Functional mapping of sensorimotor activation in the human thalamus at 9.4 Tesla

Functional connectivity of thalamic nuclei during sensorimotor task-based fMRI at 9.4 Tesla

The thalamus is the brain's central communication hub, playing a key role in processing and relaying sensorimotor and cognitive information between the cerebral cortex and other brain regions. It consists of specific and non-specific nuclei, each with a different role. Specific thalamic nuclei relay sensory and motor information to specific cortical and subcortical regions to ensure precise communication. In contrast, non-specific thalamic nuclei are involved in general functions such as attention or consciousness through broader and less targeted connections. In the present study, we aimed to investigate the functional connectivity patterns of the thalamic nuclei identified in our previous study as being involved in motor (finger-tapping) and sensory (finger-touch) tasks. The results of this study show that thalamic nuclei are not static hubs with a predefined role in neural signal processing, as they show different task-specific functional connectivity patterns in the anterior, middle, lateral, and posterior thalamic nuclei. Instead, they are all functional hubs that can flexibly change their connections to other brain regions in response to task demands. This work has important implications for understanding task-dependent functional connectivity between thalamic nuclei and different brain regions using task-based fMRI at 9.4 Tesla.

Submillimeter Ultra-High Field 9.4 T Brain MR Image Collection and Manual Cortical Segmentations

The UltraCortex repository houses magnetic resonance imaging data of the human brain obtained at an ultra-high field strength of 9.4 T. It contains 86 structural MR images with spatial resolutions ranging from 0.6 to 0.8 mm. Additionally, the repository includes segmentations of 12 brains into gray and white matter compartments. These segmentations have been independently validated by two expert neuroradiologists, thus establishing them as a reliable gold standard. This resource provides researchers with access to high-quality brain imaging data and validated segmentations, facilitating neuroimaging studies and advancing our understanding of brain structure and function. Existing repositories do not accommodate field strengths beyond 7 T, nor do they offer validated segmentations, underscoring the significance of this new resource.

Tracking longitudinal thalamic volume changes during early stages of SCA1 and SCA2

PURPOSE

Spinocerebellar ataxia SCA1 and SCA2 are adult-onset hereditary disorders, due to triplet CAG expansion in their respective causative genes. The pathophysiology of SCA1 and SCA2 suggests alterations of cerebello-thalamo-cortical pathway and its connections to the basal ganglia. In this framework, thalamic integrity is crucial for shaping efficient whole-brain dynamics and functions. The aims of the study are to identify structural changes in thalamic nuclei in presymptomatic and symptomatic SCA1 and SCA2 patients and to assess disease progression within a 1-year interval.

MATERIAL AND METHODS

A prospective 1-year clinical and MRI assessment was conducted in 27 presymptomatic and 23 clinically manifest mutation carriers for SCA1 and SCA2 expansions. Cross-sectional and longitudinal changes of thalamic nuclei volume were investigated in SCA1 and SCA2 individuals and in healthy participants (n = 20).

RESULTS

Both SCA1 and SCA2 patients had significant atrophy in the majority of thalamic nuclei, except for the posterior and partly medial nuclei. The 1-year longitudinal evaluation showed a specific pattern of atrophy in ventral and posterior thalamus, detectable even at the presymptomatic stage of the disease.

CONCLUSION

For the first time in vivo, our exploratory study has shown that different thalamic nuclei are involved at different stages of the degenerative process in both SCA1 and SCA2. It is therefore possible that thalamic alterations might significantly contribute to the progression of the disease years before overt clinical manifestations occur.

A scoping review on examination approaches for identifying tactile deficits at the upper extremity in individuals with stroke

PURPOSE

Accurate perception of tactile stimuli is essential for performing and learning activities of daily living. Through this scoping review, we sought to summarize existing examination approaches for identifying tactile deficits at the upper extremity in individuals with stroke. The goal was to identify current limitations and future research needs for designing more comprehensive examination tools.

METHODS

A scoping review was conducted in accordance with the Joanna Briggs Institute methodological framework and the PRISMA for Scoping Reviews (PRISMA-ScR) guidelines. A database search for tactile examination approaches at the upper extremity of individuals with stroke was conducted using Medline (Ovid), The Cochrane Library (Wiley), CINAHL Plus with Full Text (Ebsco), Scopus (Elsevier), PsycInfo (Ebsco), and Proquest Dissertations and Theses Global. Original research and review articles that involved adults (18 years or older) with stroke, and performed tactile examinations at the upper extremity were eligible for inclusion. Data items extracted from the selected articles included: if the examination was behavioral in nature and involved neuroimaging, the extent to which the arm participated during the examination, the number of possible outcomes of the examination, the type(s) of tactile stimulation equipment used, the location(s) along the arm examined, the peripheral nerves targeted for examination, and if any comparison was made with the non-paretic arm or with the arms of individuals who are neurotypical.

RESULTS

Twenty-two articles met the inclusion criteria and were accepted in this review. Most examination approaches were behavioral in nature and involved self-reporting of whether a tactile stimulus was felt while the arm remained passive (i.e., no volitional muscle activity). Typically, the number of possible outcomes with these behavioral approaches were limited (2-3), whereas the neuroimaging approaches had many more possible outcomes ( > 15 ). Tactile examinations were conducted mostly at the distal locations along the arm (finger or hand) without targeting any specific peripheral nerve. Although a majority of articles compared paretic and non-paretic arms, most did not compare outcomes to a control group of individuals who are neurotypical.

DISCUSSION

Our findings noted that most upper extremity tactile examinations are behavioral approaches, which are subjective in nature, lack adequate resolution, and are insufficient to identify the underlying neural mechanisms of tactile deficits. Also, most examinations are administered at distal locations of the upper extremity when the examinee's arm is relaxed (passive). Further research is needed to develop better tactile examination tools that combine behavioral responses and neurophysiological outcomes, and allow volitional tactile exploration. Approaches that include testing of multiple body locations/nerves along the upper extremity, provide higher resolution of outcomes, and consider normative comparisons with individuals who are neurotypical may provide a more comprehensive understanding of the tactile deficits occurring following a stroke.

Simultaneous cortical, subcortical, and brainstem mapping of sensory activation

Nonpainful tactile sensory stimuli are processed in the cortex, subcortex, and brainstem. Recent functional magnetic resonance imaging studies have highlighted the value of whole-brain, systems-level investigation for examining sensory processing. However, whole-brain functional magnetic resonance imaging studies are uncommon, in part due to challenges with signal to noise when studying the brainstem. Furthermore, differentiation of small sensory brainstem structures such as the cuneate and gracile nuclei necessitates high-resolution imaging. To address this gap in systems-level sensory investigation, we employed a whole-brain, multi-echo functional magnetic resonance imaging acquisition at 3T with multi-echo independent component analysis denoising and brainstem-specific modeling to enable detection of activation across the entire sensory system. In healthy participants, we examined patterns of activity in response to nonpainful brushing of the right hand, left hand, and right foot (n = 10 per location), and found the expected lateralization, with distinct cortical and subcortical responses for upper and lower limb stimulation. At the brainstem level, we differentiated the adjacent cuneate and gracile nuclei, corresponding to hand and foot stimulation respectively. Our findings demonstrate that simultaneous cortical, subcortical, and brainstem mapping at 3T could be a key tool to understand the sensory system in both healthy individuals and clinical cohorts with sensory deficits.

Simultaneous cortical, subcortical, and brainstem mapping of sensory activation

Non-painful tactile sensory stimuli are processed in the cortex, subcortex, and brainstem. Recent functional magnetic resonance imaging (fMRI) studies have highlighted the value of whole-brain, systems-level investigation for examining pain processing. However, whole-brain fMRI studies are uncommon, in part due to challenges with signal to noise when studying the brainstem. Furthermore, the differentiation of small sensory brainstem structures such as the cuneate and gracile nuclei necessitates high resolution imaging. To address this gap in systems-level sensory investigation, we employed a whole-brain, multi-echo fMRI acquisition at 3T with multi-echo independent component analysis (ME-ICA) denoising and brainstem-specific modeling to enable detection of activation across the entire sensory system. In healthy participants, we examined patterns of activity in response to non-painful brushing of the right hand, left hand, and right foot, and found the expected lateralization, with distinct cortical and subcortical responses for upper and lower limb stimulation. At the brainstem level, we were able to differentiate the small, adjacent cuneate and gracile nuclei, corresponding to hand and foot stimulation respectively. Our findings demonstrate that simultaneous cortical, subcortical, and brainstem mapping at 3T could be a key tool to understand the sensory system in both healthy individuals and clinical cohorts with sensory deficits.

MR-Compatible Tactile Stimulator System: Application for Individuals with Brain Injuries

Accurate perception of tactile information is essential for performing activities of daily living and learning new sensorimotor skills like writing. Deficits in perceiving tactile stimuli are associated with severity in physical disability. The mechanisms contributing to tactile deficits in individuals with brain injuries remain poorly understood in part due to insufficient assessment methods. Here, we provide a tactile stimulator system for studying the neural mechanisms contributing to tactile deficits in individuals with brain injuries during functional magnetic resonance imaging (fMRI). This tactile stimulator system consists of a pneumatically-controlled inflatable and deflatable balloon that interfaces with a digit of the hand to provide small forces. The magnitude of the applied force is delivered and controlled by modifying the air pressure in the balloon. The tactile simulator provides an 8 mm diameter tactile stimulus. The device's interface at the finger is compact, allowing it to be used with individuals who have a closed-fist posture following brain injury such as stroke or cerebral palsy. The tactile stimulator contains no metallic components and can be used in MRI research. The tactile stimulator system can repeatedly apply a force between 1 N and 2.4 N. This tactile stimulator system addresses limitations in past fMRI methodologies for assessing tactile perception by providing precise and repeatable force stimuli to a small area of the finger. Custom software automates the application of the force stimuli and permits synchronization with acquired fMRI data. This system can be used in subsequent testing to investigate deficits in sensory functioning in those with brain injuries.

Disuse-driven plasticity in the human thalamus and putamen

Motor adaptation in cortico-striato-thalamo-cortical loops has been studied mainly in animals using invasive electrophysiology. Here, we leverage functional neuroimaging in humans to study motor circuit plasticity in the human subcortex. We employed an experimental paradigm that combined two weeks of upper-extremity immobilization with daily resting-state and motor task fMRI before, during, and after the casting period. We previously showed that limb disuse leads to decreased functional connectivity (FC) of the contralateral somatomotor cortex (SM1) with the ipsilateral somatomotor cortex, increased FC with the cingulo-opercular network (CON) as well as the emergence of high amplitude, fMRI signal pulses localized in the contralateral SM1, supplementary motor area and the cerebellum. From our prior observations, it remains unclear whether the disuse plasticity affects the thalamus and striatum. We extended our analysis to include these subcortical regions and found that both exhibit strengthened cortical FC and spontaneous fMRI signal pulses induced by limb disuse. The dorsal posterior putamen and the central thalamus, mainly CM, VLP and VIM nuclei, showed disuse pulses and FC changes that lined up with fmri task activations from the Human connectome project motor system localizer, acquired before casting for each participant. Our findings provide a novel understanding of the role of the cortico-striato-thalamo-cortical loops in human motor plasticity and a potential link with the physiology of sleep regulation. Additionally, similarities with FC observation from Parkinson Disease (PD) questions a pathophysiological link with limb disuse.

Denoising task-correlated head motion from motor-task fMRI data with multi-echo ICA

Motor-task functional magnetic resonance imaging (fMRI) is crucial in the study of several clinical conditions, including stroke and Parkinson's disease. However, motor-task fMRI is complicated by task-correlated head motion, which can be magnified in clinical populations and confounds motor activation results. One method that may mitigate this issue is multi-echo independent component analysis (ME-ICA), which has been shown to separate the effects of head motion from the desired blood oxygenation level dependent (BOLD) signal but has not been tested in motor-task datasets with high amounts of motion. In this study, we collected an fMRI dataset from a healthy population who performed a hand grasp task with and without task-correlated amplified head motion to simulate a motor-impaired population. We analyzed these data using three models: single-echo (SE), multi-echo optimally combined (ME-OC), and ME-ICA. We compared the models' performance in mitigating the effects of head motion on the subject level and group level. On the subject level, ME-ICA better dissociated the effects of head motion from the BOLD signal and reduced noise. Both ME models led to increased t-statistics in brain motor regions. In scans with high levels of motion, ME-ICA additionally mitigated artifacts and increased stability of beta coefficient estimates, compared to SE. On the group level, all three models produced activation clusters in expected motor areas in scans with both low and high motion, indicating that group-level averaging may also sufficiently resolve motion artifacts that vary by subject. These findings demonstrate that ME-ICA is a useful tool for subject-level analysis of motor-task data with high levels of task-correlated head motion. The improvements afforded by ME-ICA are critical to improve reliability of subject-level activation maps for clinical populations in which group-level analysis may not be feasible or appropriate, for example, in a chronic stroke cohort with varying stroke location and degree of tissue damage.

Altered brain function and structure pre- and post- COVID-19 infection: a longitudinal study

BACKGROUND

Evidence indicates that the SARS-CoV-2 virus can infect the brain, resulting in central nervous system symptoms. However, there is a lack of a longitudinal imaging study investigating the impact of Coronavirus disease 2019 (COVID-19) infection on brain function. Consequently, this study aimed to fill this knowledge gap using functional magnetic resonance imaging (fMRI).

METHODS

Twenty-one participants underwent two resting-state fMRI scans before and after infection. The amplitude of low-frequency fluctuations (ALFF) and regional homogeneity (ReHo) were assessed to identify the brain function changes. Additionally, voxel-based morphometry (VBM) was utilized to assess changes in brain structure. Subsequently, brain regions that showed significant differences were identified as regions of interest (ROI) in functional connectivity analysis (FC).

RESULTS

After infection, ALFF was increased in the bilateral paracentral lobe and postcentral gyrus while decreased in the bilateral precuneus. Moreover, ReHo was decreased in the cerebellar vermis, accompanied by a decrease in FC with the bilateral postcentral gyrus. Furthermore, gray matter volume (GMV) reduction was observed in the left thalamus. The results of the correlation analysis revealed a negative correlation between ALFF values in the bilateral precuneus and scores on the self-rating anxiety scale (SAS) in pre- and post-infection datasets.

CONCLUSION

Neuroimaging alterations may occur before the manifestation of clinical symptoms, indicating that the functioning of the motor and sensory systems, as well as their connection, might be affected following infection. This alteration can potentially increase the potential of maladaptive responses to environmental stimuli. Furthermore, patients may be susceptible to future emotional disorders.