Why are elderly people frequent victims of implausible ‘get rich’ scams? This study suggests the elderly are less able to detect reward prediction errors – the difference between the predicted reward (what they are promised) and the actual reward (what they get).
Young and old participants were given a gambling task to guess which of two images would pay off based on past performance. The senior group was further divided and took L-DOPA or a placebo. Older group on placebo underperformed while the group on L-DOPA raised their performance to equal the younger group.
Dopamine restores reward prediction errors in old age
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.