Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Alberta, Canada.
Neurochemical Research Unit, University of Alberta, Edmonton, Alberta, Canada.
PLoS One. 2021 Apr 29;16(4):e0236684. doi: 10.1371/journal.pone.0236684. eCollection 2021.
Artificial forms of mechanical limb stimulation are used within multiple fields of study to determine the level of cortical excitability and to map the trajectory of neuronal recovery from cortical damage or disease. Square-wave mechanical or electrical stimuli are often used in these studies, but a characterization of sensory-evoked response properties to square-waves with distinct fundamental frequencies but overlapping harmonics has not been performed. To distinguish between somatic stimuli, the primary somatosensory cortex must be able to represent distinct stimuli with unique patterns of activity, even if they have overlapping features. Thus, mechanical square-wave stimulation was used in conjunction with regional and cellular imaging to examine regional and cellular response properties evoked by different frequencies of stimulation. Flavoprotein autofluorescence imaging was used to map the somatosensory cortex of anaesthetized C57BL/6 mice, and in vivo two-photon Ca2+ imaging was used to define patterns of neuronal activation during mechanical square-wave stimulation of the contralateral forelimb or hindlimb at various frequencies (3, 10, 100, 200, and 300 Hz). The data revealed that neurons within the limb associated somatosensory cortex responding to various frequencies of square-wave stimuli exhibit stimulus-specific patterns of activity. Subsets of neurons were found to have sensory-evoked activity that is either primarily responsive to single stimulus frequencies or broadly responsive to multiple frequencies of limb stimulation. High frequency stimuli were shown to elicit more population activity, with a greater percentage of the population responding and greater percentage of cells with high amplitude responses. Stimulus-evoked cell-cell correlations within these neuronal networks varied as a function of frequency of stimulation, such that each stimulus elicited a distinct pattern that was more consistent across multiple trials of the same stimulus compared to trials at different frequencies of stimulation. The variation in cortical response to different square-wave stimuli can thus be represented by the population pattern of supra-threshold Ca2+ transients, the magnitude and temporal properties of the evoked activity, and the structure of the stimulus-evoked correlation between neurons.
人工形式的机械肢体刺激在多个研究领域中被用于确定皮质兴奋性水平，并绘制皮质损伤或疾病后神经元恢复的轨迹。在这些研究中，通常使用方波机械或电刺激，但尚未对方波的感觉诱发电响应特性进行特征描述，这些方波具有不同的基频但重叠的谐波。为了区分躯体刺激，初级躯体感觉皮层必须能够用独特的活动模式来表示不同的刺激，即使它们具有重叠的特征。因此，使用机械方波刺激结合区域和细胞成像来检查不同刺激频率引起的区域和细胞响应特性。利用黄素蛋白自发荧光成像来绘制麻醉 C57BL/6 小鼠的躯体感觉皮层，并在体内使用双光子 Ca2+成像来定义在不同频率（3、10、100、200 和 300 Hz）对侧前肢或后肢进行机械方波刺激时神经元的激活模式。数据显示，对各种频率的方波刺激做出反应的肢体相关躯体感觉皮层内的神经元表现出刺激特异性的活动模式。发现一些神经元子集具有感觉诱发性活动，其对单个刺激频率的反应主要，或者对肢体刺激的多个频率广泛反应。高频刺激被证明能引起更多的群体活动，更多的群体反应，更多的细胞具有高振幅反应。这些神经元网络中的刺激诱发细胞间相关性随刺激频率而变化，使得每个刺激引起的图案在同一刺激的多个试验中比在不同刺激频率的试验中更一致。因此，不同方波刺激对皮质的反应可以用超阈值 Ca2+瞬变的群体模式、诱发活动的幅度和时间特性以及神经元之间刺激诱发相关性的结构来表示。
