Bill Briggs writes:What’s scarier than bats in the belfry?

Easy: tarantulas in an MRI tube.

To observe the brain’s panic-response network in full freak, British researchers asked 20 volunteers to lie inside a functional magnetic resonance imaging machine. One by one, the scientists then had each person view a screen that showed a tarantula crawling closer ... and ... closer to the subject’s feet.

As the spider advanced, MRI scans allowed researchers to see flashes of activity switch from the volunteer’s prefrontal cortex – a region associated with anxiety – to a spot in the midbrain known to involve intense fear. But the neural terror waned when the tarantula retreated, “regardless of the spider’s absolute proximity,” wrote the study’s authors. In other words, as long as the spider was moving away, no matter how close it still was, the volunteers relaxed.

Titled “Neural Activity associated with monitoring the oscillating threat value of a Tarantula,” the study was published today by the National Academy of Sciences. They could simply have dubbed their paper: “Watching the Willies.” What the researchers glimpsed, they say, was the brain’s danger-tracking system at work.

Before you brand the scientists as sadists, you should know two things.

First: the findings may make it easier to diagnose and treat patients who suffer from clinical phobias, said Dr. Dean Mobbs, one of the authors.

“We first show that multiple (brain) systems are involved in fear and that a goal of future research should be to try and understand which parts of the system break down,” said Mobbs, who works at the MRC-Cognition and Brain Sciences Unit at the University of Cambridge Medical School. “If we can understand this, then we can better engage people with phobias and other types of fear. To cure we must first understand.”

Second: the volunteers were actually watching pre-recorded images of the spiders walking to and fro. The MRI tubes never contained real critters.

But why tarantulas? Why not rats or bats or scorpions?

“The UK has one of the highest amounts of spider phobics in the world. This is despite the fact that we have no deadly spiders in the UK,” Mobbs said.

He then admitted: “I mainly used spiders because I have a slight fear of them.”

What scares you the most? Tell us about it in the comments.

Find The Body Odd on Twitter and on Facebook.

Want more weird health news? Find The Body Odd on Facebook.

Writes Bill Briggs: You jump, yelp and quake. You hug tighter and breathe harder. Then, you giggle it all away.

The hormonal storm that cascades through your body before, during and after a frightfully fun moment is – as haunted house artist Timothy Haskell likes to say – “a beautiful pathos.”

“It’s a complete journey from anticipation to anxiety to experiencing the fear and having the adrenaline rush to coming down afterward,” says Haskell, an Off-Broadway director whose latest ghostly creation, “Nightmare: Superstitions,” runs Sept. 24-Nov. 6 in Manhattan. “Fear and hilarity are very close to each other. It’s the same (neuro)transmitter that’s being engaged. A lot of times, you’ll get startled and find the very next reaction is to laugh.”

Crazy for coasters: For some, track goes on forever

Which explains why so many of us purposely love to be scared: It’s an internal roller coaster ride that delivers us safely back to reality. Whether bungee-cord jumping or watching horror flicks, we’re drawn to the chemical surge of controlled danger.

Adding to the blood-curdling bliss: your body can’t discern between the intentional thrill you ignite by, say, parachuting for sport and the anxiety that grips you if you stumble into true peril.

“People think this is all in your head. No, it’s all in your kidney rind,” says Dr. Christoph Leonhard, a psychologist and professor at the Chicago School of Professional Psychology.

In an alarming situation, your adrenal glands (which sit atop your kidneys) dump the hormone epinephrine into your blood steam. That gush triggers a series of bodily reactions – the “fight or flight response” – including a burst in heart rate and breathing.

“The very exciting experiences and the anxious experiences are difficult to differentiate just on a physiological level,” Leonhard says. “So if you’re going bungee-cord jumping or if you are having a panic attack driving over a big bridge, biologically speaking, it’s almost identical.”

After the terror lifts, your body unleashes a compensatory hormonal wave – noradrenaline – to restore heart and breathing rates. What you feel then is “that peaceful, relaxed, deeply pleasurable state,” Leonhard says. “People get addicted to that as much as they get addicted to the excitement.”

Our joy-jolt is further revved by watching others freak out. Due to biological differences, some of us simply startle easier – “just like,” Leonhard says, “it takes more beer to get some people drunk.”

Typically, those of us who seek the big scare like to do it in packs. Psychologically, Leonhard says, we enjoy trying on roles that come with actual creepy situations: We become the caretaker or we allow someone to protect us. We bond.

People often attend Haskell’s “Nightmare” events in groups and because, he says, they “share communally.” (The backdrop for his 2010 haunted house: a 35-minute stroll through a former New York City insane asylum).

“They like being the safety buffer as well as being the person who needs a safety buffer.” Haskell says. “People like to bring their girlfriend and boyfriend – whoever they have to hold onto.”

Roller coasters, scary movies, bungee jumping -- what's your favorite way to freak yourself out? Tell us about your favorite adrenaline source in the comments.

Find The Body Odd on Twitter and on Facebook.

Want more weird health news? Find The Body Odd on Facebook.

Visit msnbc.com for breaking news, world news, and news about the economy

Bill Briggs writes: Turn on, tune in … download?

The teen fad known as i-Dosing – an allegedly trippy state of ecstasy reached, some claim, by listening through earphones to a pair of carefully mixed audio streams – has led some parents to worry, some teachers to panic and some narcotics authorities to start monitoring the so-called “digital drug.”

Unfamiliar with the notion of getting high via audio file? Websites boast that when repetitive beats are synchronized with brainwaves, it can alter the listener's mood or simulate the feeling of being high.

But one brain expert offers a decidedly blunt, low-tech take on this i-Trend: “It’s really much B.S., honestly,” said Damir Janigro, a Cleveland Clinic neurosurgery researcher. While music has the power to change moods, the medical concept behind i-Dosing is little more than a money-making scheme – just a dose of cyber-snake oil, Janigro adds.

To get the effect, users plug into “i-Dosers” through their headphones. The MP3 downloads (often accompanied by kaleidoscopic videos) send a distinct tone into one ear while simultaneously filling the other ear with staticky, white noise or an electrical hum, allegedly changing brain waves and bathing listeners in euphoric bliss. At least one track mixed in what sounded like a woman having an orgasm.

YouTube contains a number of free i-Dose “sound drugs,” including “Leviticus Green” or “Gates of Hades” which instructs people to listen alone in a dark room to maximize the “hallucinogenic effects.” Several websites sell i-Dose downloads for everything from smoking cessation to anxiety relief. They can cost about $20 for a 55-minute audio sample.

The grown-up hysteria over i-Dosing started with some YouTube videos that show users looking freaked out as they listen to the trippy tracks. Because i-Dosing fans – usually teenagers – claim they reach altered states through these sound streams, scattered packs of authorities have wagged their fingers at the practice. In March, three students at an Oklahoma high school were ordered to the principal’s office for admittedly i-Dosing. Consequently, the Oklahoma Bureau of Narcotics said it was “concerned” about the fad because some i-Dosing websites offer links to buy prescription drugs or marijuana.

The late Timothy Leary would have undoubtedly loved the hoopla. But Janigro, a music aficionado who collaborated on the Cleveland Clinic’s study of deep brain stimulation, says i-Dosing is a medical dud. Any effects shown by users, he believes, are either triggered by the accompanying use of marijuana or simply by the power of suggestion.

“I really don’t think there is any danger in this,” Janigro says. “People are trying to make money ... simply using the same music that we’ve always had.”

Indeed, music can affect disposition: that’s why music is played at funerals, Janigro says. That’s why exercisers often tune into songs while working out. But the impact varies with each person. For some, “Beethoven makes them cry, for others Beethoven makes them bored.”

What’s more, sending one tone and beat into one ear, and another tone and beat into the opposite ear is as old as Beethoven – and symphony attendees don’t walk out stoned or craving munchies.

“Your awareness of music is bilateral: you hear music with both sides of your brain,” Janigro says. “At every orchestra, the strings on the left may be playing in three-quarter (time) and the cellos on the right in two quarter. So that’s nothing new.”

What i-Dosing fans ignore is “that [what comes through the right and left] ear canals are both crossing in the brain,” says Janigro. It’s not that the sound that goes into right ear goes to right side of your brain, or the left ear goes to the left side. “They cross so that in the left brain you hear from both ears and in the right brain you hear from both ears.”

Getting high digitally? “I don’t think there is a future in it,” he says.

Then, knowing kids, fads and scams of all types, the researcher quickly corrects himself.

“I don’t think there is any honest future in it.”

What do you think about i-Dosing? Is it a real danger -- or simply B.S., as Janigro puts it? Tell us in the comments.

To read more Body Odd posts, click here. You can also find us on Twitter and on Facebook.

Want more weird health news? Find The Body Odd on Facebook.