Adult Neurogenesis | Can We Grow New Brain Cells Throughout Life?

Adult neurogenesis is the process through which new neurons, or nerve cells, are generated from neural stem cells in the adult brain. For a long time, it was believed that the brain was fixed after a certain age and could not create new neurons. However, substantial evidence now confirms that this process occurs in specific regions of the brain throughout our lives. The two primary sites for adult neurogenesis are the subgranular zone (SGZ) of the dentate gyrus in the hippocampus, and the subventricular zone (SVZ) of the lateral ventricles. In the hippocampus, a brain region critical for learning and memory, these newborn neurons must undergo a multi-step process: proliferation (cell division), differentiation (becoming a specific type of neuron), migration to their correct location, and functional integration into existing neural circuits. This integration is vital, as it allows the new neurons to contribute to brain functions. These new cells are particularly important for forming new memories, enhancing cognitive flexibility—the ability to adapt to new situations—and regulating emotional responses. The successful maturation and survival of these neurons mean that the brain's structure and function are not static but are continuously being modified by experience.

The hippocampus is a central hub for learning, memory, and spatial navigation. Its unique role makes it a critical site for neurogenesis. The continuous addition of new neurons in this area is fundamental to what is known as brain plasticity—the brain's ability to reorganize itself by forming new neural connections. This plasticity allows us to learn new skills, form and recall memories, and adapt to changing environments. Specifically, new neurons in the hippocampus are thought to play a key role in pattern separation. This is the cognitive function that allows the brain to distinguish between similar but distinct memories, such as remembering where you parked your car today versus yesterday. By adding new, highly excitable neurons to the circuit, the hippocampus can encode subtle differences in experiences more effectively. Furthermore, this process is deeply linked to mood. A healthy rate of neurogenesis supports emotional resilience, while a decline in the production of new neurons is associated with mood disorders like depression and anxiety.

Several lifestyle factors have been scientifically proven to promote the generation and survival of new neurons. Aerobic exercise, such as running or swimming, is one of the most effective enhancers. It increases blood flow to the brain and stimulates the release of growth factors like brain-derived neurotrophic factor (BDNF), which supports the growth and differentiation of new neurons. Another significant factor is continuous learning and environmental enrichment. Engaging in mentally stimulating activities, learning a new skill, or exposing yourself to novel environments challenges the brain and promotes the survival and integration of these new cells. Diet also plays a crucial role; foods rich in omega-3 fatty acids (found in fish) and flavonoids (found in berries and dark chocolate) have been shown to support brain health and neurogenesis.

Just as some factors can boost neurogenesis, others can significantly impair it. Chronic stress is a primary inhibitor. The prolonged release of the stress hormone cortisol is toxic to new neurons and can suppress their production in the hippocampus. Sleep deprivation is another major negative factor; deep sleep is when the brain consolidates memories and clears out toxins, and a lack of it disrupts the environment needed for new neurons to thrive. Aging is naturally associated with a decline in neurogenesis, although this can be mitigated by the positive lifestyle factors mentioned earlier. Additionally, a diet high in saturated fats and refined sugars can induce inflammation and negatively impact the cellular processes required for the birth of new neurons.

The link between adult neurogenesis and mental health, particularly depression and anxiety, is a critical area of modern neuroscience research. A substantial body of evidence indicates that individuals with major depressive disorder often exhibit a reduced volume of the hippocampus and a decreased rate of neurogenesis. Chronic stress, a major risk factor for depression, is known to suppress the production of new neurons. This reduction in neurogenesis impairs the hippocampus's ability to perform its functions in memory and mood regulation, contributing to the cognitive and emotional symptoms of depression, such as hopelessness and difficulty concentrating. Interestingly, many common antidepressant treatments, including Selective Serotonin Reuptake Inhibitors (SSRIs) and electroconvulsive therapy, are believed to exert their therapeutic effects in part by stimulating an increase in the rate of neurogenesis. By promoting the birth and integration of new neurons, these treatments may help restore normal hippocampal function, leading to improved emotional regulation and cognitive flexibility, and ultimately alleviating the symptoms of depression and anxiety.