Processing of retinal signals in the Limulus brain
Abstract: Limulus retina sends signals to the brain through optic nerve fibers with processes terminating in both the first and second optic ganglia, called lamina and medulla. At the lamina, OFF signals are generated and sent to the medulla. Medullar cells extend fibers to the other parts of the brain. To understand the neural mechanisms of their visually guided mating behavior, it is important to investigate responses in the medulla. However, there are only very few studies on medulla due to experimental difficulties. In this paper, we developed two experimental setups to study the medulla ex vivo and succeeded in recording responses and in mapping receptive fields. Responses of medullar cells share many features with responses of ganglion cells in vertebrate retina. The recorded responses can be classified as non-spiking, sustained and transient ON, sustained and transient OFF, ON-OFF, inhibition, and bilateral and contralateral types. Their receptive fields vary from 6 degrees to more than 180 degrees. Some cells have receptive fields classified as ON-center and OFF-center. In addition, one medullar cell had a separated receptive field extending over 90 degrees in the horizontal direction.
Keywords: visual processing, intracellular recording, medulla, brain, invertebrate, Limulus