Neuronal Coding in the Retina and Fixational Eye Movements Friday Seminar Talk November 6, 2009 Friday Seminar Talk November 6, 2009 Christian Mendl Tim Gollisch Lab Christian Mendl Tim Gollisch Lab

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

ganglion cells Experimental Setup

Fixational Eye Movements source: Martinez-Conde laboratory Constant feature of normal vision Visual perception fading Enhancement of spatial resolution 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) Meister M, Lagnado L and Baylor DA. Concerted signaling by retinal ganglion cells. Science (1995) Martinez-Conde S et al. Microsaccades counteract visual fading during fixation. Neuron (2006)

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)

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?

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

Observed Data stimulus period: 800 ms

Spike Timing Cross-Correlations

Spike Timing Cross-Correlations II stimulus period

Encoding the Spike Train stimulus-locked binning unlocked binning Encoding spike patterns → observer knows the stimulus phase

Information Theory Mutual information I mutual → 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

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

Population Code: Synergy Synergy versus mutual information for several recordings unlocked binning stimulus-locked binning

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

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

Acknowledgements Tim Gollisch Lab Tim Gollisch Daniel Bölinger Vidhya Krishnamoorthy Thesis Advisory Board Tim Gollisch Erwin Frey (LMU) Andreas Herz Günther Zeck Boehringer Ingelheim Fonds Foundation for Basic Research in Medicine