The role of GABA in detecting visual motion.

The basic computations underlying the extraction of motion from the visual environment have been characterized in great detail. A non-linear interaction, such as a multiplication, between neighbouring visual elements was shown to be the core of biological motion detectors in different species ranging from insects to man. GABA (gamma-aminobutyric acid)-ergic inhibitory synapses suppressing the responses to motion in one direction but not in the other are widely accepted to be the cellular basis for this non-linear interaction. Based on model predictions we can show in combined pharmacological and electrophysiological experiments that in the fly motion detection system GABAergic synapses do not play this role but rather are involved in another important step of motion computation. This makes a reconsideration of the role of inhibition in other motion detection systems necessary.