Senescence affects the ability to utilize information about the likelihood of rewards for optimal decision-making. Using functional magnetic resonance imaging in humans, we found that healthy older adults had an abnormal signature of expected value, resulting in an incomplete reward prediction error (RPE) signal in the nucleus accumbens, a brain region that receives rich input projections from substantia nigra/ventral tegmental area (SN/VTA) dopaminergic neurons. Structural connectivity between SN/VTA and striatum, measured by diffusion tensor imaging, was tightly coupled to inter-individual differences in the expression of this expected reward value signal. The dopamine precursor levodopa (L-DOPA) increased the task-based learning rate and task performance in some older adults to the level of young adults. This drug effect was linked to restoration of a canonical neural RPE. Our results identify a neurochemical signature underlying abnormal reward processing in older adults and indicate that this can be modulated by L-DOPA.
Friday, May 24, 2013
Renewing our brain's ability to make decisions.
Our dopamine neurons, which enable enable our brains to make better choices, based on outcomes, gradually die off as part of the normal aging process. Chowdhury and colleagues have now found that increasing dopamine levels in the brain of healthy older participants increased the rate with which they learned from rewarding outcomes and changed activity in the striatum, a brain region that supports learning from rewards. To relate brain activity and behavior, they utilized fMRI, diffusion tensor imaging, reinforcement learning tasks, and computational models of behavior. Their data might suggest that some variant of the dopamine therapy used for Parkinson's disease patient, might help older people make decisions. Here is their more technical abstract: