Freeman J H, Cuppernell C, Flannery K, Gabriel M
Department of Psychology, University of Illinois, Urbana 61801, USA.
J Neurosci. 1996 Feb 15;16(4):1538-49. doi: 10.1523/JNEUROSCI.16-04-01538.1996.
This study assessed the context specificity of learning-related neuronal activity: whether the same physical stimuli would elicit different neuronal responses depending on the learning situation. Neuronal activity was recorded simultaneously in six limbic areas as rabbits learned to approach a spout for water reinforcement after a tone (CS+) and to ignore the spout after a different tone (CS-). The rabbits then received avoidance training in which they learned to prevent a foot-shock by stepping in an activity wheel after one tone (CS+) and to ignore a different tone (CS-). Avoidance training sessions were alternated (1 session daily) with sessions in the well learned approach task. The tone assigned as the CS+ for approach training was the CS- for avoidance training and vice versa. The neuronal records of the anterior ventral and medial dorsal thalamic nuclei and the anterior and posterior cingulate cortices showed neuronal discrimination appropriate to the approach task during pretraining in the avoidance training apparatus with unpaired presentations of the tones and foot-shock. This finding demonstrated that the discriminative neuronal activity for approach learning was unaffected by a change in context in the pretraining session. However, context-appropriate discrimination occurred in both tasks thereafter, with the exception that medial dorsal thalamic neurons no longer showed discrimination during overtraining in the approach task. Hippocampal area CA1 neurons showed entirely context-appropriate discrimination in both tasks, with no carryover of the approach-relevant discrimination to the avoidance training apparatus. Avoidance training stage-specific peaks of training-induced excitation in different brain areas were not elicited by the same physical stimuli during concurrent approach training sessions. The results are consistent with an involvement of limbic-circuit neuronal activity in the use of context cues for mnemonic retrieval. Differential persistence of the approach-related neuronal discrimination in anterior and posterior cingulate cortex confirmed the previously hypothesized distinct mnemonic functions of these areas.
相同的物理刺激是否会根据学习情境引发不同的神经元反应。当兔子学会在一种音调（条件刺激+，CS+）后接近一个喷嘴以获取水强化，并在另一种不同音调（条件刺激-，CS-）后忽略该喷嘴时，同时在六个边缘区域记录神经元活动。然后，兔子接受回避训练，它们学会在一种音调（CS+）后通过踩动活动轮来避免足部电击，并忽略另一种不同音调（CS-）。回避训练课程与已经熟练掌握的接近任务课程交替进行（每天1节）。在接近训练中被指定为CS+的音调在回避训练中是CS-，反之亦然。在回避训练装置中进行预训练时，丘脑前腹侧核和背内侧核以及前扣带回和后扣带回皮质的神经元记录显示，在音调与足部电击未配对呈现的情况下，神经元辨别与接近任务相适应。这一发现表明，接近学习的辨别性神经元活动在预训练阶段不受情境变化的影响。然而，此后在两项任务中都出现了与情境相适应的辨别，不同的是，背内侧丘脑神经元在接近任务的过度训练期间不再表现出辨别。海马体CA1区神经元在两项任务中均表现出完全与情境相适应的辨别，与接近相关的辨别没有延续到回避训练装置中。在同时进行的接近训练课程中，不同脑区由训练诱导的兴奋的回避训练阶段特异性峰值不是由相同的物理刺激引发的。这些结果与边缘回路神经元活动参与利用情境线索进行记忆检索一致。前扣带回和后扣带回皮质中与接近相关的神经元辨别持续时间的差异证实了先前假设的这些区域不同的记忆功能。
