One of the long-standing debates about brains has centered around whether we stop making new brain cells in the hippocampus – the engine room of memories – when we reach adulthood or if we continue to restock the supply of neurons throughout our lives.
Published in this week’s Nature Medicine, a new study has weighed in on the debate and claims to have found evidence that we produce fresh neurons in the hippocampus throughout our adult life, and well into old age.
The research also noted that the production of new neurons in the hippocampus was significantly slower in the brains of people with Alzheimer’s disease, suggesting new insights into treating this chronic neurodegenerative disease.
The process of creating new neurons is called neurogenesis. Due to its links to memories and learning, scientists have been particularly interested to see the extent of new neuron creation in the hippocampus, known as adult hippocampal neurogenesis. Obviously, this process happens when an embryo is developing, but it’s unclear how widely this process continues after childhood.
Last year, an authoritative study found that neurogenesis does not occur in the hippocampus after our early years. This new study stands in direct opposition to that. Scientists led by the Autonomous University of Madrid in Spain studied the brain tissue of 58 recently-deceased people who were aged between 43 and 97; of whom 45 had Alzheimer's disease and 13 had no signs of neurodegenerative disease.
Using state-of-the-art tissue processing methods, they discovered that healthy brains contained thousands of immature neurons that appeared to be relatively young. The people with Alzheimer’s also had these “newborn” neurons, although there appeared to be a "marked and progressive decline" in this number as the disease progressed.
It’s also worth noting that the number of these young neurons dropped with age. Between the ages of 40 and 70, the number of fresh neurons dropped from about 40,000 to less than 30,000 per cubic millimeter. That said, evidence of the immature neurons was still spotted in even the oldest brain, which belonged to a 97-year-old.
"I believe we would be generating new neurons as long as we need to learn new things,” lead author Dr Maria Llorens-Martin told BBC News. "And that occurs during every single second of our life."
As ever, further research is needed to back up these claims, but the research does point to some deeply intriguing new insights into the nature of Alzheimer’s disease. Perhaps – and this is just a perhaps, for now – it could eventually lead to a new treatment for Alzheimer’s that focuses on the rate of adult hippocampal neurogenesis and the generation of new neurons.