Revealed: Why women feel anxious at 'that time of the month'

A new study, led by the University of California has claimed that brain cells, called GABA receptors, are to blame for many women's monthly mood swings, according to a report in the 'New Scientist'.

To investigate potential mechanisms behind premenstrual dysphoric disorder (PMDD), the scientists used a PET scan, which shows where glucose is being metabolised to identify activity in the brain.

The idea was to analyse the brain activity of 12 women with PMDD and 12 without the condition, at various times throughout their menstrual cycle. Before each scan, the women rated the severity of any symptoms they had on a scale of one to six. Blood samples were taken to test their hormone levels.

Fluctuating hormones were not to blame -- all women experienced similar jumps in progesterone levels throughout their cycle, irrespective of whether they had PMDD or not.

However, brain analyses showed that in the late luteal phase women with PMDD had heightened activity in their cerebellum. The scientists also discovered that the larger the spike in activity, the worse the symptoms.

Women without PMDD had no such spike in activity, even though their progesterone levels were also rising during this time, the findings revealed.

Rapkin said that in PMDD, progesterone alters the shape of GABA receptors in the cerebellum, making it harder for GABA to bind to them and damp down anxiety.

Suzanne Abraham, a gynaecologist at Royal North Shore Hospital in Sydney, said that PMDD was not taken seriously as a condition, but this study confirms it "is 'real' and can be measured".

The findings have been published in the 'Biological Psychiatry' journal.