The Brain and Drug Addiction

 

Why are drugs addictive?

Firstly let's start with how the brain works. The brain consists of billions of neurons that form interconnected networks. Neurons send and receive chemical and electrical signals within the brain and to nerves throughout the body. Neurotransmitters are the chemical messengers that neurons release into the synapse which then binds to receptors on the receiving neuron. The neurotransmitters binding to the neurons’ receptors trigger the signaling and communication between neurons and thus a chain reaction of receiving and sending signals is created in the neural network. However, once the neurotransmitters bind to the receptors they are transported out of the synapse and back into the neuron. This controls how long the signalling between the neurons lasts.

In summary, the neuron sends signals through the release of neurotransmitters, which are stopped by the reabsorption of the neurotransmitters back into the signaling neuron and away from the receptors of the receiving neuron.

So what happens when drugs are consumed?

Drugs disrupt the communication between neurons. Many drugs including cocaine and nicotine can bind to the receptors on the neurons because their structures are similar to that of the neurotransmitters. However, when drugs bind to the receptors they do not elicit the same response as when neurotransmitters naturally bind to neurons. Instead, drugs such as cocaine cause neurons to release ample amounts of neurotransmitters and prevent the reabsorption of neurotransmitters from the synapse. This leads to an increased surge of neurotransmitters that also have a longer-lasting effect on the neurons, altering communication in the neural network.

What causes drug addiction?

Dopamine is the neurotransmitter that is commonly released when drugs bind to the receptors on neurons. Dopamine is responsible for feelings of pleasure and euphoria and is part of the reward system in the brain. Naturally, dopamine is released in the nucleus accumbens of the brain when we socialise with people whose company we enjoy, when we eat enjoyable food and when we exercise. By nature, our brain is wired to repeat activities that release dopamine and make us feel euphoric. Hence when dopamine is released our brain reinforces those networks and the memories related to activities that increase dopamine. This means that when we consume drugs which increase our dopamine levels intensely, our brain reinforces our memories of taking the drugs and the euphoric feeling we experience. Over time the surge of dopamine caused by drug consumption causes hyperactivity in the nucleus accumbens and weakens the neural connection to the prefrontal cortex. The weakened connections in the prefrontal cortex reduce impulse control and judgement, leading to repetitive drug use and eventually drug addiction. Eventually, a person develops a tolerance to the drug and larger amounts of the drug are needed to achieve a “high” or euphoric state.

Let's clarify some terminology:

Synapse: the space between neurons where signals are transmitted

Receptors: proteins that molecules bind to, to elicit a specific response (e.g. the release of dopamine)

Nucleus Accumbens: the area of the brain related to reward, motivation and reinforcement of learning. Dopamine is released in this region of the brain.

Prefrontal cortex: the area of the brain responsible for personality, language emotional processing, behaviour and other executive functions