Human ocular dominance columns as revealed by high-field functional magnetic resonance imaging.

We mapped ocular dominance columns (ODCs) in normal human subjects using high-field (4 T) functional magnetic resonance imaging (fMRI) with a segmented echo planar imaging technique and an in-plane resolution of 0.47 x 0.47 mm(2). The differential responses to left or right eye stimulation could be reliably resolved in anatomically well-defined sections of V1. The orientation and width ( approximately 1 mm) of mapped ODC stripes conformed to those previously revealed in postmortem brains stained with cytochrome oxidase. In addition, we showed that mapped ODC patterns could be largely reproduced in different experiments conducted within the same experimental session or over different sessions. Our results demonstrate that high-field fMRI can be used for studying the functions of human brains at columnar spatial resolution.     

Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging

The majority of functional neuroscience studies have focused on the brain's response to a task or stimulus. However, the brain is very active even in the absence of explicit input or output. In this Article we review recent studies examining spontaneous fluctuations in the blood oxygen level dependent (BOLD) signal of functional magnetic resonance imaging as a potentially important and revealing manifestation of spontaneous neuronal activity. Although several challenges remain, these studies have provided insight into the intrinsic functional architecture of the brain, variability in behaviour and potential physiological correlates of neurological and psychiatric disease.     

Reproducibility of human brain activity evoked by esophageal stimulation using functional magnetic resonance imaging

Functional MRI is a popular tool for investigating central processing of visceral pain in healthy and clinical populations. Despite this, the reproducibility of the neural correlates of visceral sensation by use of functional MRI remains unclear. The aim of the present study was to address this issue. Seven healthy right-handed volunteers participated in the study. Blood oxygen level-dependent contrast images were acquired at 1.5 T while subjects received nonpainful and painful phasic balloon distensions ("on-off" block design, 10 stimuli per "on" period, 0.3 Hz) to the distal esophagus. This procedure was repeated on two further occasions to investigate reproducibility. Painful stimulation resulted in highly reproducible activation over three scanning sessions in the anterior insula, primary somatosensory cortex, and anterior cingulate cortex. A significant decrease in strength of activation occurred from session 1 to session 3 in the anterior cingulate cortex, primary somatosensory cortex, and supplementary motor cortex, which may be explained by an analogous decrease in pain ratings. Nonpainful stimulation activated similar brain regions to painful stimulation, but with greater variability in signal strength and regions of activation between scans. Painful stimulation of the esophagus produces robust activation in many brain regions. A decrease in subjective perception of pain and brain activity from the first to the final scan suggests that serial brain imaging studies may be affected by habituation. These findings indicate that for brain imaging studies that require serial scanning, development of experimental paradigms that control for the effect of habituation is necessary.     

Neural responses to intravenous serotonin revealed by functional magnetic resonance imaging.

We examined the sequence of neural responses to the hypotension, bradycardia, and apnea evoked by intravenous administration of 5-hydroxytryptamine (serotonin). Functional magnetic resonance imaging signal changes were assessed in nine isoflurane-anesthetized cats during baseline and after a bolus intravenous low dose (10 microg/kg) or high dose (20-30 microg/kg) of 5-hydroxytryptamine. In all cats, high-dose challenges elicited rapid-onset, transient signal declines in the intermediate portion of the solitary tract nucleus, caudal midline and caudal and rostral ventrolateral medulla, and fastigial nucleus of the cerebellum. Slightly delayed phasic declines appeared in the dentate and interpositus nuclei and dorsolateral pons. Late-developing responses also emerged in the solitary tract nucleus, parapyramidal region, periaqueductal gray, spinal trigeminal nucleus, inferior olivary nucleus, cerebellar vermis, and fastigial nucleus. Amygdala and hypothalamic sites showed delayed and prolonged signal increases. Intravenous serotonin infusion recruits cerebellar, amygdala, and hypothalamic sites in addition to classic brain stem cardiopulmonary areas and exhibits site-specific temporal patterns.     

Spontaneous brain activity observed with functional magnetic resonance imaging as a potential biomarker in neuropsychiatric disorders

As functional magnetic resonance imaging (fMRI) studies have yielded increasing amounts of information about the brain’s spontaneous activity, they have revealed fMRI’s potential to locate changes in brain hemodynamics that are associated with neuropsychiatric disorders. In this paper, we review studies that support the notion that changes in brain spontaneous activity observed by fMRI can be used as potential biomarkers for diagnosis and treatment evaluation in neuropsychiatric disorders. We first review the methods used to study spontaneous activity from the perspectives of (1) the properties of local spontaneous activity, (2) the spatial pattern of spontaneous activity, and (3) the topological properties of brain networks. We also summarize the major findings associated with major neuropsychiatric disorders obtained using these methods. Then we review the pilot studies that have used spontaneous activity to discriminate patients from normal controls. Finally, we discuss current challenges and potential research directions to further elucidate the clinical use of spontaneous brain activity in neuropsychiatric disorders.     

Human cerebellar dimensions as evidenced by magnetic resonance imaging

Magnetic resonance imaging data were analyzed in 340 patients (224 males, 116 females) aged 20 to 80 years. The dimensions of cerebellum were estimated on its standards sections. A relationship was found between the cross dimension of the cerebellum and the craniometric indices. The cerebellar dimensions in males were greater than those in females. Decreased cerebellar dimensions were observed in subjects over 60 years of age.     

High-resolution functional magnetic resonance imaging of the animal brain

To fully understand brain function, one must look beyond the level of a single neuron. By elucidating the spatial properties of the columnar and laminar functional architectures, information regarding the neural processing in the brain can be gained. To map these fine functional structures noninvasively and repeatedly, functional magnetic resonance imaging (fMRI) can be employed. In this article the basic principles of fMRI are introduced, including specific hardware requirements and the equipment necessary for animal magnetic resonance research. Since fMRI measures a change in secondary hemodynamic responses induced by neural activity, it is critical to understand the principles and potential pitfalls of fMRI techniques. Thus, the underlying physics of conventional blood oxygenation, cerebral blood flow, and cerebral blood volume-based fMRI techniques are extensively discussed. Tissue-specific signal change is close to the site of neural activity, while signals from large vessels can be distant from the actual active site. Thus, methods to minimize large vessel contributions and to maximize tissue signals are described. The fundamental limitation of fMRI spatial resolution is the intrinsic hemodynamic response. Based on our high-resolution fMRI studies, the hemodynamic response is regulated at submillimeter functional domains and thus spatial resolution can be achieved to an order of 100 microm. Since hemodynamic responses are sluggish, it is difficult to obtain very high temporal resolution. By using an approach with multiple experiments with different stimulus conditions, temporal resolution can be improved on the order of 100 ms. With current fMRI technologies, submillimeter columnar- and laminar-specific specific functional images can be obtained from animal brains.     

Self-regulation of local brain activity using real-time functional magnetic resonance imaging (fMRI)

Functional magnetic resonance imaging (fMRI) measures the blood oxygen level-dependent (BOLD) signal related to neuronal activity. So far, this technique has been limited by time-consuming data analysis impeding on-line analysis. In particular, no brain-computer interface (BCI) was available which provided on-line feedback to learn physiological self-regulation of the BOLD signal. Recently, studies have shown that fMRI feedback is feasible and facilitates voluntary control of brain activity. Here we review these studies to make the fMRI feedback methodology accessible to a broader scientific community such as researchers concerned with functional brain imaging and the neurobiology of learning. Methodological and conceptual limitations were substantially reduced by artefact control, sensitivity improvements, real-time algorithms, and adapted experimental designs. Physiological self-regulation of the local BOLD response is a new paradigm for cognitive neuroscience to study brain plasticity and the functional relevance of regulated brain areas by modification of behaviour. Voluntary control of abnormal activity in circumscribed brain areas may even be applied as psychophysiological treatment.     

事件相关功能磁共振成像

事件相关设计是功能磁共振成像的一种新的实验范式,与传统的组块设计相比,其主要特点有三：（1）任务刺激和刺激间隔时间的随机化;（2）可基于任务类型和被试反应类型进行选择性处理;（3）提供更加细致的脑的局部信息。     

Real-time functional magnetic resonance imaging.

Magnetic resonance imaging (MRI) has been shown to be useful in the detection of brain activity via the relatively indirect coupling of neural activity to cerebral blood flow and subsequently to magnetic resonance signal intensity. Recent technical advances have made possible the continuous collection of successive images at a rate rapid compared with such signal changes and in the statistical processing of these image time series to produce tomographic maps of brain activity in real time, with updates of 10 frames/s or better. We describe here our preferred method of real-time functional MRI and some of the early results we have obtained with its use.     

Physiological basis and image processing in functional magnetic resonance imaging: Neuronal and motor activity in brain

Functional magnetic resonance imaging (fMRI) is recently developing as imaging modality used for mapping hemodynamics of neuronal and motor event related tissue blood oxygen level dependence (BOLD) in terms of brain activation. Image processing is performed by segmentation and registration methods. Segmentation algorithms provide brain surface-based analysis, automated anatomical labeling of cortical fields in magnetic resonance data sets based on oxygen metabolic state. Registration algorithms provide geometric features using two or more imaging modalities to assure clinically useful neuronal and motor information of brain activation. This review article summarizes the physiological basis of fMRI signal, its origin, contrast enhancement, physical factors, anatomical labeling by segmentation, registration approaches with examples of visual and motor activity in brain. Latest developments are reviewed for clinical applications of fMRI along with other different neurophysiological and imaging modalities.     

Control of breathing and brain activation in human subjects seen by functional magnetic resonance imaging.

Functional magnetic resonance imaging (fMRI) was used to demonstrate the brain activation during transition from unconscious to conscious breathing in seven healthy human subjects. In right-handed volunteers, the activated areas were found in both hemispheres. The medial part of the precentral gyrus (area 4) was constantly activated in the left hemisphere. Additional activated areas were demonstrated in the premotor cortex and in the posterior parietal cortex. The activated cortical sites exhibited analogous distribution in the right hemisphere. In two out of the seven subjects. activated sites were also observed in the cerebellar hemispheres, and in the lentiform and caudate nuclei.     

The effect of tryptophan depletion on brain activation measured by functional magnetic resonance imaging during the Stroop test in healthy subjects

We investigated the role of serotonin in cognitive activation of the frontal cortex. The serotonergic system was affected by the administration of an amino acids mixture without tryptophan (tryptophan depletion). In a placebo-controlled double-blind cross-over study with 20 healthy volunteers, we tested the hypothesis that a tryptophan (serotonin) decrease affects the activation of prefrontal cortex by the Stroop test. Cognitive brain activation was evaluated by functional magnetic resonance imaging (fMRI). Tryptophan depletion decreased the plasma tryptophan level up to 90 % for five hours after the tryptophan-free drink had been consumed when compared with the same mixture with tryptophan (p?0.0001). Tryptophan depletion did not affect the Stroop test performance. We compared fMRI activation in both conditions (tryptophan depletion and placebo) with plasma tryptophan levels as the covariates. The tryptophan depletion increased the activation (fMRI signal) in the bilateral mediofrontal cortex, anterior cingulate and left dorsolateral prefrontal cortex. The present findings allow the postulate that serotonergic medial forebrain and cingulum bundle pathways play a role in the activity of cortical structures involved in Stroop test processing.     

Evoked activity of the human brain during perception of illusory stimuli

Evoked activity of the human brain was studied in 19 right-handed men during the perception of illusory images in Go/NoGo tasks. It was found that the recognition of illusory images was associated with changes in the amplitudes of both early (P1 and P2) and late (P3a and P3b) components of the evoked potentials and with an increase in the latencies of the late components recorded from the occipital, central, and frontal cortical areas, which could be explained by the necessity to store a template in the memory, compare a perceived image with the template, and prepare and execute (or inhibit) a motor response. At the same time, the operation of the brain was more differentiated during the NoGo task compared to the Go task.     

Anatomical and functional assessment of brown adipose tissue by magnetic resonance imaging

Brown adipose tissue (BAT) is the primary tissue responsible for nonshivering thermogenesis in mammals. The amount of BAT and its level of activation help regulate the utilization of excessive calories for thermogenesis as opposed to storage in white adipose tissue (WAT) which would lead to weight gain. Over the past several years, BAT activity in vivo has been primarily assessed by positron emission tomography-computed tomography (PET-CT) scan using 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG) to measure glucose utilization associated with BAT mitochondrial respiration. In this study, we demonstrate the feasibility of mapping and estimating BAT volume and metabolic function in vivo in rats at a 9.4T magnetic resonance imaging (MRI) scanner using sequences available from clinical MR scanners. Based on the morphological characteristics of BAT, we measured the volume distribution of BAT with MRI sequences that have strong fat-water contrast. We also investigated BAT volume by utilizing spin-echo MRI sequences. The in vivo MRI-estimated BAT volumes were correlated with direct measurement of BAT mass from dissected samples. Using MRI, we also were able to map hemodynamic responses to changes in BAT metabolism induced pharmacologically by β3-adrenergic receptor agonist, CL-316,243 and compare this to BAT activity in response to CL-316,243 assessed by PET 18F-FDG. In conclusion, we demonstrate the feasibility of measuring BAT volume and function in vivo using routine MRI sequences. The MRI measurement of BAT volume is consistent with quantitative measurement of the tissue ex vivo.     

Nuclear magnetic resonance imaging of the brain in children

A preliminary study of nuclear magnetic resonance imaging of the brains of four normal children (36 weeks'' postmenstrual age to 5 years) showed long T₁ areas in the periventricular region of the neonate as well as evidence of progressive myelinisation with increasing age. Study of 18 patients of 40 weeks'' postmenstrual age to 4 years showed an apparent deficit in myelinisation in an infant with probable rubella embryopathy and another with ventricular dilatation of unknown cause. Abnormal scans were obtained in an infant with congenital muscular dystrophy, and abnormalities were visualised at the lateral ventricular margins in a case of acute hydrocephalus after shunt blockage. Periventricular regions of increased T₂ were seen in a term infant aged 4 days after severe birth asphyxia and convulsions.Nuclear magnetic resonance imaging appears to provide a unique demonstration of myelinisation in vivo and shows changes in pathological processes of importance in paediatric practice.     

Postnatal changes in functional activities of the pig's brain: a combined functional magnetic resonance imaging and immunohistochemical study

Developmental changes in brain activation after pain stimulation and after passive movement of the hind paw were assessed by functional magnetic resonance imaging (fMRI) in pigs of postnatal ages 2, 4 and 6 months. Response patterns were correlated with histological maturation parameters. At 2 months, fMRI failed to detect brain activation after pain stimulation and revealed weak, but widespread activation after passive movement. At 4 months, strong reaction of numerous cortical areas on the contralateral side was seen after pain stimulation. Following passive movement, activation was weaker but more widespread, and the brainstem was also involved. By 6 months, cortical activation became more restricted to the contralateral sensory cortex and brainstem after pain stimulation and to the contralateral sensory and ipsilateral premotor and motor cortices after passive movement. Neocortical synaptophysin immunoreaction increased significantly between 2 and 4 months and slightly decreased by 6 months. The density of GABA-immunoreactive neurons and fibers significantly increased, reaching a maximum at 6 months. Our studies indicate that remodeling of synapses and development of inhibitory GABA neurons last until 6 months postnatally, when the fMRI response of the pig's brain also attains its mature adult pattern.     

Effects of mandibular advancement on brain activation during inspiratory loading in healthy subjects: a functional magnetic resonance imaging study.

Oral appliances have been a popular treatment option for subjects with obstructive sleep apnea. However, little information is available on how brain activation induced by respiratory challenge is modulated by mandibular advancement with these appliances. We hypothesized that the brain activation caused by respiratory stress may be alleviated by mandibular advancement. Respiratory stress was induced in 12 healthy subjects by resistive inspiratory loading. The effects of mandibular advancement during resistive inspiratory loading were assessed subjectively by using a visual analog scale. These effects were also evaluated objectively by using blood oxygenation level-dependent functional magnetic resonance imaging. The score for the visual analog scale significantly decreased with mandibular advancement. Cortical deactivation, in association with mandibular advancement, was localized to several specific regions, including the left cingulate gyrus and the bilateral prefrontal cortexes. These regions are known to be involved in respiratory control. Our results suggest that mandibular advancement with an oral appliance appears to be useful for reducing respiratory stress, based on both subjective and neuronal criteria.