Neurons in the deep layers of the avian optic tectum (SGC) respond preferentially to small moving objects with a limit of speed sensitivity beyond 30 deg/s (Troje and Frost, SFN Abstract 24:642.9, 1998). We studied the circuit comprised of anatomically defined SGC type I cells and their presynaptic small retinal ganglion cells with respect to their ability for motion detection using a slice preparation. Type I SGC cells responded with one or multiple bursts (chattering) to depolarizing somatic current injection. Electrical stimulation of the retinal ganglion cell axons caused an EPSP/spike response in the SGC I soma with a sharp onset. Direct electrical stimulation of the SGC I dendrites caused a response in the soma similar in shape to synaptic stimulation. The sharp onset response to dendritic stimulation persisted when the soma was hyperpolarized below -100 mV, but was abolished in saline containing 1 μM TTX. The duration of the sharp onset response increased when Ca2+ in the saline was replaced with Ba...