When Mike and Alanna Clear celebrated their blissful romance at their 2008 wedding, neither of them thought proving their love would result in brain scans and an excruciating trip to test their feelings for each other.
Despite being head over heels in love, Mike Clear became nervous after he read a statistic that half of all marriages ended in divorce. He started to wonder if his marriage would also collapse.
"That really kind of struck me. Everyone who goes to the altar to get married is in it for the long run, and yet 50 percent of them fail," he explained. "How do we know which half we're in?"
To find out, he came up with a radical idea: The two would take the road trip of a lifetime and put their young love to an ultimate test. He and his new bride would tackle the world's longest road -- the Pan American Highway, a 29,800-mile trek from Alaska to Argentina -- while riding on a motorcycle with a sidecar.
The London couple quit their advertising jobs and planned for a nine-month journey through 16 countries.
"It was really scary," Alanna Clear admitted.
Before venturing out, they decided to see how deep their love was for each other, and whether their wild adventure would change it over time. The two contacted world-renowned anthropologist Helen Fisher to have their brains scanned.
Mike Clear had read about Fisher in the newspaper, and he got in touch with her on the off chance that she would do her compatibility test on them. But Fisher suggested the two have their brains scanned instead.
"If I looked into the brain, I could perhaps find out what's going on when people are feeling that rush of romantic love," Fisher said.
According to Fisher, three types of love can be seen in the brain: sexual love, romantic love and attachment love. She said the scans don't lie, and that sometimes people came to see her and said they were in love but their brains showed otherwise.
With their scan results in a sealed envelope, the Clears headed to Anchorage, Alaska, where they picked up the motorcycle. They wouldn't look at the results until after the trip.
Heading out on June 21, 2009, their journey hit a rough patch immediately. Alanna Clear failed her motorcycle license test, and her husband had to accept the fact that he would be driving the entire way.
"I think I was more upset than she was with the idea of having to drive 20,000 miles on my own," he said.
Along the way, they stopped and interviewed other couples, seeking advice and insight into what made a happy marriage. Some of the responses, such as "don't run out of gas" and "keep your ups and downs in the bedroom," were funny and uplifting, but Alanna Clear still struggled.
"I was like, 'I don't think I can do this.' I don't think I can listen to people telling me about their love stories that then will make me question our own," she said.
Forging south, their trip continued to have its hiccups. Day after day of straight driving left the two tired, muddy and in desperate need of a shower. It wasn't long before their patience began to strain.
Two months in, they reached Utah, and the trip almost came to an abrupt halt when Mike accidently drove the bike off the road and into a ditch.
"I was talking to him about having a baby over the microphone, and he lost concentration in a moment of pure terror," his wife said.
As days turned into weeks on the road, the Clears had their share of highs and miserable lows: delightful nights of tangoing and horseback riding, mixed with extreme weather changes and low blood sugar levels that took their toll.
And there were of course fights about directions.
"She lost a GPS in Las Vegas. Unbelievable," Mike exclaimed.
"Low moment, low," Alanna agreed.
Their spirits sank even lower when they drove closer to South America, and the region was in the midst of its tropical rain season. Rain would fill all around Alanna as she sat in the sidecar.
"We'd be driving through lightning storms, and we couldn't see anything and nothing dried because it was so wet," she said. "It was really unromantic."
The Clears love was further tested when they reached Peru and met with a man and his six wives.
"[It was] the biggest fight that we had, which actually challenged our core beliefs," Alanna said. "He talked about those women as slaves."
When the man told one of his wives to kiss his feet, and instructed Alanna to do the same to her husband, she refused and created an awkward situation.
"I said, 'I won't,' and he said, 'Well, then you don't love him,'" she said. "I said, 'Well, I'll do it for him if he does it for me first,' and there was a collective intake of breath from all the wives around the table."
Alanna said that afterward she demanded that her husband explain why he hadn't defended her, and cried for days.
Pushing forward, the trip came to a close in February 2010, and the Clears decided they had finally earned the chance to find out whether they had been in love before their adventure. Taking out Fisher's initial brain scans, the two reviewed the results and were excited about what they saw.
Their scans showed that both had been deep in love before their trip began: The romantic love centers of their brains appeared lit up like Christmas trees.
But now that the trip was over, would their brains still flare up in the same way? The second test followed a few days later, when the Clears found themselves back in Fisher's office. The second set of results would shock them both.
Find out what was in the second envelope and watch the Clears' full story tonight on "Secrets of Your Mind" at 10 p.m. ET