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How Does The Brain Protect Itself Against Cognitive Decline?

How Does The Brain Protect Itself Against Cognitive Decline?

People with higher levels of cognitive reserve have been found to be at lower risk for dementia [1]. Cognitive reserve refers to the capacity of the brain to withstand changes due to age or disease-related pathology that typically leads to a decline in cognitive function. It is a measure of the resiliency of the brain that is related to its efficiency and flexibility [2].

Efficient brains can carry out simple tasks by activating the least number of neurons, and progressively engage more neurons as the complexity of the task increases. Therefore, in the face of neuron loss, efficient brains can continue to perform all but the most complex of tasks. In contrast, inefficient brains need to engage large numbers of the neurons for all tasks, so if any part gets damaged then it makes it difficult for the brain to perform even simple tasks. Flexible brains can complete the same task using multiple different neural networks, so if one network gets damaged, the brain is still able to function normally by switching to an alternate network. 

But how does someone build up cognitive reserve, or in other words, how does someone develop a more flexible and efficient brain? Cognitive engagement during childhood, such as through education, is often used as a proxy for assessing cognitive reserve, because the brain is most adaptable in youth [3]. However, there is evidence showing that cognitive reserve is influenced by various factors throughout one’s entire lifetime [4]. A recent study assessed the contribution of six of these factors. 

The study followed 1,602 participants in the Rush Memory and Aging Project and examined the role of cognitive and social engagement over the course of a lifetime in building protective cognitive reserve [1]. The six factors included: 1) years of education; 2) early-life cognitive activity; 3) mid-life cognitive activity; 4) late-life cognitive activity; 5) late-life social activity; and 6) late-life social network. 

The measure for cognitive activity was based on a 37-item questionnaire assessing the frequency of participating in cognitively engaging activities, such as reading, writing and playing games, during different stages of life. Social activity was assessed based on the frequency in participating in six social activities: 1) going out to restaurants or sporting events; 2) going on trips; 3) visiting friends or relatives; 4) doing volunteer work; 5) participating in community groups; and 6) attending religious services. Social network size was based on the number of close friends or relatives seen at least once per month.

The researchers found that cognitive activity, social activity, and social network all contribute to building up cognitive reserve, such that engaging in more of these activities leads to higher levels of overall cognitive reserve and a greater reduction in dementia risk. The protective effect for lifetime cognitive reserve was found in people with and without Alzheimer’s related pathology, suggesting that high levels of cognitive reserve can delay the onset of Alzheimer’s related dementia.

Since the measurement of each factor was based on self-reported questionnaires, the accuracies may be subject to recall bias, especially for early-life events. But taking that caveat into account, the cognitive reserve building factor that was most strongly associated with reduced dementia risk was late-life social activity. This is consistent with another study showing that the decline in social engagement associated with retirement can accelerate cognitive decline [5]. Participating in a social group may be particularly beneficial because it can also influence other protective factors, such as increasing one’s social network and the frequency of engaging in cognitively stimulating activities. 

This study indicates that we have the capacity to build up the resiliency of our brain throughout our lifetime, and that maintaining an active social life can serve as both a fun and effective way to do it.

  1. Xu H, Yang R, Qi Xet al.(2019) Association of Lifespan Cognitive Reserve Indicator With Dementia Risk in the Presence of Brain Pathologies. JAMA Neurology 76, 1184-1191.
  2. Steffener J, Stern Y (2012) Exploring the neural basis of cognitive reserve in aging. Biochim Biophys Acta  1822, 467-473.
  3. Malek-Ahmadi M, Lu S, Chan Yet al.(2017) Static and Dynamic Cognitive Reserve Proxy Measures: Interactions with Alzheimer's Disease Neuropathology and Cognition. J Alzheimers Dis Parkinsonism 7, 390.
  4. Richards M (2003) Nikolov P, Adelman A (2019) Do Pension Benefits Accelerate Cognitive Decline? Evidence from Rural China. IZA Institute of Labor Economics DP No. 12524.

Betsy Mills, PhD, is Senior Program Manager of Aging and Alzheimer’s Prevention at the Alzheimer’s Drug Discovery Foundation. She earned her doctorate in neuroscience at Johns Hopkins University School of Medicine, where she studied the role of glial cells in the optic nerve and their contribution to neurodegeneration in glaucoma; and completed a Postdoctoral fellowship at the University of Michigan, where she worked to uncover genes that could promote retina regeneration. Dr. Mills has a strong passion for community outreach, and served as program presenter with the Michigan Great Lakes Chapter of the Alzheimer's Association to promote dementia awareness.

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