Brain matures till age 26

I have read two articles in the last 10 days which seem to be very relevant to each other, although the authors did not note the connection.

The first was a review article (click here) stating that the human brain does not completely mature until about the age of 26 years, and that the particular circuits involved in that late maturing are based on cannabinoid receptors. “Recent studies show that cannabinoids manufactured by our own nerve cells play a crucial role in wiring the brain, both prenatally and during adolescence.”

Hence the not unreasonable assumption that teenage smokers of cannabis would likely interfere with that maturing.

The second research article (click here) talked about the corticostriatal network in the brain, which continues to develop until “at least age 25”. It went on to describe how that network connected areas involved in ‘reward’, to areas controlling behaviour. Their experiments showed that older subjects would modify their behaviour to perform better if the stakes were high, whereas adolescent subjects put the same amount of effort in, regardless of whether the stakes were high or low. This tends to explain why adolescents can be nonchalant about risky behaviour – statistically we know that adolescents drive more dangerously for example. They pointed out that evolutionarily speaking, this may not be bad – adolescents may spread their attention to a wide range of activities, before specialising more as adults. But, in modern life this may not work so well.

So, putting the two articles together, it maybe implies that adolescent cannabis smokers may prejudice their ability to mature in matching risk to reward.

I also wonder whether there is a case for raising the voting age to 25 or 26?


Paradigm of neuron/synapse model challenged

Transplantation of human astrocytes into mouse brain made the mice smarter

It has been assumed for decades that the brain learns and responds by virtue of the pattern of connection, via synapses, between wire-like axons of neurons which carry high-speed electrical signals. But recent experiments suggest that astrocytes, a different type of cell, previously thought to have only structural function, may play a powerful role in modulating signalling.

Read the New Scientist article here

The paradigm has been that repetitive firing, strengthening synaptic connections, is thought to be the cellular basis for memory, just as repetition in learning helps form lasting memories.

The recent research has shown that when human astrocytes were transplanted into the brains of young mice, the astrocytes integrated well into the mouse brain. This despite the fact that human astrocytes are much bigger than, and very different from mouse astrocytes. (Though mouse and human neurons are quite similar.)

When these mice were given standardized behavioral tests of learning and memory, the mice engrafted with human astrocytes outperformed mice injected with astrocytes from other mice as a control.

Hence the inference that astrocytes have a much more important role in human brain function than was thought previously. This seems to be by modulation of the synapse activity. A substance released from astrocytes (TNFalpha) was found to be increased after transplantation, and counteracting TNFalpha with drugs erased the enhanced performance of these chimeric mice in learning tests.