Plasma acetylcholine and nicotinic acid are correlated with focused preference for photographed females in depressed males: an economic game study

This study showed depressed males have a narrower preference for female photographs (only preferring good looking ones) which is a marker for lower cognitive flexibility. The less nicotinic acid in their body, the narrower their preference. This indicates nicotinic acid may regulate human social decision-making (especially preference-related behaviors) by acting on the HCAR2 in microglia (the resident immune cells of the brain and spinal cord which constantly patrol the cerebral microenvironment to respond to pathogens and damage).