Oleson T D, Ashe J H, Weinberger N M
J Neurophysiol. 1975 Sep;38(5):1114-39. doi: 10.1152/jn.1975.38.5.1114.
The role of sensory systems in the development of behavioral conditioned responses was investigated by recording multiple-unit activity in the auditory and somatosensory pathways during Pavlovian conditioning of the pupillary-dilation responses of paralyzed cats. Establishment of conditioned pupillary-dilation responses to a white noise CS+, pupillary discrimination between the CS+ and a tone CS-, and subsequent discrimination reversal provided the behavioral foundation for examining neural changes related to behavioral learning. Multiple-unit responses to the acoustic CS+ were significantly enhanced in the auditory cortex, cochlear nucleus, and somatic cortex, but not in the cuneate nucleus. The possibility that these effects could be due to changes in stimulus intensity at the sensory receptor, to mo-ement artifacts, or to feedback from skeletal responses were ruled out because the animals were immobilized. Nor could these neural changes be attributable to sensitization, as those brain areas which showed conditioned enhancement to the CS+ exhibited significantly larger responses to the CS+ than to the CS-. Furthermore, the changes in neural activity followed the significance of the CS; after reversal of the reinforcement contingencies, the amount of multiple-unit activity evoked by the stimuli gradually reversed too. Although the somatic cortex showed conditioning and discrimination, greater stimulus specificity was found in the auditory system. Only in the somatic cortex was there a significant increase in responses to the CS- as well as the CS4. Furthermore, both somatosensory loci exhibited enhanced responses to those tactile probes presented during the acoustic CS, suggesting a phasic increase in neural excitability to all stimuli. Analysis of the number of trials required to attain an acquisition criterion indicated that the neural changes occurred first in the auditory cortex, then the cochlear nucleus, followed in turn by the somatic cortex, and finally the cuneate nucleus. However, none of these neural changes preceded acquisition of conditioned pupillary dilations. These results suggest that sensory system changes are not essential for the initial associative process. These findings indicate that the study of autonomic conditioned responses may prove beneficial in seeking the critical neural events which underlie the initial association between two stimuli. A hypothetical model, which explains the development of pupillary and sensory system conditioned responses, was also presented.
通过在瘫痪猫的瞳孔扩张反应的巴甫洛夫条件反射过程中记录听觉和躯体感觉通路中的多单位活动，研究了感觉系统在行为条件反应发展中的作用。对白色噪音条件刺激（CS+）建立条件性瞳孔扩张反应、CS+与纯音条件刺激（CS-）之间的瞳孔辨别以及随后的辨别反转，为检查与行为学习相关的神经变化提供了行为基础。在听觉皮层、耳蜗核和躯体皮层中，对听觉CS+的多单位反应显著增强，但在楔束核中没有。由于动物被固定，排除了这些效应可能是由于感觉感受器处刺激强度的变化、运动伪迹或骨骼反应的反馈所致的可能性。这些神经变化也不能归因于敏化作用，因为那些对CS+表现出条件性增强的脑区对CS+的反应明显大于对CS-的反应。此外，神经活动的变化与条件刺激的显著性相关；在强化意外事件反转后，刺激诱发的多单位活动量也逐渐反转。虽然躯体皮层表现出条件反射和辨别能力，但在听觉系统中发现了更高的刺激特异性。只有在躯体皮层中，对CS-以及CS+的反应才有显著增加。此外，两个躯体感觉位点对听觉CS期间呈现的那些触觉探针的反应都增强了，这表明对所有刺激的神经兴奋性有阶段性增加。对达到习得标准所需试验次数的分析表明，神经变化首先发生在听觉皮层，然后是耳蜗核，接着依次是躯体皮层，最后是楔束核。然而，这些神经变化都没有先于条件性瞳孔扩张的习得。这些结果表明，感觉系统的变化对于初始联想过程不是必需的。这些发现表明，自主条件反应的研究可能有助于寻找两种刺激之间初始联想背后的关键神经事件。还提出了一个解释瞳孔和感觉系统条件反应发展的假设模型。
