It can be "so devastating the person feels like they're inside a bowl, [and] you can't even get up the sides," Snyderman said. "It's like pulling someone down, down, down, down, down — until they just don't feel like they can get out anymore. It's a true mental break."
Smalldon, the forensic psychologist, says there have been cases in which extremely depressed people may have difficulty separating their own identity from others'.
The sufferer believes murder is a way to deliver the victim to a better life than the current miserable life he or she is having, he said.
Such a person also may have been experiencing what is called "magical thinking," a mental state in which reality is distorted and the person believes an extreme act will relieve the pressure, he said.
"They come to believe that murder is the one thing to do to get out of the predicament," Smalldon said.
Domestic Violence Can Play a Role
A number of other factors have played roles in previous cases, though it is not clear what may have caused Wednesday's alleged killings.
Julie Blackman, a social psychologist who practices in New York City, said there is no simple answer as to why a mother might kill her children.
"There is no formula as to why a mother would kill her own children, especially so many," Blackman said, when asked to speculate on the deaths of the Yates children. "But there are risk factors."
Those factors have included violence in the home from an abusing husband, financial stress, multiple births in succession coupled with fathers not helping and psychotic breakdowns, Blackman said.
ABCNEWS' Michael S. James contributed to this report.