He has complained about the cold and the rice-based menu, sources say, though he has told embassy visitors he is being well-treated although he has shed a lot of weight.
He has been stripped of his leadership roles at Nissan and Mitsubishi Motors but the third member of the auto alliance he helped forge, French automaker Renault, has kept him as nominal head while he fights the charges.
Ghosn’s detention has also laid bare tensions in the alliance he created, which together sells more cars than any of its rival groups.
Meanwhile, fresh claims against Ghosn appear almost daily in the Japanese media.
According to Friday’s edition of the Nikkei business daily, Ghosn paid nearly $50 million to businesses run by two Middle Eastern acquaintances from the “CEO reserve”, a pot of cash that the boss was able to use at his discretion.