A gustatory hallucination is a sensation of taste without having tasted or eaten something. It is caused by random internally-generated electrochemical signals that stimulate the centers of the brain that control the sense of taste.
This type of hallucination is commonly seen in persons who suffer from some types of focal epilepsy (such as temporal lobe epilepsy) and emanates from the insula and sylvian fossa of the brain. Temporal lobe epilepsy is characterized by recurrent, unprovoked epileptic seizures that originate in the temporal lobe of the brain. Gustatory hallucinations can also be a symptom of schizophrenia. Typically the tastes experienced are unusual and not pleasant.
For example, a person experiencing a gustatory hallucination may perceive they are eating spoiled food even when they are not.