The idea of drugs tunneling their way through the brain, worms to the mind's apple, is a frequent metaphor I hear. I wrote on the topic for Discovery's Curiosity and resurfaced it to prepare material for drug education talks with high schoolers. Here's a simple look back at the common question, which never fails to remind me just how complex, yet undeniably vulnerable, our brains are:

Drugs may not drill holes actual holes through your brain, but they can turn your mental processing powers into Swiss cheese. Here’s how it works: the brain is filled with different kinds of neurotransmitters, or cells that ferry information. They make our nervous system run and function normally. A good example is a neurotransmitter called dopamine, which fills many roles in the brain, including your motivation, cognition and punishment/reward systems.

Neurotransmitters like dopamine shuttle around and bind to specific receptors to communicate messages in the brain. Drugs can wreak havoc on this system in several ways – they may commit the cellular equivalent of a hostage situation and bind to receptors in the place of neurotransmitters. If this happens, neurotransmitters can’t enter or exit their receptors, and parts of your nervous system can’t communicate with your brain. Worse yet, they can thwart the chemical reactions that create neurotransmitters, your electrical messaging, in the first place. They also may overstimulate or block receptors so that neurotransmitters can’t deliver their messages.

If flooded or blocked, your neuron receptors can become desensitized or oversensitized to neurotransmitters like dopamine. This means your brain isn’t recognizing or receiving the information needed to work your crucial parts of your nervous system, like those that control your emotional or motivation structures. Ultimately, you have “holes” in different parts of your mental systems, and which exact parts depend upon the kind of drug you take.

Here's a video illustrating the concept from BBC's "How Drugs Work" series, describing cocaine's influence on the brain's dopamine.