Sahley C L, Ready D F
Department of Biology, Yale University, New Haven, Connecticut 06511.
J Neurosci. 1988 Dec;8(12):4612-20. doi: 10.1523/JNEUROSCI.08-12-04612.1988.
We report that 2 behaviors, stepping and shortening, are modified by associative learning in the leech, Hirudo medicinalis. Experiment 1 explored conditioning of the "stepping" response. Paired presentations of touch to the medial dorsal surface of the leech and shock to the tail of the leech resulted in the development of stepping to the touch. Leeches in control groups experiencing the CS alone, US alone, or explicitly unpaired presentations of the CS and US did not. In experiments 2-4, classical conditioning explored conditioning of the touch-elicited shortening reflex. We found that the reflex was enhanced following paired CS-US presentations but not following CS alone, US alone, or explicitly unpaired presentations of the stimuli. Moreover, the learning was extinguished following 15 unreinforced presentations of the CS but was retained for at least 24 hr without extinction training. Moreover, the associative effect was not evident when the CS and US were presented in a backward relationship. That is, no learning was observed when the US preceded the CS. Lastly, the hand-held stimuli were replaced with implanted electrodes. Using a 3 V pulse that mimicked the touch stimulus (CS), we found that paired CS-US presentations produced a significant enhancement in the shortening reflex. Again, no enhancement was observed following unpaired CS, US presentations.
我们报告称，水蛭（医用水蛭）的两种行为——踏步和缩短，会通过联想学习得到改变。实验1探究了“踏步”反应的条件作用。将水蛭内侧背表面的触觉刺激与水蛭尾部的电击配对呈现，导致水蛭对触觉产生踏步反应。单独经历条件刺激（CS）、单独经历非条件刺激（US）或明确将CS和US非配对呈现的对照组水蛭则不会产生这种反应。在实验2 - 4中，经典条件作用探究了触觉引发的缩短反射的条件作用。我们发现，在CS - US配对呈现后，该反射增强，但单独呈现CS、单独呈现US或明确将刺激非配对呈现后则不然。此外，在对CS进行15次无强化呈现后，学习消退，但在没有消退训练的情况下至少保留24小时。而且，当CS和US以反向关系呈现时，联想效应不明显。也就是说，当US先于CS呈现时，未观察到学习现象。最后，将手持刺激物替换为植入电极。使用模拟触觉刺激（CS）的3V脉冲，我们发现CS - US配对呈现会使缩短反射显著增强。同样，在CS、US非配对呈现后未观察到增强现象。
