Not all of Michael Jackson’s body was lying inside a gold casket at Tuesday’s memorial service in Los Angeles. The King of Pop's brain was literally elsewhere.

Investigators are holding a portion of Jackson’s brain for more tests, and it will be returned to his family once those tests are complete, said Los Angeles County Assistant Chief Coroner Ed Winter.

Dr. Michael Baden, a forensic pathologist who has been involved in many high-profile autopsies, including those of Anna Nicole Smith and David Carradine, told FOXNews.com that it isn't unusual to perform further tests on a brain.

“With Michael, the brain is important for two reasons,” Baden said. “One, you try to determine whether any type of the unusual behaviors he demonstrated throughout the years may be associated with an abnormality of the brain. Also, if, say, he overdosed a month ago, that may show in the brain.”

During an initial autopsy, the coroner is unable to cut a brain finely enough to do a detailed analysis of it, Baden said. When the cause of death is easily determined, a detailed analysis is not usually necessary.

But in a case like Jackson’s, where the body was in surprisingly good health and a specific cause of death could not be determined, a more thorough study is needed – hence the need to hold the brain.

Baden said Jackson’s brain will be preserved in formaldehyde to keep it from deteriorating while a neuropathologist — a brain specialist — studies it over the next several weeks.

“This permits the neuropathologist to look at any microscopic lesions in the brain,” Baden said. “These lesions can show whether he had overdosed in the past, whether he’s suffered some sort of brain damage, whether there was injury from drugs. It can also show whether he was beaten as a child or was born with some sort of congenital abnormality.”

The brain is also used for toxicology or drug screening. After the brain is studied, it is then incinerated or returned to the family to be buried with the body, Baden said.

Jackson’s death certificate, which was released on Tuesday, did not list a cause of death. An official determination could still be several weeks away, as toxicology tests have not been concluded.

Investigators are still looking at drugs that were administered to Jackson, who had difficulty sleeping. The powerful sedative Diprivan, which is usually administered by anesthesiologists in hospitals, was found in his home, according to a law enforcement official.

RELATED: How Did Michael Jackson Get Diprivan?

The Associated Press contributed to this report.