May 21, 2012 -- B.D., a 34-year-old with a lifelong fear of spiders, found his phobia intensified after a trip to Australia where he encountered the Huntsman variety, a hairy tarantula that scuttles out from behind curtains and is notorious for entering cars and scurrying across the dashboard.

But today, after two hours of exposure therapy as part of a study at Northwestern University, B.D. finds spiders tame and amusing -- so much so that he allowed a hairy, Chilean rose tarantula named Florence to amble up his arm.

"It was like the ultimate extreme sport, a chance to face my fears in a very literal sense," B.D., an administrative assistant, wrote on a blog about his experience on his blog, "Room 101."

"It's been three years now, but I am still amazed whenever I react calmly and reasonably to their presence in my life," he wrote. "Just yesterday I helped a big green fellow off my desk, marveling that I didn't flee the room instead."

In 2009, B.D. was paid $100 to take part in a study at Northwestern University's Feinberg's School of Medicine, the first to document the immediate and long-term brain changes after exposure therapy. There, 12 terrified subjects were exposed to a variety of spiders -- first in photos, then in a terrarium and finally in the palm of their hands.

The study revealed that a single brief therapy session for adults with a lifelong fear of spiders -- or arachnophobia -- showed lasting changes to the brain's response to fear.

"Signing up for the study was one of the bravest things I've ever done, and I'm very proud," he wrote.

Arachnophobia is one of the most common specific phobias, and those who are afraid will go to great lengths to make sure they never see a spider. They may avoid hiking or camping or any situation where a spider might be present.

Specific phobias, which fall under anxiety disorders, affect about 7 percent of the population, according to the researchers. The most common include fear of blood, needles, snakes, flying and enclosed spaces.

But they say that their study may be applicable to all kinds of common phobias, as well as obsessive-compulsive disorder and post traumatic stress disorder.

"Before treatment, some of these participants wouldn't walk on grass for fear of spiders or would stay out of their home or dorm room for days if they thought a spider was present," said lead researcher Katherina Hauner, a post-doctoral fellow in neurology.

"But after a two or three-hour treatment, they were able to walk right up and touch or hold a tarantula. And they could still touch it after six months. They were thrilled by what they accomplished."

The study, which was published in the journal, Proceedings of the National Academy of Sciences, was the first to use functional MRIs to measure anxiety in the brain before and after exposure to the feared object.

Not only were patients less afraid after the two-hour therapy session, but they were phobia-free six months later.

The anxiety levels in their brain were measured at different intervals. When subjects experienced fear, certain parts of the brain, like the amygdala, insula, and cingulate cortex, lit up with activity on a functional MRI scan.

When the same study participants were asked to handle the tarantula six months later, "they walked right up to it and touched it," according to Hauner.

Study participants had to meet the criteria for specific phobias as defined by the American Psychiatric Association's a Diagnostic and Statistical Manual of Mental Disorders.

"They had to be much more afraid of spiders than the average person," said Hauner. "And to meet the diagnostic criteria, it had to interfere with their life."

"Some wouldn't go home or stay in a dorm room for days if they thought a spider was there," she said. "One person avoiding traveling -- but after the study, they went on a trip."

Spider Phobia Cured Through Exposure Therapy

Researchers used hierarchical steps to introduce patients to the feared object, first in photos of different spiders and then approaching a live one.

"We would begin 10 feet away from the spider in a terrarium with the top closed," said Hauner. "For all of them, that was the most difficult part of the study. They had no idea what to expect at that point -- for some it was the first time they had ever looked at a spider."

Subjects were encouraged to move closer, as Hauner educated them about spiders -- Florence was not venomous, in fact she was afraid of humans. And they don't jump around erratically, but defensively hunker down when people approach them.

"They thought the tarantula might be capable of jumping out of the cage and on to them," she said. "Some thought the tarantula was capable of planning something evil to purposefully hurt them. I would teach them the tarantula is fragile and more interested in trying to hide herself. "

B.D. and others learned spiders were practically blind creatures, not aggressive at all. If dropped from four feet, they die.

"After seeing so many photos of terrible spiders, I was emboldened enough to approach the a whole two feet closer to the Dread Cage, meaning that I got within eight feet before my fear level went up ?" writes B.D.

Eventually the phobics touched the glass wall of the terrarium, then the tarantula itself, first with a paintbrush and then with their hands.

"They learned the spider was predictable and controllable," said Hauner. "That's when the major change takes place. And they are totally amazed at the end."

Slowly, by exposing subjects like B.D. to the creature, researchers normalized the experience for them. For some, it was a pleasant experience.

"And so," writes B.D., "I was fascinated to learn that Florence, at least, was beautiful. She had so much hair, that, really she could be called fluffy, and it was the same color as my mother's cat."

B.D.'s motivation was "key" to his success, according to researcher Hauner. "Most came have faith in the therapy -- knowing it was worth it."

One subject wrote a thank you note to Hauner from Europe, because she was able to enjoy travel again. "Their worst nightmare ended up being something very exciting and amazing to overcome," she said.

As for B.D., he writes that he is still "nervous" about spiders, but that has been decreasing over time, especially because he is "no longer so terrified of them."

"I'm very proud of myself for doing this," said B.D. "I had originally conceived of it as being like an extreme sport, or like a ritual test of courage, an ordeal."

But now, he has pledged to get a tattoo of the arachnid -- "so that I'll always have something to remember it by."