1.2.2 ElectricalCouplingintheRetina
Electrical coupling was first proposed by Baylor et al. to exist between cone photoreceptors
when receptive field measurements from individual cones in the turtle retina gave results
much larger than the size of an individual cone [16]. Later, a pair of papers by Lamb and
Simon analyzed voltage noise in the turtle cones [69, 70]. With the help of Hodgkin, they
proposed several analytical models for the voltage response in the cone network, which are
also reproduced and discussed in section 5.4 of this thesis. Lamb and Simon showed that
voltage noise is inversely proportional to the length constant in the coupled network, and
pointed out that coupling causes the signal-to-noise ratio for small stimuli to be degraded
compared to uncoupled cones [69]. Detwiler and Hodgkin further analyzed coupling in the
turtle cones using both microelectrodes and and light stimuli [32], demonstrating a length
constant of 25 μ m. They acknowleged that the length constant measured with light stimuli
may be an overestimate as a result of light scattering in the retinal tissue. They also made
note of the ’’negative propagation” delay in studies of turtle rods [33, 34]. Following these
studies, Torre and Owen examined high pass filtering that causes this phenomenon in the
toad rod network [103]. Attwell and Wilson made recordings of salamander rod coupling
using microelectrodes, reporting a 300 MΩ coupling resistance [5]. From this data, they
used a Hodgkin-Huxley type model of a single Ia current to describe lateral signal propaga-
tion in the rod network. Later, Attwell et al. used the same framework to model interactions
between rods and cones, estimating the coupling resistance between the two cells as 5000
MΩ [7]. Attwell and Wilson also demonstrated how coupling in the rod network affects the