The family of twins joined at the head has decided against separation surgery after learning the process would cause severe mental damage to both girls.

Doctor Douglas Cochrane, one of the seven experts working on the unique case, shared results of recent tests with the family on Friday.

The results showed the operation would not be safe for Tatiana and Krista Hogan because the girls share brain cells and blood vessels.

Felicia Simms, the twins' mother, said she was happy to finally have a definitive answer.

"I am relieved to know," Simms said. "(Now) we just live our lives the way we have been -- just normal lives."

Simms also told CTV the decision came after doctors discovered the twins were more intricately connected than they had predicted.

"Tatiana has a lot of the blood flow ... but it's more significant than what we originally thought," Simms said.

"There is blood flow, but also electric flow ... they share vibes between each other."

Simms explained the electric flow explains why one girl smiling prompts the other to do the same.

Cochrane also said last October other physiological reactions show the babies share vital neural tissue.

Dr. Douglas said when one of the girls is tickled, the other jumps -- showing how intertwined their sensory networks are.

"They have a bonding that is quite different than we would expect under any other condition," Cochrane told The Canadian Press.

"As one cried, a soother in the mouth of the other settled both. As we stimulated and tickled the legs of one, the other legs responded."

Dr. Brian Lupton, a neonatologist overseeing the girls' care right after they were born, said last year they appeared to be neurologically similar to other children their age besides their unusual connection.

He also said the challenges moving the babies around because of their connection will be figured out with time.

Don Hogan, the twins' grandfather, told The Canadian Press the nine-month-old babies are doing well.

Hogan says Tatiana has one bottom tooth and that her sister Krista is the heavier of the two and helps them flip over.

Simms said one of the main worries about keeping the two together is Tatiana developing high blood pressure from filtering most of the blood through both girls.

"We are still kind of worried about blood pressure," Simms said. "(Tatiana's) pretty much saving her sister the work -- she's doing it all."

"But as long as we can keep her blood pressure down ... everything is fine."

The twins' mother, who has two other children, said she won't have to make as many trips to the hospital now that they know the girls are staying together.

"We will probably still have to come down, but not as frequently," Simms said.

"Just for checkups to make sure at that (Tatiana's) heart is still functioning fine ... and make sure they are still growing."

With a report from CTV's Dr. Rhonda Low and files from The Canadian Press