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1 Physiology and Biophysics, Faculty of Medicine, University of Chile, Santiago, Chile
2 Neurophysiology, MPI Brain Research, Frankfurt, Germany
3 Neuroinformatics, Free University, Berlin, Germany
4 Computational Neuroscience Group, RIKEN Brain Science Institute, Wako-Shi, Saitama, Japan
* To whom correspondence should be addressed. E-mail: pedro{at}neuro.med.uchile.cl.
When inspecting visual scenes, primates perform on average four saccadic eye movements per second which implies that scene segmentation, feature binding and identification of image components is accomplished in less than 200ms. Thus, individual neurons can contribute only a small number of discharges for these complex computations, suggesting that information is encoded not only in the discharge rate but also in the timing of action potentials. While monkeys inspected natural scenes we registered with multi-electrodes from primary visual cortex, the discharges of simultaneously recorded neurons. Relating these signals to eye movements, revealed that discharge rates peaked around 90ms after fixation onset and then decreased to near baseline levels within 200ms. Unitary event analysis revealed that preceding this increase in firing, there was an episode of enhanced response synchronization during which discharges of spatially distributed cells coincided within 5ms windows significantly more often than predicted by the discharge rates. This episode started 30ms after fixation onset and ended by the time discharge rates had reached their maximum. When the animals scanned a blank screen a small change in firing rate but no excess synchronization was observed. The short latency of the stimulation related synchronization phenomena suggests a fast acting mechanism for the coordination of spike timing that may contribute to the basic operations of scene segmentation.
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