Women may become brainier when they are at their most fertile – and their brains then shrink during their time of the month.
A brain area central to forming memories, moods and emotions was shown to grow in size in parallel with increases in a key sex hormone.
German researchers analysing the connection between hormones in women and severe mood swings found that rising levels of oestrogen were found to enlarge the hippocampus.
This area of the brain is where memories are first formed and which has a key role in emotions.
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When oestrogen is at its highest level, during ovulation – when an egg is released from the ovaries into the fallopian tubes – the brain structure is also at its largest. Then, when oestrogen levels drop as the woman begins to menstruate, the brain area shrinks.
The growth in size and later shrinkage happens ‘with astonishing regularity’, the scientists write.
But, they discovered, only oestrogen has this effect.
The other main female sex hormone, progesterone, does not change the size of the brain.
The experts, from 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 dysphoric disorder – the condition is thought to affect one in 12 women, according to the authors.
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Co-author Julia Sacher 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 scientists used an MRI brain scanner to measure the size of the hippocampus in a 32-year-old white 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.
The authors also hope that their findings, published in the journal Scientific Reports, will shed light on the large differences between men and women regarding 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 childbirth.
Lead author Claudia Barth wrote: ‘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 what the effects of the growth of the hippocampus are.
Whether the changes improve a woman’s memory, or improve her mood, ‘remain a mystery’.
They suggest the increase in size in the hippocampus may be caused by the presence of a ‘brain-derived neurotrophic growth factor’ – or a hormone that makes the brain grow after learning.
But the researchers added: ‘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.’
Daily Mail