It has taken a woman – who may or may not suffer from the condition herself but I would imagine it would make her curious – to investigate this. Erika Timby in her recent doctoral dissertation at Umeå University in Sweden revealed the role of the hormone allopregnanolone in PMS. It seems that sensitivity to this naturally-occurring hormone in the body (after ovulation and during pregnancy), changes during the course of the menstrual cycle. What she has observed is that it is different in women with severe pre-menstrual syndrome (PMS) from women who do not suffer from the condition
This is only a limited number study for her dissertation but in her sample she found that women who don’t suffer from mood changes prior to menstruation are more sensitive to allopregnanolone immediately afterwards and less sensitive before. On the other hand, sensitivity to allopregnanolone in women who suffer from severe PMS who have pronounced mood shifts before every period is the exact opposite: these women are more sensitive before than after.
Her conclusion is that this may mean that they have less ability to adapt to hormonal variations prior to menstruation. It is not clear what causes this, but it may be that these women have an altered function in one of the brain’s signal substance system, the so-called GABA system. The researchers are able to monitor this by monitoring the speed of eye movements when the subject follows a moving point of light. In the study the women were given allopregnanolone in doses to those normally seen during pregnancy. A fatiguing effect was recorded in the form of slower eye movement and increased feeling of tiredness.
Sadly this does not yet provide us with the information that could help relieve symptoms of PMS but if you wish to know more then there is an excellent series of articles by Dr Tony Coope – of which the first one is here: https://www.bio-hormone-health.com/2010/06/22/premenstrual-syndrome-pms/