Pain and Analgesia Imaging Neuroscience Group, McLean Hospital, Belmont, Massachusetts, United States of America.
PLoS One. 2009 Nov 24;4(11):e8016. doi: 10.1371/journal.pone.0008016.
Pain is difficult to assess due to the subjective nature of self-reporting. The lack of objective measures of pain has hampered the development of new treatments as well as the evaluation of current ones. Functional MRI studies of pain have begun to delineate potential brain response signatures that could be used as objective read-outs of pain. Using Diffuse Optical Tomography (DOT), we have shown in the past a distinct DOT signal over the somatosensory cortex to a noxious heat stimulus that could be distinguished from the signal elicited by innocuous mechanical stimuli. Here we further our findings by studying the response to thermal innocuous and noxious stimuli.
METHODOLOGY/PRINCIPAL FINDINGS: Innocuous and noxious thermal stimuli were applied to the skin of the face of the first division (ophthalmic) of the trigeminal nerve in healthy volunteers (N = 6). Stimuli temperatures were adjusted for each subject to evoke warm (equivalent to a 3/10) and painful hot (7/10) sensations in a verbal rating scale (0/10 = no/max pain). A set of 26 stimuli (5 sec each) was applied for each temperature with inter-stimulus intervals varied between 8 and 15 sec using a Peltier thermode. A DOT system was used to capture cortical responses on both sides of the head over the primary somatosensory cortical region (S1). For the innocuous stimuli, group results indicated mainly activation on the contralateral side with a weak ipsilateral response. For the noxious stimuli, bilateral activation was observed with comparable amplitudes on both sides. Furthermore, noxious stimuli produced a temporal biphasic response while innocuous stimuli produced a monophasic response.
CONCLUSIONS/SIGNIFICANCE: These results are in accordance with fMRI and our other DOT studies of innocuous mechanical and noxious heat stimuli. The data indicate the differentiation of DOT cortical responses for pain vs. innocuous stimuli that may be useful in assessing objectively acute pain.
由于自我报告的主观性，疼痛很难评估。缺乏客观的疼痛测量方法不仅阻碍了新疗法的开发，也阻碍了现有疗法的评估。疼痛的功能性磁共振成像研究已经开始描绘出潜在的大脑反应特征，可以作为疼痛的客观读出。我们过去曾使用漫射光学断层扫描 (DOT) 显示，在躯体感觉皮层上，对有害热刺激的 DOT 信号与无害机械刺激引起的信号明显不同。在这里，我们通过研究对热无害和有害刺激的反应进一步扩展了我们的发现。
方法/主要发现：无害和有害的热刺激应用于健康志愿者（N=6）三叉神经第一分支（眼支）的皮肤。根据每个受试者的情况调整刺激温度，以在言语评定量表（0/10=无/最大疼痛）中引起温暖（相当于 3/10）和疼痛热（7/10）感觉。使用 Peltier 热模，以 5 秒为一组（每组 26 个刺激），在每个温度下施加刺激，刺激间隔在 8 到 15 秒之间变化。使用 DOT 系统在头部两侧的初级躯体感觉皮质区域 (S1) 捕获皮质反应。对于无害刺激，组结果主要显示对侧激活，同侧反应较弱。对于有害刺激，观察到双侧激活，两侧幅度相当。此外，有害刺激产生双相时程反应，而无害刺激产生单相反应。
结论/意义：这些结果与 fMRI 和我们对无害机械和有害热刺激的其他 DOT 研究一致。这些数据表明，DOT 皮质反应可用于区分疼痛与无害刺激，这可能有助于客观评估急性疼痛。
