A team of researchers has created the first brain-wide map of brain regions to understand how sex relates to lasting love.

They created the map of brain regions active in the experimental model during mating and pair bonding.

The experimental model is one of the few known to form long-term, monogamous relationships.

The researchers from The University of Texas at Austin found that bonding voles experience a storm of brain activity distributed across 68 distinct brain regions that make up seven brain-wide circuits.

The brain activity correlates with three stages of behaviour -- mating, bonding and the emergence of a stable, enduring bond.

Most of these brain regions the researchers identified were not previously associated with bonding, so the map reveals new places to look in the human brain to understand how we form and maintain close relationships.

Earlier studies concluded that male and female brains often use fundamentally different mechanisms to produce the same behaviours, such as mating and nurturing offspring.

But in this study, bonding males and females had nearly identical patterns of brain activity.

"That was a surprise," said Steven Phelps, Professor of Integrative Biology at UT Austin.

"Sex hormones like testosterone, oestrogen and progesterone are important for sexual, aggressive and parental behaviours, so the prevailing hypothesis was that brain activity during mating and bonding would also be different between the sexes," he added, in the study published in the journal eLife.

The researchers were able to pinpoint with high resolution which brain cells were active in vole brains at various points over the course of the process that leads to and includes bonding.

This is the first time such a method has been applied to the experimental models.

By studying more than 200 experimental models across multiple times during mating and bonding, the researchers produced an unprecedented and foundational data set.

The strongest predictor of activity across the 68 brain regions that the researchers identified surprised them.

It was male ejaculation, suggesting the experience elicits a profound emotional state -- and not only in the affected males.

Females, too, had more bonding-related brain activity than males who reached that milestone.

"The brain and behaviour data suggest that both sexes may be having orgasm-like responses, and these 'orgasms' coordinate the formation of a bond," Phelps said.

"If true, it would imply that orgasms can serve as a means to promote connection, as has long been suggested in humans."