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Neuronal Coding in the Retina and Fixational Eye Movements

Neuronal Coding in the Retina and Fixational Eye Movements. Christian Mendl Tim Gollisch Lab. Friday Seminar Talk November 6, 2009. Outline. Experimental setup Review of fixational eye movements Research questions and strategy A look at the observed data

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Neuronal Coding in the Retina and Fixational Eye Movements

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  1. Neuronal Coding in the Retinaand Fixational Eye Movements Christian Mendl Tim Gollisch Lab Friday Seminar Talk November 6, 2009

  2. Outline • Experimental setup • Review of fixational eye movements • Research questions and strategy • A look at the observed data • Spike timing cross-correlations • Information theory: entropy, mutual information, synergy, ... • Summary and outlook

  3. Experimental Setup ganglion cells

  4. Fixational Eye Movements • Constant feature of normal vision • Visual perception fading • Enhancement of spatial resolution Martinez-Conde S et al. Microsaccades counteract visual fading during fixation. Neuron (2006) source: Martinez-Conde laboratory Meister M, Lagnado L and Baylor DA. Concerted signaling by retinal ganglion cells. Science (1995) Riggs LA and Ratliff F. The effects of counteracting the normal movements of the eye. Journal of the Optical Society of America (1952) Ditchburn RW and Ginsborg BL. Vision with a stabilized retinal image. Nature (1952)

  5. Fixational Eye Movements II Eye movements of the turtle during fixation • Periodic component at approximately 5 Hz • Imitating fixational eye movements → retina better encoder • Neurons synchronize more Greschner, Ammermüller et.al. Nature Neuroscience (2002)

  6. Research Questions • How can the brain discriminate between various stimuli in the context of fixational eye movements? Optimal decoding strategy? • Synchronized responses of several retinal ganglion cells → population code?

  7. Research Strategy Concrete task: based on spike responses, discriminate 5 different angles

  8. Observed Data stimulus period: 800 ms

  9. Spike Timing Cross-Correlations

  10. Spike Timing Cross-Correlations II stimulusperiod

  11. Encodingthe Spike Train unlocked binning Encodingspikepatterns stimulus-locked binning → observer knows the stimulus phase

  12. Information Theory Mutual information Imutual → How much information („bits“) do the spikes contain about the stimulus Synergy → How much additional information is contained in the simultaneous activity of two cells as compared to the individual cells’ responses

  13. Mutual Information unlocked binning individual cells stimulus-locked binning cell pairs

  14. Population Code: Synergy unlocked binning stimulus-locked binning Synergyversus mutual informationfor several recordings

  15. Summary • Fixational eye movements provide information about the stimulus • If the brain uses individual cells, it needs to know the phase of the fixational eye movements • For multiple cells, the phase information becomes less important since the cells are synergistic

  16. Outlook • Effect of shorter stimulus periods and smaller amplitudes? • Try different decoding stategies: optimal patterns, bin sizes?

  17. Acknowledgements Tim Gollisch Lab • Tim Gollisch • Daniel Bölinger • Vidhya Krishnamoorthy • Thesis Advisory Board • Tim Gollisch • Erwin Frey (LMU) • Andreas Herz • Günther Zeck BoehringerIngelheimFonds Foundation for Basic Research in Medicine

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