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Abstract:
Despite tremendous efforts and uncountable approaches it is still rather unclear how the brain encodes and processes information. Changes in net neuronal activity like firing rates have been the favorite concept for the vast majority of investigators. Although these signals formally carry
various and sometimes huge amounts of information, it is not at all clear whether the brain actually decodes these changes and uses this information or whether it operates reliable despite these changes and extracts the required information from other signals present at the same time. One such signal is correlated firing which can be caused by coactivation e.g. through a stimulus which simultaneously activates many different neurons. Often such coactivation patterns have been addressed as ‘noise’ correlations and have more recently been described to be reduced when neuronal populations became engaged in processing different
aspects of sensory input. However, this has only been observed under conditions of passive viewing while neuronal populations which had to actively encode and maintain information during memory express non-random coactivation patterns which carry surprisingly large amounts of information about the stimuli. A third type of signal that may be responsible for the coding of information in neuronal activity is precise timing of spike discharge, either with or without time lags. The former type of temporal code has been conceptualized as ‘synfire chains’
the latter as precise spike synchronization with or without oscillatory modulation of the carrier signals. As is true for all of these coding options, none of these have yet been proven as relevant for the information processing of brains. I will present evidence for all three of the
above coding options and hope to discuss how a causal relation between information arriving from the environment, neuronal operations and the behavioral output can be established in a convincing way.
