People with episodic amnesia, stemming from damage to their brain’s hippocampus, may no longer be able to imagine their future, but they can still make decisions about it, a finding that surprised York psychology Professor Shayna Rosenbaum.
“It suggests that there is a lot more going on than previously thought,” says Rosenbaum. “You might think that all aspects of future imagining and decision-making would be obliterated in hippocampal amnesia, but that’s not the case.”
Left: Shayna Rosenbaum
Rosenbaum was the senior author of “Future Decision-Making without Episodic Mental Time Travel”, written with her PhD student Donna Kwan, who was lead author, and collaborators from Washington University in St. Louis, and published online this month in the Hippocampus journal.
Researchers already know that piecing together a narrative about the past and even the future is affected when there is damage to the hippocampus. What Kwan, Rosenbaum and colleagues have found is that when people with episodic amnesia are given tasks that don’t require constructing a narrative, they do much better at making future-oriented decisions.
Using a temporal discounting paradigm borrowed from economics, Kwan and Rosenbaum tested the future decision-making abilities of people with amnesia. They gave them a task that didn’t require constructing a narrative but did require thinking about the future.
The study looked at the ability of an amnesic person, K.C., who has extensive bilateral hippocampus damage compared to a control group of 18 healthy males. The participants were told they could choose to get a certain amount of money now or a larger amount in the future. The amounts varied from $20, $50 or $200 now or either $100 or $2,000 a week, one month, three months, six months, one year, three years or 10 years in the future.
Right: Donna Kwan
“The prediction is that someone who can’t imagine the future might consistently accept the current amount. The other possibility would be that they might consistently choose the future amount,” says Rosenbaum. The expectation would be that there would only be these two extremes, not a variety of responses.
K.C.’s decisions to either delay or opt for the immediate reward, however, were consistent with the control group, even though he couldn’t imagine what he would do with the future money. Neither could he explain why he sometimes chose the larger future amount, rather than the smaller, immediate amount. K.C. chose both the smaller, immediate reward as well as the larger, future reward depending on variables, such as the amount of each reward and the distance of time.
What this study shows, says Rosenbaum, is having the ability to make decisions about future rewards is not tied to the ability to imagine future personal experiences or remember personal pasts, what has been referred to as “mental time travel.” This runs counter to the current belief that for a person to be able to make choices affecting the future, they need to be able to anticipate future events.
Rosenbaum says she and her PhD student Kwan and MA student Nicole Carson are continuing to investigate this line of research, which was supported by a Canadian Institutes of Health Research (CIHR) grant, New Investigator Award and a Sloan Research Fellowship.
Left: Nicole Carson
This research follows on the heels of earlier research by Kwan, Carson and Rosenbaum looking at the interconnection between the “ability to remember past personal experiences and the ability to envision future personal experiences,” as reported in the article, “Deficits in Past Remembering Extend to Future Imagining in a Case of Developmental Amnesia” published in the February 2010 issue of Neuropsychologia.
This study looked at whether the failure of the ability to remember past personal experiences to emerge in early development precluded the development of the ability to envision future personal experiences and vice-versa.
To study this, the researchers tested H.C., who had developed amnesia at an early age. What they found was a parallel pattern of impairment. H.C.’s narratives for both past and future personal experiences were deficient. The research was funded by a CIHR grant and a New Investigator Award.
The findings of this line of research could impact interventions down the line for patients who’ve suffered a brain injury, stroke or encephalitis or who have Alzheimer’s.
By Sandra McLean, YFile writer