Spatio-Temporal Analysis of Synchronous Oscillatory Activities in Visual System

一些研究表明，猫的视觉皮层（A17）的细胞表现出刺激诱发的振荡放电（30-60Hz）和多个细胞之间的同步。以前我们报道过外侧膝状核（LGN）的细胞也表现出更高频率范围（60-100Hz）的刺激引起的同步振荡放电。它们频率范围的差异表明，皮层的振荡活动不太可能来自LGN。另一方面，Gray等人报道了皮层振荡局部场电位同步的短暂性，即在一个试验持续时间内可以发生异步和同步状态之间的转换。为了进一步比较两个区域之间的同步，我们研究了这种时间调制（非平稳性）是否也存在于LGN的-同步中。由于传统的互相关图方法由于对试验持续时间进行时间平均而失去了非平稳性的信息，我们采用了统一事件（UE）分析来跟踪脉冲同步的动态。我们发现，在LGN中，即使在静止点刺激下，也有相当一部分同步活动是非平稳的。ue数的调制与两个细胞的速率调制具有明显不同的时间尺度（小于几百毫秒）。这一结果可能表明同步在视觉信息处理中起着不同于触发率的功能作用。在此基础上，将统一事件分析应用于个体试验的尖峰序列。我们发现，在不同的试验中，单一事件的大小和持续时间都有相当大的可变性和短暂性。

Several studies have shown that cells in the visual cortex (A17) of the cat display stimulus-evoked oscillatory firings (30-60Hz) and synchronization among multiple cells. Previously we reported that the cells in the lateral geniculate nucleus (LGN) also showed stimulus evoked synchronous oscillatory firings of higher frequency range (60-100Hz). The difference in their frequency ranges suggested that the oscillatory activity in the cortex was not likely to derive from that in the LGN. On the other hand, Gray et al. reported a transient nature of the synchronization of the oscillatory local field potentials in the cortex, that is, the transition between asynchronous and synchronous states could occur within a trial duration. For further comparison of the synchronization between the two areas, we investigated whether such temporal modulation (non-stationarity) exists also in the -synchronization in the LGN. Since the traditional method of the cross-correlogram loses any information on the non-stationarity by the temporal averaging ovei-the trial duration, we adopted the unitary event (UE) analysis to trace the dynamics of the spike synchrony. We found that also in the LGN, a reasonable portion of synchronous activities was non-stationary even under the presentation of the stationary spot stimulus. The modulation of the number of the UEs had apparently different time scale (less than a few hundred milliseconds) from the rate modulations of the two cells. This result may suggest that the synchrony plays a different functional role from the firing rate in the visual information processing. Furthermore, the unitary event analysis was applied to the spike trains of individual trials. We found a rather large variability and transiency in both the magnitude and the duration of the unitary events over different trials.