Some Layers of Your Brain Actually Get Stronger as You Age

Ageing is often assumed to bring an unavoidable decline in brain tissue, yet new evidence indicates that this isn’t uniformly true across all brain regions.

A fresh assessment of mouse and human brains suggests that parts of the somatosensory cortex - the brain area responsible for handling sensory input - don’t merely avoid the thinning seen elsewhere. Some sections may actually become more robust over time.

Taken together, the findings imply that the brain can keep adjusting and reshaping itself well into later life - and that frequent use could help strengthen certain neural systems.

Primary somatosensory cortex: layered tissue that doesn’t age evenly

"Until now, it had not been considered that the primary somatosensory cortex consists of a stack of several extremely thin layers of tissue, each with its own architecture and function. We have now found that these layers age differently," explains neuroscientist Esther Kühn of the German Center for Neurodegenerative Diseases and the Hertie Institute for Clinical Brain Research in Germany.

"Although the cerebral cortex becomes thinner overall, some of its layers remain stable or, surprisingly, are even thicker with age. Presumably because they are particularly solicited and thus retain their functionality. We therefore see evidence for neuroplasticity, that is, adaptability, even in senior people."

In this context, neuroplasticity refers to the brain’s capacity to respond to changing demands by reorganising and rewiring neural connections. It’s widely assumed that neuroplasticity is greatest in youth and then steadily falls away; however, that idea is not necessarily backed by strong evidence.

Why the cerebral cortex needed a closer look

Under the direction of neuroscientists Peng Liu and Juliane Doehler of Otto von Guericke University Magdeburg in Germany, researchers set out to explore how ageing might affect the human cerebral cortex - a folded brain region that is generally observed to thin as people get older.

"It is generally assumed that less brain volume means reduced function," Kühn says. "However, little is known about how exactly the cortex actually ages. This is remarkable, given that many of our daily activities depend on a functioning cortex. That's why we examined the situation with high-resolution brain scans."

High-resolution MRI focused on touch processing

To investigate, the team used especially sensitive MRI brain scans from 61 adults aged 21 to 80. Their attention was on a small area at the top of the brain: the primary somatosensory cortex, which receives tactile sensory information.

The scans indicated that this region is organised rather like a stack of crêpes: numerous extremely thin, fragile layers of tissue, each associated with a different function. Crucially, the imaging suggested that these layers look different depending on age.

Some layers were thinner in older adults, as would typically be expected. Yet the middle and upper layers appeared thicker in older participants than the corresponding layers in younger people.

Thickening where haptic stimuli are processed

"The middle layer is effectively the gateway for haptic [touch] stimuli. In the layers above, further processing occurs," says Kühn. "For example, in the case of sensory stimuli from the hand, the upper layers are particularly involved in the interaction between neighboring fingers. This is important when grasping objects."

By contrast, the lower layers showed thinning in the older group. These lower layers are involved in modulation - adjusting tactile signals up or down depending on the situation. For instance, you typically don’t notice the sensation of your clothes unless you direct attention to it, in a similar way to how the brain effectively removes your nose from your field of view.

A possible “use it or lose it” explanation

As for why some layers expand while others diminish with age, the researchers propose a familiar possibility: "use it or lose it".

"The middle and upper layers of the cortex are most directly exposed to external stimuli. They are permanently active because we have constant contact with our environment," Kühn says. "The neural circuits in the lower layers are stimulated to a lesser extent, especially in later life. I therefore see our findings as an indication that the brain preserves what is used intensively. That's a feature of neuroplasticity."

Myelin changes may help compensate for shrinkage

Notably, even though the lower layers contract, they may still offset cellular decline in another way. The researchers found increased myelin content there, associated with a rise in a particular neuron type that boosts the modulation signal.

This, too, points towards ongoing adaptability. The team hopes that future work may identify ways to encourage these kinds of adaptive processes.

"Together, our findings are consistent with the general idea that we can do something good for our brains with appropriate stimulation. I think it's an optimistic notion that we can influence our aging process to a certain degree," Kühn says.

The research has been published in Nature Neuroscience.