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Active Vision

Saccade-related synchrony in visually evoked spikes

  • Neuronal processing during free viewing of natural scenes
  • Mechanisms for spike synchronization in relation to eye movements

Modified from figure 1a in Ito et al. 2011Ito et al. 2011, figure 1 (modified)

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.

Selected references:

-Ito, Maldonado, and Grün (2013) Cross-frequency interaction of the eye-movement related LFP signals in V1 of freely viewing monkeys. Front Syst Neurosci 7:1 DOI: 10.3389/fnsys.2013.00001
-Berger, Pazienti, Flores, Nawrot, Maldonado, and Grün (2012) Viewing strategy of Cebus monkeys during free exploration of natural images. Brain Research 1434: 34-46 DOI: 10.1016/j.brainres.2011.10.013
-Ito, Maldonado, Singer, and Grün (2011) Saccade-related modulations of neuronal excitability support synchrony of visually elicited spikes. Cereb Cortex 21 (11): 2482-2497 DOI: 10.1093/cercor/bhr020
-Maldonado, Babul, Singer, Rodriguez, Berger, and Grün (2008) Synchronization of neuronal responses in primary visual cortex of monkeys viewing natural images. J Neurophysiol, 100: 1523-1532

Impact of top-down influence on visual processing during free viewing

  • Top-down and bottom-up influences on local processing at various stages of the visual pathway
  • Processing across cortical layers

German-Japanes Collaboration ActiveVision

Primates perform frequent sequences of saccadic eye movements (duration about 30 msec) followed by fixations (duration about 200 msec) to sample visual information from their environment. During such a sequence, incoming visual information is processed, the next eye movement is prepared, and behavior is initiated. The information flow through the neuronal system causing these events is, however, unknown. The short time duration of the sequences suggests that incoming, sensory information and the preparation of the next eye movements are largely processed in parallel and tightly coordinated.

This joint German-Japanese project aims at getting a better understanding of the complex neuronal processing during free viewing, with a special emphasis on the interaction within and across multiple visual areas. The project requires on the one hand highly demanding experiments, which combine behavioral tasks and simultaneous electrophysiological recordings of massively parallel activity of multiple single neurons of the visual pathway. On the other hand it requires the analysis of higher-order correlations for identification of neuronal interactions within these complex multi-area multi-channel data.

German - Japanese Collaborations in Computational Neuroscience