Cross-Correlograms for Neuronal Spike Trains. Different Types of Temporal Correlation in Neocortex, their Origin and Significance
2000
After a presentation of the method of computation of the cross-correlation histogram, the major interpretations of cortical synchronization are reviewed. These include indicators of different brain states (sleep, waking state), indication of cortical connectivity, participation in cell assemblies, and a different form of neural coding. It is then argued that there are several types of synchronization, reflected in the existence of CCH peaks of different widths. The function of these different forms of synchronization in cortical processing and their possible underlying generation mechanisms are discussed. KEYWORDS: Synchronization; Cell assembly; Binding; Cortex; Vision; Crosscorrelogram Synchronization of neuronal activity is a topic that has recently received a lot of interest. The major reason for this is certainly related to the publication of experimental results that supported the idea that the relative timing of action potentials between different neurones could play an essential role in perception. The enthusiasm raised by these experiments has not been shared by the whole community, and a number of criticisms have been made. Scientific controversies are often related to a misunderstanding of certain definitions. In our case, the essential question is: what does synchronization really mean and imply? This chapter is an attempt to examine synchronization in depth. First, we recall the basic principles of the cross-correlation technique, as it is the method used most frequently for tracking synchrony at the level of action potentials. Next, we present a historical perspective on synchronization, which leads to the realization that the meaning of synchronization has varied a lot at different periods. In a third section we show that one should not talk about synchronization as a single factor, but about several different types of synchronization. Having acknowledged this basic fact, we attempt to review the possible mechanisms that lead to the generation of these different forms of synchronization. Finally, we review recent results and the current status on the functional roles of synchronization.