Arterial Spin Labeling Reveals Disrupted Brain Networks and Functional Connectivity in Drug-Resistant Temporal Epilepsy

Magnetic resonance imaging in canine idiopathic epilepsy: a mini-review

Magnetic resonance imaging (MRI) in an integral part of the diagnostic workup in canines with idiopathic epilepsy (IE). While highly sensitive and specific in identifying structural lesions, conventional MRI is unable to detect changes at the microscopic level. Utilizing more advanced neuroimaging techniques may provide further information on changes at the neuronal level in the brain of canines with IE, thus providing crucial information on the pathogenesis of canine epilepsy. Additionally, earlier detection of these changes may aid clinicians in the development of improved and targeted therapies. Advances in MRI techniques are being developed which can assess metabolic, cellular, architectural, and functional alterations; as well alterations in neuronal tissue mechanical properties, some of which are currently being applied in research on canine IE. This mini-review focuses on novel MRI techniques being utilized to better understand canine epilepsy, which include magnetic resonance spectroscopy, diffusion-weighted imaging, diffusion tensor imaging, perfusion-weighted imaging, voxel based morphometry, and functional MRI; as well as techniques applied in human medicine and their potential use in veterinary species.

Body mass, neuro-hormonal stress processing, and disease activity in lean to obese people with multiple sclerosis

Overweight and obesity can worsen disease activity in multiple sclerosis (MS). Although psychobiological stress processing is increasingly recognized as important obesity factor that is tightly connected to proinflammatory metabolic hormones and cytokines, its role for MS obesity remains unexplored. Consequently, we investigated the interplay between body mass index (BMI), neural stress processing (functional connectivity, FC), and immuno-hormonal stress parameters (salivary cortisol and T cell glucocorticoid [GC] sensitivity) in 57 people with MS (six obese, 19 over-, 28 normal-, and four underweight; 37 females, 46.4 ± 10.6 years) using an Arterial-Spin-Labeling MRI task comprising a rest and stress stage, along with quantitative PCR. Our findings revealed significant positive connections between BMI and MS disease activity (i.e., higher BMI was accompanied by higher relapse rate). BMI was positively linked to right supramarginal gyrus and anterior insula FC during rest and negatively to right superior parietal lobule and cerebellum FC during stress. BMI showed associations with GC functioning, with higher BMI associated with lower CD8+ FKBP4 expression and higher CD8+ FKBP5 expression on T cells. Finally, the expression of CD8+ FKBP4 positively correlated with the FC of right supramarginal gyrus and left superior parietal lobule during rest. Overall, our study provides evidence that body mass is tied to neuro-hormonal stress processing in people with MS. The observed pattern of associations between BMI, neural networks, and GC functioning suggests partial overlap between neuro-hormonal and neural-body mass networks. Ultimately, the study underscores the clinical importance of understanding multi-system crosstalk in MS obesity.

Disrupted resting-state functional connectivity and network topology in mild traumatic brain injury: an arterial spin labelling study

Mild traumatic brain injury can cause different degrees of cognitive impairment and abnormal brain structure and functional connectivity, but there is still a lack of research on the functional connectivity and topological organization of cerebral blood flow fluctuations. This study explored the cerebral blood flow, functional connectivity and topological organization of the cerebral blood flow network in acute mild traumatic brain injury patients. In total, 48 mild traumatic brain injury patients and 46 well-matched healthy controls underwent resting-state arterial spin labelling perfusion MRI and neuropsychological assessments. The functional connectivity and topological organization of the cerebral blood flow network were analysed. Then, the correlation between the changes in cerebral blood flow network characteristics and cognitive function was explored. Acute mild traumatic brain injury patients showed decreased cerebral blood flow in the right insula and increased cerebral blood flow in the right inferior temporal gyrus and left superior temporal gyrus. Abnormal cerebral blood flow network connection patterns mainly occur in sensorimotor network, default mode network, cingulo-opercular network and occipital network-related regions. Furthermore, mild traumatic brain injury disrupted the topological organization of the whole brain, which manifested as (i) reduced global efficiency; (ii) abnormal degree centrality, betweenness centrality, nodal clustering coefficient and nodal efficiency; and (iii) decreased intermodular connectivity between the occipital network and sensorimotor network. Finally, the change in network topology was correlated with the cognitive score of the mild traumatic brain injury. This study provided evidence of abnormal functional connectivity and network topology based on cerebral blood flow in acute mild traumatic brain injury patients, revealing their potential use as early markers for mild traumatic brain injury, which may contribute to both disease diagnosis and assessment.

Similar neural pathways link psychological stress and brain-age in health and multiple sclerosis

Clinical and neuroscientific studies suggest a link between psychological stress and reduced brain health in health and neurological disease but it is unclear whether mediating pathways are similar. Consequently, we applied an arterial-spin-labeling MRI stress task in 42 healthy persons and 56 with multiple sclerosis, and investigated regional neural stress responses, associations between functional connectivity of stress-responsive regions and the brain-age prediction error, a highly sensitive machine learning brain health biomarker, and regional brain-age constituents in both groups. Stress responsivity did not differ between groups. Although elevated brain-age prediction errors indicated worse brain health in patients, anterior insula-occipital cortex (healthy persons: occipital pole; patients: fusiform gyrus) functional connectivity correlated with brain-age prediction errors in both groups. Finally, also gray matter contributed similarly to regional brain-age across groups. These findings might suggest a common stress-brain health pathway whose impact is amplified in multiple sclerosis by disease-specific vulnerability factors.

The cerebellum's understated role and influences in the epilepsies

Approximately 1 in 26 people will develop epilepsy in their lifetime, but current treatment options leave as many as half of all epilepsy patients with uncontrolled seizures. In addition to the burden of the seizures themselves, chronic epilepsy can be associated with cognitive deficits, structural changes, and devastating negative outcomes such as sudden unexpected death in epilepsy (SUDEP). Thus, major challenges in epilepsy research surround the need to both develop new therapeutic targets for intervention as well as shed light on the mechanisms by which chronic epilepsy can lead to comorbidities and negative outcomes. Despite not being traditionally associated with epilepsy or seizures, the cerebellum has emerged as not only a brain region that can serve as an important target for seizure control, but one that may also be profoundly impacted by chronic epilepsy. Here, we discuss targeting the cerebellum for potential therapeutic intervention and discuss pathway insights gained from recent optogenetic studies. We then review observations of cerebellar alterations during seizures and in chronic epilepsy, as well as the potential for the cerebellum to be a seizure focus. Cerebellar alterations in epilepsy may be critical to patient outcomes, highlighting the need for a more comprehensive understanding and appreciation of the cerebellum in the epilepsies.

Alterations of Cerebral Blood Flow and its Connectivity Patterns Measured with Arterial Spin Labeling in Mild Cognitive Impairment

OBJECTIVES

Cerebral blood flow (CBF) is an important index for measuring brain function. Studies have shown that regional CBF changes inconsistently in mild cognitive impairment (MCI). Arterial spin labeling (ASL) is widely used in the study of CBF in patients with MCI. However, alterations in CBF connectivity in these patients remain poorly understood.

METHODS

In this study, 3D pseudo-continuous arterial spin labeling (3D-pCASL) technology was used to investigate the changes in regional CBF and CBF connectivity between 32 MCI patients and 32 healthy controls. The normalized CBF was used to reduce inter-subject variations. Both group comparisons in the CBF and correlations between CBF alterations and cognitive scores were assessed. CBF connectivity of brain regions with regional CBF differences was also compared between groups.

RESULTS

We found that compared with that in controls, the CBF was significantly reduced in the left superior parietal gyrus in MCI patients, whereas it was increased in the left precentral gyrus, right superior temporal gyrus, right putamen, and left supplementary motor area. In patients with MCI, significant correlations were identified between CBF and neuropsychological scales. Importantly, MCI patients exhibited CBF disconnections between the left supplementary motor area and the left superior parietal gyrus.

CONCLUSION

This study found that there are not only changes in regional CBF but also in CBF connectivity patterns in MCI patients compared with controls. These observations may provide a novel explanation for the neural mechanism underlying the pathophysiology in patients with Alzheimer's disease and MCI.

Recent Technical Developments in ASL: A Review of the State of the Art

This review article provides an overview of a range of recent technical developments in advanced arterial spin labeling (ASL) methods that have been developed or adopted by the community since the publication of a previous ASL consensus paper by Alsop et al. It is part of a series of review/recommendation papers from the International Society for Magnetic Resonance in Medicine Perfusion Study Group. Here, we focus on advancements in readouts and trajectories, image reconstruction, noise reduction, partial volume correction, quantification of nonperfusion parameters, fMRI, fingerprinting, vessel selective ASL, angiography, deep learning, and ultrahigh field ASL. We aim to provide a high level of understanding of these new approaches and some guidance for their implementation, with the goal of facilitating the adoption of such advances by research groups and by MRI vendors. Topics outside the scope of this article that are reviewed at length in separate articles include velocity selective ASL, multiple-timepoint ASL, body ASL, and clinical ASL recommendations.

Brain networks in patients with isolated or recurrent transient global amnesia

OBJECTIVES

The aim of this study was to investigate differences in cerebral blood flow (CBF) and functional networks between transient global amnesia (TGA) patients with a single event and those with recurrent events using arterial spin labeling (ASL) MRI.

METHODS

We enrolled patients with TGA and classified them into two groups according to the number of TGA events: TGA patients with a single event and those with recurrent events. MRI scans were performed within 24 h after TGA ictal onset in all patients. We quantified CBF and analyzed the functional network based on CBF using graph theory, and determined the differences in CBF and functional networks between the groups.

RESULTS

We enrolled 44 patients with TGA. Among them, 6 patients had recurrent TGA events, whereas 38 patients had a single TGA event. No regions had significantly different CBFs between TGA patients with recurrent events and those with a single event. The global functional network analysis found that the eccentricity was significantly higher in TGA patients with recurrent events than in those with a single event (5.829 vs. 4.657, p = .001). The local functional network analysis showed that several regions had significantly different betweenness centrality and eccentricity measures between TGA patients with recurrent events and those with a single event.

CONCLUSIONS

We demonstrated the differences in the functional network based on CBF using graph theory according to recurrence in patients with TGA. These findings suggest that TGA is a network disease, and functional network alterations in TGA are related to clinical symptoms.

Advances in resting state fMRI acquisitions for functional connectomics

Resting state functional magnetic resonance imaging (rs-fMRI) is based on spontaneous fluctuations in the blood oxygen level dependent (BOLD) signal, which occur simultaneously in different brain regions, without the subject performing an explicit task. The low-frequency oscillations of the rs-fMRI signal demonstrate an intrinsic spatiotemporal organization in the brain (brain networks) that may relate to the underlying neural activity. In this review article, we briefly describe the current acquisition techniques for rs-fMRI data, from the most common approaches for resting state acquisition strategies, to more recent investigations with dedicated hardware and ultra-high fields. Specific sequences that allow very fast acquisitions, or multiple echoes, are discussed next. We then consider how acquisition methods weighted towards specific parts of the BOLD signal, like the Cerebral Blood Flow (CBF) or Volume (CBV), can provide more spatially specific network information. These approaches are being developed alongside the commonly used BOLD-weighted acquisitions. Finally, specific applications of rs-fMRI to challenging regions such as the laminae in the neocortex, and the networks within the large areas of subcortical white matter regions are discussed. We finish the review with recommendations for acquisition strategies for a range of typical applications of resting state fMRI.

The cerebellum and epilepsy

Epilepsy is the fourth most common neurological disorder, but current treatment options provide limited efficacy and carry the potential for problematic adverse effects. There is an immense need to develop new therapeutic interventions in epilepsy, and targeting areas outside the seizure focus for neuromodulation has shown therapeutic value. While not traditionally associated with epilepsy, anatomical, clinical, and electrophysiological studies suggest the cerebellum can play a role in seizure networks, and importantly, may be a potential therapeutic target for seizure control. However, previous interventions targeting the cerebellum in both preclinical and clinical studies have produced mixed effects on seizures. These inconsistent results may be due in part to the lack of specificity inherent with open-loop electrical stimulation interventions. More recent studies, using more targeted closed-loop optogenetic approaches, suggest the possibility of robust seizure inhibition via cerebellar modulation for a range of seizure types. Therefore, while the mechanisms of cerebellar inhibition of seizures have yet to be fully elucidated, the cerebellum should be thoroughly revisited as a potential target for therapeutic intervention in epilepsy. This article is part of the Special Issue "NEWroscience 2018.

Altered cerebral blood flow in patients with unilateral venous pulsatile tinnitus: an arterial spin labeling study

Objectives:

Abnormal neuronal activity and functional connectivity have been reported in patients with venous pulsatile tinnitus (PT). As neuronal activity is closely coupled to regional brain perfusion, the purpose of this study was to investigate the cerebral blood flow (CBF) alterations in patients with unilateral venous PT using arterial spin labeling (ASL).

Methods:

This study included patients with right-sided PT between January 2018 and July 2019. A healthy control (HC) group matched 1:1 for gender and age was also recruited. All subjects underwent ASL scanning using 3.0T MRI. The correlation between altered CBF and Tinnitus Handicap Inventory (THI) score as well as PT duration was analyzed.

Results

Twenty-one patients with right-sided PT and 21 HCs were included. The mean PT duration of the patients was 35.9 ± 32.2 months, and the mean THI score was 64.1 ± 20.3. Compared with the HCs, the PT patients exhibited increased CBF in the left inferior parietal gyrus and decreased CBF in the bilateral lingual gyrus (family-wise error corrected, p < 0.05). The increased CBF in the left inferior parietal gyrus showed a positive correlation with the THI score in PT patients (r = 0.501, p = 0.021).

Conclusions

PT patients exhibit regional CBF alterations. The increased CBF in the left inferior parietal gyrus may reflect the severity of PT.

Advances in knowledge:

This study not only presents evidence for the potential neuropathology of PT from the perspective of CBF alterations but also offers a new method for investigating the neuropathological mechanism of PT.

Noise removal in resting-state and task fMRI: functional connectivity and activation maps

OBJECTIVE

Blood-oxygenated-level dependent (BOLD)-based functional magnetic resonance imaging (fMRI) is a widely used non-invasive tool for mapping brain function and connectivity. However, the BOLD signal is highly affected by non-neuronal contributions arising from head motion, physiological noise and scanner artefacts. Therefore, it is necessary to recover the signal of interest from the other noise-related fluctuations to obtain reliable functional connectivity (FC) results. Several pre-processing pipelines have been developed, mainly based on nuisance regression and independent component analysis (ICA). The aim of this work was to investigate the impact of seven widely used denoising methods on both resting-state and task fMRI.

APPROACH

Task fMRI can provide some ground truth given that the task administered has well established brain activations. The resulting cleaned data were compared using a wide range of measures: motion evaluation and data quality, resting-state networks and task activations, FC.

MAIN RESULTS

Improved signal quality and reduced motion artefacts were obtained with all advanced pipelines, compared to the minimally pre-processed data. Larger variability was observed in the case of brain activation and FC estimates, with ICA-based pipelines generally achieving more reliable and accurate results.

SIGNIFICANCE

This work provides an evidence-based reference for investigators to choose the most appropriate method for their study and data.

Excitation, but not inhibition, of the fastigial nucleus provides powerful control over temporal lobe seizures

KEY POINTS

On-demand optogenetic inhibition of glutamatergic neurons in the fastigial nucleus of the cerebellum does not alter hippocampal seizures in a mouse model of temporal lobe epilepsy. In contrast, on-demand optogenetic excitation of glutamatergic neurons in the fastigial nucleus successfully inhibits hippocampal seizures. With this approach, even a single 50 ms pulse of light is able to significantly inhibit seizures. On-demand optogenetic excitation of glutamatergic fastigial neurons either ipsilateral or contralateral to the seizure focus is able to inhibit seizures. Selective excitation of glutamatergic nuclear neurons provides greater seizure inhibition than broadly exciting nuclear neurons without cell-type specificity.

ABSTRACT

Temporal lobe epilepsy is the most common form of epilepsy in adults, but current treatment options provide limited efficacy, leaving as many as one-third of patients with uncontrolled seizures. Recently, attention has shifted towards more closed-loop therapies for seizure control, and on-demand optogenetic modulation of the cerebellar cortex was shown to be highly effective at attenuating hippocampal seizures. Intriguingly, both optogenetic excitation and inhibition of cerebellar cortical output neurons, Purkinje cells, attenuated seizures. The mechanisms by which the cerebellum impacts seizures, however, are unknown. In the present study, we targeted the immediate downstream projection of vermal Purkinje cells - the fastigial nucleus - in order to determine whether increases and/or decreases in fastigial output can underlie seizure cessation. Though Purkinje cell input to fastigial neurons is inhibitory, direct optogenetic inhibition of the fastigial nucleus had no effect on seizure duration. Conversely, however, fastigial excitation robustly attenuated hippocampal seizures. Seizure cessation was achieved at multiple stimulation frequencies, regardless of laterality relative to seizure focus, and even with single light pulses. Seizure inhibition was greater when selectively targeting glutamatergic fastigial neurons than when an approach that lacked cell-type specificity was used. Together, these results suggest that stimulating excitatory neurons in the fastigial nucleus may be a promising approach for therapeutic intervention in temporal lobe epilepsy.