Women become brainier when they are at their most fertile – and their brains then shrink during period, according to a recent study.
A brain area central to forming human memories, moods and emotions was shown to increase in size in parallel with increases in a key sex hormone.
Investigators researching the connection between hormones in women and severe mood swings found that rising levels of oestrogen were found to enlarge the hippocampus.
The authors used an MRI brain scanner to measure the size of the hippocampus in a 32-year-old woman every two or three days over two menstrual cycles.
In all they conducted 30 scans in total over two months, with each scan conducted at 7.30am.
Lead author Claudia Barth wrote in the journal Nature Scientific Reports : ‘We found, that in parallel to the rising oestrogen levels leading up to ovulation, the Hippocampus also increases in volume – the volume of the grey matter as well as that of the white matter.’
This area of the brain is where memories are first formed and which has a key role in emotions.
When oestrogen was at its highest level, during ovulation – when an egg is released from the ovaries into the fallopian tubes – the brain structure is at its largest.
As oestrogen levels drop as the woman starts to menstruate, the brain area shrinks.
The growth in size and later shrinkage happen ‘with astonishing regularity’ the researchers write.
But only oestrogen has the effect.
The other main female sex hormone, progesterone, did not affect the size of the brain.
The researchers at the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig hope the discovery will help them understand a disorder which causes severe mood swings, listlessness and depression in menstruating women.
Called PMDD – pre-menstrual dysphoria disorder – the condition is thought to affect one in 12 women, according to the authors.
Julia Sacher, co-author said of PMDD: ‘To get a better understanding of this disorder, we first have to find out which monthly rhythm the brain of a healthy woman follows.
‘Only then can we reveal the differences in persons affected by PMDD.’
The authors also hope that the findings will shed light on the large differences between men and women in mood disorders.
Women are twice as likely as men to be diagnosed with depression.
Steep drops in oestrogen levels have been linked to depressed mood, particularly in menopausal women and also immediately after child birth, the authors write.
The authors used an MRI brain scanner to measure the size of the hippocampus in a 32-year-old woman every two or three days over two menstrual cycles.
In all they conducted 30 scans in total over two months, with each scan conducted at 7.30am.
Lead author Claudia Barth wrote in the journal Nature Scientific Reports : ‘We found, that in parallel to the rising oestrogen levels leading up to ovulation, the Hippocampus also increases in volume – the volume of the grey matter as well as that of the white matter.’
The authors do not speculate on the effects of the growth of the hippocampus.
Whether the changes improve a woman’s memory, or improve her mood, ‘remain a mystery’ the authors write.
But the researchers write: ‘The hippocampus plays a crucial role in our memories, our mood, and our emotions. In mice it has already been proven that it is not just this brain structure but also different behaviours which underlie a type of monthly cycle.’
The authors suggest the increase in size in the hippocampus may be caused by the presence of brain-derived neurotrophic growth factor, a hormone that makes the brain grow after learning.
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