Fitzgerald K, Wright W G, Marcus E A, Carew T J
Department of Psychology and Biology, Yale University, New Haven, Connecticut 06520.
Philos Trans R Soc Lond B Biol Sci. 1990 Aug 29;329(1253):171-8. doi: 10.1098/rstb.1990.0162.
A complete understanding of the cellular mechanisms underlying the formation of associations between stimuli, as occurs during classical conditioning, requires an understanding of the non-associative effects of the individual stimuli. The siphon withdrawal reflex of Aplysia exhibits both non-associative and associative learning when a tactile stimulus to the siphon serves as a conditioned stimulus, and tail shock serves as an unconditioned stimulus. In this chapter we describe experiments which examine the non-associative effects of tail shock at three different levels of analysis. At a behavioural level we found that the magnitude, and even the sign of reflex modulation induced by tail shock depended critically on three parameters: (i) the state of the reflex (habituated or non-habituated); (ii) the strength of the tail shock, and (iii) the time of testing after tail shock. Specifically, when non-habituated responses produced by water jet stimuli to the siphon were examined, tail shock produced transient inhibition 90 s later; facilitation of non-habituated responses (sensitization) only emerged after a considerable delay of 20-30 min. When habituated responses were examined, tail shock produced immediate facilitation (dishabituation); the amount of facilitation was inversely related to the strength of tail shock, with stronger shock producing no dishabituation. At a cellular level it was found that the complex excitatory postsynaptic potential (EPSP) in siphon motor neurons produced by water jet stimuli to the siphon provides a reliable cellular correlate of several of the non-associative effects of tail shock that we observe behaviourally. When non-decremented complex EPSPS were examined, strong tail shock produced transient inhibition at a test 90 s after shock.(ABSTRACT TRUNCATED AT 250 WORDS)
要全面理解经典条件反射过程中刺激之间形成关联背后的细胞机制，就需要了解各个刺激的非关联效应。当对海兔的虹吸管进行触觉刺激作为条件刺激，尾部电击作为非条件刺激时，海兔的虹吸管退缩反射既表现出非关联学习，也表现出关联学习。在本章中，我们描述了在三个不同分析层面研究尾部电击非关联效应的实验。在行为层面，我们发现尾部电击引起的反射调节幅度甚至方向，关键取决于三个参数：（i）反射状态（习惯化或未习惯化）；（ii）尾部电击的强度；（iii）尾部电击后的测试时间。具体而言，当检查由喷水刺激虹吸管产生的未习惯化反应时，尾部电击在90秒后产生短暂抑制；对未习惯化反应的易化作用（敏感化）仅在20 - 30分钟的相当长时间延迟后才出现。当检查习惯化反应时，尾部电击产生即时易化作用（去习惯化）；易化程度与尾部电击强度呈负相关，较强的电击不会产生去习惯化。在细胞层面发现，喷水刺激虹吸管时，虹吸管运动神经元中产生的复杂兴奋性突触后电位（EPSP），为我们在行为上观察到的尾部电击的几种非关联效应提供了可靠的细胞关联。当检查未衰减的复杂EPSP时，强烈的尾部电击在电击后90秒的测试中产生短暂抑制。
