Name: Short-Latency Afferent Inhibition (Sensorimotor Task)
Uploaded: 2023-04-21T14:45:00
Description: Watch this Scientific Journal Video about Short-Latency Afferent Inhibition Sensorimotor Task at JoVE.com

short-latency afferent inhibition (sensorimotor task)

联合周围神经刺激和可控脉搏参数 TMS

Multiple sensorimotor loops converge in the motor cortex to shape pyramidal tract projections to spinal motor neurons and interneurons1. However, how these sensorimotor loops interact to shape corticospinal projections and motor behavior remains an open question. Short-latency afferent inhibition (SAI) provides a tool to probe the functional properties of convergent sensorimotor loops in motor cortex output. SAI combines motor cortical transcranial magnetic stimulation (TMS) with electrical stimulation of the corresponding peripheral afferent nerve.
TMS is a non-invasive method to safely stimulate pyramidal motor neurons trans-synaptically in the human brain2,3. TMS involves passing a large, transient electric current through a coiled wire placed on the scalp. The transient nature of the electrical current creates a rapidly changing magnetic field that induces an electric current in the brain4. In the case of a single TMS stimulus, the induced current activates a series of excitatory inputs to the pyramidal motor neurons5-7. If the strength of the generated excitatory inputs is sufficient, the descending activity elicits a contralateral muscular response known as the motor-evoked potential (MEP). The latency of the MEP reflects the corticomotor conduction time8. The amplitude of the MEP indexes the excitability of the corticospinal neurons9. The single TMS stimulus that elicits the MEP can also be preceded by a conditioning stimulus10,11,12. These paired-pulse paradigms can be used to index the effects of various interneuron pools on the corticospinal output. In the case of SAI, the peripheral electrical conditioning stimulus is used to probe the impact of the afferent volley on the motor cortical excitability11,13,14,15. The relative timing of the TMS stimulus and peripheral electrical stimulation aligns the action of the TMS stimulus on the motor cortex with the arrival of the afferent projections to the motor cortex. For SAI in the distal upper limb muscles, the median nerve stimulus typically precedes the TMS stimulus by 18-24 ms11,13,15,16. At the same time, SAI increases as the strength of the afferent volley induced by the peripheral stimulus increases13,17,18.
Despite its strong association with the extrinsic properties of the afferent projection to the motor cortex, SAI is a malleable phenomenon implicated in many motor control processes. For example, SAI is reduced in task-relevant muscles before an impending movement19,20,21 but is maintained in adjacent task-irrelevant motor representations19,20,22. The sensitivity to task relevancy is hypothesized to reflect a surround inhibition mechanism23 that aims to reduce unwanted effector recruitment. More recently, it was proposed that the reduction in SAI in the task-relevant effector may reflect a movement-related gating phenomenon designed to suppress expected sensory afference21 and facilitate corrections during sensorimotor planning and execution24. Regardless of the specific functional role, SAI is correlated with reductions in manual dexterity and processing efficiency25. Altered SAI is also associated with an increased risk of falling in older adults26 and compromised sensorimotor function in Parkinson&#39;s disease26,27,28 and individuals with focal hand dystonia29.
Clinical and pharmacological evidence indicates that the inhibitory pathways mediating SAI are sensitive to central cholinergic modulation30. For example, administering the muscarinic acetylcholine receptor antagonist scopolamine reduces SAI31. In contrast, increasing the half-life of acetylcholine via acetylcholinesterase inhibitors enhances SAI32,33. Consistent with pharmacological evidence, SAI is sensitive to several cognitive processes with central cholinergic involvement, including arousal34, reward35, the allocation of attention21,36,37, and memory38,39,40. SAI is also altered in clinical populations with cognitive deficits associated with the loss of cholinergic neurons, such as Alzheimer&#39;s disease41,42,43,44,45,46,47, Parkinson&#39;s disease (with mild cognitive impairment)48,49,50, and mild cognitive impairment47,51,52. The differential modulation of SAI by various benzodiazepines with differential affinities for various &#947;-aminobutyric acid type A (GABAA) receptor subunit types suggests that the SAI inhibitory pathways are distinct from pathways mediating other forms of paired-pulse inhibition30. For example, lorazepam decreases SAI but enhances short-interval cortical inhibition (SICI)53. Zolpidem reduces SAI but has little effect on SICI53. Diazepam increases SICI but has little impact on SAI53. The reduction in SAI by these positive allosteric modulators of GABAA receptor function, coupled with the observation that GABA controls the release of acetylcholine in the brain stem and cortex54, has led to the hypothesis that GABA modulates the cholinergic pathway that projects to the sensorimotor cortex to influence SAI55.
Recently, SAI has been used to investigate interactions between the sensorimotor loops that set procedural motor control processes and those that align procedural processes to explicit top-down goals and cognitive control processes21,36,37,38. The central cholinergic involvement in SAI31 suggests that&#160;SAI may index an executive influence over procedural sensorimotor control and learning. Importantly, these studies have begun to identify the unique effects of cognition on specific sensorimotor circuits by assessing SAI using different TMS current directions. SAI studies typically employ posterior-anterior (PA) induced current, while only a handful of SAI studies have employed anterior-posterior (AP) induced current55. However, using TMS to induce AP compared with PA current during SAI assessment recruits distinct sensorimotor circuits16,56. For example, AP-sensitive, but not PA-sensitive, sensorimotor circuits are altered by cerebellar modulation37,56. Furthermore, AP-sensitive, but not PA-sensitive, sensorimotor circuits are modulated by attention load36. Finally, attention and cerebellar influences may converge on the same AP-sensitive sensorimotor circuits, leading to maladaptive alterations in these circuits37.
Advances in TMS technology provide additional flexibility to manipulate the configuration of the TMS stimulus employed during single-pulse, paired-pulse, and repetitive applications57,58. Controllable pulse parameter TMS (cTMS) stimulators are now commercially available for research use worldwide, and these provide flexible control over the pulse width and shape57. The increased flexibility arises from controlling the discharge duration of two independent capacitors, each responsible for a separate phase of the TMS stimulus. The biphasic or monophasic nature of the stimulus is governed by the relative discharge amplitude from each capacitor, a parameter called the M-ratio. cTMS studies have combined pulse width manipulation with different current directions to demonstrate that the fixed pulse widths used by conventional TMS stimulators (70-82 &#181;s)59,60 likely recruit a mix of functionally distinct sensorimotor circuits during SAI56. Therefore, cTMS is an exciting tool to disentangle further the functional significance of various convergent sensorimotor loops in sensorimotor performance and learning.
This manuscript details a unique SAI approach to studying sensorimotor integration that integrates peripheral electrical stimulation with cTMS during sensorimotor behaviors. This approach improves on the typical SAI approach by assessing the effect of afferent projections on select interneuron populations in the motor cortex that govern the corticospinal output during ongoing sensorimotor behavior. Although relatively new, cTMS provides a distinct advantage in studying sensorimotor integration in typical and clinical populations. Furthermore, the current approach can be easily adapted for use with conventional TMS stimulators and to quantify other forms of afferent inhibition and facilitation, such as long-latency afferent inhibition (LAI)13 or short-latency afferent facilitation (SAF)15.

作者聚焦： 结合周围神经刺激和可控脉搏参数经颅磁刺激以探测感觉运动控制和学习  

结合周围神经刺激和可控脉搏参数经颅磁刺激探测感觉运动控制和学习

This technique provides insight into how sensory information is integrated into motor planning and execution. The implementation of controllable pulse parameter TMS enables us to identify specific sensory to motor pathways and how these pathways may be disrupted in neurological disorders. Motor scale acquisition and performance requires a fine balance between the conscious declarative and subconscious procedural process.Short latency afferent inhibition is a potential marker of how cognition may shape different procedural sensory motor circuits in the motor cortex of healthy and clinical populations. afferent inhibition quantifies the impact of afferent inputs on motor cortical output as elicited by transcranial magnetic stimulation. As a measure of sensory motor integration, it compliments functional magnetic resonance imaging and on electroencephalography by probing the contributions of specific neuronal populations on global hemodynamic and electrical responses elicited by skilled motor behavior.The lock parameters of magnetic stimuli generated by traditional transcranial magnetic stimulators recruit a mixture of sensory motor circuits. On the other hand, controllable pulse parameter transcranial magnetic stimulators unlock several stimulus parameters, enhancing the specificity of sensory motor circuits probed by afferent inhibition during skilled behavior. Assessing sensory motor inhibition during performance is critical to establishing markers of skilled and unskilled motor execution.Reliable and valid markers are an important step in developing enhanced models of motor control that will enhance or boost best practices in healthy populations, as well as minimize the impact of movement disorders through effective clinical interventions. Enhanced modeling of sensory motor circuits and the factors that influence their function can help provide objective markers of function and dysfunction that will inform best practices for motor performance, skill acquisition, and rehabilitation in both healthy and neurological populations. Continued definition of psychomotor and pharmacological influences over sensory motor circuits converging in motor cortex is critical.Combining afferent inhibition with electroencephalography provides an exciting opportunity to quantify afferent inhibition in non-motor areas as a marker of movement disorders and neuropsychiatric disorders.

Watch this Scientific Journal Video about Short-Latency Afferent Inhibition Sensorimotor Task at JoVE.com

Short-Latency Afferent Inhibition (Sensorimotor Task)  

短潜伏期传入抑制（感觉运动任务）

将诱导大脑中PA电流的线圈连接到CTMS刺激器。将脉冲类型设置为单相正，脉冲宽度设置为 120 微秒，M 比设置为 0.2。最后，将刺激强度设置为一毫伏阈值。设置外围电刺激强度后，在个人计算机或PC上启动感觉运动任务软件例程1。接下来，将外围电刺激和TMS刺激之间的刺激间隔设置为21毫秒。将TMS线圈放在第一个背侧骨间或FDI运动热点上，并要求参与者保持FDI肌肉的轻微收缩。将所需数量的无条件和有条件试验保持在每种条件下 8 到 24 次刺激之间。运行感觉运动任务软件例程来控制感觉运动任务，并将行为锁定的数字触发器发送到外围和CTMS刺激器。使用在大脑中感应 AP 电流的线圈重复 AP30 电流配置的过程。外周电调节刺激的平均效果是抑制 TMS 刺激引起的皮质脊髓输出，如条件 MEP 中较小的原始、平均、峰峰值 MEP 振幅与非条件 MEP 和短潜期传入抑制 （SAI） 比率小于 1 所示。AP30 SAI 的 MEP 发病潜伏期越长，反映了皮质脊髓神经元输入的潜伏期越长。在差异效应中，PA120 SAI对于食指反应同样得到增强，无论参与者是排队到食指还是需要在无效队列后将其反应重新映射到食指到非食指。相比之下，AP30 SAI 似乎是根据无效队列是否需要重新映射或朝向食指进行差分调制的。

Research

JoVE Journal

Neuroscience

Short-Latency Afferent Inhibition (Sensorimotor Task)

Combined Peripheral Nerve Stimulation and Controllable Pulse Parameter Transcranial Magnetic Stimulation to Probe Sensorimotor Control and Learning

Skilled motor ability depends on efficiently integrating sensory afference into the appropriate motor commands. Afferent inhibition provides a valuable ...

科研

神经科学

﻿Participant Screening for Transcranial Magnetic Stimulation

Participant Screening for Transcranial Magnetic Stimulation  

经颅磁刺激的受试者筛查

Electromyography (EMG) Electrode Placement

肌电图 （EMG） 电极放置

Peripheral Electrical Stimulator Electrode Placement

外围电刺激器电极放置

Determination of Median Nerve Stimulus Intensity and Optimal Coil Trajectory for TMS

确定TMS的正中神经刺激强度和最佳线圈轨迹

Short-Latency Afferent Inhibition (No Task Baseline)

短潜伏期传入抑制（无任务基线）