Fig. 8. Blocking of backpropagation by TTX. (Left) Diagram of experimental setup showing position of recording electrodes in outer molecular layer (M) and ganglionic layer (G). Green spot and shaded area represent site of TTX application in the deep fiber layer and its diffusion outwards. (Right) Color representation of field potentials obtained from M (top) and G (bottom) recording points. N₂ and N₃ are indicated in the upper panel. Dotted line indicates the moment at which TTX was applied. The ganglionic layer response disappeared 45 s after TTX application and simultaneously N₃ disappeared in the molecular layer response. N₂ persisted for a further 1.5 min.