Quantifying cortical resilience in experimental, clinical and epidemiological studies: A conceptually grounded method using non-invasive brain stimulation.
- 作者列表："Hall PA","Erickson K","Lowe C","Sakib MN
OBJECTIVE:Cortical resilience can be defined as the ability of the cortex of the human brain to rebound efficiently from perturbation. This concept is important in both research and clinical practise contexts. However, no direct measure of cortical resilience exists. Inhibitory variants of repetitive Transcranial Magnetic Stimulation (rTMS), such as continuous Theta Burst Stimulation (cTBS), provide a standardized method for inducing a perturbation; when coupled with the assessment of recovery rate from the perturbation, such a paradigm might provide a standardized measure of cortical resilience. This article describes a standardized method for quantifying cortical resilience using TBS protocols. METHODS:A descriptive overview of a method for assessing cortical resilience is presented. Links are drawn between critical facets of the resilience construct and the protocol described. RESULTS:The Cortical Challenge and Recovery Task (CCaRT) method makes use of existing stimulation parameters and cognitive testing paradigms to provide a flexible and conceptually meaningful measure of cortical resilience. CONCLUSIONS:The CCaRT paradigm is potentially useful in research and contexts where cortical resilience is to be measured. The CCaRT paradigm has applicability to epidemiological studies and laboratory experimentation as well as diagnostic practise and clinical trial outcome measures.
目的: 皮质弹性可以被定义为人脑皮层从扰动中有效反弹的能力。这一概念在研究和临床实践背景下都很重要。然而，不存在直接测量皮质弹性的方法。重复经颅磁刺激 (rTMS) 的抑制性变体，如连续 θ 爆发刺激 (cTBS)，提供了诱导扰动的标准化方法; 当与来自扰动的治愈率评估相结合时，这样的范例可能提供皮质弹性的标准化测量。本文描述了使用 TBS 协议量化皮质弹性的标准化方法。 方法: 对评估皮质弹性的方法进行描述性概述。在弹性结构的关键方面和所描述的方案之间绘制链接。 结果: 皮质挑战和恢复任务 (cart) 方法利用现有的刺激参数和认知测试范式，提供了一种灵活的、概念上有意义的皮质弹性测量方法。 结论: 在测量皮质弹性的研究和背景下，cpart 范式可能是有用的。Cart 范式适用于流行病学研究和实验室实验以及诊断实践和临床试验结果指标。
METHODS::In recent years, transcranial electrical stimulation (tES) has been used to improve cognitive and perceptual abilities and to boost learning. In the visual domain, transcranial random noise stimulation (tRNS), a type of tES in which electric current is randomly alternating in between two electrodes at high frequency, has shown potential in inducing long lasting perceptual improvements when coupled with tasks such as contrast detection. However, its cortical mechanisms and online effects have not been fully understood yet, and it is still unclear whether these long-term improvements are due to early-stage perceptual enhancements of contrast sensitivity or later stage mechanisms such as learning consolidation. Here we tested tRNS effects on multiple spatial frequencies and orientation, showing that tRNS enhances detection of a low contrast Gabor, but only for oblique orientation and high spatial frequency (12 cycles per degree of visual angle). No improvement was observed for low contrast and vertical stimuli. These results indicate that tRNS can enhance contrast sensitivity already after one training session, however this early onset is dependent on characteristics of the stimulus such as spatial frequency and orientation. In particular, the shallow depth of tRNS is likely to affect superficial layers of the visual cortex where neurons have higher preferred spatial frequencies than cells in further layers, while the lack of effect on vertical stimuli might reflect the optimization of the visual system to see cardinally oriented low contrast stimuli, leaving little room for short-term improvement. Taken together, these results suggest that online tRNS effects on visual perception are the result of a complex interaction between stimulus intensity and cortical anatomy, consistent with previous literature on brain stimulation.
METHODS:OBJECTIVE:There is growing interest in treating diseases by electrical stimulation and block of peripheral autonomic nerves, but a paucity of studies on excitation and block of small diameter autonomic axons. We conducted in vivo quantification of the strength-duration properties, activity-dependent slowing (ADS), and responses to kilohertz frequency (KHF) signals for the rat vagus nerve (VN). APPROACH:We conducted acute in vivo experiments in urethane-anesthetised rats. We placed two cuff electrodes on the left cervical VN and one cuff electrode on the anterior subdiaphragmatic VN. The rostral cervical cuff was used to deliver pulses to quantify recruitment and ADS. The caudal cervical cuff was used to deliver KHF signals. The subdiaphragmatic cuff was used to record compound action potentials (CAPs). MAIN RESULTS:We quantified the input-output recruitment and strength-duration curves. Fits to the data using standard strength-duration equations were qualitatively similar, but the resulting chronaxie and rheobase estimates varied substantially. We measured larger thresholds for the slowest fibres (0.5 to 1 m/s), especially at shorter pulse widths. Using a novel cross-correlation CAP-based analysis, we measured ADS of ~2.3% after 3 min of 2 Hz stimulation, which is comparable to ADS reported for sympathetic efferents in somatic nerves, but much smaller than ADS in cutaneous nociceptors. We found greater ADS with higher stimulation frequency and non-monotonic changes in CV in select cases. We found monotonically increasing block thresholds across frequencies from 10 to 80 kHz for both fast and slow fibres. Further, following 25 s of KHF signal, neural conduction could require tens of seconds to recover. SIGNIFICANCE:The quantification of mammalian autonomic nerve responses to conventional and KHF signals provides essential information for development of peripheral nerve stimulation therapies and for understanding their mechanisms of action.
METHODS:BACKGROUND:Early accounts of forced thought were reported at the onset of a focal seizure, and characterized as vague, repetitive, and involuntary intellectual auras distinct from perceptual or psychic hallucinations or illusions. Here, we examine the neural underpinnings involved in conceptual thought by presenting a series of 3 patients with epilepsy reporting intrusive thoughts during electrical stimulation of the left lateral prefrontal cortex (PFC) during invasive surgical evaluation. We illustrate the widespread networks involved through two independent brain imaging modalities: resting state functional magnetic resonance imaging (fMRI) (rs-fMRI) and task-based meta-analytic connectivity modeling (MACM). METHODS:We report the clinical and stimulation characteristics of three patients with left hemispheric language dominance who demonstrate forced thought with functional mapping. To examine the brain networks underlying this phenomenon, we used the regions of interest (ROI) centered at the active electrode pairs. We modeled functional networks using two approaches: (1) rs-fMRI functional connectivity analysis, representing 81 healthy controls and (2) meta-analytic connectivity modeling (MACM), representing 8260 healthy subjects. We also determined the overlapping regions between these three subjects' rs-fMRI and MACM networks through a conjunction analysis. RESULTS:We identified that left PFC was associated with a large-scale functional network including frontal, temporal, and parietal regions, a network that has been associated with multiple cognitive functions including semantics, speech, attention, working memory, and explicit memory. CONCLUSIONS:We illustrate the neural networks involved in conceptual thought through a unique patient population and argue that PFC supports this function through activation of a widespread network.