Oram M W, Hatsopoulos N G, Richmond B J, Donoghue J P
School of Psychology, University of St. Andrews, Fife KY16 9JU, United Kingdom.
J Neurophysiol. 2001 Oct;86(4):1700-16. doi: 10.1152/jn.2001.86.4.1700.
Previous studies have shown that measures of fine temporal correlation, such as synchronous spikes, across responses of motor cortical neurons carries more directional information than that predicted from statistically independent neurons. It is also known, however, that the coarse temporal measures of responses, such as spike count, are not independent. We therefore examined whether the information carried by coincident firing was related to that of coarsely defined spike counts and their correlation. Synchronous spikes were counted in the responses from 94 pairs of simultaneously recorded neurons in primary motor cortex (MI) while monkeys performed arm movement tasks. Direct measurement of the movement-related information indicated that the coincident spikes (1- to 5-ms precision) carry approximately 10% of the information carried by a code of the two spike counts. Inclusion of the numbers of synchronous spikes did not add information to that available from the spike counts and their coarse temporal correlation. To assess the significance of the numbers of coincident spikes, we extended the stochastic spike count matched (SCM) model to include correlations between spike counts of the individual neural responses and slow temporal dependencies within neural responses (approximately 30 Hz bandwidth). The extended SCM model underestimated the numbers of synchronous spikes. Therefore as with previous studies, we found that there were more synchronous spikes in the neural data than could be accounted for by this stochastic model. However, the SCM model accounts for most (R(2) = 0.93 +/- 0.05, mean +/- SE) of the differences in the observed number of synchronous spikes to different directions of arm movement, indicating that synchronous spiking is directly related to spike counts and their broad correlation. Further, this model supports the information theoretic analysis that the synchronous spikes do not provide directional information beyond that available from the firing rates of the same pool of directionally tuned MI neurons. These results show that detection of precisely timed spike patterns above chance levels does not imply that those spike patterns carry information unavailable from coarser population codes but leaves open the possibility that excess synchrony carries other forms of information or serves other roles in cortical information processing not studied here.
先前的研究表明，运动皮层神经元反应间精细的时间相关性测量指标，如同步发放的尖峰，比根据统计独立神经元预测的携带更多方向信息。然而，也已知反应的粗略时间测量指标，如尖峰计数，并非独立。因此，我们研究了同时发放所携带的信息是否与粗略定义的尖峰计数及其相关性所携带的信息有关。在猴子执行手臂运动任务时，对初级运动皮层（MI）中94对同时记录的神经元的反应中的同步尖峰进行计数。对与运动相关信息的直接测量表明，同时出现的尖峰（精确到1至5毫秒）携带的信息约占两个尖峰计数编码所携带信息的10%。同步尖峰的数量并未为尖峰计数及其粗略时间相关性所提供的信息增加额外信息。为了评估同时出现的尖峰数量的重要性，我们扩展了随机尖峰计数匹配（SCM）模型，以纳入单个神经反应的尖峰计数之间的相关性以及神经反应内缓慢的时间依赖性（约30赫兹带宽）。扩展后的SCM模型低估了同步尖峰的数量。因此，与先前的研究一样，我们发现神经数据中的同步尖峰数量比该随机模型所能解释的更多。然而，SCM模型解释了观察到的同步尖峰数量在手臂向不同方向运动时差异的大部分（R(2) = 0.93 +/- 0.05，平均值 +/- 标准误），表明同步发放与尖峰计数及其广泛相关性直接相关。此外，该模型支持信息理论分析，即同步尖峰所提供的方向信息并不超出同一组方向调谐的MI神经元发放率所提供的信息。这些结果表明，检测到高于偶然水平的精确计时尖峰模式并不意味着这些尖峰模式携带了从更粗略的群体编码中无法获得的信息，但也留下了这样一种可能性，即过度同步携带了其他形式的信息或在皮层信息处理中发挥了此处未研究的其他作用。
