Institute for Theoretical Computer Science, Graz University of Technology Graz, Austria.
Front Comput Neurosci. 2010 Jun 2;4:14. doi: 10.3389/fncom.2010.00014. eCollection 2010.
Processing and storage of sensory information is based on the interaction between different neural populations rather than the isolated activity of single neurons. In order to characterize the dynamic interaction and transient cooperation of sub-circuits within a neural network, multivariate autoregressive (MVAR) models have proven to be an important analysis tool. In this study, we apply directed functional coupling based on MVAR models and describe the temporal and spatial changes of functional coupling between simultaneously recorded local field potentials in extrastriate area V4 during visual memory. Specifically, we compare the strength and directional relations of coupling based on generalized partial directed coherence (GPDC) measures while two rhesus monkeys perform a visual short-term memory task. In both monkeys we find increases in theta power during the memory period that are accompanied by changes in directed coupling. These interactions are most prominent in the low frequency range encompassing the theta band (3-12 Hz) and, more importantly, are asymmetric between pairs of recording sites. Furthermore, we find that the degree of interaction decreases as a function of distance between electrode positions, suggesting that these interactions are a predominantly local phenomenon. Taken together, our results show that directed coupling measures based on MVAR models are able to provide important insights into the spatial and temporal formation of local functionally coupled ensembles during visual memory in V4. Moreover, our findings suggest that visual memory is accompanied not only by a temporary increase of oscillatory activity in the theta band, but by a direction-dependent change in theta coupling, which ultimately represents a change in functional connectivity within the neural circuit.
感觉信息的处理和存储是基于不同神经元群体之间的相互作用，而不是单个神经元的孤立活动。为了描述神经网络中子电路的动态相互作用和瞬时协同，多元自回归 (MVAR) 模型已被证明是一种重要的分析工具。在这项研究中，我们应用基于 MVAR 模型的有向功能耦合，并描述了在两只猕猴执行视觉短期记忆任务期间，外纹状区 V4 中同时记录的局部场电位之间功能耦合的时空变化。具体来说，我们比较了基于广义部分定向相干度 (GPDC) 测量的耦合强度和方向关系，而两只猕猴执行视觉短期记忆任务。在两只猴子中，我们都发现记忆期间θ功率增加，伴随着有向耦合的变化。这些相互作用在包含θ频段 (3-12 Hz) 的低频范围内最为明显，更重要的是，在记录位点对之间是不对称的。此外，我们发现相互作用的程度随电极位置之间的距离而降低，这表明这些相互作用主要是局部现象。总之，我们的结果表明，基于 MVAR 模型的有向耦合测量能够为 V4 中视觉记忆期间局部功能耦合集合的时空形成提供重要的见解。此外，我们的发现表明，视觉记忆不仅伴随着θ频段的振荡活动暂时增加，而且伴随着θ耦合的方向依赖性变化，这最终代表了神经回路中功能连接的变化。
