The means by which information from sensory receptors is encoded is an important general problem in neurobiology. This project is a study of a specific example of this problem, the coding of visual information in a relatively simple neuronal network, the crayfish lamina ganglion. The ganglia of the crayfish optical system are arranged in columnar fashion. Their neurons are distributed in an ordered manner such that they form a map of the retina. Each point in visual space is encoded by five ganglion neurons which form a single column. These neurons have graded responses to light. Thus, each column can encode intensity, local contrast, orientation of polarized light, and wavelength (color) at a small region of the visual field. The Principal Investigator has characterized the morphology and connections of many of the ganglion cells in this neural network, and has also determined the chemical messengers by which some of them communicate. In this project he hopes to determine how the neural circuits already identified compute the values of various aspects of the stimulus, including polarization angle and velocity of movement, and how visual behavior is influenced by their activity. The methods he is using include electrical recording from neurons that can be identified microscopically from dye injected into them at the time of recording, and using immunocytochemical and pharmacological procedures to identify their chemical messengers (neurotransmitters).
