EVERYONE has had the experience. You are confronted by a complex problem, with a not-so-obvious solution. You pore over it, engrossed, but still the answer will not come. Fearing you will be stuck for ever, you take a walk. Then suddenly, from nowhere, there it is. Eureka!

But did it really come from nowhere? A piece of research about to be published in the Journal of Cognitive Neuroscience, by Joydeep Bhattacharya at Goldsmiths' College in London and Bhavin Sheth at the University of Houston, in Texas, suggests that although people are not consciously aware of it, their brains have to be in a certain state for an insight to take place. Moreover, that state can be detected electrically several seconds in advance of the “aha!” moment itself.

The question of where insights come from has become a hot topic in neuroscience, despite the fact that they are not easy to induce experimentally in a laboratory. Some researchers have used getting the punch line of a riddle as an example of an insightful outcome. Critics complain, however, that this is less an insight than an “outsight”. Other experiments have used word tasks. In these, a person might be given three seemingly unrelated words, such as “skirts”, “black” and “put”, and asked to come up with a fourth that can link to each of the other three. (In this case, “out”.) But those tasks may say more about lexical ability than true insight.

Dr Bhattacharya and Dr Sheth have taken a third approach. They have selected some brain-teasing but practical problems in the hope that these would get closer to mimicking real insight. To qualify, a puzzle had to be simple, not too widely known and without a methodical solution. The researchers then asked 18 young adults to try to solve these problems while their brainwaves were monitored using an electroencephalograph (EEG).

A typical brain-teaser went like this. There are three light switches on the ground-floor wall of a three-storey house. Two of the switches do nothing, but one of them controls a bulb on the second floor. When you begin, the bulb is off. You can only make one visit to the second floor. How do you work out which switch is the one that controls the light?

That light-bulb moment

This problem, or one equivalent to it, was presented on a computer screen to a volunteer when that volunteer pressed a button. The electrical activity of the volunteer's brain (his brainwave pattern, in common parlance) was recorded by the EEG from the button's press. Each volunteer was given 30 seconds to read the puzzle and another 60 to 90 seconds to solve it. If he had not done so in the time allotted, a hint appeared. In the case of the light-switch puzzle, the suggestion was that you turn one switch on for a while, then turn it off.

Some people worked it out; others did not. The significant point, though, was that the EEG predicted who would fall where. Those volunteers who went on to have an insight (in this case that on their one and only visit to the second floor they could use not just the light but the heat produced by a bulb as evidence of an active switch) had had different brainwave activity from those who never got it. In the right frontal cortex, a part of the brain associated with shifting mental states, there was an increase in high-frequency gamma waves (those with 47-48 cycles a second). Moreover, the difference was noticeable up to eight seconds before the volunteer realised he had found the solution. Dr Sheth thinks this may be capturing the “transformational thought” (the light-bulb moment, as it were) in action, before the brain's “owner” is consciously aware of it.

There is a precedent for such observations of unconscious thought in action. In the 1980s Benjamin Libet of the University of California, San Francisco, showed that simple decisions, such as when to move a finger, are made about three-tenths of a second before the brain's owner is aware of them, and subsequent work has found that the roots of such decisions can be seen up to ten seconds before they become conscious. But this is the first occasion that such a long lead time has been shown for more complex thought processes.

This finding, combined with Libet's, poses fascinating questions about how the brain really works. Conscious thought, it seems, does not solve problems. Instead, unconscious processing happens in the background and only delivers the answer to consciousness once it has been arrived at. Food for further thought, indeed.