Understanding neuroimaging

Deep EEG source localization via EMD-based fMRI high spatial frequency

Brain imaging with a high-spatiotemporal resolution is crucial for accurate brain-function mapping. Electroencephalography (EEG) and functional Magnetic Resonance Imaging (fMRI) are two popular neuroimaging modalities with complementary features that record brain function with high temporal and spatial resolution, respectively. One popular non-invasive way to obtain data with both high spatial and temporal resolutions is to combine the fMRI activation map and EEG data to improve the spatial resolution of the EEG source localization. However, using the whole fMRI map may cause spurious results for the EEG source localization, especially for deep brain regions. Considering the head's conductivity, deep regions' sources with low activity are unlikely to be detected by the EEG electrodes at the scalp. In this study, we use fMRI's high spatial-frequency component to identify the local high-intensity activations that are most likely to be captured by the EEG. The 3D Empirical Mode Decomposition (3D-EMD), a data-driven method, is used to decompose the fMRI map into its spatial-frequency components. Different validation measurements for EEG source localization show improved performance for the EEG inverse-modeling informed by the fMRI's high-frequency spatial component compared to the fMRI-informed EEG source-localization methods. The level of improvement varies depending on the voxels' intensity and their distribution. Our experimental results also support this conclusion.

Does Multisession Cathodal Transcranial Direct Current Stimulation of the Left Dorsolateral Prefrontal Cortex Prime the Effects of Cognitive Behavioral Therapy on Fear of Pain, Fear of Movement, and Disability in Patients with Nonspecific Low Back Pain? A Randomized Clinical Trial Study

Many studies have shown that low back pain (LBP) is associated with psychosomatic symptoms which may lead to brain changes. This study aimed to investigate the effect of the concurrent application of cognitive behavioral therapy (CBT) and transcranial direct electrical stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) on fear of pain, fear of movement, and disability in patients with nonspecific LBP. This study was performed on 45 LBP patients (23 women, 22 men; mean age 33.00 ± 1.77 years) in three groups: experimental (2 mA cathodal tDCS (c-tDCS)), sham (c-tDCS turned off after 30 s), and control (only received CBT). In all groups, CBT was conducted for 20 min per session, with two sessions per week for four weeks. Fear of pain, fear of movement, and disability were evaluated using questionnaires at baseline, immediately after, and one month after completion of interventions. Results indicated that all three different types of intervention could significantly reduce fear and disability immediately after intervention (p > 0.05). However, improvement in the experimental group was significantly higher than in the other groups immediately after and at the one-month follow-up after interventions (p < 0.05). DLPFC c-tDCS can prime the immediate effects of CBT and also the lasting effects on the reduction in the fear of pain, fear of movement, and disability in LBP patients.

Functional MRI evidence for reorganization of language networks after stroke

In this chapter, we review fMRI evidence for language reorganization in individuals with poststroke aphasia. Several studies in the current literature have utilized fMRI as a tool to understand patterns of functional reorganization in poststroke aphasia. Consistent with previous models that have been proposed to explain the trajectory of language recovery, differential patterns of language processing and language recovery have been identified across individuals with poststroke aphasia in different stages of recovery. Overall, a global network breakdown typically occurs in the early stages of aphasia recovery, followed by normalization in "traditional" left hemisphere language networks. Depending on individual characteristics, right hemisphere regions and bilateral domain-general regions may be further recruited. The main takeaway of this chapter is that poststroke aphasia recovery does not depend on individual neural regions, but rather involves a complex interaction among regions in larger networks. Many of the unresolved issues and contrastive findings in the literature warrant further research with larger groups of participants and standard protocols of fMRI implementation.

Spatial muscle activation patterns during different leg exercise protocols in physically active adults using muscle functional MRI: a systematic review

An emerging method to measure muscle activation patterns is muscle functional magnetic resonance imaging (mfMRI), where preexercise and postexercise muscle metabolism differences indicate spatial muscle activation patterns. We evaluated studies employing mfMRI to determine activation patterns of lumbar or lower limb muscles following exercise in physically active adults. Electronic systematic searches were conducted until March 2020. All studies employing ≥1.5 Tesla MRI scanners to compare spatial muscle activation patterns at the level of or inferior to the first lumbar vertebra in healthy, active adults. Two authors independently assessed study eligibility before appraising methodological quality using a National Institutes of Health assessment tool. Because of heterogeneity, findings were synthesized without meta-analysis. Of the 1,946 studies identified, seven qualified for inclusion and pertained to hamstring (n = 5), quadriceps (n = 1) or extrinsic foot (n = 1) muscles. All included studies controlled for internal validity, with one employing assessor blinding. MRI physics and differing research questions explain study methodology heterogeneity. Significant mfMRI findings were: following Nordic exercise, hamstrings with previous trauma (strain or surgical autograft harvest) demonstrated reduced activation compared with unharmed contralateral muscles, and asymptomatic individuals preferentially activated semitendinosus; greater biceps femoris long head to semitendinosus ratios reported following 45° hip extension over Nordic exercise; greater rectus femoris activation occurred in "flywheel" over barbell squats. mfMRI parameters differ on the basis of individual research questions. Individual muscles show greater activation following specific exercises, suggesting exercise specificity may be important for rehabilitation, although evidence is limited to single cohort studies comparing interlimb differences preexercise versus postexercise.

Neuroimaging of pain in animal models: a review of recent literature

Neuroimaging of pain in animals allows us to better understand mechanisms of pain processing and modulation. In this review, we discuss recently published brain imaging studies in rats, mice, and monkeys, including functional magnetic resonance imaging (MRI), manganese-enhanced MRI, positron emission tomography, and electroencephalography. We provide an overview of innovations and limitations in neuroimaging techniques, as well as results of functional brain imaging studies of pain from January 1, 2016, to October 10, 2018. We then discuss how future investigations can address some bias and gaps in the field. Despite the limitations of neuroimaging techniques, the 28 studies reinforced that transition from acute to chronic pain entails considerable changes in brain function. Brain activations in acute pain were in areas more related to the sensory aspect of noxious stimulation, including primary somatosensory cortex, insula, cingulate cortex, thalamus, retrosplenial cortex, and periaqueductal gray. Pharmacological and nonpharmacological treatments modulated these brain regions in several pain models. On the other hand, in chronic pain models, brain activity was observed in regions commonly associated with emotion and motivation, including prefrontal cortex, anterior cingulate cortex, hippocampus, amygdala, basal ganglia, and nucleus accumbens. Neuroimaging of pain in animals holds great promise for advancing our knowledge of brain function and allowing us to expand human subject research. Additional research is needed to address effects of anesthesia, analysis approaches, sex bias and omission, and potential effects of development and aging.

Non-invasive imaging modalities to study neurodegenerative diseases of aging brain

The aim of this article is to highlight current approaches for imaging elderly brain, indispensable for cognitive neuroscience research with emphasis on the basic physical principles of various non-invasive neuroimaging techniques. The first part of this article presents a quick overview of the primary non-invasive neuroimaging modalities used by cognitive neuroscientists such as transcranial magnetic stimulation (TMS), transcranial electrical stimulation (tES), electroencephalography (EEG), magnetoencephalography (MEG), single photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance spectroscopic imaging (MRSI), Profusion imaging, functional magnetic resonance imaging (fMRI), near infrared spectroscopy (NIRS) and diffusion tensor imaging (DTI) along with tractography and connectomics. The second part provides a comprehensive overview of different multimodality imaging techniques for various cognitive neuroscience studies of aging brain.

Functional magnetic resonance imaging in chronic ischaemic stroke

Ischaemic stroke is the leading cause of adult disability worldwide. Effective rehabilitation is hindered by uncertainty surrounding the underlying mechanisms that govern long-term ischaemic injury progression. Despite its potential as a sensitive non-invasive in vivo marker of brain function that may aid in the development of new treatments, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has found limited application in the clinical research on chronic stage stroke progression. Stroke affects each of the physiological parameters underlying the BOLD contrast, markedly complicating the interpretation of BOLD fMRI data. This review summarizes current progress on application of BOLD fMRI in the chronic stage of ischaemic injury progression and discusses means by which more information may be gained from such BOLD fMRI measurements. Concomitant measurements of vascular reactivity, neuronal activity and metabolism in preclinical models of stroke are reviewed along with illustrative examples of post-ischaemic evolution in neuronal, glial and vascular function. The realization of the BOLD fMRI potential to propel stroke research is predicated on the carefully designed preclinical research establishing an ischaemia-specific quantitative model of BOLD signal contrast to provide the framework for interpretation of fMRI findings in clinical populations.This article is part of the themed issue 'Interpreting BOLD: a dialogue between cognitive and cellular neuroscience'.

Magnetic resonance spectroscopy of the occipital cortex and the cerebellar vermis distinguishes individual cats affected with alpha-mannosidosis from normal cats

A genetic deficiency of lysosomal alpha-mannosidase causes the lysosomal storage disease alpha-mannosidosis (AMD), in which oligosaccharide accumulation occurs in neurons and glia. The purpose of this study was to evaluate the role of magnetic resonance spectroscopy (MRS) in detecting the oligosaccharide accumulation in AMD. Five cats with AMD and eight age-matched normal cats underwent in vivo MRS studies with a single voxel short echo time (20 ms) STEAM spectroscopy sequence on a 4.7T magnet. Two voxels were studied in each cat, from the cerebellar vermis and the occipital cortex. Metabolites of brain samples from these regions were extracted with perchloric acid and analyzed by high resolution NMR spectroscopy. A significantly elevated unresolved resonance signal between 3.4 and 4. ppm was observed in the cerebellar vermis and occipital cortex of all AMD cats, which was absent in normal cats. This resonance was shown to be from carbohydrate moieties by high resolution NMR of tissue extracts. Resonances from the Glc-NAc group (1.8-2.2 ppm) along with anomeric proton signals (4.6-5.4 ppm) from undigested oligosaccharides were also observed in the extract spectra from AMD cats. This MRS spectral pattern may be a useful biomarker for AMD diagnosis as well as for assessing responses to therapy.

Tactile sensory and pain networks in the human spinal cord and brain stem mapped by means of functional MR imaging

BACKGROUND AND PURPOSE

Touch and brush sensory stimuli elicit activity in discriminative touch pathways involving specific regions in the spinal cord and brain stem. However, no study has mapped normal sensory activity noninvasively in healthy humans. The purpose of this study is to map the neuronal activity of sensory input to understand abnormal sensory transmission.

MATERIALS AND METHODS

In the present study, spinal fMRI (by using SEEP) was used to map the activity involved with light touch (2 g and 15 g von Frey filaments) and brush stimuli in the brain stem and spinal cords of 8 healthy volunteers. The results were spatially normalized and analyzed with custom-made software. Areas of SEEP activity were identified by using general linear model analysis.

RESULTS

The 2 g von Frey filament showed predominant activity in the medulla around the ipsilateral dorsal gracile and cuneate nuclei. The 15 g filament elicited significant activity in the ipsilateral dorsal and contralateral ventral gray matter areas of the spinal cord, areas around the olivary nuclei, pontine reticular formation, periaqueductal gray, and raphe nuclei in the rostral pons and midbrain. The brush stimuli elicited more activity in the medulla around the ipsilateral cuneate and gracile nuclei.

CONCLUSIONS

The 2 g filament and brush stimuli activated areas associated with a touch response. The 15 g filament activated areas associated with a pain response. The results from this study identify specific neuronal regions in the brain stem and spinal cord involved in sensory transmission and help understand altered sensory and pain states.

Reorganization of brain function during force production after stroke: a systematic review of the literature

BACKGROUND AND PURPOSE

Damage to motor areas of the brain caused by stroke can produce devastating motor deficits, including aberrant control of force. Reorganization of brain function is a fundamental mechanism involved in recovery of motor control after stroke, and recent advances in neuroimaging have enabled study of this reorganization. This review focuses on neuroimaging studies that have examined reorganization of brain function during force production and force modulation after stroke.

METHODS

The type and extent of reorganization after stroke were characterized by three factors: severity of injury, time after stroke, and impact of therapeutic interventions on brain activation during force production. Twenty-six studies meeting the inclusion criteria could be identified in MEDLINE (1980-2007).

RESULTS

Relevant characteristics of studies (lesion location, chronicity of stroke, and motor task) and mapping techniques varied. During force production, increased activation in secondary motor areas occurred in persons with more severe strokes. Reduced recruitment of secondary motor areas during force production was found as a function of increased time since stroke. During force modulation, increased activation in motor areas occurred with greater force generation. Persons with more severe stroke showed greater activation with increasing force compared with persons with less severe stroke. Alteration of brain activation during and after rehabilitative interventions was identified in some studies.

DISCUSSION AND CONCLUSION

This systematic review establishes that reorganization of brain function during force production and force modulation can occur after stroke. These findings imply that therapeutic strategies may target brain reorganization to improve force control and functional recovery after stroke.

SPECT neuroimaging in translational research of CNS disorders

High resolution SPECT imaging is an emerging field and there are only limited studies as yet available in this direction. Still there is continuous effort to achieve better spatial and temporal resolution in order to obtain detailed structural and functional information of different brain regions in small experimental animals. Recently, SPECT imaging system has been used to perform in vivo imaging using specific radioligands to further elucidate the role of dopaminergic, serotonergic, and cholinergic neurotransmission in relation to regional cerebral blood flow in various human CNS disorders and in gene-manipulated mouse models of neurodegeneration. Although in vivo and non-invasive translational research can be performed by high-resolution microPET imaging system, its limited spatial resolution restricts detailed anatomical and functional information of different brain regions involved in disease process. Recently developed NanoSPECT/CT imaging system has a better spatial resolution hence can be used to correlate and confirm microPET imaging data and determine the precise structural and functional anatomy of CNS disorders and their remission. Moreover SPECT imaging system reduces the cost and number of animals and provides detailed information of CNS disorders at the cellular, molecular and genetic level. Furthermore, SPECT system is economical, provides less radiation burden, and can be used to study bio-distribution of newly synthesized radioligands with increased target to non-target ratios, quality control, and clinical applications. It is envisaged that high-resolution SPECT imaging system will further improve in vivo non-invasive translational research on CNS disorders of unknown etiopathogenesis and their treatment in future.

fMRI reliability in subjects with stroke

Functional MRI (fMRI) has become one of the most commonly used neuroimaging tools to assess the cortical effects associated with rehabilitation, learning, or disease recovery in subjects with stroke. Despite this, there has been no systematic study of the reliability of the fMR signal in this population. The purpose of this study was to examine the within- and between-session reliability of fMRI in cortical and cerebellar structures in subjects with stroke during a complex, continuous visual motor task performed with the less affected hand. Nine subjects with stroke underwent four testing trials during two sessions separated by three weeks. Subjects performed a drawing task using an MRI compatible joystick while in the MRI. Methods of analysis evaluated included: percent signal intensity change, active voxel count and a voxel by voxel stat value analysis within and between testing sessions. Reliability was determined with Interclass correlation coefficients (ICC) in the following regions of interest: primary motor (M1), primary sensory (S1), premotor cortex (PMC), medial cerebellum (MCB), and lateral cerebellum (LCB). Results indicate that intensity change has superior reliability to the other methods of analysis (Average ICC across brain regions and trials: intensity change: 0.73, voxel count: 0.58, voxel by voxel: 0.67) and that generally with any analysis method, within-session reliability was higher than between-session, as indicated by higher ICC values across brain regions. Overall, when comparing between-session results, moderate to good reliability was obtained with intensity change (ICC: M1: 0.52, S1: 0.80, SMA: 0.78, PMC: 0.94, MCB: 0.86, and LCB: 0.59). These results show good reliability in subjects with stroke when performing a continuous motor task. These findings give confidence for interpreting fMRI test/retest research in subjects with stroke.