Prefrontal and striatal activation in elderly subjects during concurrent implicit and explicit sequence learning

Decreased function in the prefrontal cortex (PFC) is regarded as a primary mechanism of cognitive aging. However, despite a strong association between the prefrontal cortex and the neostriatum, the role of the neostriatum in cognitive aging is less certain. In the current study, event-related functional MRI was used to distinguish the cognitive contributions of neostriatal and prefrontal function in elderly versus young subjects. Twenty healthy subjects, 9 elderly (mean age 67.6 years), and 11 young (mean age 22 years) performed a concurrent implicit and explicit sequence learning task while undergoing functional MR imaging. Both groups showed learning in both the implicit and explicit task conditions. Relative to the young subjects, the elderly subjects showed decreased activation in the left PFC during both implicit and explicit learning, decreased activation in the right putamen during implicit learning, and increased activation in the right PFC during explicit learning. Our results support the theory that changes in a network of brain regions, including the dorsolateral prefrontal cortex and the striatum, are related to cognitive aging. Moreover, these changes are observed during an implicit task, and thus do not seem to be mediated by awareness.