THAT'S THE WHY:The history of medicine is replete with drugs that came into use because they can bring about the desired effect even if we don't quite know why.

Lithium is a case in point: if you recall your chemistry classes from school, lithium is an element; a soft, silver-white metal which was discovered and named in the 19th century, and enjoyed a wide range of industrial applications.

Then, in the mid-20th century, it came to light that lithium salts could have a tranquillising effect, and later they got approval as treatment for forms of mania and depression.

But how lithium acts as a mood stabiliser is still open to question.

Lithium appears to have several effects on brain cells, and recent findings from cells in the lab have been pointing to its impact on a signalling molecule called phosphatidylinositol (3,4,5)-trisphosphate, which is mercifully shortened to PIP3.

“PIP3 is a major signalling molecule in neurons, and suppression of PIP3 signalling may have significant neuromodulatory effects in bipolar mood disorder patients,” write the authors of the 2009 study in Disease Models Mechanisms.

Prof Adrian Harwood of Cardiff School of Biosciences, who led the research, said in a statement: “We still cannot say definitively how lithium can help stabilise bipolar disorder.

“However, our research does suggest a possible pathway for its operation. By better understanding lithium, we can learn about the genetics of bipolar disorder and develop more potent and selective drugs.”