Prut Y, Vaadia E, Bergman H, Haalman I, Slovin H, Abeles M
Department of Physiology, School of Medicine and the Interdisciplinary Center for Neural Computation, The Hebrew University of Jerusalem, Jerusalem 91120, Israel.
J Neurophysiol. 1998 Jun;79(6):2857-74. doi: 10.1152/jn.1998.79.6.2857.
The study was designed to reveal occurrences of precise firing sequences (PFSs) in cortical activity and to test their behavioral relevance. Two monkeys were trained to perform a delayed-response paradigm and to open puzzle boxes. Extracellular activity was recorded from neurons in premotor and prefrontal areas with an array of six microelectrodes. An algorithm was developed to detect PFSs, defined as a set of three spikes and two intervals with a precision of +/-1 ms repeating significantly more than expected by chance. The expected level of repetition was computed based on the firing rate and the pairwise correlation of the participating units, assuming a Poisson distribution of event counts. Accordingly, the search for PFSs was corrected for rate modulations. PFSs were found in 24/25 recording sessions. Most PFSs (76%) were composed of spikes of more than one unit but usually not more than two units (67%). The PFSs spanned hundreds of milliseconds, and the average interval between two events within the PFSs was 200 ms. No traces of periodic oscillations were found in the PFS intervals. The bins of the matrix that were defined as PFSs were isolated temporally: the spikes that generated PFSs were not associated with high-frequency bursts or rapid coherent rate fluctuations. A given PFS tended to be correlated with the animal's behavior. Furthermore, for 19% of the PFS pairs that shared the same unit composition, each member of the pair was associated with a different type of behavior. The PFSs often appeared in clusters that were associated with particular phases of the behavior. The firing rate of single units did not provide a full explanation for the timing and structure of these clusters. A reduced spike train (RST) was defined for each unit by taking all spikes of that unit that were part of any PFS. In 88% of the cases the degree of modulation of the RST was higher than that of the complete spike train. The results suggest that relevant information is carried by the fine temporal structure of cortical activity. A coding scheme that involves such temporal structures is rich and sufficiently flexible to facilitate a rapid organization of cortical neurons into functional groups. The results can be accounted for by the synfire chain model, which suggests that cortical activity is mediated by synchronous activation of neural groups in a reverberatory mode.
该研究旨在揭示皮层活动中精确放电序列（PFSs）的出现情况，并测试它们与行为的相关性。训练两只猴子执行延迟反应范式并打开拼图盒。用一组六个微电极记录运动前区和前额叶区神经元的细胞外活动。开发了一种算法来检测PFSs，PFSs被定义为一组三个尖峰和两个间隔，精度为+/-1毫秒，其重复次数显著高于偶然预期。基于放电率和参与单元的成对相关性，假设事件计数服从泊松分布，计算预期的重复水平。因此，对PFSs的搜索针对速率调制进行了校正。在24/25次记录会话中发现了PFSs。大多数PFSs（76%）由一个以上单元的尖峰组成，但通常不超过两个单元（67%）。PFSs跨越数百毫秒，PFSs内两个事件之间的平均间隔为200毫秒。在PFS间隔中未发现周期性振荡的痕迹。被定义为PFSs的矩阵区间在时间上是孤立的：产生PFSs的尖峰与高频爆发或快速相干速率波动无关。给定的PFS往往与动物的行为相关。此外，对于19%具有相同单元组成的PFS对，该对中的每个成员都与不同类型的行为相关。PFSs经常出现在与行为特定阶段相关的簇中。单个单元的放电率并不能完全解释这些簇的时间和结构。通过选取该单元中属于任何PFS的所有尖峰，为每个单元定义了一个简化尖峰序列（RST）。在88%的情况下，RST的调制程度高于完整尖峰序列。结果表明，相关信息由皮层活动的精细时间结构携带。涉及这种时间结构的编码方案丰富且足够灵活，便于将皮层神经元快速组织成功能组。这些结果可以用同步放电链模型来解释，该模型表明皮层活动是由神经组以回响模式同步激活介导的。
