Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue. More advanced and serious symptoms include seizures or convulsions, tremors, hallucinations, and memory problems.

Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection. The most common causes of acute viral encephalitis are rabies virus, Herpes simplex, poliovirus, measles virus, and JC virus. Other causes include infection by flaviviruses such as Japanese encephalitis virus, St. Louis encephalitis virus or West Nile virus, or by Togaviridae such as Eastern equine encephalitis virus (EEE virus), Western equine encephalitis virus (WEE virus) or Venezuelan equine encephalitis virus (VEE virus).

It can be caused by a bacterial infection, such as bacterial meningitis, spreading directly to the brain (primary encephalitis), or may be a complication of a current infectious disease syphilis (secondary encephalitis). Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Lyme disease and/or Bartonella henselae may also cause encephalitis. Cryptococcus neoformans is notorious for causing fungal encephalitis in the immunocompromised. Streptococci, staphylococci and certain Gram-negative bacilli cause cerebritis prior to the formation of a brain abscess.

Oliver Wolf Sacks, CBE (born 9 July 1933, London, England), is a British neurologist, psychologist, writer, and amateur chemist who has spent the major portion of his career in the United States. He lives in New York City, and is professor of neurology and psychiatry at Columbia University, where he also holds the position of "Columbia Artist". He previously spent many years on the clinical faculty of Yeshiva University's Albert Einstein College of Medicine.

Sacks is the author of numerous bestselling books, including several collections of case studies of people with neurological disorders. His 1973 book Awakenings was adapted into an Academy Award-nominated film of the same name in 1990 starring Robin Williams and Robert De Niro. He, and his book Musicophilia: Tales of Music and the Brain, were the subject of "Musical Minds", an episode of the PBS series Nova.

Sacks was the youngest of four children born to a North London Jewish couple: Samuel Sacks, a physician (died June 1990), and Muriel Elsie Landau, one of the first female surgeons in England. Sacks had a large extended family, and among his first cousins are Israeli statesman Abba Eban, writer and director Jonathan Lynn, and economist Robert Aumann.