Have you ever had trouble remembering a word or name for something, or had difficulty recalling something you were just told? When this happens to younger people, they will often joke that they must be getting older because their memory is starting to go. This joke pops into people’s heads because a decline in memory is commonly associated with aging, and is a common occurrence in healthy elderly people. A decline in memory function is a trait of healthy aging and has been linked to neuron loss in many brain regions, but we do not know much about the neural processes that causes memory decline. To try and get a better understanding of the mechanisms of healthy aging memory decline, Steiger et al. (2016) looked at iron and myelin levels and their impact on memory performance in healthy elderly humans.
Iron levels and the degree of myelination were measured in brain regions associated with memory using indirect markers. One region in particular was the ventral striatum. This region is part of the basal ganglia, which is a collection of cell groups in the forebrain (Bear et al. 2016). The ventral striatum was of particular interest because age related accumulation of iron has been observed in this region of the brain. Iron is an essential element for a variety of metabolic processes, including myelin production, but too much may cause oxidative stress and inflammation in brain regions (Steiger et al. 2016). Myelin covers axons and acts like an insulator to ensure the electrical signals travel down the axon efficiently. Iron levels and myelin volume have an inverse relationship, similar to a teeter-totter. If iron levels stay normal and balanced, myelin production is normal, and the teeter-totter is level. But when iron accumulates and increases, inflammation causes myelin degeneration, so myelin volume decreases. In their study, Steiger el al. (2016) were interested in if there was a relationship between memory performance and these physiological changes that occur in healthy elderly humans.
Steiger et al. (2016) used quantitative MRI techniques to measure the degree of myelination and iron accumulation. They compared healthy young brains with healthy elderly brains, and used statistical analyses to look at the differences between iron levels and myelin volume in the young and elderly brains. To test learning and memory performance, all elderly participants took a verbal learning memory test (VLMT), where the higher the score, the better the individuals memory performance. Through their analysis, they saw a decrease in myelin volume and an increase in iron levels in the elderly relative to the younger patients (Steiger et al. 2016). They then compared the VLMT scores of individuals with their MRI scans using linear regression models. Individuals with a higher volume of myelin had higher VLMT scores, and those with higher iron levels had lower VLMT scores. In a nutshell, this means that individuals that had a lot of myelin had good memory, and individuals that had more iron had a poorer memory. They were also able to predict VLMT scores by looking at the ratio of myelin volume/iron levels. Essentially, as iron levels increase, myelin volume decreases so the ratio of myelin/iron gets smaller, which correlated with lower VLMT scores. This indicates that iron and myelin can account for individual performance differences in the memory of the elderly (Steiger et al. 2016).
Overall, this study showed that in elderly humans, there was an increase in iron levels, and a decrease in myelin volume, which correlated with lower memory performance. This provides new insights into possible neural mechanisms associated with memory decline during healthy aging.
Sources:
Bear, M.F., Connors, B.W., and Paradiso, M.A. (2016). Neuroscience: Exploring the Brain 4th Edition. Philadelphia, PA: Wolters Kluwer
Steiger, T.K., Weiskopf, N., and Bunzeck, N. (2016). Iron Level and Myelin Content in the Ventral Striatum Predict Memory Performance in the Aging Brain. J. Neurosci. 36(12): 3552-3558.
