Abstract

FR.15.06

Selective isolation of neural substrates underlying diseases of the inner retina and higher visual pathways by functional diagnostics

Michael Bach
Universitäts-Augenklinik Freiburg

Objective
The components of the flash ERG are well understood and one can fairly reliably correlate them and their pathophysiological alterations with the underlying neural structures (rods, cones, on- and off bipolars). Structures further up the visual pathway are not as well selectively accessible.
Methods
While it is rather certain that ganglion cell function is mirrored in the pattern ERG (PERG), the exact substrate of the PERG components is not as well understood. Our current working hypothesis is that the P50 component originates within the ganglion cells and represents the local summation of incoming excitatory and inhibitory potentials; the N95 component reflects action potentials from the ganglion cells.
Results
Ongoing experiments by Luo & Frishman with selective pharmacological interventions are suited to test and possibly falsify the above hypothesis: I-APB selectively deactivates the on-pathway, PDA the on-pathway, and TTX inhibits voltage-sensitive sodium channels and thus blocks action potentials. Forthcoming results will soon allow us to closely relate the PERG components and underlying physiology.
Conclusions
Differentially isolating neural modules beyond the retinal ganglion cells with electrophysiological methods remains difficult. Even selectively activating the magno-, parvo- and coniocellular pathway is highly questionable. Successful, on the other hand, is selective stimulation of visual dimensions like colour, motion, stereo, texture etc.

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