Rapisarda C, Palmeri A, Sapienza S
Cattedra di Fisiologia Generale, Università di Bologna, Italy.
Exp Brain Res. 1992;88(1):140-50. doi: 10.1007/BF02259135.
The nature and organization of cortical influences on somatosensory thalamic neurons were investigated in the guinea pig in order to ascertain if mechanisms subserving sensory-motor integration in the thalamus are as precise as has previously been demonstrated in the agranular frontal cortex (AGr) and granular parietal cortex (Gr). The study was carried out on 14 chronically-implanted awake animals. In each experiment one or two motor foci within AGr and Gr were identified according to the region of the movement evoked by intracortical microstimulation at the lowest threshold stimulation (usually 5-15 microA). Spontaneous activity of 182 thalamo-cortical single neurons was recorded in the nucleus ventralis thalami (VT). The neurons were also identified by their response to activation of cutaneous receptive fields (RFs) located in regions of vibrissae or limbs, and then tested for cortical stimulation with a pulse intensity equal to the threshold for evoking motor effects. During the cortico-thalamic tests, the duration of stimulating trains was reduced in order to avoid the appearance of limb or vibrissa movements which could activate somatosensory ascending pathways forwarding peripheral messages to VT. The cortical control on VT neurons appears to be organized in a very precise manner. It was seen that: 1) The influences on these neurons relaying exteroceptive signals specifically emanated from AGr and Gr areas which in turn received exteroceptive input. 2) The vibrissa units responded to stimulation of foci in either AGr or Gr but the reactivity was greater upon stimulation of Gr than AGr. The incidence of responses was very high when the vibrissa RF was overlapping or adjacent to the region of the cortically-evoked vibrissa movement. The response pattern was mostly excitatory. Responses were rarely observed when vibrissa RF lay distant from the vibrissa moved by cortical stimulation. 3) Neurons with limb RFs responded constantly to stimulation of Gr foci only when the RF was overlapping or adjacent to the region of the cortical motor target; in these two conditions the response pattern was excitatory and inhibitory, respectively. Inhibitions only concerned neurons with forelimb RFs. Responses to stimulation of AGr were rarely obtained. From a functional point of view, the excitatory nature of the cortical control on thalamo-cortical VT neurons suggests that a cortical signal inducing movement of a given body part is able to enhance the afferent transmission of somatosensory messages arising in the same body part.(ABSTRACT TRUNCATED AT 400 WORDS)
为了确定丘脑内支持感觉运动整合的机制是否像先前在无颗粒额叶皮质（AGr）和颗粒顶叶皮质（Gr）中所证明的那样精确，对豚鼠丘脑体感神经元的皮质影响的性质和组织进行了研究。该研究在14只长期植入电极的清醒动物身上进行。在每个实验中，根据皮质内微刺激在最低阈值刺激（通常为5 - 15微安）时诱发运动的区域，在AGr和Gr内确定一个或两个运动焦点。在丘脑腹侧核（VT）记录了182个丘脑 - 皮质单神经元的自发活动。这些神经元还通过它们对位于触须或肢体区域的皮肤感受野（RFs）激活的反应来识别，然后用等于诱发运动效应阈值的脉冲强度进行皮质刺激测试。在皮质 - 丘脑测试期间，缩短刺激串的持续时间，以避免出现可能激活将外周信息传递到VT的体感上行通路的肢体或触须运动。对VT神经元的皮质控制似乎以非常精确的方式组织。可以看到：1）对这些传递外感受信号的神经元的影响特别来自AGr和Gr区域，而这两个区域又接收外感受输入。2）触须单元对AGr或Gr中的焦点刺激有反应，但对Gr刺激的反应性大于AGr。当触须RF与皮质诱发的触须运动区域重叠或相邻时，反应发生率非常高。反应模式大多是兴奋性的。当触须RF远离皮质刺激移动的触须时，很少观察到反应。3）只有当肢体RF与皮质运动目标区域重叠或相邻时，具有肢体RF的神经元才会持续对Gr焦点刺激做出反应；在这两种情况下，反应模式分别是兴奋性和抑制性的。抑制仅涉及具有前肢RF的神经元。很少获得对AGr刺激的反应。从功能角度来看，皮质对丘脑 - 皮质VT神经元的兴奋性控制表明，诱导给定身体部位运动的皮质信号能够增强同一身体部位产生的体感信息的传入传递。（摘要截断于400字）
