The third ventricle is one of four ventricles in the brain that communicate with one another. The third ventricle sends messages to and receives messages from the lateral ventricles, which is located in front of the third ventricle, and the aqueduct of the midbrain, which is located directly behind the third ventricle. It is filled with cerebrospinal fluid and helps to protect the brain from injury. It is a narrow cavity that is located between the two lateral halves of the brain. The hypothalamus and thalamus are located on the sides of the third ventricle. Abnormalities of the third ventricle are associated with various conditions including hydrocephalus, meningitis, and ventriculitis. Hydrocephalus is an excessive buildup of fluid on the brain. Meningitis and ventriculitis are both caused by trauma to a ventricle, including the third ventricle that may lead to an infection. An enlarged third ventricle has been associated with psychiatric illnesses, such as schizophrenia; however, the accuracy of this theory hasn't been conclusively proven.