On 31 January 2013, Jennifer Viegas  reported following news at news.discovery.com:

Scientists have just observed a thought swimming through the brain of a live fish, and that thought concerned getting something good to eat.

The footage and analysis were made possible with a very sensitive fluorescent probe that detects the activity of neurons.

“In the future, we can interpret an animal’s behavior, including learning and memory, fear, joy, or anger, based on the activity of particular combinations of neurons. This has the potential to shorten the long processes for the development of new psychiatric medications,” 

dnews-files-2013-01-Fish-660x433-jpg