' into a unified percept, suggesting that these mechanisms are also shared in waking and dreaming and that the sharing goes beyond the expected visual scanning mechanisms. Surprisingly, REMs were associated with a decrease in signal in specific periventricular subregions, matching the distribution of the serotonergic supraependymal plexus. REMs might serve as a useful task-free probe into major brain systems for functional brain imaging. Hum Brain Mapp 2009. © 2008 Wiley-Liss, Inc. [source] Resting state sensorimotor functional connectivity in multiple sclerosis inversely correlates with transcallosal motor pathway transverse diffusivityHUMAN BRAIN MAPPING, Issue 7 2008Mark J. Lowe Abstract Recent studies indicate that functional connectivity using low-frequency BOLD fluctuations (LFBFs) is reduced between the bilateral primary sensorimotor regions in multiple sclerosis. In addition, it has been shown that pathway-dependent measures of the transverse diffusivity of water in white matter correlate with related clinical measures of functional deficit in multiple sclerosis. Taken together, these methods suggest that MRI methods can be used to probe both functional connectivity and anatomic connectivity in subjects with known white matter impairment. We report the results of a study comparing anatomic connectivity of the transcallosal motor pathway, as measured with diffusion tensor imaging (DTI) and functional connectivity of the bilateral primary sensorimotor cortices (SMC), as measured with LFBFs in the resting state. High angular resolution diffusion imaging was combined with functional MRI to define the transcallosal white matter pathway connecting the bilateral primary SMC. Maps were generated from the probabilistic tracking employed and these maps were used to calculate the mean pathway diffusion measures fractional anisotropy ,FA,, mean diffusivity ,MD,, longitudinal diffusivity ,,1,, and transverse diffusivity ,,2,. These were compared with LFBF-based functional connectivity measures (Fc) obtained at rest in a cohort of 11 multiple sclerosis patients and ,10 age- and gender-matched control subjects. The correlation between ,FA, and Fc for MS patients was r = ,0.63, P < 0.04. The correlation between all subjects ,,2, and Fc was r = 0.42, P < 0.05. The correlation between all subjects ,,2, and Fc was r = ,0.50, P < 0.02. None of the control subject correlations were significant, nor were ,FA,, ,,1,, or ,MD, significantly correlated with Fc for MS patients. This constitutes the first in vivo observation of a correlation between measures of anatomic connectivity and functional connectivity using spontaneous LFBFs. Hum Brain Mapp, 2008. © 2008 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||||||||