Centre for Integrative Physiology, University of Edinburgh, Hugh Robson Building, Edinburgh EH8 9XD, UK.
Neuron. 2013 Jan 9;77(1):141-54. doi: 10.1016/j.neuron.2012.11.032.
Cortical circuits are thought to multiplex firing rate codes with temporal codes that rely on oscillatory network activity, but the circuit mechanisms that combine these coding schemes are unclear. We establish with optogenetic activation of layer II of the medial entorhinal cortex that theta frequency drive to this circuit is sufficient to generate nested gamma frequency oscillations in synaptic activity. These nested gamma oscillations closely resemble activity during spatial exploration, are generated by local feedback inhibition without recurrent excitation, and have clock-like features suitable as reference signals for multiplexing temporal codes within rate-coded grid firing fields. In network models deduced from our data, feedback inhibition supports coexistence of theta-nested gamma oscillations with attractor states that generate grid firing fields. These results indicate that grid cells communicate primarily via inhibitory interneurons. This circuit mechanism enables multiplexing of oscillation-based temporal codes with rate-coded attractor states.
皮质电路被认为将发射率码与依赖于振荡网络活动的时间码进行复用，但将这些编码方案组合在一起的电路机制尚不清楚。我们通过光遗传学激活内侧隔核的第 II 层发现，θ 频率驱动该电路足以在突触活动中产生嵌套的伽马频率振荡。这些嵌套的伽马振荡与空间探索期间的活动非常相似，是由局部反馈抑制而不是递归兴奋产生的，并且具有时钟样特征，适合作为多路复用率编码网格发射场中的时间码的参考信号。在从我们的数据推断出的网络模型中，反馈抑制支持θ嵌套伽马振荡与产生网格发射场的吸引子状态共存。这些结果表明网格细胞主要通过抑制性中间神经元进行通信。这种电路机制使基于振荡的时间码与基于率编码的吸引子状态的复用成为可能。
