Questions continue about what motivated Jérôme Kerviel, 31, the junior banker who bought Société Générale to its knees, costing it $7.2 billion with his wrong bets and fraud.

The man himself has told the press that that while he made some mistakes, Société Générale is turning him into a scapegoat and that bank knew and approved of his unauthorised bets and that other traders had engaged in similar practices.

His comments go to the heart of the issue of why these sorts of meltdowns keep happening. As I said in a column last weekend, the qualities that make a great trader can also make a chillingly competent fraudster..

But now we have studies, reported here, showing that there might be a bit of Kerviel in all of us and that our brains are actually hard-wired to give us the thrill of taking big risks and making money. One of the findings was that brain images of drug addicts who are about to take another hit are indistinguishable from those of traders who are making money and about to place another trade.

If this is right, we always have traders playing the odds and helping themselves to the spoils. This problem won't go away and tightening up laws is not going to help.