How does brain signal variability relate to plasticity during perceptual learning for younger, middle-aged, and older adults?

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Considerable effort has been invested in identifying neuroimaging markers of how brain function is altered during healthy aging, and how these alterations relate to cognitive resilience. Recent work suggests that brain signal variability is an important marker of processing integrity and flexibility in the brain. Variability facilitates movement from one network configuration to another, and enables the exploration many networks to generate many behaviours. In the context of brain aging, variability research suggests that young and older adults process information differently. Increasing age is associated with an increased reliance on local information processing and decreased long-range interactions with distant brain regions. It remains unclear, however, if these processing changes are merely the brain's response to structural and functional decline, or if they are compensatory in that they support better performance. Importantly, if brain signal variability enables the exploration of multiple networks and the generation of new behaviours, then it may be the mechanism that drives plasticity (the brain's ability to change in response to experience). The differing variability profiles for young and older adults should drive learning-related plasticity differently. For older adults, increased reliance on local processing should favour local alterations in the excitability of brain regions that support behaviour. For younger adults, the increased reliance on long-range processing should favour global alterations in connectivity between brain regions, or the addition of new regions to the network that supports behaviour. Here, we will examine plasticity across the adult lifespan during visual perceptual learning, where the ability to discriminate differences in simple stimulus attributes progressively improves with practice. Perceptual learning is considered a manifestation of plasticity. It is is ideally suited for examining age-associated changes in plasticity because the neural substrates that support learning are well defined, and the level of challenge posed by learning can be adjusted to match task difficulty across individuals despite age-associated differences in visual and attentional function. In Objective 1, we will examine how plasticity and brain signal variability are influenced by structural decline that occurs with age, and link these findings to cognitive resilience using a longitudinal design. In Objective 2, we will examine what type of brain changes are most effective in supporting new learning, and how this is influenced by the shifting in the balance between local and long-range processing across the adult lifespan. In Objective 3, we test variability as a putative mechanism for promoting plasticity. Our findings will afford more precise predictions about the circumstances under which older adults can maintain cognitive resilience, and provide new insights into a specific mechanism that may drive plasticity.