Altered directional functional connectivity underlies post-stroke cognitive recovery

Important role of the right hemisphere in post-stroke cognitive impairment: a functional near-infrared spectroscopy study

Significance

The current neuromodulation treatment for post-stroke cognitive impairment (PSCI) is formulated based on interhemispheric inhibition, which is particularly relevant in the context of motor disorders after stroke. However, the pathological mechanism of PSCI remains unclear, which is completely different from motor disorders. Therefore, exploring the pathological brain characteristics of PSCI can provide a reliable theoretical basis for effective neuromodulation treatment for it.

Aim

We explored different functional connectivity (FC) manifestations of PSCI with or without aphasia via functional near-infrared spectroscopy (fNIRS) to provide a pathological basis for the neuromodulation strategy.

Approach

We collected cognitive performance and fNIRS data from patients with PSCI without aphasia (PSCI group, n = 33 ) and patients with post-stroke aphasia (PSA group, n = 31 ), using normal cognition stroke patients (SC group, n = 32 ) and healthy subjects (HC group, n = 31 ) as controls. Differences in FC among different types of stroke-related cognitive impairment were analyzed.

Results

The overall FC in the PSCI group was lower than that in the SC or HC group, and the FCs of the right hemisphere, the right default mode network (DMN), and the right central executive network (CEN) of PSCI patients were significantly lower than those of the left ones. In the PSA group, the FCs of the DMN and CEN were not lower than those in the SC and HC groups, and the FC of the left hemisphere was significantly greater than that of the right hemisphere. In addition, the FC of PSCI patients with right lesions was weaker than that of left lesions, which was closely correlated with the cognitive scale.

Conclusions

Unlike the left hemisphere activation strategy commonly used previously, our results suggest that the important role of the right hemisphere may be overlooked in PSCI patients with or without aphasia. Future treatment options and studies could consider focusing on the right hemisphere or bilateral hemispheres.

Natural Antioxidants: An Effective Strategy for the Treatment of Alzheimer's Disease at the Early Stage

The critical role of oxidative stress in Alzheimer's disease (AD) has been recognized by researchers recently, and natural antioxidants have been demonstrated to have anti-AD activity in animal models, such as Ginkgo biloba extract, soy isoflavones, lycopene, and so on. This paper summarized these natural antioxidants and points out that natural antioxidants always have multiple advantages which are help to deal with AD, such as clearing free radicals, regulating signal transduction, protecting mitochondrial function, and synaptic plasticity. Based on the available data, we have created a relatively complete pathway map of reactive oxygen species (ROS) and AD-related targets and concluded that oxidative stress caused by ROS is the core of AD pathogenesis. In the prospect, we introduced the concept of a combined therapeutic strategy, termed "Antioxidant-Promoting Synaptic Remodeling," highlighting the integration of antioxidant interventions with synaptic remodeling approaches as a novel avenue for therapeutic exploration.

Functional balance at rest of hemispheric homologs assessed via normalized compression distance

Introduction

The formation and functioning of neural networks hinge critically on the balance between structurally homologous areas in the hemispheres. This balance, reflecting their physiological relationship, is fundamental for learning processes. In our study, we explore this functional homology in the resting state, employing a complexity measure that accounts for the temporal patterns in neurodynamics.

Methods

We used Normalized Compression Distance (NCD) to assess the similarity over time, neurodynamics, of the somatosensory areas associated with hand perception (S1). This assessment was conducted using magnetoencephalography (MEG) in conjunction with Functional Source Separation (FSS). Our primary hypothesis posited that neurodynamic similarity would be more pronounced within individual subjects than across different individuals. Additionally, we investigated whether this similarity is influenced by hemisphere or age at a population level.

Results

Our findings validate the hypothesis, indicating that NCD is a robust tool for capturing balanced functional homology between hemispheric regions. Notably, we observed a higher degree of neurodynamic similarity in the population within the left hemisphere compared to the right. Also, we found that intra-subject functional homology displayed greater variability in older individuals than in younger ones.

Discussion

Our approach could be instrumental in investigating chronic neurological conditions marked by imbalances in brain activity, such as depression, addiction, fatigue, and epilepsy. It holds potential for aiding in the development of new therapeutic strategies tailored to these complex conditions, though further research is needed to fully realize this potential.

Rethinking Remapping: Circuit Mechanisms of Recovery after Stroke

Stroke is one of the most common causes of disability, and there are few treatments that can improve recovery after stroke. Therapeutic development has been hindered because of a lack of understanding of precisely how neural circuits are affected by stroke, and how these circuits change to mediate recovery. Indeed, some of the hypotheses for how the CNS changes to mediate recovery, including remapping, redundancy, and diaschisis, date to more than a century ago. Recent technological advances have enabled the interrogation of neural circuits with ever greater temporal and spatial resolution. These techniques are increasingly being applied across animal models of stroke and to human stroke survivors, and are shedding light on the molecular, structural, and functional changes that neural circuits undergo after stroke. Here we review these studies and highlight important mechanisms that underlie impairment and recovery after stroke. We begin by summarizing knowledge about changes in neural activity that occur in the peri-infarct cortex, specifically considering evidence for the functional remapping hypothesis of recovery. Next, we describe the importance of neural population dynamics, disruptions in these dynamics after stroke, and how allocation of neurons into spared circuits can restore functionality. On a more global scale, we then discuss how effects on long-range pathways, including interhemispheric interactions and corticospinal tract transmission, contribute to post-stroke impairments. Finally, we look forward and consider how a deeper understanding of neural circuit mechanisms of recovery may lead to novel treatments to reduce disability and improve recovery after stroke.