A study published online in Nature Neuroscience has demonstrated that a drug widely used to treat Parkinson’s Disease can help to reverse age-related impairments in decision making in some older people. Researchers from Wellcome Trust Centre for Neuroimaging describe the changes in the patterns of brain activity of adults in their seventies that help to explain why they are worse at making decisions than younger people.
Poorer decision-making is a natural part of the aging process that is believed to stem from a decline in our brains’ ability to learn from our experiences. Part of the decision-making process involves learning to predict the likelihood of getting a reward from the choices that we make. The nucleus accumbens area of the brain is responsible for interpreting the difference between the reward that we’re expecting to get from a decision and the reward that is actually received. These so called ‘prediction errors’, are modulated by dopamine to help us to learn from our actions and modify our behavior to make better future choices.
Researchers using a combination of behavioral testing and brain imaging techniques, investigated the decision-making process in 32 healthy volunteers in their early seventies compared with 22 volunteers in their mid-twenties. Older participants were tested on and off L-DOPA, a drug that increases levels of dopamine in the brain – a drug that is widely used to treat Parkinson’s disease.
The participants were asked to complete a behavioral learning task called the two-arm bandit, which mimics the decisions that gamblers make while playing slot machines. Players were shown two images and had to choose the one that they thought would give them the biggest reward. Their performance before and after drug treatment was assessed by the amount of money they won in the task.
The older subjects performed worst in the task, and were less able to predict the likelihood of a reward from their decisions. They did, however, demonstrate a significant improvement following drug treatment.
The researchers then looked at brain activity in the participants as they played the game using functional Magnetic Resonance Imaging (fMRI), and measured connections between areas of the brain that are involved in reward prediction using Diffusor Tensor Imaging (DTI). The findings reveal that the older adults who performed best in the gambling game before drug treatment had greater integrity of their dopamine pathways. Older adults who performed poorly before drug treatment were not able to adequately signal reward expectation in the brain – this was corrected by L-DOPA and their performance improved on the drug.