insane in the membrane, insane in the brain!

Is neurogenesis perhaps the most interesting scientific discovery of the times? I rather think it is. The government minister's version: until quite recently, we thought that once you passed a certain early age, that was it for your supply of neurons, and you would only lose them. Paradoxically, that wasn't incompatible with learning, as ones you use more are preferentially conserved, and a sort of evolutionary process might therefore be at work. I remember being taught this at school in the early 1990s.

The City of Bradford Metropolitan Council can probably be forgiven this; the theory that adult brains do not regenerate was only decisively falsified in 1989. We now know that new brain cells are created throughout life at a surprisingly high rate, and in fact your brain is constantly being replaced. It's a top field of research, and new discoveries are frequent. For example, we know that neurogenesis is somehow associated with the olfactory system (new neurons crawl along blood vessels to the olfactory bulb, then move on to their new roles elsewhere in the brain, a bit like geeks flocking into the one interesting session at the conference), that its regulation is involved in depression and Alzheimer's disease, both of which seem to involve abnormally low levels of it, and that various external factors influence it.

Learning new things, socialising, taking physical exercise, and falling in love (or lust) all increase the rate at which new neurons are produced. More medically, neurons are produced from stem cells, which opens up the possibility of acting directly on the process. We don't know yet what the consequences of overdoing it would be; science fiction is, however, working on it.

Lab monkeys demonstrate unusually, indeed pathologically, low levels of neurogenesis, which is believed to be caused by a sterile and boring environment; in fact, Elizabeth Gould, the discoverer of neurogenesis, had to redesign the lab in order to verify that this was so.

Fascinatingly, childhood poverty reduces neurogenesis, and it does this by increasing levels of chronic stress. Transient stress seems to regulate neurogenesis up - hardly surprising, given that this is how we often learn - but permanent insecurity makes you stupid, depressed, and vulnerable to dementia.

At the moment, the government is terribly keen on "happiness" and especially on administering cognitive-behavioural therapy to the poor. Unfortunately, the hard scientific facts seem to suggest that they would be much better advised to concentrate on a sort of Attleean agenda of economic security and broadening culture, of whatever kind. Over the last 30 or so years, we've had a rash of economists (mostly) claiming to offer tough, quantitative answers to society's questions, in opposition to a Left that deals in vague generalities or rabble-rousing. But the answers from science - real science, with radiation and monkeys and scalpels - are diametrically opposed to the ones from half-science.

Economics, in academia, is coping reasonably well with its own scientific revolution, the onslaught of Tversky and Kahnemann; its policy-advising function is largely a failure, hopelessly trapped by a dead weight of hacks and ideologues. But there is now a second wave of intellectual disruption heading for it from the life sciences. I was discussing the cognitive-bias revolution on a mailing list recently, and there was talk about what a new school of thought aiming to incorporate the new insights should call itself. It's not a trivial issue; the Friedmanites' triumph had much to do with their marketing, "Free to Choose", "rational expectations", "economic rationalism" in Australia. My suggestion was "realistic economics". Nobody wants to be on the side of unrealism, after all, which is what pre-Kahnemann economics offers.