Role of functional imaging in neurological disorders

Exploring the application and challenges of fNIRS technology in early detection of Parkinson's disease

Background

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that significantly benefits from early diagnosis for effective disease management and intervention. Despite advancements in medical technology, there remains a critical gap in the early and non-invasive detection of PD. Current diagnostic methods are often invasive, expensive, or late in identifying the disease, leading to missed opportunities for early intervention.

Objective

The goal of this study is to explore the efficiency and accuracy of combining fNIRS technology with machine learning algorithms in diagnosing early-stage PD patients and to evaluate the feasibility of this approach in clinical practice.

Methods

Using an ETG-4000 type near-infrared brain function imaging instrument, data was collected from 120 PD patients and 60 healthy controls. This cross-sectional study employed a multi-channel mode to monitor cerebral blood oxygen changes. The collected data were processed using a general linear model and β values were extracted. Subsequently, four types of machine learning models were developed for analysis: Support vector machine (SVM), K-nearest neighbors (K-NN), random forest (RF), and logistic regression (LR). Additionally, SHapley Additive exPlanations (SHAP) technology was applied to enhance model interpretability.

Results

The SVM model demonstrated higher accuracy in differentiating between PD patients and control group (accuracy of 85%, f1 score of 0.85, and an area under the ROC curve of 0.95). SHAP analysis identified the four most contributory channels (CH) as CH01, CH04, CH05, and CH08.

Conclusion

The model based on the SVM algorithm exhibited good diagnostic performance in the early detection of PD patients. Future early diagnosis of PD should focus on the Frontopolar Cortex (FPC) region.

Reorganization of the brain in spinal cord injury: a meta-analysis of functional MRI studies

PURPOSE

Reorganization of the brain is considered the key mechanism of functional recovery in patients after spinal cord injury (SCI). This meta-analysis assessed abnormal brain activation in SCI patients to understand the pattern of reorganization in the brain after SCI.

METHODS

Functional magnetic resonance imaging (fMRI) studies that compared SCI patients with controls and were published before August 30, 2018, were extracted from the PubMed, Web of Science, and EMBASE databases. Voxel-wise whole-brain meta-analysis and region-of-interest meta-analysis of group differences were separately performed. Then, meta-regression analysis was conducted with several clinical characteristics as regressors.

RESULTS

Sixteen studies that met the inclusion criteria were identified. Compared with control individuals, SCI patients showed increased activation in the sensorimotor cortex in both whole-brain and region-of-interest (ROI) analyses. In addition, whole-brain meta-analysis revealed increased activation in the cerebellum, and this increase was positively correlated with lesion level and injury severity.

CONCLUSION

Our results demonstrated that reorganization occurred mainly in the sensorimotor system of the brain after SCI, implying that brain functions involved in sensorimotor demands can still be preserved in this condition. These findings provide opportunities for future studies in terms of therapeutic strategies and prognosis assessment.

Validations of apomorphine-induced BOLD activation correlations in hemiparkinsonian rhesus macaques

Identification of Parkinson's disease at the earliest possible stage of the disease may provide the best opportunity for the use of disease modifying treatments. However, diagnosing the disease during the pre-symptomatic period remains an unmet goal. To that end, we used pharmacological MRI (phMRI) to assess the function of the cortico-basal ganglia circuit in a non-human primate model of dopamine deficiency to determine the possible relationships between phMRI signals with behavioral, neurochemical, and histological measurements. Animals with unilateral treatments with the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), that expressed stable, long-term hemiparkinsonism were challenged with the dopaminergic receptor agonist, apomorphine, and structure-specific phMRI blood oxygen level-dependent (BOLD) activation responses were measured. Behavioral, histopathological, and neurochemical measurements were obtained and correlated with phMRI activation of structures of the cortico-basal ganglia system. Greater phMRI activations in the basal ganglia and cortex were associated with slower movement speed, decreased daytime activity, or more pronounced parkinsonian features. Animals showed decreased stimulus-evoked dopamine release in the putamen and substantia nigra pars compacta and lower basal glutamate levels in the motor cortex on the MPTP-lesioned hemisphere compared to the contralateral hemisphere. The altered neurochemistry was significantly correlated with phMRI signals in the motor cortex and putamen. Finally, greater phMRI activations in the caudate nucleus correlated with fewer tyrosine hydroxylase-positive (TH⁺) nigral cells and decreased TH⁺ fiber density in the putamen. These results reveal the correlation of phMRI signals with the severity of the motor deficits and pathophysiological changes in the cortico-basal ganglia circuit.

•

Apomorphine in hemiparkinsonian animals can evoke changes in functional MRI signals.

•

Cortico-basal ganglia activation correlates to behavior, neurochemistry, histology

•

Pharmacological MRI has potential to be biomarker for Parkinson's disease.

Neurogliovascular dysfunction in a model of repeated traumatic brain injury

Traumatic brain injury (TBI) research has focused on moderate to severe injuries as their outcomes are significantly worse than those of a mild TBI (mTBI). However, recent epidemiological evidence has indicated that a series of even mild TBIs greatly increases the risk of neurodegenerative and psychiatric disorders. Neuropathological studies of repeated TBI have identified changes in neuronal ionic concentrations, axonal injury, and cytoskeletal damage as important determinants of later life neurological and mood compromise; yet, there is a paucity of data on the contribution of neurogliovascular dysfunction to the progression of repeated TBI and alterations of brain function in the intervening period.

Methods: Here, we established a mouse model of repeated TBI induced via three electromagnetically actuated impacts delivered to the intact skull at three-day intervals and determined the long-term deficits in neurogliovascular functioning in Thy1-ChR2 mice. Two weeks post the third impact, cerebral blood flow and cerebrovascular reactivity were measured with arterial spin labelling magnetic resonance imaging. Neuronal function was investigated through bilateral intracranial electrophysiological responses to optogenetic photostimulation. Vascular density of the site of impacts was measured with in vivo two photon fluorescence microscopy. Pathological analysis of neuronal survival and astrogliosis was performed via NeuN and GFAP immunofluorescence.

Results: Cerebral blood flow and cerebrovascular reactivity were decreased by 50±16% and 70±20%, respectively, in the TBI cohort relative to sham-treated animals. Concomitantly, electrophysiological recordings revealed a 97±1% attenuation in peri-contusional neuronal reactivity relative to sham. Peri-contusional vascular volume was increased by 33±2% relative to sham-treated mice. Pathological analysis of the peri-contusional cortex demonstrated astrogliosis, but no changes in neuronal survival.

Conclusion: This work provides the first in-situ characterization of the long-term deficits of the neurogliovascular unit following repeated TBI. The findings will help guide the development of diagnostic markers as well as therapeutics targeting neurogliovascular dysfunction.

Overexpression of GSN could decrease inflammation and apoptosis in EAE and may enhance vitamin D therapy on EAE/MS

The decrease of gelsolin (GSN) in the blood has been reported in multiple sclerosis (MS) patients and experimental allergic encephalomyelitis (EAE) animals, but the protective effect of GSN on EAE/MS lacks of evidence. In our study, we increased the GSN level in EAE by injecting GSN-overexpress lentivirus (LV-GSN) into the lateral ventricle and caudal vein and found that GSN administration can delay the onset and decrease the severity of EAE. Vitamin D is proven to have a therapeutic effect on MS/EAE; however, we previously found that vitamin D caused a downregulation of GSN, which might limit vitamin D efficacy. In our current research, we obtained a better symptom and a slowing down progression in EAE after combining vitamin D treatment with a proper increase of GSN. Furthermore, we discovered that the mediation of vitamin D on GSN might occur through the vitamin D receptor (VDR) by using gene interruption and overexpression to regulate the level of VDR in PC12 cells (a rat sympathetic nerve cell line). We also confirmed the anti-apoptotic function of GSN by GSN RNA interference in PC12. Collectively, these results support the therapeutic effect of GSN in EAE, which might enhance Vitamin D therapy in EAE/MS.

Uncovering the etiology of conversion disorder: insights from functional neuroimaging

Conversion disorder (CD) is a syndrome of neurological symptoms arising without organic cause, arguably in response to emotional stress, but the exact neural substrates of these symptoms and the underlying mechanisms remain poorly understood with the hunt for a biological basis afoot for centuries. In the past 15 years, novel insights have been gained with the advent of functional neuroimaging studies in patients suffering from CDs in both motor and nonmotor domains. This review summarizes recent functional neuroimaging studies including functional magnetic resonance imaging (fMRI), single photon emission computerized tomography (SPECT), and positron emission tomography (PET) to see whether they bring us closer to understanding the etiology of CD. Convergent functional neuroimaging findings suggest alterations in brain circuits that could point to different mechanisms for manifesting functional neurological symptoms, in contrast with feigning or healthy controls. Abnormalities in emotion processing and in emotion-motor processing suggest a diathesis, while differential reactions to certain stressors implicate a specific response to trauma. No comprehensive theory emerges from these clues, and all results remain preliminary, but functional neuroimaging has at least given grounds for hope that a model for CD may soon be found.

Changes in brain activation in stroke patients after mental practice and physical exercise: a functional MRI study

Mental practice is a new rehabilitation method that refers to the mental rehearsal of motor imagery content with the goal of improving motor performance. However, the relationship between activated regions and motor recovery after mental practice training is not well understood. In this study, 15 patients who suffered a first-ever subcortical stroke with neurological deficits affecting the right hand, but no significant cognitive impairment were recruited. 10 patients underwent mental practice combined with physical practice training, and 5 patients only underwent physical practice training. We observed brain activation regions after 4 weeks of training, and explored the correlation of activation changes with functional recovery of the affected hands. The results showed that, after 4 weeks of mental practice combined with physical training, the Fugl-Meyer assessment score for the affected right hand was significantly increased than that after 4 weeks of practice training alone. Functional MRI showed enhanced activation in the left primary somatosensory cortex, attenuated activation intensity in the right primary motor cortex, and enhanced right cerebellar activation observed during the motor imagery task using the affected right hand after mental practice training. The changes in brain cortical activity were related to functional recovery of the hand. Experimental findings indicate that cortical and cerebellar functional reorganization following mental practice contributed to the improvement of hand function.

Neuroimaging in amyotrophic lateral sclerosis

The catastrophic system failure in amyotrophic lateral sclerosis is characterized by progressive neurodegeneration within the corticospinal tracts, brainstem nuclei and spinal cord anterior horns, with an extra-motor pathology that has overlap with frontotemporal dementia. The development of computed tomography and, even more so, MRI has brought insights into neurological disease, previously only available through post-mortem study. Although largely research-based, radionuclide imaging has continued to provide mechanistic insights into neurodegenerative disorders. The evolution of MRI to use advanced sequences highly sensitive to cortical and white matter structure, parenchymal metabolites and blood flow, many of which are now applicable to the spinal cord as well as the brain, make it a uniquely valuable tool for the study of a multisystem disorder such as amyotrophic lateral sclerosis. This comprehensive review considers the full range of neuroimaging techniques applied to amyotrophic lateral sclerosis over the last 25 years, the biomarkers they have revealed and future developments.

Auditory processing in autism spectrum disorder: a review

For individuals with autism spectrum disorder or 'ASD' the ability to accurately process and interpret auditory information is often difficult. Here we review behavioural, neurophysiological and imaging literature pertaining to this field with the aim of providing a comprehensive account of auditory processing in ASD, and thus an effective tool to aid further research. Literature was sourced from peer-reviewed journals published over the last two decades which best represent research conducted in these areas. Findings show substantial evidence for atypical processing of auditory information in ASD at behavioural and neural levels. Abnormalities are diverse, ranging from atypical perception of various low-level perceptual features (i.e. pitch, loudness) to processing of more complex auditory information such as prosody. Trends across studies suggest auditory processing impairments in ASD are most likely to present during processing of complex auditory information and are more severe for speech than for non-speech stimuli. The interpretation of these findings with respect to various cognitive accounts of ASD is discussed and suggestions offered for further research.

[Neuroimaging in medicine]

Neuroimaging has in recent years greatly contributed to our understanding of a wide range of aspects of central neurological diseases. These include the classification and localization of disease (e.g., in headache), the understanding of pathology (e.g., in Parkinson's disease), mechanisms of reorganization (e.g., in stroke), and the subclinical progress of disease (e.g., in degenerative diseases). Apart form presurgical mapping, clinical applications of fMRI are limited. However, functional imaging enables the formulation of neurobiological hypotheses that can be tested clinically and is suited to test classical clinical hypotheses about how the brain works. Understanding the mechanisms and the site of pathology, e.g., in cluster headaches, will lead and has led to new therapeutic strategies. New methodological developments for neuroscientific applications are aimed at the integration of functional and morphological connectivity through a combination of magnetic resonance techniques (fMRI, DTI) and electrophysiological (EEG, MEG) recordings. In addition to stimulus-dependent activations, resting state activity has found increasing interest, for example, in sleep research and various psychiatric diseases (e.g., schizophrenia, borderline).

MRI-based functional neuroimaging in ALS: an update

With non-invasive functional imaging techniques, neuroscience has reached a new era of connecting anatomy and function. Although other techniques bear the advantage of either higher temporal or spatial resolution, functional magnetic resonance imaging (fMRI) is the most widely used non-invasive brain imaging technique. fMRI provides an acceptable balance between low patient load and high information capacity with good spatial resolution, making it ideal for clinical research in patients with physical restrictions like those with ALS. Most fMRI studies have provided evidence of a spatial shift of function in motor and extramotor areas in ALS patients. Furthermore, MRI-based functional imaging has supported the clinical findings of frontal cortical involvement not only in patients with ALS/dementia complex but also in patients with ALS and sub-clinical cognitive impairment. Functional MRI will identify the preserved but non-executable functions in ALS patients in the end stage and will set the direction for a new way of thinking on the functional capacities of these patients which will have a major impact on our way of thinking about end-of-life decisions.

Reorganization and preservation of motor control of the brain in spinal cord injury: a systematic review

Reorganization of brain function in people with CNS damage has been identified as one of the fundamental mechanisms involved in the recovery of sensorimotor function. Spinal cord injury (SCI) brain mapping studies during motor tasks aim for assessing the reorganization and preservation of brain networks involved in motor control. Revealing the activation of cortical and subcortical brain areas in people with SCI can indicate principal patterns of brain reorganization when the neurotrauma is distal to the brain. This review assessed brain activation after SCI in terms of intensity, volume, and somatotopic localization, as well as preservation of activation during attempted and/or imagined movements. Twenty-five studies meeting the inclusion criteria could be identified in Medline (1980 to January 2008). Relevant characteristics of studies (level of lesion, time after injury, motor task) and mapping techniques varied widely. Changes in brain activation were found in both cortical and subcortical areas of individuals with SCI. In addition, several studies described a shift in the region of brain activation. These patterns appeared to be dynamic and influenced by the level, completeness, and time after injury, as well as extent of clinical recovery. In addition, several aspects of reorganization of brain function following SCI resembled those reported in stroke. This review demonstrates that brain networks involved in different demands of motor control remain responsive even in chronic paralysis. These findings imply that therapeutic strategies aimed at restoring spinal cord function, even in people with chronic SCI, can build on preserved competent brain control.

Experience--a double edged sword for restorative neural plasticity after brain damage

During the time period following damage, the brain undergoes widespread reorganizational processes. Manipulations of behavioral experience can be potent therapeutic interventions for shaping this reorganization and enhancing long-term functional outcome. Recovery of function is a major concern for survivors of central nervous system damage and management of post-injury rehabilitation is increasingly becoming a topic of chief importance. Animal research, the focus of this review, suggests that, in the absence of behavioral manipulations, the brain is unlikely to realize its full potential for supporting function. However, experiences also have the capacity to be maladaptive for brain and behavioral function. From a treatment perspective, it may be unwise to adopt the canon of "first, do no harm" because maladaptive experiences include behaviors that individuals learn to do on their own. A better understanding of how behavioral experience interacts with brain reorganization could result in rehabilitative therapies, individually tailored and optimized for functional outcome.

[Clinical interest of fMRI and functional exploration methods of brain activity and interactivity: physical and neurophysiological considerations]

After having provided a brief reminder of the principle of the blood oxygen level-dependent (BOLD) contrast effect, the physiological bases of brain activity and the concepts of functional integration and effective connectivity, we describe the most recent approaches, which permit to explore brain activity and putative networks of interconnected active areas in order to examine the normal brain physiology and its dysfunctions. We present various methods and studies of brain activity analysis clinically applicable, and we detail the concepts of functional and effective connectivity, which allow to study the cerebral plasticity which occurs at the child's during the maturation (e.g., dyslexia), at the adult during the ageing (e.g., Alzheimer disease), or still in schizophrenia or Parkinson disease. The study of specific circuits in networks has to allow defining in a more realistic way the dynamic of the central nervous system, which underlies various cerebral functions, both in physiological and pathological conditions. This connectivity approach should improve the diagnostic and facilitate the development of new therapeutic strategies.

Probing overtly spoken language at sentential level: a comprehensive high-field BOLD-fMRI protocol reflecting everyday language demands

Regarding the application of functional magnetic resonance imaging (fMRI) to preoperative mapping of language, the majority of previous studies applied silent vocalization at word level. Since mapping of language targets the protection of overt communication, the selection of the stimulation paradigm is a crucial issue. Typically, everyday language demands overt speech with construction of syntactically and semantically complete sentences. Here, 23 healthy right-handed subjects performed overt vocalization of complete german sentences. Subjects produced these sentences based on visually presented semantic choices. Special efforts were undertaken to minimize motion artifacts and maximize signal gain on a 3-T MR unit. Compared to previous studies, results showed a larger amount of highly reliable fMRI activations over the whole brain. Particularly, high sensitivity was found for Broca's and Wernicke's regions, as well as anterior and inferior temporal areas. Regarding the left hemisphere, simultaneous "Broca" and "Wernicke" activities were found in 95% of all subjects. When including atypical lateralizations, "Broca" and "Wernicke" activations were found in every subject. Overt vocalization at sentential level represents a new comprehensive language task with the potential to generate reliable activation maps that reflect brain activity associated with everyday language demands.

Investigation of human cervical and upper thoracic spinal cord motion: implications for imaging spinal cord structure and function

Spinal cord (SC) motion is thought to be the dominant source of error in current diffusion and spinal functional MRI (fMRI) methods. However, until now, such motion has not been well characterized in three dimensions. While previous studies have predominantly examined motion in the superior/inferior (S/I) direction, the foci of the present study were the anterior/posterior (A/P) and right/left (R/L) components of human cervical and upper thoracic SC motion. Cardiac-gated, turbofast low-angle shot (turbo-FLASH) cinematic MRI was employed at 3T to acquire images of the cord at 24 phases throughout the cardiac cycle. Time-dependent signal fluctuations within voxels adjacent to the cord/cerebrospinal fluid (CSF) interface were then used to measure SC motion, which was found to occur predictably as a function of cardiac activity. Cord movement was largest in the A/P direction, for which principal components of motion were calculated, thereby indicating consistent patterns of SC oscillation that can potentially be used to improve SC imaging.

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

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

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

The clinical potential of functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) has had a huge impact on understanding the healthy human brain. To date it has had much less impact in clinical neuroscience or clinical practice. The reasons for this are in part that the image acquisition, paradigm design, and data analysis strategies used presently are not sufficiently standardized. This makes the comparison of results across individuals, scanning sessions, and centers difficult. Nevertheless, there are emerging applications for clinical fMRI, and as the field matures the number of applications is likely to grow. It seems certain that fMRI has an important role to play in helping us understand the mechanisms of neuropsychiatric diseases and in helping to identify effective therapeutic strategies.