Prof. Dr. Dorothea Hämmerer, Department of Developmental Psychology, University of Innsbruck, and Institute for Cognitive Neurology and dementia Research, Otto von Guericke University Magdeburg: There are surprisingly many things that are still unknown about this question. This is because, until now, the brain has mostly been examined post mortem, i.e., after death, when it has already aged, and not during the aging process. However, thanks to new technologies, this is currently changing, so that brains can now also be examined throughout the aging process.

It is generally assumed that aging begins in the third decade of life. In the second decade of life, there is a point at which the brain is at its biological peak – after that, various things are lost functionally at different rates. The Gray matter of the brain, which contains the neuronal cell bodies, appears to shrink earlier than the white matter, which represents the connections between the cells.

The rate of shrinkage increases with age. However, this does not necessarily lead to noticeable losses in cognitive function. Normally, it is not to be expected that an older person will have a similar cognitive level to a person in their 20s. However, 80-year-olds with a cognitive level that is normal for their age may well have lost a considerable amount of brain mass. There are large inter-individual differences in how much brain mass is lost.

The extent of the loss is also related to the fact that our brain is changeable and adapts. The brain also has compensation mechanisms, so that, for example, you concentrate more when your attention is no longer as good, or think a little more when Memory recall has become more difficult.

An interesting aspect of brain aging is that not all brain regions shrink equally. It is well known that memory in particular declines with age. In addition, Executive functions suffer, i.e., how well you can concentrate and how quickly you can think, how flexibly you can switch from one topic to another, or how well you can do several things at once. Studies on cognition have shown this for some time. However, the brain can now be visualized very well using Magnetic resonance imaging (MRI). This has confirmed that regions that support memory and executive functions – such as the prefrontal cortex and temporal areas such as the Hippocampus – shrink earlier than brain regions that process auditory, visual, or motor information.

Why the brain shrinks heterogeneously, i.e., faster in some areas than in others, is not yet fully understood. However, there are a few interesting explanations. Comparing the brains of humans with those of their closest relatives shows that not the entire brain of Homo sapiens is larger or richer in neurons. Rather, this is particularly true of the areas that we lose more quickly in old age. However, this does not apply to all areas of the brain.

It is also possible to investigate which areas of the brain take longer to mature in adulthood. Here, too, there is a clear overlap with the areas that are lost more quickly in old age. This also makes sense when you consider that humans can process visual, auditory, or motor information early in their development – long before they are capable of higher cognitive performance.

As mentioned above, the areas of the brain that develop later and those that shrink earlier in old age partially overlap. There is a suspiciously similar pattern, although it is not identical. The name for this hypothesis is “last in, first out,” but it cannot be confirmed for all regions of the brain. In summary, it can therefore be said that there are areas of the brain that are slightly more changeable than others. This applies in evolution, in personal development into adulthood, and also in aging.

Another aspect of brain aging that is currently the focus of research is vascularization, i.e., the supply of blood vessels. This involves investigating the influence of blood flow on aging. This is possible thanks to improved imaging techniques in living humans. Major vascular events, such as strokes, have long been visually represented using these techniques. The ever-increasing resolution of MRI machines now also allows microvascular structures to be visualized and analyzed.

The vascular system of the brain resembles the increasingly fine root network of a tree: from large blood vessels to very fine ones. Even today, the finest capillaries cannot be visualized in MRI images. However, what researchers can see in the millimeter range are mini-strokes that lead to micro-lesions, i.e., tiny areas of damage. This is a very common phenomenon that affects well over half of people over the age of 60. Mini-strokes can be decisive for subsequent volume loss because they cut off the supply of nutrients. There is a strong hypothesis that signs of aging, such as difficulties with balance or concentration, are related to these microvascular injuries. How mini-strokes and micro-lesions affect volume loss later in life is now being investigated in more detail.

Recorded by Stefanie Flunkert