Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, Olav Kyrres gate 9, MTFS, 7491 Trondheim, Norway.
Center for Learning and Memory, The University of Texas at Austin, Austin, Texas 78712-0805, USA.
Nature. 2014 Jun 5;510(7503):143-7. doi: 10.1038/nature13162. Epub 2014 Apr 16.
Accumulating evidence points to cortical oscillations as a mechanism for mediating interactions among functionally specialized neurons in distributed brain circuits. A brain function that may use such interactions is declarative memory--that is, memory that can be consciously recalled, such as episodes and facts. Declarative memory is enabled by circuits in the entorhinal cortex that interface the hippocampus with the neocortex. During encoding and retrieval of declarative memories, entorhinal and hippocampal circuits are thought to interact via theta and gamma oscillations, which in awake rodents predominate frequency spectra in both regions. In favour of this idea, theta-gamma coupling has been observed between entorhinal cortex and hippocampus under steady-state conditions in well-trained rats; however, the relationship between interregional coupling and memory formation remains poorly understood. Here we show, by multisite recording at successive stages of associative learning, that the coherence of firing patterns in directly connected entorhinal-hippocampus circuits evolves as rats learn to use an odour cue to guide navigational behaviour, and that such coherence is invariably linked to the development of ensemble representations for unique trial outcomes in each area. Entorhinal-hippocampal coupling was observed specifically in the 20-40-hertz frequency band and specifically between the distal part of hippocampal area CA1 and the lateral part of entorhinal cortex, the subfields that receive the predominant olfactory input to the hippocampal region. Collectively, the results identify 20-40-hertz oscillations as a mechanism for synchronizing evolving representations in dispersed neural circuits during encoding and retrieval of olfactory-spatial associative memory.
越来越多的证据表明，皮层振荡是介导分布式脑回路中功能特化神经元相互作用的一种机制。一种可能利用这种相互作用的大脑功能是陈述性记忆，即可以有意识地回忆起的记忆，例如事件和事实。陈述性记忆是由内嗅皮层中的回路实现的，这些回路将海马体与新皮层连接起来。在陈述性记忆的编码和检索过程中，内嗅皮层和海马体回路被认为通过θ波和γ波振荡相互作用，而在清醒的啮齿动物中，这两种波在这两个区域都占主导地位。在这个想法的支持下，已经在经过良好训练的大鼠的稳态条件下观察到了内嗅皮层和海马体之间的θ-γ耦合；然而，区域间耦合与记忆形成之间的关系仍知之甚少。在这里，我们通过在联想学习的连续阶段进行多点记录表明，在大鼠学会使用气味线索来指导导航行为时，直接连接的内嗅-海马体回路中的发射模式的相干性会随着学习而演变，并且这种相干性总是与每个区域中独特试验结果的集合表示的发展相关联。内嗅-海马体耦合仅在 20-40 赫兹频带中观察到，并且仅在海马体 CA1 的远端部分和内嗅皮层的外侧部分之间观察到，这是接收海马区主要嗅觉输入的亚区。总的来说，这些结果确定了 20-40 赫兹的振荡是在编码和检索嗅觉空间联想记忆过程中同步分散神经回路中不断演变的表示的一种机制。
