Negative-Valence Neurons in the Larval Zebrafish Pallium.

An organism's survival depends on the rapid classification of sensory events as either harmful or beneficial. In mammals, this computation is partially performed by neurons in the amygdala that respond to signals with negative or positive valence. The larval zebrafish pallium is thought to contain homologs of the mammalian amygdala, isocortex, and hippocampus; however, the signals encoded by pallial neurons remain largely uncharacterized. Using two-photon light-sheet microscopy to image 7-9-day-old zebrafish that express pan-neuronal GCaMP6s, we recorded calcium dynamics throughout the brain while presenting a panel of strongly aversive stimuli including infrared heat, electric shock, and a whole-field looming shadow, together with milder threats including vibration, loud sound, light transitions, and a partial looming stimulus. A compact cluster of neurons in the rostrolateral dorsal pallium (Rl) responded vigorously to strongly noxious and fully looming stimuli, but not to the milder cues. In contrast, neurons in the ventromedial pallium and habenula responded to all stimuli tested. Rl neurons are characterized by high tiam2a expression, suggesting they can be genetically accessed. Our results identify a dedicated negative valence locus in the teleost pallium and underscore the evolutionary conservation of valence coding circuits.