A fierce debate has raged over whether Breivik is mentally competent to face criminal punishment.
The mass killing on July 22 was the single largest loss of life in Norway since World War II.
Breivik is accused of killing eight people in a bomb attack in Oslo, then going to Utoya island outside the city and systematically gunning down 69 more people, many of them teens and young adults.
Breivik has pleaded not guilty, though he has admitted carried out the attacks, the judge handling his case said previously.
His trial is due to start April 16 and is expected to last 10 weeks.
The court case is designed to demonstrate his guilt or innocence. His punishment, if he is found guilty, will then be based on the determination of his sanity.
Last month, a court ordered him to undergo a fresh round of psychiatric evaluation as experts seek to determine his mental state ahead of a trial.
Two court-appointed psychiatric experts recommended that he spend four weeks under 24-hour psychiatric monitoring so the court can get the fullest possible picture of his behavior, court documents released February 10 said.
The two experts were appointed to evaluate his mental state after the court requested a second opinion because of the importance of the question of sanity to Breivik's trial.
In November, prosecutors said psychiatrists had determined Breivik was paranoid and schizophrenic at the time of the attacks and during 13 interviews experts conducted with him afterward.
It may not be possible for him to be sentenced to the maximum punishment for the crimes if he's deemed insane.
Breivik reiterated some of his extremist views during a hearing last month, which began with him entering with a smile and offering up a raised, clenched-fist salute.
He insists nobody could believe that he was insane, and describes questions about his mental condition as ridiculous, his lawyer, Geir Lippestad, told the court.
Breivik claims the shooting rampage was a matter of self-defense, meant to save Norway from being taken over by multicultural forces and to prevent ethnic cleansing of Norwegians, Lippestad said.
Authorities have described him as a right-wing Christian extremist. A 1,500-page manifesto attributed to Breivik posted on the Internet is critical of Muslim immigration and European liberalism, including Norway's Labour Party.
The victims on Utoya Island were among 700 mostly young people attending a Labour Party camp on Utoya island.