Applications of fMRI in translational medicine and clinical practice

Characterization of Nyquist ghost in EPI-fMRI acquisition sequences implemented on two clinical 1.5 T MR scanner systems: effect of readout bandwidth and echo spacing

In EPI‐fMRI acquisitions, various readout bandwidth (BW) values are used as a function of gradients' characteristics of the MR scanner system. Echo spacing (ES) is another fundamental parameter of EPI‐fMRI sequences, but the employed ES value is not usually reported in fMRI studies. Nyquist ghost is a typical EPI artifact that can degrade the overall quality of fMRI time series. In this work, the authors assessed the basic effect of BW and ES for two clinical 1.5 T MR scanner systems (scanner‐A, scanner‐B) on Nyquist ghost of gradient‐echo EPI‐fMRI sequences. BW range was: scanner‐A, 1953‐3906 Hz/pixel; scanner‐B, 1220‐2894 Hz/pixel. ES range was: scanner‐A, scanner‐B: 0.75‐1.33 ms. The ghost‐to‐signal ratio of time series acquisition (GSRts) and drift of ghost‐to‐signal ratio (DRGSR) were measured in a water phantom. For both scanner‐A (93% of variation) and scanner‐B (102% of variation) the mean GSRts significantly increased with increasing BW. GSRts values of scanner‐A did not significantly depended on ES. On the other hand, GSRts values of scanner‐B significantly varied with ES, showing a downward trend (81% of variation) with increasing ES. In addition, a GSRts spike point at ES=1.05ms indicating a potential resonant effect was revealed. For both scanners, no significant effect of ES on DRGSR was revealed. DRGSR values of scanner‐B did not significantly vary with BW, whereas DRGSR values of scanner‐A significantly depended on BW showing an upward trend from negative to positive values with increasing BW. GSRts and DRGSR can significantly vary with BW and ES, and the specific pattern of variation may depend on gradients performances, EPI sequence calibrations and functional design of radiofrequency coil. Thus, each MR scanner system should be separately characterized. In general, the employment of low BW values seems to reduce the intensity and temporal variation of Nyquist ghost in EPI‐fMRI time series. On the other hand, the use of minimum ES value might not be entirely advantageous when the MR scanner is characterized by gradients with low performances and suboptimal EPI sequence calibration.

PACS numbers: 87.61.‐c, 87.61.Qr, 87.61.Hk

Clinical applications of resting state functional connectivity

During resting conditions the brain remains functionally and metabolically active. One manifestation of this activity that has become an important research tool is spontaneous fluctuations in the blood oxygen level-dependent (BOLD) signal of functional magnetic resonance imaging (fMRI). The identification of correlation patterns in these spontaneous fluctuations has been termed resting state functional connectivity (fcMRI) and has the potential to greatly increase the translation of fMRI into clinical care. In this article we review the advantages of the resting state signal for clinical applications including detailed discussion of signal to noise considerations. We include guidelines for performing resting state research on clinical populations, outline the different areas for clinical application, and identify important barriers to be addressed to facilitate the translation of resting state fcMRI into the clinical realm.

Medial prefrontal cortex activity during memory encoding of pictures and its relation to symptomatic improvement after citalopram treatment in patients with major depression

BACKGROUND

Brain imaging studies of major depressive disorder have shown alterations in the brain regions typically involved in episodic memory, including the prefrontal cortex and medial temporal areas. Some studies of major depressive disorder have linked episodic memory performance to treatment response. In this study, we sought to identify brain regions whose activity, measured during the encoding of pictures, predicted symptomatic improvement after 8 weeks of citalopram treatment.

METHODS

We included 20 unmedicated depressed patients. These patients performed an episodic recognition memory task during functional magnetic resonance imaging. During the encoding phase, 150 pictures depicting emotionally positive, negative or neutral content were presented, and the participants were required to classify each picture according to its emotional valence. The same 150 pictures were presented, along with 150 new ones, for a recognition task. We asked participants to distinguish the old pictures from the new ones. We assessed symptom severity by use of the 21-item Hamilton Rating Scale for Depression (HAM-D) at baseline and after 8 weeks of citalopram treatment. We performed subsequent memory effect analyses using SPM2 software. We explored the relation between brain activation during successful encoding of pictures and symptomatic improvement.

RESULTS

Patients showed a mean symptomatic improvement of 54.5% on the HAM-D after 8 weeks. Symptomatic improvement was significantly and positively correlated with picture recognition memory accuracy. We also found that the activity of the ventromedial prefrontal cortex and anterior cingulate cortex during successful encoding was significantly correlated with symptomatic improvement. Finally, we found greater activation in the ventromedial prefrontal cortex during the successful encoding of positive pictures in comparison with neutral pictures.

LIMITATIONS

During the recognition memory task, 5 participants (among the best responders to treatment) were not included in the valence-specific analyses because they had very few errors. A more challenging task would have allowed the inclusion of most patients.

CONCLUSION

Different types of functional imaging paradigms have been used to explore whether the activity of specific brain regions measured at baseline is predictive of a better response to treatment in major depressive disorder. Among these regions, the medial prefrontal cortex and anterior cingulate cortex usually show the strongest predictive value. According to our results, the medial prefrontal cortex and anterior cingulate cortex could have an effect on treatment response in major depressive disorder by contributing to the successful encoding of positively valenced information.

In contrast to BOLD: signal enhancement by extravascular water protons as an alternative mechanism of endogenous fMRI signal change

Despite the popularity and widespread application of functional magnetic resonance imaging (fMRI) in recent years, the physiological bases of signal change are not yet fully understood. Blood oxygen level-dependant (BOLD) contrast - attributed to local changes in blood flow and oxygenation, and therefore magnetic susceptibility - has become the most prevalent means of functional neuroimaging. However, at short echo times, spin-echo sequences show considerable deviations from the BOLD model, implying a second, non-BOLD component of signal change. This has been dubbed "signal enhancement by extravascular water protons" (SEEP) and is proposed to result from proton-density changes associated with cellular swelling. Given that such changes are independent of magnetic susceptibility, SEEP may offer new and improved opportunities for carrying out fMRI in regions with close proximity to air-tissue and/or bone-tissue interfaces (e.g., the prefrontal cortex and spinal cord), as well as regions close to large blood vessels, which may not be ideally suited for BOLD imaging. However, because of the interdisciplinary nature of the literature, there has yet to be a thorough synthesis, tying together the various and sometimes disparate aspects of SEEP theory. As such, we aim to provide a concise yet comprehensive overview of SEEP, including recent and compelling evidence for its validity, its current applications and its future relevance to the rapidly expanding field of functional neuroimaging. Before presenting the evidence for a non-BOLD component of endogenous functional contrast, and to enable a more critical review for the nonexpert reader, we begin by reviewing the fundamental principles underlying BOLD theory.

Preoperative sensorimotor mapping in brain tumor patients using spontaneous fluctuations in neuronal activity imaged with functional magnetic resonance imaging: initial experience

OBJECTIVE

To describe initial experience with resting-state correlation mapping as a potential aid for presurgical planning of brain tumor resection.

METHODS

Resting-state blood oxygenation-dependent functional magnetic resonance imaging (fMRI) scans were acquired in 17 healthy young adults and 4 patients with brain tumors invading sensorimotor cortex. Conventional fMRI motor mapping (finger-tapping protocol) was also performed in the patients. Intraoperatively, motor hand area was mapped using cortical stimulation.

RESULTS

Robust and consistent delineation of sensorimotor cortex was obtained using the resting-state blood oxygenation-dependent data. Resting-state functional mapping localized sensorimotor areas consistent with cortical stimulation mapping and in all patients performed as well as or better than task-based fMRI.

CONCLUSION

Resting-state correlation mapping is a promising tool for reliable functional localization of eloquent cortex. This method compares well with "gold standard" cortical stimulation mapping and offers several advantages compared with conventional motor mapping fMRI.

The role of functional magnetic resonance imaging in the study of brain development, injury, and recovery in the newborn

Development of brain functions and the structural-functional correlates of brain injury remain difficult to evaluate in the young infant. Thus, new noninvasive methods capable of early functional diagnosis are needed. This review describes the use of functional magnetic resonance imaging (fMRI) for studying localization of brain function in the developing brain when standard clinical investigations are not available or conclusive. This promising neuroimaging technique has been successfully used in healthy newborns and in newborns with brain injury using different paradigms, including passive visual, somato-sensorial, and auditory stimulation. We summarize the major findings of previous fMRI studies in young infants, describe ongoing methodological challenges, and propose exciting future developments in using resting-state protocols and functional connectivity techniques to assist in evaluating early life brain function and its recovery from injury.

How neuroimaging studies have challenged us to rethink: is chronic pain a disease?

In this review, we present data from functional, structural, and molecular imaging studies in patients and animals supporting the notion that it might be time to reconsider chronic pain as a disease. Across a range of chronic pain conditions, similar observations have been made regarding changes in structure and function within the brains of patients. We discuss these observations within the framework of the current definition of a disease.

PERSPECTIVE

Neuroimaging studies have made a significant scientific impact in the study of pain. Knowledge of nociceptive processing in the noninjured and injured central nervous system has grown considerably over the past 2 decades. This review examines the information from these functional, structural, and molecular studies within the framework of a disease state.

[Methodological problems with clinical functional MRI investigations]

During presurgical diagnostics clinical functional magnetic resonance imaging is increasingly being performed to improve the management of epilepsy and tumor patients. Rapid technical developments in fMRI technology continuously further new diagnostic applications. Safe clinical application requires a profound and critical handling of the various methodological problems inherent with this complex technique. This article reviews relevant problems and solutions for patient investigations up to the preparation of an individual clinical fMRI report.

Investigating hemodynamic response variability at the group level using basis functions

Introduced is a general framework for performing group-level analyses of fMRI data using any basis set of two functions (i.e., the canonical hemodynamic response function and its first derivative) to model the hemodynamic response to neural activity. The approach allows for flexible implementation of physiologically based restrictions on the results. Information from both basis functions is used at the group level and the limitations avoid physiologically ambiguous or implausible results. This allows for investigation of specific BOLD activity such as hemodynamic responses peaking within a specified temporal range (i.e., 4-5 s). The general nature of the presented approach allows for applications using basis sets specifically designed to investigate various physiologic phenomena, i.e., age-related variability in poststimulus undershoot, hemodynamic responses measured with cerebral blood flow imaging, or subject-specific basis sets. An example using data from a group of healthy young participants demonstrates the methods and the specific steps to study poststimulus variability are discussed. The approach is completely implemented within the general linear model and requires minimal programmatic calculations.

Neuroimaging as a tool for pain diagnosis and analgesic development

Neuroimaging makes it possible to study pain processing beyond the peripheral nervous system, at the supraspinal level, in a safe, noninvasive way, without interfering with neurophysiological processes. In recent years, studies using brain imaging methods have contributed to our understanding of the mechanisms responsible for the development and maintenance of chronic pain. Moreover, neuroimaging shows promising results for analgesic drug development and in characterizing different types of pain, bringing us closer to development of mechanism-based diagnoses and treatments for the chronic pain patient.

The role of neuroimaging in translational cognitive neuroscience

Despite the current enthusiasm for neuroimaging as a key method in translational neuroscience, there is a lack of debate about the nosological framework within which neuroimaging measures should be related to diagnostic categories. Here, the aim was to stimulate a debate about the role of cognitive neuroscience and neuroimaging in mediating between molecular/genetic, clinical diagnostic, and symptom-based descriptions of neuropsychiatric disorders. The diagnostic role of neuroimaging in translational neuroscience is stressed, namely, to be combined with cognitive measures to define cognitive-anatomical syndromes as an intermediate diagnostic category that mediates between clinical diagnoses and psychoreactive as well as neurobiological etiologic factors. This multilevel approach will be illustrated by reviewing recent insights into the cognitive-anatomical basis of inappropriate social behavior and social knowledge in frontotemporal dementia and by discussing its implications for the study of neuropsychiatric disorders such as major depressive disorder in which neuroanatomical abnormalities are more subtle.

Pooling FMRI data: meta-analysis, mega-analysis and multi-center studies

The quantitative analysis of pooled data from related functional magnetic resonance imaging (fMRI) experiments has the potential to significantly accelerate progress in brain mapping. Such data-pooling can be achieved through meta-analysis (the pooled analysis of published results), mega-analysis (the pooled analysis of raw data) or multi-site studies, which can be seen as designed mega-analyses. Current limitations in function-location brain mapping and how data-pooling can be used to remediate them are reviewed, with particular attention to power aggregation and mitigation of false positive results. Some recently developed analysis tools for meta- and mega-analysis are also presented, and recommendations for the conduct of valid fMRI data pooling are formulated.

Donepezil improves episodic memory in young individuals vulnerable to the effects of sleep deprivation

STUDY OBJECTIVES

We investigated if donepezil, a long-acting orally administered cholinesterase inhibitor, would reduce episodic memory deficits associated with 24 h of sleep deprivation.

DESIGN

Double-blind, placebo-controlled, crossover study involving 7 laboratory visits over 2 months. Participants underwent 4 functional MRI scans; 2 sessions (donepezil or placebo) followed a normal night's sleep, and 2 sessions followed a night of sleep deprivation.

SETTING

The study took place in a research laboratory.

PARTICIPANTS

26 young, healthy volunteers with no history of any sleep, psychiatric, or neurologic disorders.

INTERVENTIONS

5 mg of donepezil was taken once daily for approximately 17 days.

MEASUREMENTS AND RESULTS

Subjects were scanned while performing a semantic judgment task and tested for word recognition outside the scanner 45 minutes later. Sleep deprivation increased the frequency of non-responses at encoding and impaired delayed recognition. No benefit of donepezil was evident when participants were well rested. When sleep deprived, individuals who showed greater performance decline improved with donepezil, whereas more resistant individuals did not benefit. Accompanying these behavioral effects, there was corresponding modulation of task-related activation in functionally relevant brain regions. Brain regions identified in relation to donepezil-induced alteration in non-response rates could be distinguished from regions relating to improved recognition memory. This suggests that donepezil can improve delayed recognition in sleep-deprived persons by improving attention as well as enhancing memory encoding.

CONCLUSIONS

Donepezil reduced decline in recognition performance in individuals vulnerable to the effects of sleep deprivation. Additionally, our findings demonstrate the utility of combined fMRI-behavior evaluation in psychopharmacological studies.

Visual grading of 2D and 3D functional MRI compared with image-based descriptive measures

OBJECTIVE

A prerequisite for successful clinical use of functional magnetic resonance imaging (fMRI) is the selection of an appropriate imaging sequence. The aim of this study was to compare 2D and 3D fMRI sequences using different image quality assessment methods.

METHODS

Descriptive image measures, such as activation volume and temporal signal-to-noise ratio (TSNR), were compared with results from visual grading characteristics (VGC) analysis of the fMRI results.

RESULTS

Significant differences in activation volume and TSNR were not directly reflected by differences in VGC scores. The results suggest that better performance on descriptive image measures is not always an indicator of improved diagnostic quality of the fMRI results.

CONCLUSION

In addition to descriptive image measures, it is important to include measures of diagnostic quality when comparing different fMRI data acquisition methods.

Modulation of fusiform cortex activity by cholinesterase inhibition predicts effects on subsequent memory

Cholinergic influences on memory are likely to be expressed at several processing stages, including via well-recognized effects of acetylcholine on stimulus processing during encoding. Since previous studies have shown that cholinesterase inhibition enhances visual extrastriate cortex activity during stimulus encoding, especially under attention-demanding tasks, we tested whether this effect correlates with improved subsequent memory. In a within-subject physostigmine versus placebo design, we measured brain activity with functional magnetic resonance imaging while healthy and mild Alzheimer's disease subjects performed superficial and deep encoding tasks on face (and building) visual stimuli. We explored regions in which physostigmine modulation of face-selective neural responses correlated with physostigmine effects on subsequent recognition performance. In healthy subjects physostigmine led to enhanced later recognition for deep- versus superficially-encoded faces, which correlated across subjects with a physostigmine-induced enhancement of face-selective responses in right fusiform cortex during deep- versus superficial-encoding tasks. In contrast, the Alzheimer's disease group showed neither a depth of processing effect nor restoration of this with physostigmine. Instead, patients showed a task-independent improvement in confident memory with physostigmine, an effect that correlated with enhancements in face-selective (but task-independent) responses in bilateral fusiform cortices. Our results indicate that one mechanism by which cholinesterase inhibitors can improve memory is by enhancing extrastriate cortex stimulus selectivity at encoding, in a manner that for healthy people but not in Alzheimer's disease is dependent upon depth of processing.

Cholinergic agonism alters cognitive processing and enhances brain functional connectivity in patients with multiple sclerosis

The aim of this study is to define mechanisms underlying the pharmacological effects of brain cholinesterase inhibition on cognitive function in patients with multiple sclerosis (MS). Both a Stroop task and an N-back task were used to probe the changes in brain activity using functional magnetic resonance imaging (fMRI) in a single (investigator)-blind, crossover treatment design studying 15 patients with multiple sclerosis (12 relapsing remitting, 3 secondary progressive) taking rivastigmine (4.5 mg po bid) and domperidone (10 mg po qd) or domperidone alone. Administration of rivastigmine increased Stroop functional magnetic resonance imaging activation in the right inferior frontal gyrus for the Stroop task (P < 0.05, corrected). Incremental functional magnetic resonance imaging activation with progressively greater N-back task difficulty was enhanced by rivastigmine in prefrontal and parietal cortical regions (P < 0.01, ANOVA). Functional connectivity analysis of the N-back functional magnetic resonance imaging data based on correlations between pair-wise interregional activations showed increased connectivity between left to right prefrontal, anterior cingulate to left prefrontal and right parietal to right prefrontal regions with rivastigmine (P < 0.05, corrected). Although there were no statistically significant changes in the neuropsychological task performance with rivastigmine in this small study, 11 of 15 patients showed improvements, whereas only 4 of 15 patients showed decline in performance (P = 0.07). With regard to the previous data, these findings suggest different patterns of brain response to lower dose acute and higher dose chronic administration of rivastigmine in patients with multiple sclerosis. They showed that rivastigmine enhances the prefrontal function and alters the functional connectivity associated with cognition. We interpret this as evidence for greater efficiency of brain information transfer that should increase confidence in a potentially beneficial clinical therapeutic effect.

Preclinical Multimodality Imaging in Vivo

Multimodality small-animal molecular imaging has become increasingly important as transgenic and knockout mice are produced to model human diseases. With the ever-increasing number and importance of human disease models, particularly in rodents (mice and rats), the ability of high-resolution multimodality molecular imaging instrumentation to contribute unique information is becoming more common and necessary. Multimodality imaging with high spatial resolution and good sensitivity, which combines modalities and records sequentially or simultaneously complementary information, offers many advantages in certain research experiments. This article discusses the current trends and new horizons in preclinical multimodality imaging in-vivo and its role in biomedical research.

Resting-state spontaneous fluctuations in brain activity: a new paradigm for presurgical planning using fMRI

RATIONALE AND OBJECTIVES

Task-evoked functional MRI (fMRI) has been used successfully in the study of brain function and clinically for presurgical localization of eloquent brain regions prior to the performance of brain surgery. This method requires patient cooperation and is not useful in young children or if the patient has cognitive dysfunction or physical impairment. An alternative method that can overcome some of these disadvantages measures the intrinsic function of the brain using resting-state fMRI. This method does not require any task performance and measures the spontaneous low-frequency (<0.1 Hz) fluctuations of the fMRI signal over time. Our objective in the present work is to provide preliminary information on the possible clinical utility of this technique for presurgical planning and on possible future applications.

MATERIALS AND METHODS

Data from prior fMRI resting-state studies were reviewed for their potential use in preoperative mapping. Structural and resting-state fMRI data from normal subjects and patients with brain tumors were preprocessed and seed regions were placed in key regions of the brain; the related functional networks were identified using correlation analysis.

RESULTS

Several key functional networks can be identified in patients with brain tumors from resting-state fMRI data.

CONCLUSION

Resting-state fMRI data can provide valuable presurgical information in many patients who cannot benefit from traditional task-based fMRI. Adoption of this method has the potential to improve individualized patient-centered care.

Atomoxetine modulates right inferior frontal activation during inhibitory control: a pharmacological functional magnetic resonance imaging study

BACKGROUND

Atomoxetine, a selective noradrenaline reuptake inhibitor (SNRI) licensed for the treatment of attention-deficit/hyperactivity disorder (ADHD), has been shown to improve response inhibition in animals, healthy volunteers, and adult patients. However, the mechanisms by which atomoxetine improves inhibitory control have yet to be determined.

METHODS

The effects of atomoxetine (40 mg) were measured with a stop-signal functional magnetic resonance imaging (fMRI) paradigm in 19 healthy volunteers, in a within-subject, double-blind, placebo-controlled design.

RESULTS

Atomoxetine improved inhibitory control and increased activation in the right inferior frontal gyrus when volunteers attempted to inhibit their responses (irrespective of success). Plasma levels of drug correlated significantly with right inferior frontal gyrus activation only during successful inhibition.

CONCLUSIONS

These results show that atomoxetine exerts its beneficial effects on inhibitory control via modulation of right inferior frontal function, with implications for understanding and treating inhibitory dysfunction of ADHD and other disorders.

Effects of aging on cerebral blood flow, oxygen metabolism, and blood oxygenation level dependent responses to visual stimulation

Calibrated functional magnetic resonance imaging (fMRI) provides a noninvasive technique to assess functional metabolic changes associated with normal aging. We simultaneously measured both the magnitude of the blood oxygenation level dependent (BOLD) and cerebral blood flow (CBF) responses in the visual cortex for separate conditions of mild hypercapnia (5% CO(2)) and a simple checkerboard stimulus in healthy younger (n = 10, mean: 28-years-old) and older (n = 10, mean: 53-years-old) adults. From these data we derived baseline CBF, the BOLD scaling parameter M, the fractional change in the cerebral metabolic rate of oxygen consumption (CMRO(2)) with activation, and the coupling ratio n of the fractional changes in CBF and CMRO(2). For the functional activation paradigm, the magnitude of the BOLD response was significantly lower for the older group (0.57 +/- 0.07%) compared to the younger group (0.95 +/- 0.14%), despite the finding that the fractional CBF and CMRO(2) changes were similar for both groups. The weaker BOLD response for the older group was due to a reduction in the parameter M, which was significantly lower for older (4.6 +/- 0.4%) than younger subjects (6.5 +/- 0.8%), most likely reflecting a reduction in baseline CBF for older (41.7 +/- 4.8 mL/100 mL/min) compared to younger (59.6 +/- 9.1 mL/100 mL/min) subjects. In addition to these primary responses, for both groups the BOLD response exhibited a post-stimulus undershoot with no significant difference in this magnitude. However, the post-undershoot period of the CBF response was significantly greater for older compared to younger subjects. We conclude that when comparing two populations, the BOLD response can provide misleading reflections of underlying physiological changes. A calibrated approach provides a more quantitative reflection of underlying metabolic changes than the BOLD response alone.

Brain imaging of multiple sclerosis: the next 10 years

MR imaging has had a major impact on understanding the dynamic neuropathologic findings of multiple sclerosis (MS), early diagnosis of the disease, and clinical trial conduct. The next 10 years can be expected to see further advances with a greater emphasis on large multicenter studies, new techniques and hardware allowing greater imaging sensitivity and resolution, and the exploitation of positron emission tomography molecular imaging for MS. The impact should be felt with a new emphasis on gray matter disease and processes of repair. With new ways of monitoring the disease, new treatment targets should become practical, helping to translate advances in the understanding of immunology and regenerative medicine into novel therapies.

Ethical challenges and interpretive difficulties with non-clinical applications of pediatric FMRI

In this article, we critically examine some of the ethical challenges and interpretive difficulties with possible future non-clinical applications of pediatric fMRI with a particular focus on applications in the classroom and the courtroom - two domains in which children come directly in contact with the state. We begin with a general overview of anticipated clinical and non-clinical applications of pediatric fMRI. This is followed by a detailed analysis of a range of ethical challenges and interpretive difficulties that trouble the use of fMRI and are likely to be especially acute with non-clinical uses of the technology. We conclude that knowledge of these challenges and difficulties should influence policy decisions regarding the non-clinical uses of fMRI. Our aim is to encourage the development of future policies prescribing the responsible use of this neuroimaging technology as it develops both within and outside the clinical setting.

Evidence that increased 5-HT release evokes region-specific effects on blood-oxygenation level-dependent functional magnetic resonance imaging responses in the rat brain

This study aimed to determine the potential of in vivo functional magnetic resonance imaging (fMRI) methods as a non-invasive means of detecting effects of increased 5-HT release in brain. Changes in blood-oxygenation level-dependent (BOLD) contrast induced by administration of the 5-HT-releasing agent, fenfluramine, were measured in selected brain regions of halothane-anesthetized rats. Initial immunohistochemical measurements of the marker of neural activation, Fos, confirmed that in halothane-anesthetized rats fenfluramine (10 mg/kg i.v.) evoked cellular responses in cortical regions which were attenuated by pre-treatment with the 5-HT synthesis inhibitor p-chlorophenylalanine (300 mg/kg i.p. once daily for 2 days). Fenfluramine-induced Fos was demonstrated in numerous glutamatergic pyramidal neurons (Fos/excitatory amino acid carrier 1 (EAAC1) co-labeled), but also a small number of GABA interneurons (Fos/glutamic acid decarboxylase (GAD)(67) colabeled). Fenfluramine (10 mg/kg i.v.) evoked changes in BOLD signal intensity in a number of cortical and sub-cortical regions with the greatest effects being observed in the nucleus accumbens (-13.0%+/-2.7%), prefrontal cortex (-10.1%+/-3.2%) and motor cortex (+2.3%+/-1.0%). Pre-treatment with p-chlorophenylalanine, significantly attenuated the response to fenfluramine (10 mg/kg i.v.) in all regions with the exception of the motor cortex which showed a trend. These experiments demonstrate that increased 5-HT release evokes region-specific changes in the BOLD signal in rats, and that this effect is attenuated in almost all regions by 5-HT depletion. These findings support the use of fMRI imaging methods as a non-invasive tool to study 5-HT function in animal models, with the potential for extension to clinical studies.

Intraoperative subcortical stimulation mapping of language pathways in a consecutive series of 115 patients with Grade II glioma in the left dominant hemisphere

OBJECT

Despite better knowledge of cortical language organization, its subcortical anatomofunctional connectivity remains poorly understood. The authors used intraoperative subcortical stimulation in awake patients undergoing operation for a glioma in the left dominant hemisphere to map the language pathways and to determine the contribution of such a method to surgical results.

METHODS

One hundred fifteen patients harboring a World Health Organization Grade II glioma within language areas underwent operation after induction of local anesthesia, using direct electrical stimulation to perform online cortical and subcortical language mapping throughout the resection.

RESULTS

After detection of cortical language sites, the authors identified 1 or several of the following subcortical language pathways in all patients: 1) arcuate fasciculus, eliciting phonemic paraphasia when stimulated; 2) inferior frontooccipital fasciculus, generating semantic paraphasia when stimulated; 3) subcallosal fasciculus, inducing transcortical motor aphasia during stimulation; 4) frontoparietal phonological loop, eliciting speech apraxia during stimulation; and 5) fibers coming from the ventral premotor cortex, inducing anarthria when stimulated. These structures were preserved, representing the limits of the resection. Despite a transient immediate postoperative worsening, all but 2 patients (98%) returned to baseline or better. On control MR imaging, 83% of resections were total or subtotal.

CONCLUSIONS

These results represent the largest experience with human subcortical language mapping ever reported. The use of intraoperative cortical and subcortical stimulation gives a unique opportunity to perform an accurate and reliable real-time anatomofunctional study of language connectivity. Such knowledge of the individual organization of language networks enables practitioners to optimize the benefit-to-risk ratio of surgery for Grade II glioma within the left dominant hemisphere.

Reproducibility of fMRI in the clinical setting: implications for trial designs

With expanding potential clinical applications of functional magnetic resonance imaging (fMRI) it is important to test how reliable different measures of fMRI activation are between subjects and sessions and between centres. This study compared variability across 17 patients with multiple sclerosis (MS) and 22 age-matched healthy controls (HC) in 5 European centres performing an fMRI block design with hand tapping. We recruited subjects from sites using 1.5 T scanners from different manufacturers. 5 healthy volunteers also were studied at each of 4 of the centres. We found that reproducibility between runs and sessions for single individuals was consistently much greater than between individuals. There was greater run-to-run variability for MS patients than for HC. Measurements of maximum signal change (MSC) appeared to provide higher reproducibility within individuals and greater sensitivity to differences between individuals than region of interest (ROI) suprathreshold voxel counts. The variability in measurements between centres was not as great as that between individuals. Consistent with these observations, we estimated that power should not be reduced substantially with use of multi-, as opposed to single-, centre study designs with similar numbers of subjects. Multi-centre interventional studies in which fMRI is used as an outcome measure thus appear practical even when implemented in conventional clinical environments.

Region of interest template for the human basal ganglia: comparing EPI and standardized space approaches

Identifying task-related activation in the basal ganglia (BG) is an important area of interest in normal motor systems and cognitive neuroscience. The purpose of this study was to compare changes in brain activation in the BG using results obtained from two different masking methods: a mask drawn in standardized space from a T1-weighted anatomical image and individual region of interest (ROI) masks drawn from each subject's echo-planar image (EPI) from different tasks with reference to the high resolution fast spin echo image of each subject. Two standardized masks were used: a mask developed in Talairach space (Basal Ganglia Human Area Template (BGHAT)) and a mask developed in Montreal Neurological Institute space (MNI mask). Ten subjects produced fingertip force pulses in five separate contraction tasks during fMRI scanning. ROIs were the left caudate, putamen, external and internal portions of the globus pallidus, and subthalamic nucleus. ANOVA revealed a similar average number of voxels in the EPI mask across tasks in each BG region. The percent signal change (PSC) was consistent within each region regardless of which mask was used. Linear regression analyses between PSC in BGHAT and EPI masks and MNI and EPI masks yielded r(2) values between 0.74-0.99 and 0.70-0.99 across regions, respectively. In conclusion, PSC in different BG ROIs can be compared across studies using these different masking methods. The masking method used does not affect the overall interpretation of results with respect to the effect of task. Use of a mask drawn in standardized space is a valid and time saving method of identifying PSC in the small nuclei of the BG.

Selective changes of resting-state networks in individuals at risk for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that prominently affects cerebral connectivity. Assessing the functional connectivity at rest, recent functional MRI (fMRI) studies reported on the existence of resting-state networks (RSNs). RSNs are characterized by spatially coherent, spontaneous fluctuations in the blood oxygen level-dependent signal and are made up of regional patterns commonly involved in functions such as sensory, attention, or default mode processing. In AD, the default mode network (DMN) is affected by reduced functional connectivity and atrophy. In this work, we analyzed functional and structural MRI data from healthy elderly (n = 16) and patients with amnestic mild cognitive impairment (aMCI) (n = 24), a syndrome of high risk for developing AD. Two questions were addressed: (i) Are any RSNs altered in aMCI? (ii) Do changes in functional connectivity relate to possible structural changes? Independent component analysis of resting-state fMRI data identified eight spatially consistent RSNs. Only selected areas of the DMN and the executive attention network demonstrated reduced network-related activity in the patient group. Voxel-based morphometry revealed atrophy in both medial temporal lobes (MTL) of the patients. The functional connectivity between both hippocampi in the MTLs and the posterior cingulate of the DMN was present in healthy controls but absent in patients. We conclude that in individuals at risk for AD, a specific subset of RSNs is altered, likely representing effects of ongoing early neurodegeneration. We interpret our finding as a proof of principle, demonstrating that functional brain disorders can be characterized by functional-disconnectivity profiles of RSNs.

Atomoxetine improved response inhibition in adults with attention deficit/hyperactivity disorder

BACKGROUND

Atomoxetine, a highly selective noradrenaline reuptake inhibitor (SNRI), shows efficacy in the treatment of attention-deficit/hyperactivity disorder (ADHD). Compared with psychostimulants, atomoxetine has a distinct mode of brain action and potentially lower addictive potential. Studies have yet to assess whether atomoxetine improves cognition following a single oral dose in ADHD.

METHODS

Twenty-two adults with DSM-IV ADHD were administered a single oral dose of atomoxetine (60 mg) in a placebo-controlled double-blind crossover design. Cognitive effects were assessed using stop-signal, sustained attention, spatial working memory, and set-shifting paradigms. Normative cognitive data from 20 healthy volunteers were collected for comparison.

RESULTS

The ADHD patients under placebo conditions showed response inhibition and working memory deficits compared with healthy volunteers. Atomoxetine treatment in the ADHD patients was associated with shorter stop-signal reaction times and lower numbers of commission errors on the sustained attention task.

CONCLUSIONS

Atomoxetine improved inhibitory control, most likely via noradrenergically mediated augmentation of prefrontal cortex function. These results have implications for understanding the mechanisms by which atomoxetine exerts beneficial clinical effects and suggest novel treatment directions for other disorders of impulsivity.

Neuroimaging revolutionizes therapeutic approaches to chronic pain

An understanding of how the brain changes in chronic pain or responds to pharmacological or other therapeutic interventions has been significantly changed as a result of developments in neuroimaging of the CNS. These developments have occurred in 3 domains : (1) Anatomical Imaging which has demonstrated changes in brain volume in chronic pain; (2) Functional Imaging (fMRI) that has demonstrated an altered state in the brain in chronic pain conditions including back pain, neuropathic pain, and complex regional pain syndromes. In addition the response of the brain to drugs has provided new insights into how these may modify normal and abnormal circuits (phMRI or pharmacological MRI); (3) Chemical Imaging (Magnetic Resonance Spectroscopy or MRS) has helped our understanding of measures of chemical changes in chronic pain. Taken together these three domains have already changed the way in which we think of pain – it should now be considered an altered brain state in which there may be altered functional connections or systems and a state that has components of degenerative aspects of the CNS.

Optical brain imaging in vivo: techniques and applications from animal to man

Optical brain imaging has seen 30 years of intense development, and has grown into a rich and diverse field. In-vivo imaging using light provides unprecedented sensitivity to functional changes through intrinsic contrast, and is rapidly exploiting the growing availability of exogenous optical contrast agents. Light can be used to image microscopic structure and function in vivo in exposed animal brain, while also allowing noninvasive imaging of hemodynamics and metabolism in a clinical setting. This work presents an overview of the wide range of approaches currently being applied to in-vivo optical brain imaging, from animal to man. Techniques include multispectral optical imaging, voltage sensitive dye imaging and speckle-flow imaging of exposed cortex, in-vivo two-photon microscopy of the living brain, and the broad range of noninvasive topography and tomography approaches to near-infrared imaging of the human brain. The basic principles of each technique are described, followed by examples of current applications to cutting-edge neuroscience research. In summary, it is shown that optical brain imaging continues to grow and evolve, embracing new technologies and advancing to address ever more complex and important neuroscience questions.

Potential clinical applications for spinal functional MRI

Functional MRI (fMRI) of the spinal cord is a noninvasive technique for obtaining information regarding spinal cord neuronal function. This article provides a brief overview of recent developments in spinal cord fMRI and outlines potential applications, as well as the limitations that must be overcome, for using spinal fMRI in the clinic. This technique is currently used for research purposes, but significant potential exists for spinal fMRI to become an important clinical tool.

BOLD functional MRI in disease and pharmacological studies: room for improvement?

In the past decade the use of blood oxygen level-dependent (BOLD) fMRI to investigate the effect of diseases and pharmacological agents on brain activity has increased greatly. BOLD fMRI does not measure neural activity directly, but relies on a cascade of physiological events linking neural activity to the generation of MRI signal. However, most of the disease and pharmacological studies performed so far have interpreted changes in BOLD fMRI as "brain activation," ignoring the potential confounds that can arise through drug- or disease-induced modulation of events downstream of the neural activity. This issue is especially serious in diseases (like multiple sclerosis, brain tumours and stroke) and drugs (like anaesthetics or those with a vascular action) that are known to influence these physiological events. Here we provide evidence that, to extract meaningful information on brain activity in patient and pharmacological BOLD fMRI studies, it is important to identify, characterise and possibly correct these influences that potentially confound the results. We suggest a series of experimental measures to improve the interpretability of BOLD fMRI studies. We have ranked these according to their potential information and current practical feasibility. First-line, necessary improvements consist of (1) the inclusion of one or more control tasks, and (2) the recording of physiological parameters during scanning and subsequent correction of possible between-group differences. Second-line, highly recommended important aim to make the results of a patient or drug BOLD study more interpretable and include the assessment of (1) baseline brain perfusion, (2) vascular reactivity, (3) the inclusion of stimulus-related perfusion fMRI and (4) the recording of electrophysiological responses to the stimulus of interest. Finally, third-line, desirable improvements consist of the inclusion of (1) simultaneous EEG-fMRI, (2) cerebral blood volume and (3) rate of metabolic oxygen consumption measurements and, when relevant, (4) animal studies investigating signalling between neural cells and blood vessels.

The brain and behavior: limitations in the legal use of functional magnetic resonance imaging

Brain imaging is one of the most remarkable technological advances towards understanding the relationship of behavior to brain anatomy and physiology. Brain images provide insight to understanding behavior. Additionally, the images themselves carry great impact, particularly when used to show differences in either the anatomy or the biological functioning of two different brains. For these reasons, brain images have increasingly been used in both criminal and civil trials.

After describing some general features of brain imaging, we will focus on functional magnetic imaging (fMRI), as many believe this technology has the most potential for advancing our understanding of how parts of the brain function, including perhaps linking specific functions with cognition and behavior. Brain imaging as a field is vast and therefore our discussion will be limited. First, we will assess the advantages and limitations of fMRI, including research efforts towards standardizing equipment thereby assuring reliability and reproducibility.