During pregnancy grey matter in the mothers brain shrinks. Studies show that it can shrink by 5%. The brain is being fine-tuned and some connections are removed. The cortex thins. At the same time the amount of white matter increases. This will strengthen the connections between different parts of the brain. All this is to prepare the woman for the task ahead. The changes are hormone related and can sometimes come with a brain fog. The brain becomes much more sensitive to the behaviour of the child. Vigilance and empathy grow.
These changes can be permanent. The effect of having children can be detected in later life. For women having a second child the changes are less. The brain is “topped up” to the level experienced with a first child. This neuroplasticity is visible in 80% of women.
A Five Minute Read
The “Ageing Brain” Stereotype
In the back of the “decline” narrative of ageing sits the brain. The assumption is that age shrinks the brain. This in turn reduces cognitive ability. The brain does slow down. It is the case that sufferers of Alzheimer’s will have a smaller brain. Changes in brain size don’t necessarily fit the stereotypes. Changes do not only come with age. The story is more complex.
The first thing to say that that the size of the brain does not affect your IQ. In fact we do not know what a normal brain size is. It is only recently that researchers have tried to create what are known as brain charts. If you have children, you are familiar with the height and weight versions. Across the bottom is age. The height chart tells us about the expected height for a given age. On top of that we have percentiles showing a range of different “normals”. It was only in 2022 that similar charts were created for different measures of the physical brain. Before that neurologist used their judgement to assess what was normal.
In 2022 researchers collected 125,000 brain scans. They came from individuals from a few weeks to 100 years old. They came from all over the world. Only with todays computing power was it possible to process the images. To assess things like brain volume, brain surface area etc. They could then be put onto a brain chart or charts. They analysed close to 1,000,000,000,000,000 bytes of data . An analysis only possible on the latest super-computers. What the data showed was just how quickly the brain grows and just how early it starts to decline.
The volume of grey matter increases rapidly from 20 weeks of pregnancy. It actually peaks in total volume when we are 6 years old and then starts to decline. The subcortex controls most of our bodily functions and basic behaviour. Its volume peaks between 14 and 15 years old. White matter takes much longer to peak. It too starts to accelerate at 20 weeks but will not peak until we are nearly thirty. The decline in white matter volume starts to accelerate at the age of 50, grey matter somewhat later. Decline in size is normal and happens through most of our lives.
Neuroplasticity.
The rewiring of a mother’s brain shows that it is not fixed when we are 6 or when we are 29. Our brains are continuously evolving. They evolve physically in terms of the number of neurons. They also change the way they are wired. A research group in Cambridge was able to look at neural connections. Their sample included the brains of 3800 people from infants to the over 80’s. They found key change points at different ages.
In their version, childhood ran until the age of 9. During those early years many connections are whittled down. The infant brain has created too many. We reduce the number and keep the most useful. Adolescence runs from 9 to the age of 32. Much later than we expect. The brain is in a different state in terms of connections.
This era is defined by the efficiency of communication. Communication within regions of the brain and across the whole of the brain. White matter continues to grow. This period is associated with increasing cognitive ability. It is only at 32 that the brain’s wiring is in adult mode. It will stay there for over thirty years in a stable form. By 66 the brain has started to become more compartmentalized. In the early ageing brain stage, overarching connections are less powerful. One hypothesis is physical. This assumes that the white matter is starting to degenerate.
The late ageing brain seems to emerge around 83. There is even less connection between different parts of the brain. We depend more on certain parts. Data is very limited on this age so the researchers are very tentative.
Evolution or Ageing
When we are young the changes in the brain are called development. Somewhere around 50 those same changes are put down to decline. Certainly, our cognition and memory does not now decline until we are in our 80’s. We can compensate for any loss of processing power with our expertise.
A study this year has looked at the brain scans of new fathers. Many of the same changes in the brain occur for them too. They too have a grey matter reduction. Perhaps only 1% compared to 5% for mothers. The changes are in parts of the brain associated with social cognition, visual processing and empathy. They are being prepared to be more sensitive to infant’s cues and to respond sensitively. The more the fathers take a role in caring for the infant the greater are the changes. The scientists can even tell from the degree of change whether the father has taken paternity leave.
Becoming a father or mother changes your brain. Does the brain always evolve to fit our needs at any point? There is evidence of “use it or lose it” in the elderly. The brain wants to remain efficient. Does it just prune off what we do not need?
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