Mouly A M, Fort A, Ben-Boutayab N, Gervais R
Institut des Sciences Cognitives, CNRS UMR 5015, 67 Boulevard Pinel, 69675 Bron Cédex, France.
Neuroscience. 2001;102(1):11-21. doi: 10.1016/s0306-4522(00)00476-0.
In the present work, we investigated lasting changes induced by olfactory learning at different levels of the olfactory pathways. For this, evoked field potentials induced by electrical stimulation of the olfactory bulb were recorded simultaneously in the anterior piriform cortex, the posterior piriform cortex, the lateral entorhinal cortex and the dentate gyrus. The amplitude of the evoked field potential's main component was measured in each site before, immediately after, and 20 days after completion of associative learning. Evoked field potential recordings were carried out under two experimental conditions in the same animals: awake and anesthetized. In the learning task, rats were trained to associate electrical stimulation of one olfactory bulb electrode with the delivery of sucrose (positive reward), and stimulation of a second olfactory bulb electrode with the delivery of quinine (negative reward). In this way, stimulation of the same olfactory bulb electrodes used for inducing field potentials served as a discriminative cue in the learning paradigm. The data showed that positively reinforced learning resulted in a lasting increase in evoked field potential amplitude restricted to posterior piriform cortex and lateral entorhinal cortex. In contrast, negatively reinforced learning was mainly accompanied by a decrease in evoked field potential amplitude in the dentate gyrus. Moreover, the expression of these learning-related changes occurred to be modulated by the animals arousal state. Indeed, the comparison between anesthetized versus awake animals showed that although globally similar, the changes were expressed earlier with respect to learning, under anesthesia than in the awake state. From these data we suggest that associative olfactory learning involves different neural circuits depending on the acquired value of the stimulus. Furthermore, they show the existence of a functional dissociation between anterior and posterior piriform cortex in mnesic processes, and stress the importance of the animal's arousal state on the expression of learning-induced plasticity.
在本研究中，我们调查了嗅觉学习在嗅觉通路不同水平上引起的持久变化。为此，我们在梨状前皮质、梨状后皮质、外侧内嗅皮质和齿状回中同时记录了嗅球电刺激诱发的场电位。在联想学习完成前、完成后即刻以及完成后20天，分别在每个部位测量诱发场电位主要成分的幅度。在同一动物的两种实验条件下进行诱发场电位记录：清醒和麻醉状态。在学习任务中，训练大鼠将一个嗅球电极的电刺激与蔗糖的给予（正性奖励）相关联，将另一个嗅球电极的刺激与奎宁的给予（负性奖励）相关联。这样，用于诱发场电位的相同嗅球电极刺激在学习范式中作为辨别线索。数据表明，正性强化学习导致诱发场电位幅度持续增加，且仅限于梨状后皮质和外侧内嗅皮质。相反，负性强化学习主要伴随着齿状回中诱发场电位幅度的降低。此外，这些与学习相关的变化的表达似乎受动物觉醒状态的调节。事实上，麻醉动物与清醒动物之间的比较表明，尽管总体上相似，但在麻醉状态下，这些变化在学习方面比在清醒状态下更早出现。从这些数据中我们认为，联想性嗅觉学习涉及不同的神经回路，这取决于刺激的习得价值。此外，它们表明在记忆过程中梨状前皮质和梨状后皮质之间存在功能分离，并强调了动物觉醒状态对学习诱导可塑性表达的重要性。
