The objectivity of subjective experiences

Perhaps not enough has been made of the extent to which brain imaging techniques are beginning to enrich our understanding of the brain. Most people marvel – and with good reason – at the fact that these imaging techniques demonstrate with fair certainty that specific experiences – for example of colour or of visual motion – correlate with activity in a specific area of the brain. But imaging techniques have gone way beyond and have made what was thought to be outside the realm of objective observation the target of experimental studies, and with huge success. Fear, expectation of reward, the experience of love and of beauty – all of them thought until recently to be unverifiable, or not easily verifiable, subjective experiences - have been shown to have neural correlates specific to them. Hence, to ascertain that someone is in love, I need only show them the picture of their [suspected] lover and note whether there is any activity in the brain areas that have been shown to correlate with feelings of love. In time, no doubt lawyers will be using such evidence in court proceedings.

But there is another aspect to these studies that has escaped comment although its impact may yet turn out to be as great as the demonstration that subjective feelings have distinct neural correlates. The experience of beauty provides a very good example.

In 2004, Hideaki Kawabata and I published a paper showing that the experience of beauty correlates with activity in the orbito-frontal cortex, a part of the brain that is linked to reward. In that study, we showed subjects many paintings – abstract, landscape, portraits, still lifes – and asked them to rate the paintings in terms of their beauty. Different subjects gave different ratings to the same paintings. Sometimes, a painting judged to be of high beauty by one subject was given a low rating by another. Yet whenever a subject a painting in the scanner that they rated as beautiful viewed, there was increased activity in the orbito-frontal cortex. Moreover – and this is the critical point – the increase in activity was directly related to the declared rating assigned to the painting. Hence the subjective experience could be localized and quantified.

Ours is not the only study to show that the activity in specific parts of the brain is often quantifiably related to the declared subjective experience. At least two dozen other studies have shown the same result for different subjective experiences. This, it seems to me, is a major achievement of brain imaging studies. It brings subjective experiences firmly into the realm of measurable science.