If I offer you a bag of potato chips today or a box of chocolate truffles next week, which would you choose? Neuroscientists are interested in exploring what happens when the brain must choose between receiving a reward immediately or in the future, especially when waiting may result in a prize you like better.
A seahorse-shaped structure in the brain called the hippocampus is involved in recalling events from the past, and imagining them in the future. A new study in the journal PLOS Biology explores what role the hippocampus plays when a person has to decide between getting a reward now or later.
This study looked at healthy individuals as well as those with Alzheimer's disease, a condition characterized by memory impairment and associated with atrophy of the hippocampus, and a different brain condition called frontotemporal dementia.
The French study, led by Mael Lebreton at the Brain and Spine Institute (ICM) in Paris, looked at time-dependent choices involving money, as well as "episodic" options such as food, sports or cultural events.
In the first experiment, researchers gave 15 participants a series of decisions about choosing one reward or another, where one of the hypothetical prizes is given now, and the other later. Some options were described in labeled photos, and some as just text. Photos gave participants a visual image, but with text, the subjects were forced to imagine what they would get. Participants tended to choose the delayed rewards when they imagined them with more detail.
The second experiment involved 20 participants faced with the same kinds of decisions. Here researcher learned that participants tended to be consistent in their level of impulsiveness, regardless of whether they were choosing between amounts of money or experiences such as foods or sports tickets. Individuals tended to either want rewards right away, or they were willing to wait for something better, "arguing in favor of a common underlying impulsive trait," the study authors wrote.
This second experiment also used functional magnetic resonance imaging (fMRI) to track activation patterns in the hippocampus. Importantly, when immediate rewards were shown as pictures, and future rewards were given as text, researchers found that the amount of activity in the hippocampus was related to the selection of future rewards. But when both options are presented as pictures, or as text, the hippocampus does not show increased activation. In other words, the hippocampus helps you assess the value of waiting for a reward when you have to imagine it, compared to an immediate reward that you can see.
Researchers also studied these kinds of tasks among dementia patients compared to healthy controls. Unlike the healthy participants, Alzheimer's patients tended to not favor options written out as text, which required mental simulation. Study authors say this suggests that the damage to the hippocampus caused by Alzheimer's may impact these time-related choices. The type of dementia seems to matter, too. Patients with a behavioral variant of frontotemporal dementia tended to be impulsive in many different scenarios, whereas Alzheimer's disease patients favored immediate over delayed rewards, when they had to imagine the future rewards.
Potentially, this may mean patients with Alzheimer's disease or even general damage to the hippocampus, will have problems pursuing long-term goals because they have problems simulating future experiences in their minds, the study said.
But, given the small sample sizes for the experiments, more research is needed to confirm the findings and strengthen the possible conclusions. It is also based on associations between behaviors and brain activity, and does not prove causation.
The new study is part of a growing body of research exploring areas of the brain most associated with self-control and how they work.
In the future, scientists say, drugs may be designed to enhance these processes, so that people with impulse control problems can find relief. Understanding the processes that break down in people who can't say no to temptation as often as they would like, may lead to the eventual development of such drugs.
Read more about self control in the brain