Breivik, who is being held apart from other inmates at a high-security facility after killing 77 people in 2011, has sued the Norwegian state, accusing it of "inhuman" and "degrading" treatment in violation of the European Convention on Human Rights.
He is suffering from "clear isolation damage," his lawyer Oystein Storrvik said ahead of the March 15-18 court hearing, to be held for security reasons in the gymnasium of the Skien prison, about 100 kilometres (60 miles) southwest of Oslo where the 37-year-old killer is incarcerated.
He told AFP the fact that Breivik no longer feels up to studying was "a sign that isolation has been negative to his psychological health."
A report from Norway's ombudsman tasked with investigating injustice by public agencies concluded in November that Breivik's solitary confinement risked turning into "inhumane treatment".
But according to NRK, the Skien facility's medical staff, whose testimony is expected to be crucial to the case, is of a different opinion.
"Breivik has periodically displayed clear signs of instability. He has displayed abnormal behaviour. But the prison's medical staff, who have observed him for a long time, believe he is not suffering from his prison conditions. They see no fundamental change in his mental health," NRK wrote on its website.
The office of the attorney general, which is defending the Norwegian state, has argued that Breivik's conditions are "well within the limits of what is permitted" under the Convention.
Breivik also accuses the state of violating another aspect of the Convention, regarding his right to privacy, for censoring his mail.
Authorities have said that is necessary to prevent him from building up an "extremist network".
On July 22, 2011, Breivik killed eight people in a bomb attack outside a government building in Oslo and later murdered another 69 people, most of them teenagers, when he opened fire at a Labour Youth camp on the island of Utøya.
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He was given a 21-year prison sentence in August 2012, which can be extended if he is still considered a danger to society.
According to court documents, Breivik has access to three cells -- one for living, one for studying, and a third for physical exercise -- as well as a television, a computer without internet access and a game console. He is also able to prepare his own food and do his own laundry.
His only human interaction is with guards and professional staff.