Felix Franke: Action potential speeds compensate for travelling distance in the human retina

Institute of Molecular and Clinical Ophtamology/Universität Basel

First talk of the BCCN Berlin Alumni Lecture Series. A social will be organized afterwards.
Felix did his PhD with Klaus Obermayer.

 

Abstract:
Timing between action potentials is crucial for information processing in real neural networks. However, in the human eye the axons of retinal ganglion cells are unmyelinated - and therefore slow - but feature vastly different lengths. How is the temporal consistency of the visual image preserved, if peripheral action potentials need to travel much further than central ones?

We used human retinal explants to precisely measure paths and propagation speeds of action potentials of foveal and peripheral retinal ganglion cells with high-density microelectrode-arrays.

Axonal conduction speeds were spatially heterogeneous and depended on the location of the RGC somas. Around the fovea centralis, action potentials of temporal RGCs, that need to bend around the fovea centralis to reach the optic nerve head, traveled up to 50% faster than action potentials of nasal RGCs which go straight to the optic nerve. Peripheral axons exhibited up to three times higher conduction velocities than foveal axons.

We modelled axonal trajectories and their lengths across the entire human retinal nerve fiber. The model recapitulated well the organization of axonal trajectories and modelled axonal lengths strongly correlated with observed axonal lengths and action potential propagation speeds.

Our measurements suggest that a compensatory mechanism in the human retina contributes to synchronizing the arrival times of visual signals in the brain.

 

Pizza and beer afterwards; guests are welcome.

Organized by

Klaus Obermayer / Margret Franke