经典的疼痛学研究认为，痛觉的上传过程中存在两条平行通路，分别负责疼痛的感觉和情绪信息传递。其中，外侧通路负责传递疼痛的感觉信息，包括强度、位置和性质等，内侧通路则传递疼痛的情绪相关信息。尽管近年来有研究提示，内侧疼痛通路可能也具有编码疼痛刺激强度的能力，然而对于其编码特征与外侧通路有何差别却知之甚少。
激光刺激在内外侧痛觉通路诱发的神经反应
为此，中科院心理健康重点实验室罗非研究员、王锦琰副研究员及其团队利用清醒动物神经细胞群单位放电多通道同步记录技术，在大鼠的初级躯体感觉皮层(SI)、丘脑腹后外侧核(VPL)、前扣带皮层(ACC)以及丘脑背内侧核(MD)埋置电极，研究疼痛的内外侧通路对伤害刺激强度的编码特征。其中SI和VPL位于疼痛加工的外侧通路，而ACC和MD位于疼痛加工的内侧通路。研究人员在给予大鼠后肢足底六个递增强度的伤害性激光刺激同时，监测这四个脑区，随后分析其神经元个数、放电频率以及整体放电数这三种编码模式。
研究结果表明：在所有记录到的四个脑区都可以观察到伤害性激光刺激激活的双峰反应；激光刺激强度与有反应神经元数、放电频率以及群放电数之间分别存在显著相关，而群体放电数这种编码方式相比较另外两种编码方式，与激光刺激强度的相关性更为显著；更重要的是，通过判别分析表明，两条通路对伤害性刺激强度的的编码能力相当，且两者共同作用时，编码能力最强。
这一研究证明，内侧通路不仅能够编码伤害刺激强度，且其编码特征与外侧通路神经元相类似，两者共同贡献了对强度的编码，同时表明群放电数可能是一种最优的疼痛强度编码方式。
本研究已发表于《分子疼痛》（Moleculer Pain）。(生物谷 Bioon.com)
doi:10.1186/1744-8069-7-64
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Ensemble encoding of nociceptive stimulus intensity in the rat medial and lateral pain systems
Yang Zhang, Ning Wang, Jin-Yan Wang, Jing-Yu Chang, Donald J Woodward and Fei Luo
Background The ability to encode noxious stimulus intensity is essential for the neural processing of pain perception. It is well accepted that the intensity information is transmitted within both sensory and affective pathways. However, it remains unclear what the encoding patterns are in the thalamocortical brain regions, and whether the dual pain systems share similar responsibility in intensity coding. Results Multichannel single-unit recordings were used to investigate the activity of individual neurons and neuronal ensembles in the rat brain following the application of noxious laser stimuli of increasing intensity to the hindpaw. Four brain regions were monitored, including two within the lateral sensory pain pathway, namely, the ventral posterior lateral thalamic nuclei and the primary somatosensory cortex, and two in the medial pathway, namely, the medial dorsal thalamic nuclei and the anterior cingulate cortex. Neuron number, firing rate, and ensemble spike count codings were examined in this study. Our results showed that the noxious laser stimulation evoked double-peak responses in all recorded brain regions. Significant correlations were found between the laser intensity and the number of responsive neurons, the firing rates, as well as the mass spike counts (MSCs). MSC coding was generally more efficient than the other two methods. Moreover, the coding capacities of neurons in the two pathways were comparable. Conclusion This study demonstrated the collective contribution of medial and lateral pathway neurons to the noxious intensity coding. Additionally, we
