STARKE, Fla. (AP) _ Gov. Bob Graham has ordered an investigation into the removal of brain tissue from 11 executed prisoners without prior permission from them or their families. A medical examiner said studying the tissue would help in understanding violent behavior.

Brain tissue from 11 of the 13 men who died in Florida's electric chair since 1979 was removed by Dr. William Hamilton, the Alachua County Medical examiner, The Florida Times-Union & Jacksonville Journal reported in its Sunday editions.

Under Florida law, organs of the deceased can be removed without family authorization only to determine the cause of death.

State Attorney Gene Whitworth said Saturday that a joint investigation would be conducted by the state Medical Examiners Commission and the Florida Department of Law Enforcment.

Graham was unaware of the studies until Saturday, according to his press secretary, Jill Chamberlin. She said Graham ordered a parallel investigation.

The newspaper said Hamilton gave the almond-shaped amygdala, found at the back of the brain's temporal lobe, taken from the dead inmates to Dr. Christian Leonard, a professor of neuroscience at the University of Florida.

Hamilton defended the removal of the amygdala, one of the centers of aggressive behavior.

''In the case of executed prisoners, violent behavior usually led to the acts for which the death sentence was imposed,'' said Hamilton. ''Observation of the microscopic structure of the amygdala is distantly related to the cause of death.''

Ms. Leonard said she was hired by Hamilton to help perform the state- mandated autopsies on executed prisoners. She said she has used the brain matter to study whether childhood head trauma is related to violence later in life.

''It sounds like something out of the 1800s,'' said David Brierton, inspector general for the Department of Corrections, who said he knew nothing of the experiments when contacted Saturday. ''That would be a ghoulish prospect. That would be terrible.''

The practice was also condemned by a biomedical ethics expert.

''This has nothing whatsoever to do with the function of the medical examiner,'' Dr. Arthur Caplan of the Hastings Center, a biomedical ethics think-tank in New York, told the newspaper. ''The person didn't die because they had an unhealthy amygdala.''

Some physicians also question the validity of carrying out tests on tissue of a person who has been electrocuted.

''The brains are going to be largely destroyed,'' said Dr. Frank Elliot, a University of Pennsylvania researcher into the biological factors of human violence. ''It's almost like examining the brain with very accurate methods after shooting a bullet through it.''