2nd TAC Meeting

Christian B. MendlTim Gollisch Lab

Neuronal Coding in the Retinaand Fixational Eye Movements

April 22, 2010

Outline

• Review of last TAC meeting• Informative spike response

features• Latency coding by cell pairs• Modeling response features• Outlook

Review of Last TAC Meeting

• Fixational eye movements, microsaccades• Counteract visual perception fading• Enhancement of spatial resolution

• Last TAC meeting: information theory: mutual information, synergy → use as screening tool

• To-do:– stimulus variation: grating instead of border– neuronal model building– decoding strategies

Informative Spike Response Features

Observed spike responses of a single cell

Various Response Typesa) b)

d)c)

Informative Spike Features (cont)Observed spike responses of a single cell

Informative Spike Responses:Number of Spikes/Trial

Informative Spike Responses:Internal Structure

ISI (inter-spike-interval)

Informative Spike Responses:Latency

Latency Coding by Cell Pairs

• Latency emerges as most informative spike response feature

• Timing reference? (Brain doesn’t know stimulus onset)

• → Need several cells

Cell Pairs: Experimental Data

Relative Latencytime intervals accessible to readout by higher brain regions

Cell Pairs: Latency Scatter Plot

K-means clustering: relative weight of off-diagonal elements:19.1%

Global Drift Correction

Drift-Corrected Latency Scatter Plot

K-means clustering:relative weight ofoff-diagonal elements:9.6%

Latency Correlations

• Observation: global latency drift leads to (artificial) correlations, can correct for that

• Question: cells internally interacting on short-term scale?

• → Compare spikes shuffled by one trial

Latency Correlations (cont)

shuffled version: no correlations

Latency Correlation Statistics

Conclusions Latency Coding

• Use latency instead of spike count and inter-spike-interval

• High information content in latency data from two cells

• Correlations might improve coding

Comparison with LN Models

LN Models (cont)

Conclusions Modeling

• Qualitative agreement• But still much room for

improvement, latency data on 10 ms scale not reproduced

• Gain control might be able to reproduce experimental spike histogram

Outlook

• Fixational eye movements have been reported in Salamander

• But precise quantification still missing• → Search coil setup