Stolar N, Sparenborg S, Donchin E, Gabriel M
University of Illinois, Urbana-Champaign 61801.
Behav Neurosci. 1989 Oct;103(5):919-34. doi: 10.1037//0735-7044.103.5.919.
Past studies of the neuronal correlates of avoidance conditioning in rabbits have led to a model of information flow among structures of the limbic system. A hypothesis of the model is that unexpected stimuli activate certain hippocampal and cingulate cortical neurons. This activity in turn suppresses or "limits" the firing of limbic thalamic neurons. This hypothesis is tested in relation to stimuli classified as unexpected or expected on the basis of their incidence or "probability." Multi-unit and field potential responses in the anterior and posterior cingulate cortices (AC and PC), the dentate gyrus (DG), and the anterior ventral (AV) and medial dorsal (MD) thalamic nuclei were recorded during the acquisition and performance of a locomotor conditioned response (CR). The CR, stepping in an activity wheel in response to a 0.5-s tone (CS+), prevented the occurrence of a shock US scheduled 5 s after CS+ onset. The rabbits also learned to ignore a different tone (CS-), not predictive of the US. Training was given daily (120 trials, 60 with each CS in an irregular sequence) until behavioral discrimination reached criterion. After criterion, asymmetric probability (AP) sessions were given, in which the CS+/CS- proportions were .2/.8 or .8/.2. The AP sessions were the same as conditioning sessions except for the probability manipulation. A significant discriminative response, i.e., a greater neuronal discharge to the CS+ than to the CS-, developed in all regions during behavioral acquisition. The unit response in the AP sessions was enhanced in all areas by rare presentation of the CS-, compared with the equal and frequent CS- conditions. Rare presentation of the CS+ enhanced the unit response in the cortical areas (AC, PC, and DG), but it suppressed the firing of limbic thalamic (AV and MD) neurons. These results were supportive of the model. Rare CS+ presentations did not alter AV and PC neuronal activity in rabbits with subicular lesions, a result suggesting that an intact hippocampus is essential for normal neuronal responses to stimulus probability in the cingulate cortex and limbic thalamus.
过去对兔子回避条件作用的神经元相关性研究得出了一个边缘系统结构间信息流的模型。该模型的一个假设是，意外刺激会激活某些海马体和扣带回皮质神经元。这种活动反过来会抑制或“限制”边缘丘脑神经元的放电。基于刺激的发生率或“概率”将其分类为意外或预期刺激，以此对该假设进行检验。在运动条件反应（CR）的习得和执行过程中，记录了前扣带回皮质（AC）和后扣带回皮质（PC）、齿状回（DG）以及前腹侧（AV）和内侧背侧（MD）丘脑核的多单位和场电位反应。CR是指在听到0.5秒的音调（CS+）后在活动轮中踏步，这可防止在CS+开始5秒后安排的电击US的发生。兔子还学会忽略另一种音调（CS-），该音调不预示US。每天进行训练（120次试验，每种CS各60次，顺序不规则），直到行为辨别达到标准。达到标准后，进行非对称概率（AP）实验，其中CS+/CS-的比例为0.2/0.8或0.8/0.2。AP实验与条件训练实验相同，只是进行了概率操作。在行为习得过程中，所有区域都出现了显著的辨别反应，即对CS+的神经元放电比对CS-的更大。与CS-呈现次数相等且频繁的情况相比，在AP实验中，CS-的罕见呈现增强了所有区域的单位反应。CS+的罕见呈现增强了皮质区域（AC、PC和DG）的单位反应，但抑制了边缘丘脑（AV和MD）神经元的放电。这些结果支持了该模型。在海马下脚受损的兔子中，罕见的CS+呈现并未改变AV和PC神经元的活动，这一结果表明完整的海马体对于扣带回皮质和边缘丘脑对刺激概率的正常神经元反应至关重要。
