In 1987, the Partnership for a Drug-Free America aired a public service announcement that went on to become a classic of modern pop culture. It likened an egg to "your brain" and a hot pan to "drugs." The egg was then fried in the pan, and the viewer was informed that "this is your brain on drugs." The ad concluded: "Any questions?"

Presumably this was meant to be rhetorical, but now the ad is back in a revamped form, which includes children asking questions about drugs. "Mom, Dad, did you ever try drugs?" asks one child.

I, for one, have questions about the egg-based metaphor itself. Because while effectively conveying the message that drugs are bad, which was no doubt the intention of the ad, it is crude, misleading and even potentially stigmatizing.

For starters, there's no known drug that affects every part of the brain at once, frying or scrambling its proteins. Such a drug would be instantly lethal. It's unlikely that anyone would take the comparison that seriously, but the important thing to remember is that drugs don't instantly damage or destroy the brain — they infiltrate it.

Here's an exceedingly brief lesson in how the brain works: All activity is based on signals passed along and between neurons. Neurons signal each other using chemicals known as neurotransmitters, which travel from one cell to the next across the synapses.

Drugs can mimic these neurotransmitters, amplifying their effects. They interact with neurological systems that govern pleasure and reward sensations, and they can do this because the brain recognizes them at a molecular level.

What this all means is that drugs induce activity in the brain where there shouldn't be any. Some drugs, like cocaine, mimic the neurotransmitter dopamine, leading to increased focus and energy and to pleasure in the mesolimbic reward pathway. Other drugs, like heroin, induce activity in areas of the brain that suppress pain and cause euphoria. Marijuana acts on cannabinoid receptors in the regions that cause relaxation and a pleasant buzz, as well as interfering with memory.

The whole egg-in-a-frying-pan metaphor is, then, completely inaccurate. As if that weren't bad enough, it encourages the belief that anyone who uses drugs, in any capacity, is reckless, thoughtless and just plain stupid. Only an idiot would consume a substance that dangerous.

So what would be an accurate metaphor?

Since drugs alter existing levels of activity in the brain, that takes a toll on cells over time, exhausting and degrading them. You could say that the brain is like a car engine and drugs are the gas pedal. It's exciting and exhilarating to step on the gas — at least for a while. But overuse will make the engine splutter and smoke, and there's a much greater risk of doing damage to yourself at high speeds.

That metaphor doesn't quite cut it, though. The brain, a very flexible organ, also adapts to drug-induced activity. For example, when heroin increases activity in the pain-suppression regions of the brain, the brain also increases sensitivity to pain, bringing things back into balance. It gets so that the brain needs regular hits of the drug to maintain normal functioning. Hence, tolerance and addiction, where users have to constantly increase the dose to achieve the same effect.

Rather than an egg, perhaps the brain is like a generator, and drugs are the devices and appliances that need power. The more there are, the more the generator needs to increase its output. Then more appliances are added, so more power is needed, and you get an ever-more-demanding feedback loop.

What's worse is that drugs can make the brain turn on itself, with some parts trying to limit the effects of the drugs, while the more pleasure-focused areas actually interfere with the higher-reasoning centers. That gives users a warped sense of priorities that makes them value the drug above all else.

Maybe the brain is like a computer and drugs are malware, directing the computer's resources to its own ends despite the detriment to the whole system. So a more accurate metaphor for a brain on drugs would be a high-speed, power-generating, malware-infecting car. Obviously, such a thing doesn't exist.

The truth is, the effects of drugs on the brain are very complex and vary from person to person. To deal with drugs and the issues they cause in society, you need an approach that acknowledges this inherent complexity and takes into account the various biological, psychological and sociological factors that perpetuate their use. Fried eggs are delicious, but they aren't subtle.

— Dean Burnett is a neuroscientist who teaches at Cardiff University.

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