Schnitzler A, Volkmann J, Enck P, Frieling T, Witte O W, Freund H J
Department of Neurology, Heinrich-Heine-University, Düsseldorf, Germany.
Eur J Neurosci. 1999 Jan;11(1):305-15. doi: 10.1046/j.1460-9568.1999.00429.x.
Sensory stimuli from the visceral domain exhibit perceptual characteristics different from stimuli applied to the body surface. Compared with somatosensation there is not much known about the cortical projection and functional organization of visceral sensation in humans. In this study, we determined the cortical areas activated by non-painful electrical stimulation of visceral afferents in the distal oesophagus, and somatosensory afferents in the median nerve and the lip in seven healthy volunteers using whole-head magnetoencephalography. Stimulation of somatosensory afferents elicited short-latency responses (approximately 20-60 ms) in the primary somatosensory cortex (SI) contralateral (median nerve) or bilateral (lip) to the stimulated side, and long-latency responses (approximately 60-160 ms) bilaterally in the second somatosensory cortex (SII). In contrast, stimulation of visceral oesophageal afferents did not evoke discernible responses in SI but well reproducible bilateral SII responses (approximately 70-190 ms) in close vicinity to long-latency SII responses following median nerve and lip stimuli. Psychophysically, temporal discrimination of successive stimuli became worse with increasing stimulus repetition rates (0.25 Hz, 0.5 Hz, 1 Hz, 2 Hz) only for visceral oesophageal, but not for somatosensory median nerve stimuli. Correspondingly, amplitudes of the first cortical response to oesophageal stimulation emerging in the SII cortex declined with increasing stimulus repetition rates whereas the earliest cortical response elicited by median nerve stimuli (20 ms SI response) remained unaffected by the stimulus frequency. Our results indicate that visceral afferents from the oesophagus primarily project to the SII cortex and, unlike somatosensory afferents, lack a significant SI representation. We propose that this cortical projection pattern forms the neurophysiological basis of the low temporal and spatial resolution of conscious visceral sensation.
来自内脏区域的感觉刺激呈现出与施加于身体表面的刺激不同的感知特征。与躯体感觉相比，人类内脏感觉的皮层投射和功能组织所知甚少。在本研究中，我们使用全脑磁脑电图测定了7名健康志愿者中，远端食管内脏传入神经、正中神经躯体感觉传入神经以及唇部躯体感觉传入神经在受到非疼痛性电刺激时所激活的皮层区域。刺激躯体感觉传入神经在受刺激侧对侧（正中神经）或双侧（唇部）的初级躯体感觉皮层（SI）中引发短潜伏期反应（约20 - 60毫秒），并在双侧第二躯体感觉皮层（SII）中引发长潜伏期反应（约60 - 160毫秒）。相比之下，刺激内脏食管传入神经在SI中未引发可辨别的反应，但在正中神经和唇部刺激后的长潜伏期SII反应附近，可重复性良好的双侧SII反应（约70 - 190毫秒）。在心理物理学方面，仅对于内脏食管刺激，随着刺激重复率（0.25赫兹、0.5赫兹、1赫兹、2赫兹）增加，连续刺激的时间辨别变差，而对于躯体感觉正中神经刺激则不然。相应地，SII皮层中出现的对食管刺激的首个皮层反应的幅度随着刺激重复率增加而下降，而正中神经刺激引发的最早皮层反应（20毫秒的SI反应）不受刺激频率影响。我们的结果表明，来自食管的内脏传入神经主要投射到SII皮层，并且与躯体感觉传入神经不同，缺乏显著的SI表征。我们提出，这种皮层投射模式构成了有意识内脏感觉的低时间和空间分辨率的神经生理学基础。
