Tanaka has reportedly admitted the allegations and told police, "I thought it was better if he went into a nursing facility after being admitted into police protection than being under my care."
Ubasute is a staple of Japanese folklore and appears in poems, short stories and art.
"Many of the legends surrounding ubasute are based in the poor regions of the north and northeast of Japan and involve poor communities that are struggling to get by after a bad harvest, bad weather or some sort of disaster and they need to reduce the number of mouths they needed to feed," said Jun Okumura, a political analyst at the Meiji Institute for Global Affairs.
"But it must be pointed out that other societies had similar traditions, such as the Eskimos, who would walk out onto the ice when they became too old," he said.
While the last recorded case of an Inuit being left for dead was in 1939, there have been incidents of ubasute in recent years.
In March 2011, a 63-year-old man from northeast Japan took his disabled older sister into the mountains of Chiba prefecture, east of Tokyo, and abandoned her. Katsuo Kurokawa left his sister, Sachiko, with some food before walking away.
Kurokawa said his sister had become "troublesome" after their home was destroyed in the March 2011 earthquake that hit the Tohoku region and that he could no longer care for her. Sachiko is thought to have drowned in the Obitsu River soon afterwards.
Her brother confessed to his actions after being arrested three years later for breaking into a donations box at a shrine in Chiba.
The latest case has triggered a fierce debate online, with many describing Ritsuko Tanaka's actions as "heartless" and condemning her for being "as ungrateful as you can get".
Others have expressed understanding of the strain she must have been under caring for a person with a degenerative mind disease with little money and probably little help from health authorities.
"This is desperately sad. Why hadn't the authorities stepped in to help earlier?" asked a poster named Maria on the Japan Today website. "Or was she unable to find the information or get the help she needed? Her own mental state must be extremely fragile."
Others said at least it was not a case of a struggling carer killing the person they were meant to be looking after - reports of which have increased in recent years.
"At least she did not kill him, like so many others do," said one commenter. "She just took him somewhere and dumped him, like a puppy you don't want."
- South China Morning Post
