Neuronal Coding in the Retina
and Fixational Eye Movements
Christian Mendl, Tim Gollisch
Max Planck Institute of Neurobiology, Junior Research Group Visual Coding
Overview
• Latency emerges as most informative spike response feature
• Timing reference? (Brain doesn’t know stimulus onset)
So-called “fixational eye movements” are an important
feature of normal human vision since they counteract
visual perception fading and enhance spatial resolution.
Yet it is not yet fully understood how they influence
neuronal coding schemes. To investigate these
questions, we record the action potential of amphibian
retinal ganglion cells, mimicking fixational eye
movements by oscillatory shifts of the stimulus.
Search for Internal Mechanisms
• → Need several cells
• Relationship
between a cell’s
receptive field
position on the
grating and response
latency?
Stimuli from Rucci et al.,
Miniature eye movements
enhance fine spatial detail
• → Replace
orientations by
linear phase shifts
for easier analysis
Employing linear phase shifts (color coded).
Each pair of ellipses shows the receptive field
position relative to the oscillating grating
Concrete task: discriminate 5 different orientations
based on the spike responses of retinal ganglion
cells
Spike responses of two cells
(blue and green, respectively)
The upper
stimulus modality
imitates
oscillatory eye
movement, and
the lower
microsaccades
• Informative
spike
response
features?
• Role of
correlations?
• Population
code?
All
experiments
are
performed
on Axolotl
and Frog
(Xenopus
laevis)
Relative latency → time intervals
accessible by higher brain regions
• Observation: latencies are correlated
Latency scatter plot
Global drift correction
Spike response raster plot for a single cell
Extracellular recordings from
retinal ganglion cells using a
MEA (Multi-Electrode-Array)
Relative response latencies for
different phase shifts
• Response latency matches phase shift and follows reversal of the oscillatory
movement direction
• Latency range bigger than stimulus movement time interval
• First spike is elicited earlier when receptive field moves from a bright to a dark region
Latency Coding and Correlations
Subtracting global drift
reveals internal correlations
Shuffling trials
Summary
• Latency emerges as the most informative spike response feature
• Relative spike timings of two cells contain information and are
directly accessible to readout by higher brain regions
Spike count histogram
• Responses of cell pairs are correlated → evidence for coding
structure via intrinsic interactions
• Receptive field position on grating could predict response latency
References
Compare with latency
correlations after shuffling
Single cell responses for different
orientations (color coded)
Timing histogram of
first spike in each trial
Conclusion: there are cell pairs
showing internal correlations,
additional to global drift effects
Latency correlation statistics for
several cell pairs
•
Meister et al. (1995), Concerted signaling by retinal ganglion cells. Science 270
•
T. Gollisch and M. Meister (2008), Rapid neural coding in the retina with relative spike latencies. Science 319
•
S. Martinez-Conde et al. (2006), Microsaccades counteract visual fading during fixation. Neuron 49
•
M. Greschner et al. (2002), Retinal ganglion cell synchronization by fixational eye movements improves feature estimation. Nature Neuroscience 5
•
M. Rucci et al. (2007), Miniature eye movements enhance fine spatial detail, Nature 447
•
M.J. Schnitzer and M. Meister (2003), Multineuronal firing patterns in the signal from eye to brain. Neuron 37
•
E. Schneidman et al. (2003), Synergy, redundancy, and independence in population codes. Journal of Neuroscience 23(37)
•
D.K. Warland et al. (1997), Decoding visual information from a population of retinal ganglion cells. Journal of Neurophysiology 78