Neuronal Coding in the Retinaand 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 Spike timing cross-correlations Information theory: entropy, mutual information, synergy, ... Summary and outlook
Experimental Setup ganglion cells
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)
Fixational Eye Movements II Eye movements of the turtle during fixation Greschner, Ammermüller et.al. Nature Neuroscience (2002) Periodic component at approximately 5 Hz Imitating fixational eye movements -> retina better encoder Neurons synchronize more
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
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
Mutual Information unlocked binning individual cells stimulus-locked binning cell pairs
Population Code: Synergy unlocked binning stimulus-locked binning Synergyversus mutual informationfor several recordings
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
Erwin Frey (LMU)
BoehringerIngelheimFonds Foundation for Basic Research in Medicine