Neurons in the spinal cord of the frog responding to moving visual stimuli.

Impulse discharges were recorded extracellularly with microelectrodes from the spinal cord during visual stimulation. With a sinusoidally moved surround three classes of neurons could be discerned: S-1 neurons activated by movement of the visual stimulus to the right, S-2 neurons by movement to the left and S-3 neurons activated by stimulus movement in both directions. Maximum activation was observed at movements between 0.08 and 0.1 Hz and a marked decrease in activation above 0.2 Hz. All neurons responding to visual stimulation were also activated by vestibular stimulation.