WHO READS TEMPORAL INFORMATION CONTAINED ACROSS SYNCHRONIZED AND OSCILLATORY SPIKE TRAINS

Our inferences about brain mechanisms underlying perception rely on wh ether it is possible for the brain to 'reconstruct' a stimulus from th e information contained in the spike trains from many neurons(1-5). Ho w the brain actually accomplishes this reconstruction remains largely unknown. Oscillatory and synchronized activities in the brain of mamma ls have been correlated with distinct behavioural states or the execut ion of complex cognitive tasks(6-11) and are proposed to participate i n the 'binding' of individual features into more complex percepts(12-1 4). But if synchronization is indeed relevant, what senses it? In inse cts, oscillatory synchronized activity in the early olfactory system s eems to be necessary for fine odour discrimination(15) and enables the encoding of information about a stimulus in spike times relative to t he oscillatory 'clock'(16). Here we study the decoding of these cohere nt oscillatory signals. We identify a population of neurons downstream from the odour-activated, synchronized neuronal assemblies. These dow nstream neurons show odour responses whose specificity is degraded whe n their inputs are desynchronized. This degradation of selectivity con sists of the appearance of responses to new odours and a loss of discr imination of spike trains evoked by different odours. Such loss of inf ormation is never observed in the upstream neurons whose activity is d esynchronized. These results indicate that information encoded in time across ensembles of neurons converges onto single neurons downstream in the pathway.