Rankin C H, Carew T J
Department of Psychology, Yale University, New Haven, Connecticut 06520.
J Neurosci. 1988 Jan;8(1):197-211. doi: 10.1523/JNEUROSCI.08-01-00197.1988.
Until recently, dishabituation and sensitization have commonly been considered to reflect a unitary process: Sensitization refers to a general facilitation produced by strong or noxious stimuli that enhances subsequent responding; dishabituation has been thought to represent a special instance of sensitization in which the facilitation is simply superimposed on a habituated response level. The unitary process hypothesis was based on the observation that both decremented and nondecremented responses are facilitated by a common noxious or strong stimulus. However, this observation does not rule out the possibility that dishabituation and sensitization could reflect separate processes that are activated in parallel by a strong stimulus. Recent cellular experiments by Hochner et al. (1986) suggest that this, in fact, occurs in the sensory neurons of the gill withdrawal reflex in Aplysia. A developmental analysis of learning in the marine mollusc Aplysia permits a direct behavioral test of this hypothesis. If dishabituation and sensitization reflect a unitary process then they should emerge at the same time ontogenetically. On the other hand, if they reflect different processes, then they might emerge according to different ontogenetic timetables. In the present study we examined the temporal emergence of dishabituation and sensitization in the defensive siphon withdrawal reflex in 3 stages of juvenile Aplysia: stage 11, early stage 12, and late stage 12. Animals received one of 2 kinds of training: Dishabituation training, in which the effect of strong tail shock on habituated responses were observed, and Sensitization training, in which the effect of strong tail shock on nondecremented responses was observed. We found that, while dishabituation was present in all stages examined, sensitization did not emerge until several weeks later, in late stage 12. These results were confirmed and extended in a group of animals that were tested twice: first in stage 11, when they showed no sensitization, and again 13 weeks later, in late stage 12, when they then showed significant sensitization. Our analysis of nondecremented responses prior to the emergence of sensitization also revealed an unexpected inhibitory component of tail shock that produces reflex depression. Moreover, there was a clear progression in the net effects of tail shock during development: reflex depression was produced in stages 11 and early stage 12, followed by a transition to reflex facilitation (sensitization) in late stage 12. Finally, when sensitization emerged in late stage 12, the process of dishabituation showed a significant increase compared with previous developmental stages.(ABSTRACT TRUNCATED AT 400 WORDS)
直到最近，去习惯化和敏感化通常被认为反映了一个单一的过程：敏感化指的是由强烈或有害刺激产生的一种普遍的易化作用，这种易化作用会增强随后的反应；去习惯化被认为是敏感化的一个特殊例子，其中这种易化作用只是叠加在习惯化的反应水平上。单一过程假说基于这样的观察，即无论是递减反应还是非递减反应都会受到共同的有害或强烈刺激的易化。然而，这一观察结果并不排除去习惯化和敏感化可能反映由强烈刺激并行激活的不同过程的可能性。霍赫纳等人（1986年）最近的细胞实验表明，事实上，在海兔鳃收缩反射的感觉神经元中就是如此。对海洋软体动物海兔学习的发育分析允许对这一假说进行直接的行为测试。如果去习惯化和敏感化反映的是一个单一过程，那么它们在个体发育过程中应该同时出现。另一方面，如果它们反映的是不同的过程，那么它们可能会根据不同的个体发育时间表出现。在本研究中，我们研究了幼年海兔三个阶段（11期、12期早期和12期晚期）防御性虹吸管收缩反射中去习惯化和敏感化的时间出现情况。动物接受两种训练之一：去习惯化训练，观察强烈的尾部电击对习惯化反应的影响；敏感化训练，观察强烈的尾部电击对非递减反应的影响。我们发现，虽然在所研究的所有阶段都存在去习惯化，但敏感化直到几周后，即12期晚期才出现。这些结果在一组接受两次测试的动物中得到了证实和扩展：第一次在11期测试，当时它们没有表现出敏感化，13周后在12期晚期再次测试，此时它们表现出了显著的敏感化。我们对敏感化出现之前的非递减反应的分析还揭示了尾部电击的一个意外的抑制成分，它会导致反射抑制。此外，在发育过程中尾部电击的净效应有明显的进展：在11期和12期早期产生反射抑制，随后在12期晚期转变为反射易化（敏感化）。最后，当敏感化在12期晚期出现时，去习惯化过程与之前的发育阶段相比有显著增加。（摘要截取自400字）
