A review of the neurophysiology of the turtle retina: Photoreceptors

How the vertebrate retina encodes and analyses information concerning light New increment and decrement, form, colour and movement is not fully understood. Neurophysiological studies of turtle retina have provided insights into how different types of visual information are processed. In the visual system, distinct functional channels appear to operate in parallel, namely ON/OFF, colour opponent/non‐colour opponent and transient/sustained channels. Using the turtle retina as a model, this three‐part review shows how functional pathways emerge from interactions between retinal neurons. It discusses how distinctive receptive field properties of the various types of retinal neuron are generated, as well as their significance for visual processing. Photoreceptors, which convert light into an electrical signal, are the subject of Part I. The structure, connectivity and light responses of these highly specialised cells are discussed. Photoreceptors are unusual sensory receptors because they respond to light with membrane hyperpolarisation. This decreases the rate of release of their neurotransmitter, glutamate. The phototransmitter interacts with postsynaptic receptors on horizontal and bipolar cells. Part II focuses on these second order neurons. Part III concludes with a discussion of amacrine and ganglion cells of the inner retina.