New-rons

You can’t teach an old dog new tricks. Embedded in that piece of time-honoured wisdom is the idea that there comes a point in an organism’s life where new things cannot be learned. Of course today that is being countered by the exciting psychobabble term “neuroplasticity”. This term has gained huge mainstream currency and a self-development seminar hardly seems worth the money if the speakers don’t use the neuroplastic nature of your brain to offer encouragement for future change. What does the term neuroplastic really mean though? Is it just that neurons can form new connections or can your brain develop new neurons into adulthood? A new study seems to have the answer.

It was thought for a long time that we are born with a set number of neurons and that ageing involved a gradual loss of neurons without replacement. We know that new connections can be made between neurons well into adulthood but the new study wanted to establish if adults can also grow brand new neurons.

To test this they used a method of dating the age of neurons in deceased human bodies that is also used in archaeological dating. Carbon-14 dating is a useful but also flawed device used to date artefacts found on archaeological digs. Where it has limitations though in archaeological dating due to variations in carbon in the atmosphere, these researchers have found it very useful in dating neurons in the brain.

Carbon-14 dating is based on the fact that carbon is present in all living things, it is a basic building block for the construction of organic material. The normal molar mass of carbon is 12 however, some carbon atoms that have a molar mass of 13, and some have a molar mass of 14. These carbon-14 atoms are not stable and decay over time at a consistent rate. Plants and animals that are still alive constantly replace the supply of carbon in their systems and so the amount of carbon-14 in the system stays almost constant. However, once a plant or animal dies the carbon-14 is no longer being replaced and so the carbon-14 starts to decay at the known rate. So by measuring the amount of carbon-14 in the body of an animal or plant, or an artefact made from plant or animal material, we can deduce when the plant or animal died or when an artefact was made.

The problem with carbon dating is that levels of carbon in the atmosphere fluctuate and unless you know what those fluctuations were, then your dating can be compromised. This was not a problem though for these researchers who wanted to date the neurons in the brains of deceased persons. Since the 1963 nuclear test ban treaty levels of carbon-14 in the atmosphere have declined at a known rate so the researchers could confidently use carbon-14 to date neurons. When a human eats a plant or animal product they absorb the carbon-12 and carbon-14 ratio present in the atmosphere at the time. This ratio is stamped into the DNA of every new neuron that is born so by measuring the carbon-14 concentration in DNA from neurons in the hippocampus the researchers could tell at what stage of a person’s life those neurons had been created.

The analysis showed that more than one third of brain neurons are renewed on a regular basis throughout life and that each day during adulthood around 1,400 neurons are added each day.

This shows that your brain is not only capable of change, it is built for it. More than that, there is burgeoning thought that conditions like depression could relate to lack of neuronal growth in the hippocampus so if this kind of regeneration becomes the focus of therapy wonderful new results could arise.

If that seems like a lot of new information to take in don’t worry; by the end of the day you’ll have 1,000 or so more neurons available to handle it.