Does your brain ever stop growing?

For decades, it has been thought that the adult brain lacks plasticity and is unable to form new neurones. However, a study carried out by Columbia University has presented the most definitive evidence that neurogenesis in the hippocampus continues after adolescence. This suggests that the elderly remain more cognitively and emotionally intact than previously thought.

The study examined the hippocampus of 28 men and women aged between 14 and 79. Using a number of techniques, the degree of new blood vessel formation, the volume, and the number of cells at different stages of maturity in the dentate gyrus (an area of the hippocampus involved in memory formation) were analysed.

A study carried out by Columbia University has presented the most definitive evidence that neurogenesis in the hippocampus continues after adolescence

“We found that older people have similar ability to make thousands of hippocampal new neurons from progenitor cells as younger people do,” said the study’s lead author Maura Boldrini, Associate Professor of Neurobiology.

Undeniably, this sort of study will receive a lot of questioning and is likely to be hotly debated. Already it has been suggested that albeit findings showed continued growth of neurones throughout adulthood, this could be the existing neurones growing in size, or expansion of blood vessels or other internal support structures, and not the development of new neurones. Again, even though neuroimaging results show new neurones in older hippocampi, a recent study halted the idea, affirming that these neurones may have been present in younger brains but at undetectable levels.

Already it has been suggested that albeit findings showed continued growth of neurones throughout adulthood, this could be the existing neurones growing in size

If the brain continues to grow, as suggested by Columbia University, how can the decrease in forming episodic memories and difficulty in learning new skills be explained in older people? Analysis revealed that there was less vascular development in older brains and the formation of new neural connections declined. Researchers suggested that this could be the cause of compromised cognitive-emotional resilience in the elderly.

To further support this claim it has been revealed that the neurones in older hippocampi express lower levels of proteins associated with plasticity. Studies suggest that we are born with a finite number of pluripotent stem cells with the ability to differentiate into neurones. However, this does not mean that we can produce only a limited number of neurones, as once a stem cell has differentiated to form a neuronal cell, this cell can then undergo division producing identical daughter cells.

Studies suggest that we are born with a finite number of pluripotent stem cells with the ability to differentiate into neurones

The team found reduced levels of these pluripotent cells in the middle region of the dentate gyrus in adults, nonetheless, the levels of the cells they give rise to did not drop. But, they did find a decrease in the pool of quiescent stem cells producing substances linked to angiogenesis and neuroplasticity in the front of the dentate gyrus. This drop in plasticity may explain why even healthy people become more emotionally vulnerable with age.

The discussed results imply a new model of brain ageing, in which neurogenesis continues with age with sustained volumes of neurones, though plasticity is reduced and the ability to form neural connections is impaired. Taking this into account “we should be able to understand better how new neurons mature and how that could be manipulated,” said Boldrini.

Neurogenesis continues with age with sustained volumes of neurones, though plasticity is reduced and the ability to form neural connections is impaired

Exploring the underlying mechanisms of an exhausted quiescent progenitor pool, and less vascularisation of the neurogenic niche resulting in less neuroplasticity in older brains could help in the development of treatments for degenerative conditions such as Alzheimer’s Disease and psychiatric problems.