The results of study involving 90 women were published in April in the journal "Human Brain Mapping".

About half the women in the study were using the combination form of oral contraceptives and the rest were naturally cycling.

The research found that oral contraceptive use was significantly associated with a thinning in two areas of the brain: the lateral orbitofrontal cortex and the posterior cingulate cortex.

The study is one of the first of its kind, as far as measuring effects of the birth control pill on brain structure.

Although the study only measured brain structure, the findings suggest that there could be possible effects on behaviour.

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Questions such as these are difficult to answer because it's always difficult to distinguish diminished capacity to resist a temptation from a diminished motivation to resist. People who tell us they literally can't resist might be deceiving themselves, or they might be looking for a convenient excuse.

There are two ways we can attempt to discover whether people who say that they can't control their behaviour really are suffering from some kind of diminished capacity.

First, we can gather as much behavioural evidence as possible: with enough evidence, we might be able to build an overwhelming case that a group of people genuinely suffer from diminished capacity.

When we see the costs - social, financial, physical and psychological - that drug addicts pay to continue using, we have good reason to think they have a diminished capacity to resist.

The second way we can proceed is to use scientific evidence that bypasses people's reports about what they can and can't do. Again, the case of drug addiction is a good example: some of the neurological changes in the brain of addicts seem to be changes in areas involved in self-control.

What about sex?

Recently, a group of researchers at UCLA attempted to resolve the question whether sex addiction is genuinely an addiction, utilising the second method.

Using EEG, which measures electrical activity on the surface of the brain, they determined that people who met the diagnostic criteria for "hypersexuality" did not find sexual stimuli any more compelling than did control subjects.

This is unlike the response seen in drug addicts, who find drug-related stimuli much more attention-grabbing than do unaddicted controls.

This research has been interpreted as showing that sex addiction isn't real. In the terms I used above, it might be taken to show that purported sex addicts do not lack the capacity to control their behaviour.

They simply lack the motivation; they might be morally condemned (if they are harming their families, say) rather than given a medical excuse.

But we shouldn't place too much weight on this study. The researchers looked for a likely correlate of a difficulty controlling behaviour, but there are many others possible correlates. Continue reading

Sources

• Neil Levy in The Conversation
• Image: SF Gate

Neil Levy is Head of Neuroethics at The Florey Institute of Neuroscience and Mental Health.