In neuroscience research it is often helpful to ask whether and animal will prefer or avoid stimulating a set of brain cells. For example, stimulating cells that make dopamine is highly preferred and animals will spend most of their waking hours stimulating them if given the chance!  

The RAT can do a simple test of this feature of behavior with a task called a "Real-Time Place Preference" assay.  Here, we programmed the output of the RAT to pulse a brain-stimulation  LED at ~15Hz whenever the mouse moves to one side of a box.  In this way, we can test whether he prefers to spend time on the side that results in brain stimulation, or avoid the stimulation.  We did this with a mouse that expresses a light sensitive protein in a brain structure that receives dopamine, and is also preferred.  Here are photos of the setup and results: