Saccade-related synchrony in visually evoked spikes
- Strong LFP modulations locked to saccade onsets
- First spikes are locked to specific epochs of the LFP modulation
- Relation of the LFP modulation and spike synchronization
When inspecting visual scenes, primates perform on average four saccades per second, implying that the processing of image components may be accomplished in less than 200 ms. Individual neurons thereby contribute only with a few spikes for processing the visual information at each location, suggesting that information is encoded not only in the firing rate but also in the timing of spikes. Recently, it has been suggested that LFP oscillations modulate the timing of single spikes, and thus act as a mechanism realizing the temporal coding of neural information. We hypothesized that such a mechanism should be apparent in the neuronal activity of V1 during natural visual behavior. Therefore we measured simultaneously neuronal activities and eye movements while monkeys freely view images of natural scenes. We found that there are strong LFP modulations locked to the onset of saccades which continue into the successive fixation period. Visually induced spikes, in particular the first spikes after the onset of a fixation, are locked to a specific epoch of the LFP modulation. We suggest that the modulation of neural excitability, which is reflected by the saccade-related LFP changes, serves as a corollary signal enabling precise timing of spikes in V1 and thereby providing a mechanism for spike synchronization.