Longevity Briefs: Layers Of The Brain Age Differently

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

The outer layer of the brain, known as the cortex, is itself organized into distinct layers. You can think of them like different floors of a building, each with specialized functions. This layered architecture is important for how we process sensory information such as touch, sight, and sound.

Cognitive decline is unfortunately an inevitable part of ageing, due in part to a reduction in volume of certain brain regions. In this study, researchers ask how age-related changes manifest at the level of the cortical layers and reveal another level of complexity to human brain ageing.

The discovery:

In the study, researchers focused on the primary somatosensory cortex (SI) – the brain region responsible for processing touch, temperature, and pain. The study involved two groups of healthy adults: 41 younger adults (aged 18 to 35) and 37 older adults (aged over 65). They then used a high-resolution form of Magnetic Resonance Imaging (MRI) to visualize and analyse the individual cortical layers of the participants.

What they found was quite unexpected – not all layers of the cortex showed signs of ageing. In older adults, there was a thinning of the deeper layers, which are involved in amplifying or tuning down sensation based on the context (for example, we may notice a sensation more when concentrating on it). However, these layers also had more myelin in older people. Myelin is an insulating substance that wraps around nerve fibres and speeds up electrical impulses. The middle and upper layers of the cortex, on the other hand, showed little thinning or even became thicker in older age. These layers are the first layers to receive sensory information, and are therefore constantly stimulated.

The implications:

Ageing occurs in different ways in different tissues, even down to the layered structure of the somatosensory cortex. However, it seems that the brain is able to compensate for some of this age-related deterioration, for example through increased myelination. It was once thought that brain plasticity – the ability of the brain to adapt and rewire itself in response to external stimuli – was exclusive to young brains, but we now know that even old brains retain some level of plasticity. This gives us some hope that we may be able to enhance these compensatory mechanisms as a way to combat brain ageing.

This study is also a reminder of the complex interactions between ageing in the brain and the rest of the body. Much of what appears to be brain ageing may actually be the indirect result of ageing elsewhere leading to disuse of certain brain regions. For example, a person who becomes less physically active as they age due to reduced muscle function may also lose some motor function. Yet another reason why it is important to maintain as healthy a lifestyle as possible even into old age.