Your Brain Is Still Growing: The Science of Adult Neuroplasticity.

For most of the twentieth century, scientists believed that once the brain matured, its structure was set for life. Learning and memory were thought to depend only on existing neurons and fixed pathways. However, decades of research have revealed a very different picture. The adult brain is not static but capable of profound structural and functional change in response to experience, environment, and behavior.

From fixed to flexible

The concept of neuroplasticity, or the brain’s ability to modify its structure and function, can be traced back to the early work of Santiago Ramón y Cajal. He proposed that even adult brains might be capable of adapting, although the idea was dismissed for many years. By the late 1960s, electron microscopy studies demonstrated that neurons in adult animals could reorganize their connections after injury. This finding challenged the long-standing view that new growth or structural change was impossible beyond early development.

How experience reshapes the brain

Neuroplasticity in adulthood occurs through several mechanisms. One involves remodeling of dendrites, the branched extensions of neurons that receive input from other cells. For example, repeated exposure to stress can cause dendrites in hippocampal neurons to shrink, reducing the number of connections available for processing information. In contrast, neurons in the amygdala, which are involved in emotional regulation, can expand their branching under the same conditions. These opposing effects help explain why chronic stress can impair memory but heighten emotional reactivity. Importantly, these structural changes are reversible once the stress is removed or treated, showing that the adult brain maintains an ability to recover and rebuild connections.

Another key mechanism is neurogenesis, the birth of new neurons. Once considered impossible, adult neurogenesis was first identified in the hippocampus and olfactory bulb. Modern labeling techniques using markers such as bromodeoxyuridine (BrdU) revealed that even in adults, new neurons can integrate into existing networks. In humans, it is estimated that about 700 new neurons are generated each day in the hippocampus. These cells contribute to memory formation, learning, and mood regulation. Reduced neurogenesis, on the other hand, has been linked to stress-related conditions such as depression.

A schematic view on adult neurogenesis (Fuchs & Flügge, 2014).

What influences neuroplasticity

Many factors shape how flexible the adult brain remains. Physical activity, learning, and exposure to stimulating environments have all been shown to enhance neurogenesis and strengthen neural connections. Molecules such as brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) play critical roles in supporting these processes by promoting cell survival and growth. Hormones also contribute. For instance, estrogen can temporarily increase neurogenesis in the hippocampus, while glucocorticoids released during chronic stress can suppress it.

Research also shows that antidepressant treatments can restore normal levels of neurogenesis that have been reduced by stress. This suggests that some therapeutic effects of antidepressants may depend partly on their ability to enhance neuroplastic processes.

The significance of an adaptable brain

The discovery of adult neuroplasticity has transformed how scientists understand learning, memory, and mental health. It explains how the brain can recover from injury, adapt to new experiences, and even compensate for disease-related damage. The adult brain is therefore not a fixed structure but a growing organ capable of renewal and adaptation throughout life.

Fuchs, E., & Flügge, G. (2014). Adult neuroplasticity: more than 40 years of research. Neural plasticity, 2014, 541870. https://doi.org/10.1155/2014/541870 

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