Losing brain plasticity as we age

Have you noticed how with age and UV exposure some plastics change, becoming more brittle? Well, it seems that as we get older, our plastic brain loses some of its plasticity too.

Our middle aged brains start to notice that it gets harder to learn stuff and keep it in our heads. It takes more effort to pay attention to what we are doing and more practice to embed new memories. We’ve found out that part of this is due to a slowing down of the brains’ processing speed and our increasing levels of distractibility. But new research now indicates that there is another reason for this; our lovely plastic brain becomes less plastic.

What does this mean?

When we talk about our brain being plastic, we are referring to the ability of neurons to form new connections (synapses) with other neurons. This occurs at the level of the dendrites, fine branches that sprout out from the neurons. These dendrites have “spines” which can develop into the new synapses, These synapses are formed and lost, as part of normal rewiring of the brain.

When we are learning new information, the neurons are actively forming new synapses. However some neural pathways or connections become redundant and without use or stimulation, these synapses simply get resorbed. This then frees up more space for yet more new connections to form, so it’s a great system.

The part of the brain we use for our higher level of thinking such as planning, organising, decision-making and our working memory is the prefrontal cortex. This is the part of the brain that is the last to fully mature in humans and is the area most likely to be affected by the effects of ageing.

High levels of stress and cortisol are known to cause neurons to shrink and for synaptic connections to be lost. Fortunately, once the stress is removed, our plastic brain allows new synapses to reform.

The effect of ageing on our brains plasticity.

New research from the Mount Sinai School of Medicine has shown that the brains of middle aged and elderly rats were less able to adapt to a behavioural stress response. In other words they were less able to learn from the experience. The neurons of the younger rats did change, showing normal plasticity and rewiring. Previous studies in 2010 examining the effect of the stress response in older rat brains had found a lack of a plastic response here as well.
Does this mean that stress doesn’t affect us as much as we get older? No, it means that with age, we lose some of our resiliency to stress; our brain is less able to respond, or to produce new synapses after the stress has been removed.

Our somewhat fragile and demanding prefrontal cortex is continually rewiring itself in response to all the stimulation and experience it encounters every day. Like plastic bottles however, our level of plasticity appears to diminish with age, we become less able to respond to either learning or stress.

With brain fitness training we are encouraged to “use it or lose it.”
To keep our mental sharpness and brain plasticity, it appears essential we continue to provide our brain with a variety of new and challenging activities.

E. B. Bloss, W. G. Janssen, D. T. Ohm, F. J. Yuk, S. Wadsworth, K. M. Saardi, B. S. McEwen, J. H. Morrison. Evidence for Reduced Experience-Dependent Dendritic Spine Plasticity in the Aging Prefrontal Cortex. Journal of Neuroscience, 2011; 31 (21): 7831 DOI: 10.1523/JNEUROSCI.0839-11.2011

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