Differences in interactions between brain regions across personality types while learning in zebrafish (Danio rerio)

Learning is an important process for survival. Many studies find that variation in learning ability is related to personality type. Bold individuals generally learn faster than shy, however, the underlying neural mechanisms are not well understood. Potential mechanisms for differences in learning speed are variation in neurotransmitter activity, specifically dopamine and serotonin, and functional connectivity across the brain. In this study we quantified the number of generally active, active dopaminergic, and active serotonergic neurons using immunohistochemistry across 12 brain regions at two timepoints in bold and shy zebrafish undergoing an associative learning task. There were no interactions between treatment and personality type in any of the cell count measures suggesting that individual region activity and neurotransmitter activity do not explain learning differences. However, analyses of general neural activity networks revealed that the connection from the posterior zone of the dorsal telencephalon (olfactory cortex homolog) to lateral zone of the dorsal telencephalon (hippocampus homolog) was positive in bold but negative in shy fish undergoing learning. Overall, the results suggest that differences in activity involving reward processing in the brain may explain differences in reward learning between personality types.