Clark R E, Squire L R
Department of Psychiatry, University of California, San Diego, La Jolla, CA 92093, USA.
Science. 1998 Apr 3;280(5360):77-81. doi: 10.1126/science.280.5360.77.
Classical conditioning of the eye-blink response, perhaps the best studied example of associative learning in vertebrates, is relatively automatic and reflexive, and with the standard procedure (simple delay conditioning), it is intact in animals with hippocampal lesions. In delay conditioning, a tone [the conditioned stimulus (CS)] is presented just before an air puff to the eye [the unconditioned stimulus (US)]. The US is then presented, and the two stimuli coterminate. In trace conditioning, a variant of the standard paradigm, a short interval (500 to 1000 ms) is interposed between the offset of the CS and the onset of the US. Animals with hippocampal lesions fail to acquire trace conditioning. Amnesic patients with damage to the hippocampal formation and normal volunteers were tested on two versions of delay conditioning and two versions of trace conditioning and then assessed for the extent to which they became aware of the temporal relationship between the CS and the US. Amnesic patients acquired delay conditioning at a normal rate but failed to acquire trace conditioning. For normal volunteers, awareness was unrelated to successful delay conditioning but was a prerequisite for successful trace conditioning. Trace conditioning is hippocampus dependent because, as in other tasks of declarative memory, conscious knowledge must be acquired across the training session. Trace conditioning may provide a means for studying awareness in nonhuman animals, in the context of current ideas about multiple memory systems and the function of the hippocampus.
眨眼反应的经典条件作用，可能是脊椎动物中关联学习研究得最为透彻的例子，它相对自动化且具有反射性。采用标准程序（简单延迟条件作用）时，海马体受损的动物仍能保持这种条件作用。在延迟条件作用中，一个音调[条件刺激（CS）]在向眼睛吹气[无条件刺激（US）]之前呈现。然后呈现无条件刺激，且两种刺激同时结束。在痕迹条件作用中，这是标准范式的一个变体，在条件刺激的结束和无条件刺激的开始之间插入一个短间隔（500到1000毫秒）。海马体受损的动物无法习得痕迹条件作用。对海马体结构受损的失忆症患者和正常志愿者进行了两种版本的延迟条件作用和两种版本的痕迹条件作用测试，然后评估他们在多大程度上意识到了条件刺激和无条件刺激之间的时间关系。失忆症患者以正常速度习得延迟条件作用，但无法习得痕迹条件作用。对于正常志愿者而言，意识与成功的延迟条件作用无关，但却是成功的痕迹条件作用的一个前提条件。痕迹条件作用依赖于海马体，因为与陈述性记忆的其他任务一样，在整个训练过程中必须获取有意识的知识。痕迹条件作用可能为在当前关于多种记忆系统和海马体功能的观点背景下研究非人类动物的意识提供一种手段。
