biophysical properties and function of I∏, showing that it is a fundamental building block for
neural systems, and demonstrates how it plays an important role in photoreceptor responses
to light.
Electrical coupling between rod photoreceptors is another feature of photoreceptors that
is applicable to other neurons in the retina, myocytes in the heart, and neurons in the brain.
In the retina, electrical coupling between adjacent rods lowers their intrinsic noise level, and
allows them to average light responses over space. This thesis describes our investigations
into the relevant conductances involved in rod-rod coupling, and shows how this leads to
tradeoffs in noise tolerance versus image fidelity in the rod network. This analysis is certainly
applicable to other networks of coupled retinal neurons such as bipolar cells, but may also
be applicable to other systems in the brain where lateral coupling can serve to reduce noise
in redundant parallel pathways.
1.2 Background
The use of the tiger salamander {Ambystoma tigrinum) as a model organism began with
Lasansky,s investigations of the anatomy of the salamander retina using electron microscopy
[71]. The salamander is a convenient model organism for retinal research because its cells
are very large (a rod photoreceptor is ≈ 10 microns in diameter), facilitating easy electrical
recordings with a glass microelectrode or patch pipette. Importantly, the basic structure
of the salamander retina is the same as that of other vertebrates, including primates. This
includes a layer of photoreceptors that includes rods and cones, depolarizing and hyperpo-