Mass killer Anders Behring Breivik has claimed in court that Norway is violating his human rights by keeping him in isolation for murdering 77 people in 2011.
The right-wing extremist killed 77 people when he bombed central Oslo and shot many of the people at a youth camp on the island of Utoya.
He has been held on his own in jail since his arrest, and experts believe he will spend the rest of his life behind bars.
The Norwegian is complaining that being kept in solitary confinement is worse than the death penalty.
Breivik's lawyer, Oeystein Storrvik, said his treatment was a violation of the European Convention on Human Rights by keeping the 37-year-old isolated from other inmates.
But the lawyer representing the state said Breivik had been given opportunities for interaction with others, including meeting volunteers to play chess, but that he had declined.
Breivik irritated the judge with a Nazi salute at the start of proceedings.
What are Breivik's conditions?
Security rules mean Breivik's interaction with prison guards and a priest take place through a thick glass barrier.
The only physical contact Breivik has had since his arrest was with his mother, who was allowed to see him without the glass wall. That was a brief visit to say goodbye just before she died, his lawyer Oystein Storrvik said.
Although Breivik has three prison cells, daily exercise time, access to a computer, TV and video games and can cook and do laundry, Mr Storrvik said he was being damaged by his isolation.
The lawyer cited prison reports that said Breivik could appear disoriented and forgetful, not remembering what day or time it was.
Norwegian government lawyer Marius Emberland said Breivik had to be held in isolation because he was a dangerous man who could influence other prisoners.
This was also for Breivik's own safety, he said, citing one instance when another inmate was able to get to the door of Breivik's cell and threatened to kill him.