I remember the night I first realized I would die. It was winter in the early ’90s, I was 7 or 8, and I laid on my guard-railed bed pestering my parents with direct questions about how long humans lived. Eventually one of them cracked and explained the difference between “a really long time” and “forever.”

I had wanted them to assure me that humans lived on and on and on, but I guess I’d already sort of sussed out that this couldn’t be the case. Before things got too horrific, they shut off the light and went downstairs, and I lay in bed wondering what the world would be like without me in it, and what thoughts would race through my head in my last moments of consciousness as I realized I was dying: my mind and soul catapulting down a dark elevator shaft, or perhaps swirling in the toilet bowl of infinity. I had circles under my eyes at school the next day. For the remainder of the week, I was like a goyish female Alvie Singer. There was little mirth in my four square-playing or crustless sandwich-inhaling. But as with most things relating to youth, this despair eventually subsided, and I was able to adopt that blithe forgetfulness about my own mortality—at least until many years later, when I first got The Fear.

What is The Fear? Besides the obvious (it’s fear!), it’s the sensation you get when you smoke too much weed and become ensnared in a vivarium of freakish, circus-like physiological symptoms that paint messages on the glass walls of your consciousness, proclaiming: YOU ARE CERTAINLY GOING TO DIE, EITHER SOON OR RIGHT NOW. When I first experienced The Fear, I got hooked on the idea that my body had become like the bus in Speed. As I hyperventilated on the floor, all I could picture was my body as a rickety service vehicle, my heart as a bomb, and no Keanu to tell my brain that the pot crop had not, in fact, been sprayed with rat poison. I threw up. I cried. Later, there was no question that my symptoms were mental as opposed to physical. In actuality, I was lying on my floor shaking a soda bottle of panic inside an otherwise functional corpus.

A smoker learns to combat The Fear with an ever-growing weed crisis toolbox: Statistics that say it’s nearly impossible to die from smoking too much Grape Ape; the power of a warm bath; an extra-large pizza followed by an emergency bedtime. But The Fear can teach you two valuable lessons. The first is that one can get better at being stoned, more in control and self-aware, and triumph over The Fear with practice. The second is that, for better or worse, marijuana simultaneously enhances sensory perception and unlocks a door to a highly imaginative, vivid mental space. Your relationship to your body and your surroundings becomes so different that it can be frightening. With time, you can learn to Photoshop your fright into some close neighbor of enlightenment.

I wanted to figure out exactly what marijuana does to the brain to make your living room into Super Mario World, but that’s not as easy as it sounds—especially since I got a C in high school biology. So I got in touch with Dr. Lester Grinspoon, a marijuana luminary of sorts and retired associate professor emeritus at Harvard Medical School. He didn’t just write the book on pot (Marihuana Reconsidered, 1971), he wrote several. He was buddies with Carl Sagan and regrets misplacing the note from John Lennon he received after serving as an expert witness in his deportation hearing. At 83 years old, he is the coolest person I have talked to on the phone since I conference-called myself while astral traveling.

Given my particular history with the drug, I was especially interested in asking Grinspoon how pot makes our brains into crazy-scheme assembly lines. Grinspoon attributes this phenomenon to what he calls “enhancement” of human capacities. Two of these—sex and eating—are actually vital to our survival. Grinspoon claims that the degree of enhancement varies with the user (but, as with combating The Fear, can get better with practice). In his online collection of essays, Marijuana Uses, Grinspoon writes about the first time he felt the positive effects of smoking weed:

The first thing I noticed, within a few minutes of smoking, was the music; it was “Sgt. Pepper’s Lonely Hearts Club Band.” … I told John [Lennon] of this experience and how cannabis appeared to make it possible for me to “hear” his music for the first time in much the same way that Allen Ginsberg reported that he had “seen” Cézanne for the first time when he purposely smoked cannabis before setting out for the Museum of Modern Art. John was quick to reply that I had experienced only one facet of what marijuana could do for music, that he thought it could be very helpful for composing and making music as well as listening to it.

So how come, asks the C-average biology student, we don’t know exactly why the brain reacts that way to an ill blunt, yo? The endocannabinoid system, a crew of lipids and receptors that play roles in appetite, pain sensation and mood, is widespread throughout the brain. There’s a lot to explore, from the prefrontal cortex (birthplace of your ideas for creative nachos) to the stodgy old hypothalamus (which tells you when you’ve hadenough of those nachos). “How are we going to understand this scientifically? We’re going to find out what parts of the brain it affects,” says Grinspoon. But more scientific investment, like the studies being conducted abroad to discover how marijuana can treat Crohn’s disease and Parkinson’s, needs to come first.

So we shook our heads over the phone at the fact that there is simply not enough research to satisfy my curiosity of how to isolate the brilliant-idea effects of marijuana and silence the region that tells me to instead watch the Morgan Freeman parallel universe special again.

Had I not been busy barfing my brains out when I got The Fear, I might have reflected on The White Album. It was the backmasking of my own stoned imagination—the track that whispered “Tess is dead man, miss her, miss her” when played backwards, an almost imperceptible suggestion as I roamed the merry streets of Providence, ignoring my heartbeat. Marijuana unlocks some pretty crazy neurological doors, hidden hallways that riddle your brain. And yet a comprehensive answer to what it does, and could possibly do, is still eerily elusive. Just as you can’t unhear backmasking, visiting the strange land of the neurotransmitter anandomide or wading across the delicious fried egg geyser of your brain on drugs leaves you with a great slideshow to play when you’re sober.

“When I make a serious decision about something, I always like to think about it two ways: stoned and straight,” Grinspoon says. “Straight has the final say. But my straight self is able to encompass what I’ve explored while I was stoned, and to judge it by a straight scale, so to speak.”

My experience of thinking about my own death as a child wasn’t so different from my college experience of believing I would die wearing dirty pajamas from a rat-poisoned dime bag. But for some reason, the latter freakout gave me some comfort in retrospect. I felt as though I’d faced a years-incubated fear in some hidden neural cul-de-sac, battled it like a fanged dragon, and passed out in a victorious heap while listening to Dick’s Picks. It was an illusion, of course, but that’s the thing about the human brain: There’s something hyperreal about what goes on in there, especially when it’s all lit up with cheeba neon.

Stoners will not all write “Sgt. Pepper’s Lonely Heart’s Club Band.” The grandparents among us might not even enjoy listening to it. But we could become closer friends with a different side of our brains, and a different side of ourselves.