Sancristóbal Belén, Vicente Raul, Garcia-Ojalvo Jordi
Departament of Experimental and Health Sciences, Universitat Pompeu Fabra, Barcelona Biomedical Research Park, Barcelona, Spain,
J Comput Neurosci. 2014 Oct;37(2):193-208. doi: 10.1007/s10827-014-0495-7. Epub 2014 Feb 12.
Neuronal gamma oscillations have been described in local field potentials of different brain regions of multiple species. Gamma oscillations are thought to reflect rhythmic synaptic activity organized by inhibitory interneurons. While several aspects of gamma rhythmogenesis are relatively well understood, we have much less solid evidence about how gamma oscillations contribute to information processing in neuronal circuits. One popular hypothesis states that a flexible routing of information between distant populations occurs via the control of the phase or coherence between their respective oscillations. Here, we investigate how a mismatch between the frequencies of gamma oscillations from two populations affects their interaction. In particular, we explore a biophysical model of the reciprocal interaction between two cortical areas displaying gamma oscillations at different frequencies, and quantify their phase coherence and communication efficiency. We observed that a moderate excitatory coupling between the two areas leads to a decrease in their frequency detuning, up to ∼6 Hz, with no frequency locking arising between the gamma peaks. Importantly, for similar gamma peak frequencies a zero phase difference emerges for both LFP and MUA despite small axonal delays. For increasing frequency detunings we found a significant decrease in the phase coherence (at non-zero phase lag) between the MUAs but not the LFPs of the two areas. Such difference between LFPs and MUAs behavior is due to the misalignment between the arrival of afferent synaptic currents and the local excitability windows. To test the efficiency of communication we evaluated the success of transferring rate-modulations between the two areas. Our results indicate that once two populations lock their peak frequencies, an optimal phase relation for communication appears. However, the sensitivity of locking to frequency mismatch suggests that only a precise and active control of gamma frequency could enable the selection of communication channels and their directionality.
在多个物种不同脑区的局部场电位中已观察到神经元γ振荡。γ振荡被认为反映了由抑制性中间神经元组织的节律性突触活动。虽然γ节律产生的几个方面已得到较好理解，但关于γ振荡如何在神经元回路中促进信息处理，我们掌握的确凿证据要少得多。一种流行的假说是，远距离神经元群体之间的信息灵活路由是通过控制它们各自振荡之间的相位或相干性来实现的。在此，我们研究来自两个群体的γ振荡频率不匹配如何影响它们之间的相互作用。具体而言，我们探索了两个显示不同频率γ振荡的皮质区域之间相互作用的生物物理模型，并量化了它们的相位相干性和通信效率。我们观察到，两个区域之间适度的兴奋性耦合会导致它们的频率失谐减小，最大可达约6赫兹，且γ峰值之间不会出现频率锁定。重要的是，对于相似的γ峰值频率，尽管存在小的轴突延迟，但局部场电位（LFP）和多单元活动（MUA）均出现零相位差。对于不断增加的频率失谐，我们发现两个区域的多单元活动之间的相位相干性（在非零相位滞后时）显著降低，但局部场电位之间没有。局部场电位和多单元活动行为之间的这种差异是由于传入突触电流的到达与局部兴奋性窗口之间的失准所致。为了测试通信效率，我们评估了两个区域之间传递速率调制的成功率。我们的结果表明，一旦两个群体锁定它们的峰值频率，就会出现通信的最佳相位关系。然而，锁定对频率不匹配的敏感性表明，只有对γ频率进行精确且主动的控制，才能实现通信通道的选择及其方向性。
