A 'physiological' model for the salamander horizontal optokinetic reflex

The salamander optokinetic head nystagmus can be explained by a comparatively simple negative feedback loop with few operational units within the loop. These units may easily be represented by properties of neural elements. In particular, the retinal slip velocity is transformed into an internal excitation by a velocity transfer function derived from pretectal recordings. A velocity storage element with input-output comparator is proposed as a recurrent inhibition network. A threshold element sums up the neuronal thresholds of the units involved. An internal gain factor may be interpreted as the transformation of the neural signal to a motor output. This output occurs with a stimulus-independent delay of 1 s, which is considered to be the sum of all conduction delays in the system. The model produces an output that is in excellent conformity with the optokinetic behavior. Additionally, the model predicts behavioral responses to optokinetic stimulation with extended stimulus ranges or with central lesions.