Does Neuroplasticity Undergo Less of a Decline with Age than Thought?

"Use it or lose it" applies as much to the mind as to the body. Evidence suggests that a fair fraction of the observed loss of physical strength and fitness with age is lack of activity and training rather than inexorable processes of aging - though those inexorable processes exist, and will kill you if nothing is done about them. The situation is most likely similar for the brain. Not all of the observed loss is necessary or inevitable, even given the present lack of effective rejuvenation therapies that can address the causes of age-related neurodegeneration. Some fraction of the decline occurs because people choose to not to stretch their minds as much as they might. How large is this fraction? That is an interesting question without any precise answer at this time.

For a long time, it has been assumed that brain plasticity peaks at young age and then gradually decreases as one gets older. Interestingly, thanks to tremendous advances in medical imaging techniques for assessment of brain structure and function, mounting evidence for lifelong brain plasticity has been generated over the past years. In the context of practice-induced task learning, a key question is how brain plasticity can be optimized and this is an even more important consideration for older adults. The gold standard to elicit brain plasticity is to practice new tasks intensively and to organize the training epochs in such a way that skill learning and retention are maximized.

A critical requirement for neuroplasticity to emerge is to make the practice context sufficiently difficult for the learner. One way to challenge the environmental context is to confront learners with practicing more than one task within each practice session. More specifically, rather than performing subtasks in a sequential or blocked manner, one after the other (less challenging), one can also apply a more demanding random practice regime such that learners have to switch tasks from trial to trial during practice (more challenging). The latter condition has led to the apparent paradox that reduced performance levels are obtained during the training phase but better long-term retention and memory formation of the skill are observed at later stages as a result of more profound inter-task information processing strategies. This is generally known as 'contextual interference' (CI). Even though CI seemingly induces complication of the learning environment, it has been shown that older adults can equally cope with this increased contextual complexity as young adults do and that it benefits longer-term skill retention

Using magnetic resonance spectroscopy (MRS), we explored the neurochemical basis of the CI effect via determination of the practice-induced modulation of gamma-aminobutyric acid (GABA), i.e. the chief inhibitory neurotransmitter that also plays a major role in brain plasticity. We found that the MRS data demonstrated a training-induced decrease in occipital GABA level during random practice but an increased GABA level during blocked practice and this effect was even more pronounced in older adults. First, the data suggest that older adults can indeed cope with more complex random practice contexts that challenge their instantaneous performance but boost their learning potential and skill retention. Second, training-induced modulations in GABA appear to be a function of degree of contextual challenge and this effect is even amplified by aging. This modulatory capability is preserved in spite of the fact that initial GABA levels were lower in older as compared to young adults.

These data provide additional confirmation for task-training induced lifelong plasticity. New motor and other skills can be acquired at any age even though the progress may be somewhat attenuated in older as compared to young populations. In view of the demographic evolution of society, characterized by a steadily increasing proportion of older adults, the evidenced lifelong brain plasticity provides a critical foundation for a sustained role of older adults in society and for securing prolonged functional independence and quality of life.