Everyone is well aware of their white adipose tissue and its ability to store excess energy as fat. In fact the efficiency with which it does this has led to obesity and related metabolic diseases becoming the largest single health burden in the United States. Yet buried behind our collar-bones and inside our necks lie deposits of a less well-known brown adipose tissue, which actually burns fat to generate heat. Brown adipose tissue evolved as a way for mammals to maintain their body temperature in a range of environments and interestingly people with larger, more active deposits of brown adipose tissue tend to weigh less and be metabolically healthier than those with less. Brown fat is controlled by the brain, which sends signals via the sympathetic nervous system in response to cold temperatures or changes in diet. However, we know very little about where in the brain these signals are generated and it is currently not possible to directly measure the activity of brown fat in real-time. This makes attributing changes in its activity to changes in specific brain regions very difficult. I aim to use the latest nano-electrodes and implant them directly into the brown fat of mice, which due to their small size have large amounts of very active tissue. Previous techniques prevent long-term measurements from animals in their home environment, but the small size of nanoelectrodes will overcome this problem and allow me to record signals from the nerves controlling brown fat in freely living mice. By doing this while I switch on and off different neurons in the brain (using viruses that respond to drugs or flashes of light) I hope to identify the brain circuits that regulate brown fat activity. This may allow us to design new therapies that target these neuronal circuits in the brain and maintain higher (or lower) levels of fat burning activity in the brown adipose tissue of humans. This would be very useful for treating obesity, diabetes, heart disease and potentially even anorexia.