To quantify these effects, we computed a directional index by subtracting firing for correct movements away from each cell’s response field from firing for correct movements to be made into the response field divided by the sum (into − away/into + away). These indices were computed for two epochs. The first index examines firing from first light onset until port exit, thus capturing firing related to the first light and associated motor signals. The second epoch examines firing from the second light until fluid-well entry, thus capturing firing related to the second light and the correct movement into the fluid well. Fig. 2 C and D illustrate the distribution of indices during first and second light epochs for controls. During the first light epoch the distribution significantly shifts below zero (Fig. 2C; Wilcoxon; n = 97; µ = −0.13; P < 0.0001), indicating that the majority of neurons signaled the direction of the first light. During the second light epoch, the distribution was significantly shifted in the opposite direction (Fig. 2D; Wilcoxon; n = 97; µ = 0.05; P =
