Figure 6. Effects of 2-amino-4-phosphonobutyrat (APB) and picrotoxin (PTX) on the directional tuning of the light edge and dark edge responses in an example NOT-DTN unit.

Polar plot of the responses during stimulation with ON (A) and OFF (B) edges moving in the four cardinal directions prior to drug application (black curves), after intravitreous injection of APB (red curves), and after additional intravitreous injection of PTX (green curves). Distance from the center of the polar plots indicates neuronal activity in spikes per second given by the numbers on the circles. PD: preferred horizontal direction, NPD: non-preferred horizontal direction. Note that after APB followed by a PTX injection an increased but direction unselective response to the moving dark edge (OFF) is uncovered.