Animals are often noted sensing signs of danger and reacting. A simple form of this phenomenon is called fear conditioning, which is a type of learning commonly seen in every animal. By manipulating the activity of specific neurons of the zebrafish brain, scientists at the National Institute of Genetics (NIG) in Japan have elucidated a neuronal population essential for fear conditioning in zebrafish. The study, published in the April 25 issue of BMC Biology, suggests that such a neural circuit essential for fear conditioning exists and is conserved during vertebrate evolution.