Fig. 2: Distinct brainstem circuits encode steering turn and exploratory turn.

a–c Graph showing soma distribution and activation intensity of spinal projecting neurons (SPNs) in distinct nuclei of the brainstem during rapid steering turns induced by left or right optic flow (a). Excitatory neurons were distributed across four brainstem nuclei (2 neurons in the rostral part of MiV1; 1 neuron in the rostral part of MiV2; 1 neuron in RoM1r, and 1 neuron in RoV3) and an inhibitory neuron (1 neuron in CaD). These neurons displayed significantly larger calcium responses during ipsilateral rapid steering turns, while the rest of the neurons showed weak or no response (b, c) (N = 12 fish; paired t test). d–f Graph showing soma distribution and activation intensity of SPNs in distinct nuclei of the brainstem during explorative turns induced by left or right optic flow (d). Excitatory neurons distributed across the caudal part of both MiV1 and MiV2 displayed significantly larger calcium responses during ipsilateral explorative turns, while the rest of the neurons showed weak or no response (e, f) (N = 12 fish; paired t test). The color saturation of each point indicates the normalized maximum ∆F/F of this neuron (a, d). The color plum represents neurons that are active during steering turns, while blue indicates neurons that are active during explorative turns. The solid color depicts neurons that are ipsilateral to the direction of the turn, whereas the faded color represents neurons that are contralateral to the turn movements. Each circle corresponds to a single neuron. All data are presented as mean ± SEM. The statistical test used was two-tailed t test. ****P < 0.0001, P = 0.0053 for RoV3, ns denoting no significant difference.