The Neuroscience For Kids Web Site has some neuroscience-related questions that might spark your interest. If you browse through these books at a store or library, they may give you some ideas for a project of your own. Project Guidelines Be sure to carefully read the project guidelines for your particular science fair. Obviously, experiments should not involve illegal substances or involve clearly preventable danger to you or your research subjects. You would need to get permission before providing large amounts of high-caffeine soda pop.
Some science fairs discourage the use of food in experiments because of food allergies.
Some science fairs allow experiments with live animals and others don't. In some places around the country, that experiment would not be allowed at all. In others, you would need a special permission form guaranteeing that you will take good care of the animal. In other places, they don't yet have such restrictions. Again, use common sense.