BRUSSELS (AP) -- A man who emerged from what doctors thought was a vegetative state says he was fully conscious for 23 years but could not respond because he was paralyzed, his mother said Monday.

Rom Houben, 46, had a car crash in 1983 and doctors thought he had sunk into a coma. His family continued to believe their son was conscious and sought further medical advice.

Professor Steven Laureys of Belgium's Coma Science Group realized that the diagnosis was wrong and taught Houben how to communicate through a special keyboard, said Dr. Audrey Vanhaudenhuyse, who is on Laureys' team.

Rom used the device to tell a reporter for the German magazine Der Spiegel that: "I screamed but there was nothing to hear."

Belgian doctors who treated him early on said that Rom had gone from a coma into a vegetative condition.

Coma is a state of unconsciousness in which the eyes are closed and the patient can't be roused, as if simply asleep. A vegetative state is a condition in which the eyes are open and can move, and the patient has periods of sleep and periods of wakefulness, but remains unconscious and unaware of him or herself or others. The patient can't think, reason, respond, do anything on purpose, chew or swallow.

But Rom's parents would not accept that he was comatose or vegetative.

His mother, Fina Houben, said in a telephone interview that they took him five times to the United States for tests.

More searching finally got her in touch with Laureys, who put Houben through a PET scan that indicated he was conscious. The family and doctors then began trying to establish communication.

A breakthrough came when he was able to indicate yes or no by slightly moving his foot to push a computer device placed there by Laureys' team.

Then came the spelling of words using his finger and a touch-screen attached to his wheelchair.

"You have to imagine yourself lying in bed wanting to speak and move but unable to do so -- while in your head you are OK," Vanhaudenhuyse said. "It was extremely difficult for him and he showed a lot of anger, which is normal since he was very frustrated," she said.

The case came to light after Laureys published a study in the journal BMC Neurology this year showing that about four out of ten patients with consciousness disorders are wrongly diagnosed as being a vegetative state. Houben, although not specifically mentioned, was part of the study.

Houben has started writing a book on his experiences.

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