Infections: Bacteria, viruses and other organisms cause brain diseases such as meningitis. Injuries: Accidents and injuries cause most traumatic brain injuries. An injury to your brain can also increase your risk for other brain diseases, such as epilepsy and Alzheimer’s disease.Imaging tests, such as an MRI. Cerebrospinal fluid (CSF) testing, also called a lumbar puncture. Biopsy. Electroencephalography (EEG) or electromyography (EMG), which use small electric sensors to measure brain activity and nerve function.Depression is a disorder of the brain. It is a serious mental illness that is more than just a feeling of being “down in the dumps” or “blue” for a few days. For more than 20 million people in the United States who have depression, the feelings persist and can interfere with everyday life.Overview. Encephalitis (en-sef-uh-LIE-tis) is inflammation of the brain. There are several causes, including viral infection, autoimmune inflammation, bacterial infection, insect bites and others. When inflammation is caused by an infection in the brain, it’s known as infectious encephalitis.