Lehmann Hugo, Stykel Morgan G, Glenn Melissa J
Department of Psychology, Trent University, Peterborough, ON, Canada.
Department of Psychology, Colby College, Waterville, MA, United States.
Front Behav Neurosci. 2021 Nov 15;15:768552. doi: 10.3389/fnbeh.2021.768552. eCollection 2021.
The hippocampus (HPC) may compete with other memory systems when establishing a representation, a process termed overshadowing. However, this overshadowing may be mitigated by repeated learning episodes, making a memory resistant to post-training hippocampal damage. In the current study, we examined this overshadowing process for a hippocampal-dependent visual discrimination memory in rats. In Experiment 1, male rats were trained to criterion (80% accuracy on two consecutive days) on a visual discrimination and then given 50 additional trials distributed over 5 days or 10 weeks. Regardless of this additional learning, extensive damage to the HPC caused retrograde amnesia for the visual discrimination, suggesting that the memory remained hippocampal-dependent. In Experiment 2, rats received hippocampal damage before learning and required approximately twice as many trials to acquire the visual discrimination as control rats, suggesting that, when the overshadowing or competition is removed, the non-hippocampal memory systems only slowly acquires the discrimination. In Experiment 3, increasing the additional learning beyond criterion by 230 trials, the amount needed in Experiment 2 to train the non-hippocampal systems in absence of competition, successfully prevented the retrograde amnesic effects of post-training hippocampal damage. Combined, the findings suggest that a visual discrimination memory trace can be strengthened in non-hippocampal systems with overtraining and become independent of the HPC.
海马体（HPC）在建立表征时可能会与其他记忆系统竞争，这一过程被称为遮蔽效应。然而，这种遮蔽效应可能会因重复学习而得到缓解，从而使记忆对训练后海马体损伤具有抗性。在本研究中，我们研究了大鼠海马体依赖的视觉辨别记忆中的这种遮蔽过程。在实验1中，雄性大鼠在视觉辨别任务上训练至标准（连续两天准确率达80%），然后在5天或10周内再进行50次额外试验。无论有无这些额外学习，对HPC的广泛损伤都会导致视觉辨别逆行性遗忘，这表明该记忆仍依赖海马体。在实验2中，大鼠在学习前接受海马体损伤，与对照大鼠相比，它们需要大约两倍的试验次数来习得视觉辨别，这表明，当遮蔽效应或竞争被消除时，非海马体记忆系统只能缓慢地习得辨别能力。在实验3中，将额外学习增加到超过标准230次试验，即实验2中在无竞争情况下训练非海马体系统所需的次数，成功地防止了训练后海马体损伤的逆行性遗忘效应。综合来看，这些发现表明，通过过度训练，视觉辨别记忆痕迹可以在非海马体系统中得到强化，并变得独立于HPC。
