Electrical responses of fish optic tectum to visual stimulation; modification by cooling and conditioning

Abstract

1. Action potentials were recorded extracellularly from the optic tectum of the fishes Leuciscus, Tinca and Carassius in response to photic stimulation of the contralateral eye. 2. The following sequence of electrical responses was observed: In optic fibers of the tectal surfaces sensory spikes are found and slightly below the surface a slow negative wave in response to either “on” or “off” oft he light. Slightly deeper in the mid-layers of the tectum the negative wave is replaced by a positive wave of long duration and large amplitude. In the deepest layers where cell bodies are located much spontaneity is seen and a large negative wave. The subsurface negative wave precedes the deep negative one. The subsurface negative wave is probably an axo-dendritic synaptic potential, the deep negative one an axo-somatic synaptic potential. The positive wave in the mid-tectum is a current source. 3. If an electrical stimulus follows the light stimulus, the slow waves are enhanced and sometimes a new wave is introduced. 4. The afferent spikes are relatively insensitive to cooling, the deep negative wave is more sensitive than the subsurface one.