School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE15 5RD, UK.
Neuroscience. 2013 Mar 13;233:146-56. doi: 10.1016/j.neuroscience.2012.12.039. Epub 2013 Jan 4.
Associative learning can occur under anesthesia and its neural correlates have begun to be elucidated. During discrimination learning under anesthesia in rats, lateral amygdala excitability increases in response to a conditioned stimulus (CS+) previously paired with electrical stimulation of the paw but not to another stimulus presented alone (CS-). Similarly, medial prefrontal cortex activity increases selectively during CS+ presentation after discrimination learning but this occurs only in neurons receiving input from the basolateral amygdala (BLA), the main source of amygdaloid projections to this region. However, BLA activity during discrimination learning under anesthesia has not been investigated. Here we used in vivo electrophysiology to examine BLA activity before and after associative learning and during later memory retrieval in anesthetized rats. We examined extracellular unit and local field potential (LFP) activity using an auditory discrimination learning paradigm. Rats were repeatedly presented with two distinct sounds, one of which was paired with electrical stimulation of the paw. One hour later, the paired sound (CS+) was presented alone along with the sound not paired with electrical stimulation (CS-). We found increased unit firing late (1 h) but not early (5 min) after learning. LFP power was increased both early and late after learning. In control experiments we also found increased unit and LFP activity late after electrical stimulation alone. After discrimination learning, unit firing increased in response to CS+, but not CS-, presentation. LFP power also showed a modest increase during CS+, compared to CS-, presentation. These findings suggest that discrimination learning under anesthesia can occur at the neural level in BLA. The potential relevance of these results is discussed in relation to previous studies examining neural activity during fear learning and memory processing in conscious animals.
关联学习可以在麻醉下发生，其神经相关性已开始被阐明。在麻醉状态下的大鼠辨别学习中，外侧杏仁核的兴奋性在先前与足底电刺激配对的条件刺激 (CS+) 出现时增加，但在单独呈现的另一种刺激（CS-）时不会增加。同样，在辨别学习后，内侧前额叶皮层的活动在 CS+ 呈现时选择性地增加，但这种情况仅发生在接收来自基底外侧杏仁核（BLA）输入的神经元中，BLA 是杏仁核投射到该区域的主要来源。然而，麻醉下辨别学习期间的 BLA 活动尚未被研究过。在这里，我们使用活体电生理学方法在麻醉大鼠中在关联学习前后以及随后的记忆检索过程中检查 BLA 活动。我们使用听觉辨别学习范式检查 BLA 中的细胞外单元和局部场电位 (LFP) 活动。大鼠反复呈现两种不同的声音，其中一种与足底电刺激配对。一个小时后，单独呈现配对的声音（CS+），同时呈现未与电刺激配对的声音（CS-）。我们发现学习后 1 小时（晚期）而非 5 分钟（早期）的单位放电增加。学习后早期和晚期 LFP 功率均增加。在对照实验中，我们还发现单独进行电刺激后晚期单位和 LFP 活动增加。在辨别学习后，CS+ 出现时，单位放电增加，但 CS- 出现时不增加。与 CS- 呈现相比，LFP 功率在 CS+ 期间也略有增加。这些发现表明，在 BLA 中可以在神经水平上进行麻醉下的辨别学习。这些结果与之前在清醒动物中研究恐惧学习和记忆处理过程中的神经活动的研究有关，讨论了这些结果的潜在相关性。
