A new study has solved the puzzle as to how exposure to pornographic images may lead to erections in men.
Lead researcher Harold Mouras, at University of Picardie Jules Verne in Amiens, France, believes that mirror neurons, a special class of brain cell that fires both when people perform an action and when they observe it being performed may a crucial role in controlling erection response.
For the study, Mouras' team recruited young men, who were asked to view three types of video clips. They were shown late night fishing documentaries and snippets of Mr Bean along with erotic videos of men stroking naked women, enjoying fellatio and engaging in intercourse.
With the help of functional magnetic resonance imaging (fMRI), the researchers also studied their brains, while they watched the watched the videos.
The team also kept a track of tumescence of the other target organ, using a hand-crafted "penile plethysmograph," essentially an airtight tube in which the enlarging penis causes measurable pressure changes.
They found that all the participants got erections and many parts of the brain also lit up.
The volume of the erections was linked to strength of activation in a part of the brain called the pars opercularis, known to display mirror neuron activity.
Moreover, the brain activation came before the penile response.
"The mirror neurons are like the command. The activation comes before the erection." New Scientist quoted Mouras, as saying.
Vilayanur Ramachandran, at the University of California at San Diego, who also studies mirror neurons, calls it a "bold" study into men's sexual physiology.
He said that it is perfectly plausible that mirror neurons play a role in how porn turns us on, however suggested more research in understanding the role.
The study appears in journal NeuroImage.