Zap to the brain alters libido in unique sex study

New Science 30Nov2016

Could a brain stimulation device change our sex drive? The first study of this approach suggests that people’s libido can be turned up or down, depending on the device’s setting.

The study didn’t measure how much sex people had in real life, instead it measured participant’s sexual responsiveness. Unusually, this was done by fixing customised vibrators to people’s genitals and gauging how their brainwaves changed when they expected a stimulating buzz.

“You want to see if they want what you’re offering,” says Nicole Prause at the University of California, Los Angeles. “This is a good model for sexual desire.”

The technique involves transcranial magnetic stimulation (TMS), where a paddle held above the head uses a strong magnetic field to alter brain activity. It can be used to treat depression and migraines, and is being investigated for other uses, including preventing bed-wetting, and helping those with dyslexia.

Reward circuit

The part of the head targeted in this study – called the left dorsolateral prefrontal cortex, roughly above the left temple – is involved in the brain’s reward circuitry.

Prause’s team wondered if stimulating this area might affect how people feel about sex. One problem is that standard methods of assessing desire are too subjective, says Prause. “The only way is to ask someone, ‘How much do you want to have sex right now?’ People might not be willing or able to tell you, or be using the scales differently.”

To get around this, a vibrator was either connected to a sheath that the penis goes in or a small hood that fits over the clitoris. Electrodes on each participant’s head measured the strength of their brain’s alpha waves, which are weaker when people are more sexually aroused.

During the experiment, 20 people were given TMS for about two minutes, designed to either excite or inhibit the dorsolateral prefrontal cortex. Next, each volunteer was taken to a room where the EEG electrodes were placed on their head. They were then left to attach the vibrator themselves.

Finally, each participant carried out a task that involved pressing a button as fast as possible when shapes appeared on a screen. Depending on how quick they were, they were given a genital buzz lasting between half a second and five seconds – but only after a pause.

Desire in the lab

Their brainwaves were recorded during this waiting period. “They know they’re about to be sexually stimulated, but it hasn’t actually happened yet,” says Prause. It is the closest analogue for measuring desire in the lab, she adds.

As predicted, after excitatory TMS, participants’ alpha waves were weaker – suggesting they were more sexually aroused – than after inhibitory TMS. The team couldn’t measure any changes to people’s sex lives, as the effects of a single session of TMS are short-lived. To treat depression, for instance, people get several sessions a week, and it is supposed to induce gradual changes to the brain over several weeks.

But people’s overall sexual responsiveness in the study, as gauged by their brainwaves, did correlate with the number of orgasms they had over the next three days, either through sex or masturbation. Prause says it would be interesting to know if people having TMS for depression report any changes in their sex lives. “But no one asks them.”

Cicely Marston at the London School of Hygiene & Tropical Medicine points out that sex is an extremely complicated social phenomenon. “To think you can fix a problem by fixing the physiological components is overly simplistic,” she says. “But if it works there would be a huge market for it.”

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0165646