Vogel A, Ronacher B
Department of Biology, Institute of Behavioural Physiology, Humboldt University Berlin, Invalidenstr. 43, 10115 Berlin, Germany.
J Neurophysiol. 2007 May;97(5):3376-85. doi: 10.1152/jn.00796.2006. Epub 2007 Mar 14.
Nervous systems may encode information about sensory stimuli using the temporal relations in spiking patterns between neurons. By conducting simultaneous intracellular recordings on pairs of auditory neurons we measured the strength of correlations between elements of the first three processing levels in the metathoracic auditory network of the locust. We quantified the degree of spike synchronization and rate covariations that occur among auditory neurons during acoustic stimulation. In addition to the acoustic stimulation, current pulses were injected into both neurons to study the connectivity within this network. Our findings support the view that the metathoracic auditory system is a hierarchically organized feedforward network. Strong synaptic connections were observed only between consecutive processing levels, whereas there was no indication for strong connections between elements of the same processing level. Both spike synchronization and rate covariations were increased among neurons on higher processing levels. We further investigated the consequences that correlations may have on the common estimates of neuronal variability. For example, rate covariations caused by strong synaptic coupling between two neurons may lead to an overestimation if the variability is measured trial by trial with respect to only single neurons. For the vast majority of cell pairs tested, however, no strong synaptic coupling could be demonstrated. Thus we could show that in most cases no serious errors are made if one determines variability by following the usual procedure on the basis of single-cell recordings.
神经系统可能利用神经元之间尖峰模式的时间关系来编码有关感觉刺激的信息。通过对成对的听觉神经元进行同步细胞内记录，我们测量了蝗虫后胸听觉网络中前三个处理水平的元素之间的相关强度。我们量化了听觉神经元在声刺激期间发生的尖峰同步程度和速率协变。除了声刺激外，还向两个神经元注入电流脉冲，以研究该网络内的连接性。我们的研究结果支持这样一种观点，即后胸听觉系统是一个分层组织的前馈网络。仅在连续的处理水平之间观察到强突触连接，而没有迹象表明同一处理水平的元素之间存在强连接。在较高处理水平的神经元之间，尖峰同步和速率协变都增加了。我们进一步研究了相关性可能对神经元变异性的常见估计产生的影响。例如，如果仅相对于单个神经元逐次测量变异性，由两个神经元之间的强突触耦合引起的速率协变可能导致高估。然而，对于绝大多数测试的细胞对，没有证明存在强突触耦合。因此我们可以表明，在大多数情况下，如果按照基于单细胞记录的常规程序来确定变异性，不会产生严重误差。
