Functional mapping of the human visual cortex by magnetic resonance imaging

Changes in functional magnetic resonance imaging with Yogic meditation: A pilot study

Background:

The neural substrates of Yogic meditation are not well understood. Meditation is theorized to be a conscious mental process that induces a set of complex physiological changes within the areas of the brain termed as the “relaxation response.”

Aims and objective:

Pilot data of a functional magnetic resonance imaging (fMRI) study is presented to observe and understand the selective activations of designated brain regions during meditation.

Material and methods:

Four trained healthy Patanjali Yoga practitioners in their mid-60s participated in this prototype interventional study. A three-part 1-min block design alternating between meditation (test) and relaxation (control) phase with an imaginary visual fixation and auditory stimulation was used.

Result and observation:

The fMRI images revealed strong activation in the right prefrontal regions during the visual and auditory fixation meditation phases compared to no activations during the relaxation phase. A comparison between the visual and auditory fixations revealed shifts within the prefrontal and temporal regions. In addition, activation in occipital and temporal regions was observed during the meditation phase. Occipital lobe activation was more apparent during visual meditation phase.

Conclusion:

It is concluded that specific fMRI brain activations are observed during different forms of Yogic meditation (visual and auditory phases). Occipital and prefrontal activation could be modulating the known neurophysiological and biological effects of meditation.

Risonanza magnetica funzionale dell'encefalo in pazienti candidati ad intervento chirurgico con guida stereotassica

Negli ultimi anni la risonanza magnetica funzionale dell'encefalo (fMRI) si è proposta con successo nello studio dell'attività encefalica durante lo svolgimento di determinate funzioni. Si è inoltre delineato per essa un ruolo paricolarmente interessante nell'ambito della pianificazione preoperatoria di pazienti destinati ad un intervento chirurgico in sedi encefaliche critiche, ovvero ad alto rischio di invalidtà postoperatoria.

Il presente lavoro mira alla realizzazione di mappe di attivazione motoria in pazienti con lesioni occupanti spazio nell'encefalo mediante un tomografo a 1,5 T di non recentissima tecnologia; successivamente si è voluto valutare l'informatività di tali mappe, sia dal punto di vista neurochirurgico sia dal punto di vista neurofisiologico.

Sono stati presi in esame 5 pazienti, tutti portatori di una lesione occupante spazio in prossimità della corteccia perirolandica e tutti destinati ad un intervento chirurgico in stereotassi per l'asportazione di tale lesione. I pazienti venivano sottoposti in un'unica seduta allo studio funzionale e morfologico dell'encefalo con il casco stereotassico in sede.

Lo studio di fMRI si è svolto su uno o massimo due piani assiali orientati ortogonalmente al decorso della scissura di Rolando. Esso prevedeva come prova di attivazione il movimento della mano controlaterale all'emisfero con la lesione da asportare.

In un paziente la funzione motoria è stata studiata anche intraoperatoriamente mediante la stimolazione elettrica della corteccia cerebrale.

In 4 pazienti si è avuta una netta rappresentazione della corteccia sensitivo-motoria di tale emisfero. In 3 di essi si è vista inoltre un'attivazione dell'emisfero opposto, ipsilaterale alla mano in movimento. Altre zone di attivazione visualizzate nei nostri studi sono state messe in relazione con l'area motoria supplementare (3 pazienti) e l'area premotoria (2 pazienti).

Nel paziente in cui si è proceduto intraoperatoriamente con la stimolazione elettrica della corteccia cerebrale è stata riscontrata una buona concordanza tra lo studio elettrofisiologico e l'indagine di fMRI.

Analizzando i risultati da noi conseguiti possiamo concludere che anche un tomografo a 1,5 T di tipo convenzionale si presta ad un'indagine di fMRI in pazienti con lesioni encefaliche. Le mappe di attivazione realizzate su uno o due piani assiali sono in grado di fornire delle informazioni sui rapporti tra la lesione da asportare e la corteccia sensitivo-motoria, in particolare l'area della mano. Ciò ha notevoli implicazioni dal punto di vista neurochirurgico, considerando quanto sia importante la salvaguardia dell'integrità funzionale del soggetto che si sottopone ad un intervento neurochirurgico in una sede critica come la corteccia perirolandica.

Enhanced Interictal Responsiveness of the Migraineous Visual Cortex to Incongruent Bar Stimulation: A Functional MRI Visual Activation Study

Since visual aura is usually described as expanding zigzag lines, neurones involved with the perception of line orientation may initiate this phenomenon. A visual incongruent line stimulation protocol was developed to obtain functional magnetic resonance images (fMRI) interictally in 5 female migraine patients with typical fortification spectra and in 5 normal matched controls. Activation in the visual cortex was present contralateral to the side of stimulation in 4 of 5 patients, notably in the extrastriate visual cortex. In 4 of 5 controls activation was observed in the medial and anterior orbitofrontal cortex. In one of them additional activation at the right nucleus accumbens/ventral striatum and right ventral pallidum was present. In the remaining control subject activation was present in the left primary visual cortex. The enhanced interictal reactivity of the visual cortex in migraineurs supports the hypothesis of abnormal cortical excitability as an important pathophysiological mechanism in migraine aura, though the role of specific regions of the visual cortex remains to be explored.

Quantitative measurement of cerebral blood volume using velocity-selective pulse trains

PURPOSE

To develop a non-contrast-enhanced MRI method for cerebral blood volume (CBV) mapping using velocity-selective (VS) pulse trains.

METHODS

The new pulse sequence applied velocity-sensitive gradient waveforms in the VS label modules and velocity-compensated ones in the control scans. Sensitivities to the gradient imperfections (e.g., eddy currents) were evaluated through phantom studies. CBV quantification procedures based on simulated labeling efficiencies for arteriolar, capillary, and venular blood as a function of cutoff velocity (Vc) are presented. Experiments were conducted on healthy volunteers at 3T to examine the effects of unbalanced diffusion weighting, cerebrospinal (CSF) contamination and variation of Vc.

RESULTS

Phantom results of the used VS pulse trains demonstrated robustness to eddy currents. The mean CBV values of gray matter and white matter for the experiments using Vc = 3.5 mm/s and velocity-compensated control with CSF-nulling were 5.1 ± 0.6 mL/100 g and 2.4 ± 0.2 mL/100 g, respectively, which were 23% and 32% lower than results from the experiment with velocity-insensitive control, corresponding to 29% and 25% lower in averaged temporal signal-to-noise ratio values.

CONCLUSION

A novel technique using VS pulse trains was demonstrated for CBV mapping. The results were both qualitatively and quantitatively close to those from existing methods. Magn Reson Med 77:92-101, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Arterial spin labeling perfusion magnetic resonance imaging of non-human primates

Non-human primates (NHPs) resemble most aspects of humans in brain physiology and anatomy and are excellent animal models for translational research in neuroscience, biomedical research and pharmaceutical development. Cerebral blood flow (CBF) offers essential physiological information of the brain to examine the abnormal functionality in NHP models with cerebral vascular diseases and neurological disorders or dementia. Arterial spin labeling (ASL) perfusion MRI techniques allow for high temporal and spatial CBF measurement and are intensively used in studies of animals and humans. In this article, current high-resolution ASL perfusion MRI techniques for quantitative evaluation of brain physiology and function in NHPs are described and their applications and limitation are discussed as well.

Humanistic Neuroscience, Mentality, and Spirituality

Mentality and spirituality, the most distinctly human phenomena, have been ignored and forced underground ever since psychology was taken over by materialistic and behavioristic science. This article reviews the contemporary scientific status of mental and spiritual processes in the light of the new worldview of modern physics and other recent developments, including the overthrow of behavior by mentality, the development of humanistic neuroscience, current views concerning the relationship between religion and science, and vigorous work synthesizing religion and psychology. The main conclusion is that views and research in science, philosophy of science, theology, and psychology have converged to support an optimistic outlook for continued integration of mentality and spirituality in psychology.

Molecular fMRI

Comprehensive analysis of brain function depends on understanding the dynamics of diverse neural signaling processes over large tissue volumes in intact animals and humans. Most existing approaches to measuring brain signaling suffer from limited tissue penetration, poor resolution, or lack of specificity for well-defined neural events. Here we discuss a new brain activity mapping method that overcomes some of these problems by combining MRI with contrast agents sensitive to neural signaling. The goal of this "molecular fMRI" approach is to permit noninvasive whole-brain neuroimaging with specificity and resolution approaching current optical neuroimaging methods. In this article, we describe the context and need for molecular fMRI as well as the state of the technology today. We explain how major types of MRI probes work and how they can be sensitized to neurobiological processes, such as neurotransmitter release, calcium signaling, and gene expression changes. We comment both on past work in the field and on challenges and promising avenues for future development.

SIGNIFICANCE STATEMENT

Brain researchers currently have a choice between measuring neural activity using cellular-level recording techniques, such as electrophysiology and optical imaging, or whole-brain imaging methods, such as fMRI. Cellular level methods are precise but only address a small portion of mammalian brains; on the other hand, whole-brain neuroimaging techniques provide very little specificity for neural pathways or signaling components of interest. The molecular fMRI techniques we discuss have particular potential to combine the specificity of cellular-level measurements with the noninvasive whole-brain coverage of fMRI. On the other hand, molecular fMRI is only just getting off the ground. This article aims to offer a snapshot of the status and future prospects for development of molecular fMRI techniques.

Echo-Planar MR Cerebral Blood Volume Mapping of Gliomas

Neovascularization is a common phenomenon in gliomas. MR imaging cerebral blood volume (CBV) mapping utilizes ultrafast echo-planar imaging and simultaneous use of gadolinium-based contrast material. To determine the utility of MR CBV mapping in the clinical evaluation of gliomas, we followed 15 patients with serial studies. This technique provided functional information that was not evident with conventional CT or MR imaging. Low-grade tumors demonstrated homogeneously low CBV, while high-grade tumors often showed areas of both high and low CBV The maximum tumor CBV/white matter ratio was compared between low- (n = 3) and high-grade gliomas (n=5) in patients without previous treatment and with histologic verification (n=8) and was significantly higher in high-grade gliomas (p<0.01). High CBV foci in nonenhancing tumor areas were present in 2 cases. The distinction between radiation necrosis and active tumor could be made correctly in 3 of 4 cases. The information provided by MR CBV mapping has the potential to be an adjunct in the clinical care of glioma patients.

Sex differences in alcohol-related neurobehavioral consequences

In this chapter, we review existing research regarding sex differences in alcohol's effects on neurobehavioral functions/processes. Drawn largely from laboratory studies, literature regarding acute alcohol administration and chronic alcohol misuse is explored focusing on commonly employed neuropsychologic domains (e.g., executive function, visuospatial skills, learning and memory, gait and balance), neurophysiologic measures (e.g., electroencephalography and event-related potentials), and structural and functional neuroimaging (e.g., magnetic resonance imaging (MRI), functional MRI, diffusion tensor imaging, positron emission tomography, and magnetic resonance spectroscopy). To provide a historical perspective on the development of these questions, we have included reference to early and more recent research. Additionally, specific biases, knowledge gaps, and continuing controversies are noted.

Review : Mapping Brain Pathophysiology and Higher Cortical Function with Magnetic Resonance Imaging

Advances in magnetic resonance imaging (MRI) have moved the technology beyond its application solely as a diagnostic test to become a tool for addressing questions of in vivo pathophysiology and higher cortical function in humans. Diffusion-weighted MRI measures the apparent rate of translational movement of water molecules through brain parenchyma. This measurement can be used to determine axonal orientation within white matter, to define regions of tissue edema, and to permit early identification of ischemic neuronal injury related to impairment of Na+-K +-ATPase activity in experimental and human stroke. Changes in various aspects of cerebral perfusion—blood volume, blood flow, and hemoglobin oxygen saturation—can be mea sured with MRI, and altered cerebrovascular circulation and regional brain activation can thereby be inves tigated. Echo planar imaging is a method of ultrafast data acquisition with MRI—individual images are ac quired on the order of 100 msec. Echo planar imaging makes diffusion and perfusion measurements more practicable for diverse applications and allows for the study of temporal characteristics of regional brain responses to stimuli. Diffusion and perfusion MRI, generally termed functional MRI, are tools for studying in vivo brain physiology with MRI and are being applied to a broad range of questions in neuroscience. The Neuroscientist 1:221-235, 1995

The Brain from Within

Functional magnetic resonance imaging (fMRI) provides a powerful way to visualize brain functions and observe brain activity in response to tasks or thoughts. It allows displaying brain damages that can be quantified and linked to neurobehavioral deficits. fMRI can potentially draw a new cartography of brain functional areas, allow us to understand aspects of brain function evolution or even breach the wall into cognition and consciousness. However, fMRI is not deprived of pitfalls, such as limitation in spatial resolution, poor reproducibility, different time scales of fMRI measurements and neuron action potentials, low statistical values. Thus, caution is needed in the assessment of fMRI results and conclusions. Additional diagnostic techniques based on MRI such as arterial spin labeling (ASL) and the measurement of diffusion tensor imaging (DTI) provide new tools to assess normal brain development or disruption of anatomical networks in diseases. A cutting edge of recent research uses fMRI techniques to establish a "map" of neural connections in the brain, or "connectome". It will help to develop a map of neural connections and thus understand the operation of the network. New applications combining fMRI and real time visualization of one's own brain activity (rtfMRI) could empower individuals to modify brain response and thus could enable researchers or institutions to intervene in the modification of an individual behavior. The latter in particular, as well as the concern about the confidentiality and storage of sensitive information or fMRI and lie detectors forensic use, raises new ethical questions.

Functional magnetic resonance imaging evaluation of lumbosacral radiculopathic pain

OBJECTIVE An objective biomarker for pain is yet to be established. Functional MRI (fMRI) is a promising neuroimaging technique that may reveal an objective radiological biomarker. The purpose of this study was to evaluate fMRI technology in the setting of lumbosacral radiculopathy and discuss its application in revealing a biomarker for pain in the future. METHODS A prospective, within-participant control study was conducted. Twenty participants with painful lumbosacral radiculopathy from intervertebral disc pathology were recruited. Functional imaging of the brain was performed during a randomly generated series of nonprovocative and provocative straight leg raise maneuvers. RESULTS With a statistical threshold set at p < 0.000001, 3 areas showed significant blood oxygen level-dependent (BOLD) signal change: right superior frontal gyrus (x = 2, y = 13, z = 48, k = 29, Brodmann area 6 [BA6]), left supramarginal cortex (x = -37, y = -44, z = 33, k = 1084, BA40), and left parietal cortex (x = -19, y = -41, z = 63, k = 354, BA5). With a statistical threshold set at p < 0.0002, 2 structures showed significant BOLD signal change: right putamen (x = 29, y = -11, z = 6, k = 72) and bilateral thalami (right: x = 23, y = -11, z = 21, k = 29; x = 8, y = -11, z = 9, k = 274; and left: x = -28, y = -32, z = 6, k = 21). CONCLUSIONS The results in this study compare with those in previous studies and suggest that fMRI technology can provide an objective assessment of the pain experience.

Functional Magnetic Resonance Imaging of Semantic Memory Processes in the Frontal Lobes

Frontal-lobe activation during semantic memory performance was examined using functional magnetic resonance imaging (fMRI), a noninvasive technique for localizing neural activity associated with cognitive function Left inferior prefrontal cortex was more activated for semantic than for perceptual encoding of words, and for initial than for repeated semantic encoding of words Decreased activation for semantic encoding of repeated words reflects repetition priming, that is, implicit retrieval of memory gained in the initial semantic encoding of a word The left inferior prefrontal region may subserve semantic working memory processes that participate in semantic encoding and that have decreased demands when such encoding can be facilitated by recent semantic experience These results demonstrate that fMRI can visualize changes in an individual's brain function associated with the encoding and retrieval of new memories

Response Assessment and Magnetic Resonance Imaging Issues for Clinical Trials Involving High-Grade Gliomas

There exist multiple challenges associated with the current response assessment criteria for high-grade gliomas, including the uncertain role of changes in nonenhancing T2 hyperintensity, and the phenomena of pseudoresponse and pseudoprogression in the setting of antiangiogenic and chemoradiation therapies, respectively. Advanced physiological magnetic resonance imaging (MRI), including diffusion and perfusion (dynamic susceptibility contrast MRI and dynamic contrast-enhanced MRI) sensitive techniques for overcoming response assessment challenges, has been proposed, with their own potential advantages and inherent shortcomings. Measurement variability exists for conventional and advanced MRI techniques, necessitating the standardization of image acquisition parameters in order to establish the utility of these imaging methods in multicenter trials for high-grade gliomas. This review chapter highlights the important features of MRI in clinical brain tumor trials, focusing on the current state of response assessment in brain tumors, advanced imaging techniques that may provide additional value for determining response, and imaging issues to be considered for multicenter trials.

Sensory and optogenetically driven single-vessel fMRI

Magnetic resonance imaging (MRI) sensitivity approaches vessel specificity. We developed a single-vessel functional MRI (fMRI) method to image the contribution of vascular components to blood oxygenation level-dependent (BOLD) and cerebral blood volume (CBV) fMRI signal. We mapped individual vessels penetrating the rat somatosensory cortex with 100-ms temporal resolution by MRI with sensory or optogenetic stimulation. The BOLD signal originated primarily from venules, and the CBV signal from arterioles. The single-vessel fMRI method and its combination with optogenetics provide a platform for mapping the hemodynamic signal through the neurovascular network with specificity at the level of individual arterioles and venules.

Cognitive training can reduce the rate of cognitive aging: a neuroimaging cohort study

BACKGROUND

The neural mechanisms underlying the restorative effects of cognitive training on aging brains remain unclear. To address this issue, we examined the relationship between changes in spontaneous brain activity and cognitive performance that occur after cognitive training.

METHODS

Participants were older adults who were part of a randomized control trial within a larger longitudinal cognitive training study. We conducted single-domain and multi-domain cognitive training in two respective intervention groups. Participants were trained for 1 h, twice a week, for 12 weeks. Cognition was assessed in all participants and magnetic resonance images were obtained at baseline and 1 year after training. To assess spontaneous fluctuations in brain activity, we acquired resting-state fMRI data. Two indices-functional entropy and time-domain entropy-were used to measure the effects of training. Functional entropy increases with aging, and indicates disruptions in functional conectivity. Time-domain entropy decreases with aging, and indicates structural alterations in the brain and blood-flow reduction.

RESULTS

Seventy participants completed the study: 26 in the multi-domain cognitive training group (70.38 ± 3.30 yrs), 27 in single-domain group (70.48 ± 3.93 yrs), and 17 in a control group (68.59 ± 3.24 yrs). Functional entropy increased significantly less in the multi-domain (p = 0.047) and single-domain groups (p = 9.51 × 10(-4)) compared with the control group. In the multi-domain group, this was true in the paracentral lobule (p = 0.004, Bonferroni corrected p < 0.05). Time-domain entropy also improved with training. Compared with controls, time-domain entropy in the multi-domain group decreased less in the inferior frontal gyrus pars opercularis (p = 3.59 × 10(-4)), the medial part of superior frontal gyrus (p = 1.17 × 10(-5)), and the thalamus (p = 4.72 × 10(-5)), while that in the single-domain group decreased less in the cuneus (p = 2.58 × 10(-4), Bonferroni corrected p < 0.05). Additionally, changes in regional entropy for some regions such as hippocampus significantly correlated with improvements in cognitive performance.

CONCLUSIONS

Cognitive training can induce plastic changes in neural functional connectivity of healthy older people, and these changes may underlie the positive effect of cognitive training.

TRIAL REGISTRATION

ChiCTR-TRC-08000732 (Date of registration: 5th November, 2008).

Non-invasive quantification of absolute cerebral blood volume during functional activation applicable to the whole human brain

PURPOSE

Cerebral blood volume (CBV) changes in many diverse pathologic conditions, and in response to functional challenges along with changes in blood flow, blood oxygenation, and the cerebral metabolic rate of oxygen. The feasibility of a new method for non-invasive quantification of absolute cerebral blood volume that can be applicable to the whole human brain was investigated.

METHODS

Multi-slice data were acquired at 3 T using a novel inversion recovery echo planar imaging (IR-EPI) pulse sequence with varying contrast weightings and an efficient rotating slice acquisition order, at rest and during visual activation. A biophysical model was used to estimate absolute cerebral blood volume at rest and during activation, and oxygenation during activation, on data from 13 normal human subjects.

RESULTS

Cerebral blood volume increased by 21.7% from 6.6 ± 0.8 mL/100 mL of brain parenchyma at rest to 8.0 ± 1.3 mL/100 mL of brain parenchyma in the occipital cortex during visual activation, with average blood oxygenation of 84 ± 2.1% during activation, comparing well with literature.

CONCLUSION

The method is feasible, and could foster improved understanding of the fundamental physiological relationship between neuronal activity, hemodynamic changes, and metabolism underlying brain activation; complement existing methods for estimating compartmental changes; and potentially find utility in evaluating vascular health.

Functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) maps the spatiotemporal distribution of neural activity in the brain under varying cognitive conditions. Since its inception in 1991, blood oxygen level-dependent (BOLD) fMRI has rapidly become a vital methodology in basic and applied neuroscience research. In the clinical realm, it has become an established tool for presurgical functional brain mapping. This chapter has three principal aims. First, we review key physiologic, biophysical, and methodologic principles that underlie BOLD fMRI, regardless of its particular area of application. These principles inform a nuanced interpretation of the BOLD fMRI signal, along with its neurophysiologic significance and pitfalls. Second, we illustrate the clinical application of task-based fMRI to presurgical motor, language, and memory mapping in patients with lesions near eloquent brain areas. Integration of BOLD fMRI and diffusion tensor white-matter tractography provides a road map for presurgical planning and intraoperative navigation that helps to maximize the extent of lesion resection while minimizing the risk of postoperative neurologic deficits. Finally, we highlight several basic principles of resting-state fMRI and its emerging translational clinical applications. Resting-state fMRI represents an important paradigm shift, focusing attention on functional connectivity within intrinsic cognitive networks.

A hierarchical Bayesian model for flexible module discovery in three-way time-series data

Motivation: Detecting modules of co-ordinated activity is fundamental in the analysis of large biological studies. For two-dimensional data (e.g. genes × patients), this is often done via clustering or biclustering. More recently, studies monitoring patients over time have added another dimension. Analysis is much more challenging in this case, especially when time measurements are not synchronized. New methods that can analyze three-way data are thus needed.

Results: We present a new algorithm for finding coherent and flexible modules in three-way data. Our method can identify both core modules that appear in multiple patients and patient-specific augmentations of these core modules that contain additional genes. Our algorithm is based on a hierarchical Bayesian data model and Gibbs sampling. The algorithm outperforms extant methods on simulated and on real data. The method successfully dissected key components of septic shock response from time series measurements of gene expression. Detected patient-specific module augmentations were informative for disease outcome. In analyzing brain functional magnetic resonance imaging time series of subjects at rest, it detected the pertinent brain regions involved.

Availability and implementation: R code and data are available at http://acgt.cs.tau.ac.il/twigs/.

Contact:rshamir@tau.ac.il

Supplementary information:Supplementary data are available at Bioinformatics online.

Hyperspectral optical tomography of intrinsic signals in the rat cortex

We introduce a tomographic approach for three-dimensional imaging of evoked hemodynamic activity, using broadband illumination and diffuse optical tomography (DOT) image reconstruction. Changes in diffuse reflectance in the rat somatosensory cortex due to stimulation of a single whisker were imaged at a frame rate of 5 Hz using a hyperspectral image mapping spectrometer. In each frame, images in 38 wavelength bands from 484 to 652 nm were acquired simultaneously. For data analysis, we developed a hyperspectral DOT algorithm that used the Rytov approximation to quantify changes in tissue concentration of oxyhemoglobin ([Formula: see text]) and deoxyhemoglobin (ctHb) in three dimensions. Using this algorithm, the maximum changes in [Formula: see text] and ctHb were found to occur at [Formula: see text] and [Formula: see text] beneath the surface of the cortex, respectively. Rytov tomographic reconstructions revealed maximal spatially localized increases and decreases in [Formula: see text] and ctHb of [Formula: see text] and [Formula: see text], respectively, with these maximum changes occurring at [Formula: see text] poststimulus. The localized optical signals from the Rytov approximation were greater than those from modified Beer-Lambert, likely due in part to the inability of planar reflectance to account for partial volume effects.

Reading, listening and memory-related brain activity in children with early-stage temporal lobe epilepsy of unknown cause-an fMRI study

BACKGROUND AND AIMS

The changes in functional brain organization associated with paediatric epilepsy are largely unknown. Since children with epilepsy are at risk of developing learning difficulties even before or shortly after the onset of epilepsy, we assessed the functional organization of memory and language in paediatric patients with temporal lobe epilepsy (TLE) at an early stage in epilepsy.

METHODS

Functional magnetic resonance imaging was used to measure the blood oxygenation level-dependent (BOLD) response to four cognitive tasks measuring reading, story listening, memory encoding and retrieval in a population-based group of children with TLE of unknown cause (n = 21) and of normal intelligence and a healthy age and gender-matched control group (n = 21).

RESULTS

Significant BOLD response differences were found only in one of the four tasks. In the story listening task, significant differences were found in the right hemispheric temporal structures, thalamus and basal ganglia. Both activation and deactivation differed significantly between the groups, activation being increased and deactivation decreased in the TLE group. Furthermore, the patients with abnormal electroencephalograms (EEGs) showed significantly increased activation bilaterally in the temporal structures, basal ganglia and thalamus relative to those with normal EEGs. The patients with normal interictal EEGs had a significantly stronger deactivation than those with abnormal EEGs or the controls, the differences being located outside the temporal structures.

CONCLUSIONS

Our results suggest that TLE entails a widespread disruption of brain networks. This needs to be taken into consideration when evaluating learning abilities in patients with TLE. The thalamus seems to play an active role in TLE. The changes in deactivation may reflect neuronal inhibition.

Stability of resting state networks in the female brain during hormonal changes and their relation to premenstrual symptoms

Resting-state fMRI is a promising imaging technique to evaluate functions in the human brain in health and disease. Different hormonal stages of the female menstrual cycle and hormonal contraceptives use affect results in task-based fMRI; it is however not yet clarified whether resting state networks are also altered. A population of 18 women with a natural cycle, and 19 women using hormonal contraceptives was examined in a longitudinal study-design. The natural cycle group was scanned at 3 time-points (follicular phase, ovulation, luteal phase), and the contraceptives group was scanned twice (inactive pill-phase, active pill-phase). Blood samples were acquired to evaluate hormonal concentrations, and premenstrual symptoms were assessed through daily record of severity of problems questionnaires. Results show no major alterations in the default mode network and the executive control network between different hormonal phases, across or within groups. A positive correlation of functional connectivity in the posterior part of the default mode network (DMN) was found with premenstrual-like symptoms in the hormonal contraceptives group. Using the current methodology, the studied resting state networks seem to show a decent stability throughout menstrual cycle phases. Also, no effect of hormonal contraceptive use is found. Interestingly, we show for the first time an association of DMN alterations with premenstrual-like symptoms, experienced during the inactive pill-phase by a sub-population of women.

Radiogenomics and imaging phenotypes in glioblastoma: novel observations and correlation with molecular characteristics

Radiogenomics is a provocative new area of research based on decades of previous work examining the association between radiological and histological features. Many generalized associations have been established linking anatomical imaging traits with underlying histopathology, including associations between contrast-enhancing tumor and vascular and tumor cell proliferation, hypointensity on pre-contrast T1-weighted images and necrotic tissue, and associations between hyperintensity on T2-weighted images and edema or nonenhancing tumor. Additionally, tumor location, tumor size, composition, and descriptive features tend to show significant associations with molecular and genomic factors, likely related to the cell of origin and growth characteristics. Additionally, physiologic MRI techniques also show interesting correlations with underlying histology and genomic programs, including associations with gene expression signatures and histological subtypes. Future studies extending beyond simple radiology-histology associations are warranted in order to establish radiogenomic analyses as tools for prospectively identifying patient subtypes that may benefit from specific therapies.

Evaluation of rigid registration methods for whole head imaging in diffuse optical tomography

Functional brain imaging has become an important neuroimaging technique for the study of brain organization and development. Compared to other imaging techniques, diffuse optical tomography (DOT) is a portable and low-cost technique that can be applied to infants and hospitalized patients using an atlas-based light model. For DOT imaging, the accuracy of the forward model has a direct effect on the resulting recovered brain function within a field of view and so the accuracy of the spatially normalized atlas-based forward models must be evaluated. Herein, the accuracy of atlas-based DOT is evaluated on models that are spatially normalized via a number of different rigid registration methods on 24 subjects. A multileveled approach is developed to evaluate the correlation of the geometrical and sensitivity accuracies across the full field of view as well as within specific functional subregions. Results demonstrate that different registration methods are optimal for recovery of different sets of functional brain regions. However, the "nearest point to point" registration method, based on the EEG 19 landmark system, is shown to be the most appropriate registration method for image quality throughout the field of view of the high-density cap that covers the whole of the optically accessible cortex.

Wide-field Ca(2+) imaging reveals visually evoked activity in the retrosplenial area

Due to recent advances of genetic manipulation, mouse brain has become a useful model for studying brain function, which demands whole brain functional mapping techniques in the mouse brain. In the present study, to finely map visual responsive areas in the mouse brain, we combined high-resolution wide-field optical imaging with transgenic mice containing the genetically encoded Ca²⁺ indicator, GCaMP3. With the high signal amplitude of GCaMP3 expressing in excitatory neurons, this system allowed neural activity to be observed with relatively fine spatial resolution and cell-type specificity. To evaluate this system, we examined whether non-visual areas exhibited a visual response over the entire surface of the mouse hemisphere. We found that two association areas, the retrosplenial area (RS) and secondary motor/anterior cingulate area (M2/AC), were significantly responsive to drifting gratings. Examination using gratings with distinct spatiotemporal frequency parameters revealed that the RS strongly responded to high-spatial and low-temporal frequency gratings. The M2/AC exhibited a response property similar to that of the RS, though it was not statistically significant. Finally, we performed cellular imaging using two-photon microscopy to examine orientation and direction selectivity of individual neurons, and found that a minority of neurons in the RS clearly showed visual responses sharply selective for orientation and direction. These results suggest that neurons in RS encode visual information of fine spatial details in images. Thus, the present study shows the usefulness of the functional mapping method using a combination of wide-field and two-photon Ca²⁺ imaging, which allows for whole brain mapping with high spatiotemporal resolution and cell-type specificity.

Data integration: Combined imaging and electrophysiology data in the cloud

There has been an increasing effort to correlate electrophysiology data with imaging in patients with refractory epilepsy over recent years. IEEG.org provides a free-access, rapidly growing archive of imaging data combined with electrophysiology data and patient metadata. It currently contains over 1200 human and animal datasets, with multiple data modalities associated with each dataset (neuroimaging, EEG, EKG, de-identified clinical and experimental data, etc.). The platform is developed around the concept that scientific data sharing requires a flexible platform that allows sharing of data from multiple file formats. IEEG.org provides high- and low-level access to the data in addition to providing an environment in which domain experts can find, visualize, and analyze data in an intuitive manner. Here, we present a summary of the current infrastructure of the platform, available datasets and goals for the near future.

Emerging applications of porphyrins in photomedicine

Biomedical applications of porphyrins and related molecules have been extensively pursued in the context of photodynamic therapy. Recent advances in nanoscale engineering have opened the door for new ways that porphyrins stand to potentially benefit human health. Metalloporphyrins are inherently suitable for many types of medical imaging and therapy. Traditional nanocarriers such as liposomes, dendrimers and silica nanoparticles have been explored for photosensitizer delivery. Concurrently, entirely new classes of porphyrin nanostructures are being developed, such as smart materials that are activated by specific biochemicals encountered at disease sites. Techniques have been developed that improve treatments by combining biomaterials with photosensitizers and functional moieties such as peptides, DNA and antibodies. Compared to simpler structures, these more complex and functional designs can potentially decrease side effects and lead to safer and more efficient phototherapies. This review examines recent research on porphyrin-derived materials in multimodal imaging, drug delivery, bio-sensing, phototherapy and probe design, demonstrating their bright future for biomedical applications.

To see bruxism: a functional MRI study

OBJECTIVE

Since the pathophysiology of bruxism is not clearly understood, there exists no possible treatment. The aim of this study is to investigate the cerebral activation differences between healthy subjects and patients with bruxism on behalf of possible aetiological factors.

METHODS

12 healthy subjects and 12 patients with bruxism, a total of 24 right-handed female subjects (aged 20-27 years) were examined using functional MRI during tooth-clenching and resting tasks. Imaging was performed with 3.0-T MRI scanner with a 32-channel head coil. Differences in regional brain activity between patients with bruxism and healthy subjects (control group) were observed with BrainVoyager QX 2.8 (Brain Innovation, Maastricht, Netherlands) statistical data analysis program. Activation maps were created using the general linear model: single study and multistudy multisubject for statistical group analysis. This protocol was approved by the ethics committee of medical faculty of Kirikkale University, Turkey (02/04), based on the guidelines set forth in the Declaration of Helsinki.

RESULTS

The group analysis revealed a statistically significant increase in blood oxygenation level-dependent signal of three clusters in the control group (p<0.005), which may indicate brain regions related with somatognosis, repetitive passive motion, proprioception and tactile perception. These areas coincide with Brodmann areas 7, 31, 39 and 40. It is conceivable that there are differences between healthy subjects and patients with bruxism.

CONCLUSIONS

Our findings indicate that there was a decrease of cortical activation pattern in patients with bruxism in clenching tasks. This indicates decreased blood flow and activation in regional neuronal activity. Bruxism, as an oral motor disorder concerns dentistry, neurology and psychiatry. These results might improve the understanding and physiological handling of sleep bruxism.

Assessment of competence in surgical skills using functional magnetic resonance imaging: a feasibility study

BACKGROUND

Patient safety is fundamental to modern medical practice; safe surgery saves lives. Ensuring surgical competence is becoming more difficult at a time when surgeons are being trained in fewer hours. Accurate objective assessment of technical skills ability is lacking in standardization. Functional magnetic resonance imaging (fMRI) has a long history in neuroscience, psychiatry, and cognitive studies. Many studies have explored levels of perceived expertise in sports and musical ability. Little has been published on actual rather than perceived motor skills. This study sought to assess the feasibility of utilizing a novel assessment method by measuring blood oxygen level-dependent signal changes (BOLD) in specific brain regions via fMRI during a surgical skills task.

METHODS

Images were acquired using fMRI in a pilot study of 9 subjects (3 experts, 3 intermediates, and 3 novices) when performing and imagining performing a basic surgical procedure: hand tying of surgical knots. Level of expertise was based on years of experience and clinical grade. The quality and quantity of knots were assessed objectively by 2 experts who were independent of the study and blinded to the ability of the candidate. The effect of subject head motion caused by the task itself was assessed. The efficacy of fMRI data analyses in removing artifacts caused by this noise source in the data was explored.

RESULTS

Shifts of less than 1 voxel (3 × 3 × 3.55 mm(3)) were recorded in all participants and were successfully corrected in all cases in the fMRI preprocessing step. Decreased BOLD activity was observed in experts compared to novices when "knot tying" was compared with the control "finger tap." Increased BOLD activity was observed in experts compared with novices when "imagining a task" in the primary visual cortex, an area important in perceptual learning. Experts and intermediates performed consistently with 100% square knots. Novices had an average of 2 slip knots. Regarding knot quantity, the number of knots ranged from 14 to 26 in novices, 38 to 47 in intermediates, and 54 to 58 in experts. A Kruskal-Wallis rank sum test revealed that the difference between the 3 groups was statistically significant in the quantity of square knots tied (p = 0.147). Specific regions of interest identified concurred with findings of previous studies and included the left supramarginal, left rolandic operculum, and left postcentral regions.

CONCLUSION

We found that fMRI is a feasible method of exploring actual and perceived motor skill abilities. Head motion during performance of a motor skill does not preclude the attainment of meaningful data. Larger numbers are needed to further investigate these early findings.

Functional mapping of the human visual cortex with intravoxel incoherent motion MRI

Functional imaging with intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) is demonstrated. Images were acquired at 3 Tesla using a standard Stejskal-Tanner diffusion-weighted echo-planar imaging sequence with multiple b-values. Cerebro-spinal fluid signal, which is highly incoherent, was suppressed with an inversion recovery preparation pulse. IVIM microvascular perfusion parameters were calculated according to a two-compartment (vascular and non-vascular) diffusion model. The results obtained in 8 healthy human volunteers during visual stimulation are presented. The IVIM blood flow related parameter fD* increased 170% during stimulation in the visual cortex, and 70% in the underlying white matter.

The history of MR imaging as seen through the pages of radiology

The first reports in Radiology pertaining to magnetic resonance (MR) imaging were published in 1980, 7 years after Paul Lauterbur pioneered the first MR images and 9 years after the first human computed tomographic images were obtained. Historical advances in the research and clinical applications of MR imaging very much parallel the remarkable advances in MR imaging technology. These advances can be roughly classified into hardware (eg, magnets, gradients, radiofrequency [RF] coils, RF transmitter and receiver, MR imaging-compatible biopsy devices) and imaging techniques (eg, pulse sequences, parallel imaging, and so forth). Image quality has been dramatically improved with the introduction of high-field-strength superconducting magnets, digital RF systems, and phased-array coils. Hybrid systems, such as MR/positron emission tomography (PET), combine the superb anatomic and functional imaging capabilities of MR imaging with the unsurpassed capability of PET to demonstrate tissue metabolism. Supported by the improvements in hardware, advances in pulse sequence design and image reconstruction techniques have spurred dramatic improvements in imaging speed and the capability for studying tissue function. In this historical review, the history of MR imaging technology and developing research and clinical applications, as seen through the pages of Radiology, will be considered.

The Ionic DTI Model (iDTI) of Dynamic Diffusion Tensor Imaging (dDTI)

Measurements of water molecule diffusion along fiber tracts in CNS by diffusion tensor imaging (DTI) provides a static map of neural connections between brain centers, but does not capture the electrical activity along axons for these fiber tracts. Here, a modification of the DTI method is presented to enable the mapping of active fibers. It is termed dynamic diffusion tensor imaging (dDTI) and is based on a hypothesized “anisotropy reduction due to axonal excitation” (“AREX”). The potential changes in water mobility accompanying the movement of ions during the propagation of action potentials along axonal tracts are taken into account. Specifically, the proposed model, termed “ionic DTI model”, was formulated as follows.•

First, based on theoretical calculations, we calculated the molecular water flow accompanying the ionic flow perpendicular to the principal axis of fiber tracts produced by electrical conduction along excited myelinated and non-myelinated axons.

•

Based on the changes in molecular water flow we estimated the signal changes as well as the changes in fractional anisotropy of axonal tracts while performing a functional task.

•

The variation of fractional anisotropy in axonal tracts could allow mapping the active fiber tracts during a functional task.

Although technological advances are necessary to enable the robust and routine measurement of this electrical activity-dependent movement of water molecules perpendicular to axons, the proposed model of dDTI defines the vectorial parameters that will need to be measured to bring this much needed technique to fruition.

Survey of encoding and decoding of visual stimulus via FMRI: an image analysis perspective

A variety of exciting scientific achievements have been made in the last few decades in brain encoding and decoding via functional magnetic resonance imaging (fMRI). This trend continues to rise in recent years, as evidenced by the increasing number of published papers in this topic and several published survey papers addressing different aspects of research issues. Essentially, these survey articles were mainly from cognitive neuroscience and neuroimaging perspectives, although computational challenges were briefly discussed. To complement existing survey articles, this paper focuses on the survey of the variety of image analysis methodologies, such as neuroimage registration, fMRI signal analysis, ROI (regions of interest) selection, machine learning algorithms, reproducibility analysis, structural and functional connectivity, and natural image analysis, which were employed in previous brain encoding/decoding research works. This paper also provides discussions of potential limitations of those image analysis methodologies and possible future improvements. It is hoped that extensive discussions of image analysis issues could contribute to the advancements of the increasingly important brain encoding/decoding field.

Enhancing dentate gyrus function with dietary flavanols improves cognition in older adults

The dentate gyrus (DG) is a region in the hippocampal formation whose function declines in association with human aging and is therefore considered to be a possible source of age-related memory decline. Causal evidence is needed, however, to show that DG-associated memory decline in otherwise healthy elders can be improved by interventions that enhance DG function. We addressed this issue by first using a high-resolution variant of functional magnetic resonance imaging (fMRI) to map the precise site of age-related DG dysfunction and to develop a cognitive task whose function localized to this anatomical site. Then, in a controlled randomized trial, we applied these tools to study healthy 50-69-year-old subjects who consumed either a high or low cocoa flavanol-containing diet for 3 months. A high-flavanol intervention was found to enhance DG function, as measured by fMRI and by cognitive testing. Our findings establish that DG dysfunction is a driver of age-related cognitive decline and suggest non-pharmacological means for its amelioration.

Evaluation of esophageal sensation

Dramatic progress has been made over the past decade in the sophistication and availability of equipment to test esophageal motility and sensation. High-resolution esophageal manometry and impedance have moved from the research clinic into clinical practice. Some of the testing is costly and time consuming, and requires extensive experience to perform the testing and properly interpret the results. These sensory studies are valuable in the interpretation of clinical problems, and provide important research information. Clinicians should evaluate the research studies to advance their understanding of the pathophysiology of the esophagus.

Physiological measurements using ultra-high field fMRI: a review

Functional MRI (fMRI) has grown to be the neuroimaging technique of choice for investigating brain function. This topical review provides an outline of fMRI methods and applications, with a particular emphasis on the recent advances provided by ultra-high field (UHF) scanners to allow functional mapping with greater sensitivity and improved spatial specificity. A short outline of the origin of the blood oxygenation level dependent (BOLD) contrast is provided, followed by a review of BOLD fMRI methods based on gradient-echo (GE) and spin-echo (SE) contrast. Phase based fMRI measures, as well as perfusion contrast obtained with the technique of arterial spin labelling (ASL), are also discussed. An overview of 7 T based functional neuroimaging is provided, outlining the potential advances to be made and technical challenges to be addressed.

Sedation agents differentially modulate cortical and subcortical blood oxygenation: evidence from ultra-high field MRI at 17.2 T

BACKGROUND

Sedation agents affect brain hemodynamic and metabolism leading to specific modifications of the cerebral blood oxygenation level. We previously demonstrated that ultra-high field (UHF) MRI detects changes in cortical blood oxygenation following the administration of sedation drugs commonly used in animal research. Here we applied the UHF-MRI method to study clinically relevant sedation drugs for their effects on cortical and subcortical (thalamus, striatum) oxygenation levels.

METHODS

We acquired T2*-weighted images of Sprague-Dawley rat brains at 17.2T in vivo. During each MRI session, rats were first anesthetized with isoflurane, then with a second sedative agent (sevoflurane, propofol, midazolam, medetomidine or ketamine-xylazine) after stopping isoflurane. We computed a T2*-oxygenation-ratio that aimed at estimating cerebral blood oxygenation level for each sedative agent in each region of interest: cortex, hippocampus, thalamus and striatum.

RESULTS

The T2*-oxygenation-ratio was consistent across scan sessions. This ratio was higher with inhalational agents than with intravenous agents. Under sevoflurane and medetomidine, T2*-oxygenation-ratio was homogenous across the brain regions. Intravenous agents (except medetomidine) induced a T2*-oxygenation-ratio imbalance between cortex and subcortical regions: T2*-oxygenation-ratio was higher in the cortex than the subcortical areas under ketamine-xylazine; T2*-oxygenation-ratio was higher in subcortical regions than in the cortex under propofol or midazolam.

CONCLUSION

Preclinical UHF MRI is a powerful method to monitor the changes in cerebral blood oxygenation level induced by sedative agents across brain structures. This approach also allows for a classification of sedative agents based on their differential effects on cerebral blood oxygenation level.

Increasing fMRI sampling rate improves Granger causality estimates

Estimation of causal interactions between brain areas is necessary for elucidating large-scale functional brain networks underlying behavior and cognition. Granger causality analysis of time series data can quantitatively estimate directional information flow between brain regions. Here, we show that such estimates are significantly improved when the temporal sampling rate of functional magnetic resonance imaging (fMRI) is increased 20-fold. Specifically, healthy volunteers performed a simple visuomotor task during blood oxygenation level dependent (BOLD) contrast based whole-head inverse imaging (InI). Granger causality analysis based on raw InI BOLD data sampled at 100-ms resolution detected the expected causal relations, whereas when the data were downsampled to the temporal resolution of 2 s typically used in echo-planar fMRI, the causality could not be detected. An additional control analysis, in which we SINC interpolated additional data points to the downsampled time series at 0.1-s intervals, confirmed that the improvements achieved with the real InI data were not explainable by the increased time-series length alone. We therefore conclude that the high-temporal resolution of InI improves the Granger causality connectivity analysis of the human brain.

Dynamic functional imaging of brain glucose utilization using fPET-FDG

Glucose is the principal source of energy for the brain and yet the dynamic response of glucose utilization to changes in brain activity is still not fully understood. Positron emission tomography (PET) allows quantitative measurement of glucose metabolism using 2-[(18)F]-fluorodeoxyglucose (FDG). However, FDG PET in its current form provides an integral (or average) of glucose consumption over tens of minutes and lacks the temporal information to capture physiological alterations associated with changes in brain activity induced by tasks or drug challenges. Traditionally, changes in glucose utilization are inferred by comparing two separate scans, which significantly limits the utility of the method. We report a novel method to track changes in FDG metabolism dynamically, with higher temporal resolution than exists to date and within a single session. Using a constant infusion of FDG, we demonstrate that our technique (termed fPET-FDG) can be used in an analysis pipeline similar to fMRI to define within-session differential metabolic responses. We use visual stimulation to demonstrate the feasibility of this method. This new method has a great potential to be used in research protocols and clinical settings since fPET-FDG imaging can be performed with most PET scanners and data acquisition and analysis are straightforward. fPET-FDG is a highly complementary technique to MRI and provides a rich new way to observe functional changes in brain metabolism.

A neuron-inspired computational architecture for spatiotemporal visual processing: real-time visual sensory integration for humanoid robots

In this article, we present a neurologically motivated computational architecture for visual information processing. The computational architecture's focus lies in multiple strategies: hierarchical processing, parallel and concurrent processing, and modularity. The architecture is modular and expandable in both hardware and software, so that it can also cope with multisensory integrations - making it an ideal tool for validating and applying computational neuroscience models in real time under real-world conditions. We apply our architecture in real time to validate a long-standing biologically inspired visual object recognition model, HMAX. In this context, the overall aim is to supply a humanoid robot with the ability to perceive and understand its environment with a focus on the active aspect of real-time spatiotemporal visual processing. We show that our approach is capable of simulating information processing in the visual cortex in real time and that our entropy-adaptive modification of HMAX has a higher efficiency and classification performance than the standard model (up to ∼+6%).

A universal role of the ventral striatum in reward-based learning: evidence from human studies

Reinforcement learning enables organisms to adjust their behavior in order to maximize rewards. Electrophysiological recordings of dopaminergic midbrain neurons have shown that they code the difference between actual and predicted rewards, i.e., the reward prediction error, in many species. This error signal is conveyed to both the striatum and cortical areas and is thought to play a central role in learning to optimize behavior. However, in human daily life rewards are diverse and often only indirect feedback is available. Here we explore the range of rewards that are processed by the dopaminergic system in human participants, and examine whether it is also involved in learning in the absence of explicit rewards. While results from electrophysiological recordings in humans are sparse, evidence linking dopaminergic activity to the metabolic signal recorded from the midbrain and striatum with functional magnetic resonance imaging (fMRI) is available. Results from fMRI studies suggest that the human ventral striatum (VS) receives valuation information for a diverse set of rewarding stimuli. These range from simple primary reinforcers such as juice rewards over abstract social rewards to internally generated signals on perceived correctness, suggesting that the VS is involved in learning from trial-and-error irrespective of the specific nature of provided rewards. In addition, we summarize evidence that the VS can also be implicated when learning from observing others, and in tasks that go beyond simple stimulus-action-outcome learning, indicating that the reward system is also recruited in more complex learning tasks.

Activation of the prefrontal cortex in a nonspatial working memory task with functional MRI

Functional magnetic resonance imaging (fMRI) was used to examine the pattern of activity of the prefrontal cortex during performance of subjects in a nonspatial working memory task. Subjects observed sequences of letters and responded whenever a letter repeated with exactly one nonidentical letter intervening. In a comparison task, subjects monitored similar sequences of letters for any occurrence of a single, prespecified target letter. Functional scanning was performed using a newly developed spiral scan image acquisition technique that provides high-resolution, multislice scanning at approximately five times the rate usually possible on conventional equipment (an average of one image per second). Using these methods, activation of the middle and inferior frontal gyri was reliably observed within individual subjects during performance of the working memory task relative to the comparison task. Effect sizes (2-4%) closely approximated those that have been observed within primary sensory and motor cortices using similar fMRI techniques. Furthermore, activation increased and decreased with a time course that was highly consistent with the task manipulations. These findings corroborate the results of positron emission tomography studies, which suggest that the prefrontal cortex is engaged by tasks that rely on working memory. Furthermore, they demonstrate the applicability of newly developed fMRI techniques using conventional scanners to study the associative cortex in individual subjects. © 1994 Wiley-Liss, Inc.