The name is absent

a good understanding of how these neurons that comprise the very first interface between
the CNS and the outside world, then we will have accomplished a small but respectable step
toward understanding the CNS. This thesis undertakes a study of photoreceptor physiology
with the intent to contribute toward this goal.

A unique and notable feature of the retina is that the photoreceptors, the cells that ini-
tially respond to light, encode this light with graded potentials. This means that they rep-
resent visual information as a continuous function of their membrane voltage. In this way
they are ’analog” neurons. The photoreceptors pass on visual information to other ’’analog”
neurons called bipolar cells and horizontal cells. Eventually after being passed between and
transformed by cells with graded potentials, the information reaches ganglion cells, which
then encode the signals into an action potential. This action potential is an angle modulated*
binary signal that is characteristic of most of the rest of the neurons in the CNS.

Relevant to the introduced theme of generalizability, two features of photoreceptor phys-
iology investigated in this thesis also appear to be important in other neural systems. The
first is a type of very specialized ionic current in photoreceptors that appears to have many
interesting roles in human physiology. This current, Ih, is unique in that the ion channels
that gate it are opened by hyperpolarizing voltages in contrast to the conventional depo-
larization dependent gating characteristic of other ion channels. Ih is present in the heart,
where it acts as the primary cardiac pacemaker, and in the brain, where it may regulate
rhythmic activity and modulate gain of neuronal synapses [106]. This work investigates the

^encoded by either the firing frequency, or relative phase between firings

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