Researchers have found that a physical mechanism in the brain, the flow of cerebrospinal fluid and the shear forces generated by that flow, influences the activity of neural stem cells via a distinctive set of biochemical signals. This will in turn influence the rate of neurogenesis, the creation of new neurons and their integration into existing neural networks. This process is important in learning, neurodegeneration, and the resilience of the brain when it comes to recovery from damage.
It is worth considering this recent discovery in the context of what is already known of reduced and impeded drainage of cerebrospinal fluid with age. The system of spaces through which cerebrospinal fluid circulates is not entirely closed off from the rest of the body, and normally drainage serves to remove metabolic wastes from the brain. It is thought that loss of drainage with age is an important contributing cause of the buildup of protein aggregates found in many neurodegenerative conditions, particularly the amyloid associated with Alzheimer’s disease.