利用腦內電刺激探討視丘皮質的神經連結

Abstract

所有的體感覺皆會經過視丘，再由視丘皮質路經上傳到相對應的皮質區域。本研究首先會先找出視丘後外側核(ventral-posterolateral nucleus, VPL) 處理體感覺的兩個區域，稱之為VPL-A 與VPL-B，再去探討這兩個區域投射到初級感覺皮質 (primary somatosensory cortex, SI) 的視丘皮質路徑。 在大鼠後肢施與周邊刺激(peripheral electrical stimulation, pES) 找出後肢在VPL與SI的體表映射(somatotopic organization), 接著將建立出後肢在VPL的體表映射圖來找出VPL-A與VPL-B的反應座標與範圍。最後，我們對VPL-A與VPL-B的後肢反映區域施予腦內電刺激(deep-brain stimulation, DBS)並記錄相對應的SI反應。 從VPL的體表映射圖得知VPL-B位於VPL-A的後方，兩個區域的反應中心相差大約0.6mm。電生理實驗結果顯示VPL-A到SI與VPL-B到SI的視丘皮質路徑並不相同。腦內電刺激VPL-A所得到的皮質反應非常一致，但腦內電刺激VPL-B所得到的皮質反映在每隻大鼠都不同，且會隨著移動刺激座標而改變，因此我們將VPL-B所得到的反應分成兩群為此路徑的快與慢成分。 從研究的結果推論，VPL-A投射到SI可能只有一種視丘皮質路徑，但從VPL-B到SI的視丘皮質路徑有快與慢的成分。我們認為傳導比較快的路徑會直接從VPL投射到SI，而傳導比較慢的路徑則是會先到其他處理體感覺訊息的腦區，最後才會投射到SI。本研究發現體感覺到達VPL後是由無髓鞘神經纖維將體感覺投射到SI。

All sensory information passes the thalamus, the sensory relay nuclear, and reaches the cortex through the thalamocortical radiation. In this study, we aim to characterize the different neural information sent from the ventral posterolateral (VPL) nucleus of thalamus through thalamocortical pathway to the primary somatosensory cortex (SI). Peripheral electrical stimulation (pES) was applied to rat hindpaw to identify the hindpaw somatotopic in VPL and SI, then we mapped in VPL to determine the coordinate of VPL-A and VPL-B. Finally, deeo-brain stimulation (DBS) was applied to VPL-A and to -B and their SI-evoked responses were recorded. Based on the mapping of VPL, VPL-B was observed to locate 0.6 mm caudal to VPL-A. Different characteristics of cortical response to DBS in VPL-A and VPL-B was shown in our electrophysiological recording. While the cortical response latency evoked by VPL-A DBS was consistent, the latency evoked by VPL-B DBS was varied among coordinates and animals. The cortical response evoked by VPL-B DBS can be further divided into the fast and slow component by the latency. The fast component of cortical response to VPL-B DBS showed similar features as the cortical response to VPL-A DBS, suggesting the direct projection from the VPL to SI via the thalamocortical pathway. However, the slow component of cortical response to VPL-B DBS may reflect the indirect projection from the VPL to other somatosensory relay nuclei before reaching SI. According to the conduction velocity calculated by the distance between the VPL and SI dividing to the corresponding response latency, we concluded that somatosensory information from the VPL may be carried by the unmyelinated nerve fibers through the thalamocortical pathway to SI.