BY VIVIAN LIVESAY ’21
A team of scientists in Spain have conducted a study that suggests that the human brain can continue to produce new neurons into the ninth decade of life, far longer than previously believed. This finding has the potential to influence the field of neuroscience, though it is important not to overstate the implications of these findings as it is debated how this information can be put to practical use.
The study, spearheaded by professor María Llorens-Martín at the Autonomous University of Madrid, found that the brains of people with Alzheimer’s disease showed strikingly fewer new cells than the brains of healthy people. This may help doctors catch neurodegenerative diseases earlier, if they can compare brains that continue producing new brain cells with those that begin to slow down cell production.
Kenneth Colodner, a professor of neuroscience at Mount Holyoke College, put the results into context. “Taking the result at face value, it is very exciting for the field of neuroscience and Alzheimer’s disease research in particular. If people who suffer from Alzheimer’s disease have reduced neurogenesis [the growth of new nervous tissue], then activities that boost neurogenesis may help prevent Alzheimer’s progression.” In other words, this study may provide empirical evidence for a claim that was previously a mere correlation: exercise reduces one’s risk of developing Alzheimer’s. “In mice, exercise increases neurogenesis,” Colodner explained.
But, this is not the first time the question of adult neurogenesis has been put to the test. “There has been a lot of recent controversy surrounding adult human neurogenesis in the hippocampus — simply, whether or not it actually exists,” Colodner said. He cited a study from March of last year which found that neurogenesis declines sharply throughout childhood to become negligible in the adult hippocampus.
According to Llorens-Martín, it might be possible to account for this controversy over whether or not neurogenesis happens in the hippocampus by considering the different methods of processing and imaging brain tissue samples. Jared Schwartzer, another neuroscience professor at Mount Holyoke College, elaborated on the reasons scientists may be seeing varying results on neurogenesis in the hippocampus. “Not to be morbid,” he said, “but different labs have different methods of handling dead bodies. The methods used to preserve a tissue sample affects the data you can get from it, and when you’re studying a large sample of brains, you have to narrow the selection down to the ones that work with your process.” This also explains the small sample size of the study, which analyzed just 13 brains.
Schwartzer also cautioned against assuming that this discovery will immediately revolutionize Alzheimer’s treatment. “This could help us diagnose people with dementia before they start showing symptoms, but unfortunately we don’t have a way of testing people while they’re still alive.” Currently, these tests rely on processing tissue samples which cannot be taken from living brains without causing grave damage. But technology continues to develop, and Llorens-Martín believes that brain scans may one day be able to identify newly-developed brain cells, which would give doctors a new diagnostic tool for monitoring neurodegenerative disease.
As is usually the case in science, this will not be the final word on neurogenesis. This finding, if replicated and shown to hold up to intense scrutiny, might constitute the foundation of a new means of detecting and treating Alzheimer’s disease. Both Schwartzer and Colodner emphasized the importance of replicating this study before drawing any grand conclusions.