Normal Communication in the Brain
When the brain is healthy, the cells which compose it are constantly communicating with each other. These cells (called neurons) are linked into complex networks and send signals throughout these networks. When one neuron in the network becomes stimulated, an electrical pulse flows down the cell’s body to the end of the cell (called the synapse).
When the signal reaches the synapse, chemicals called neurotransmitters are released into the space (called the synaptic cleft) between the active neuron and the next neuron in the network. On the outside of the second neuron are small structures called neuroreceptors. The neurotransmitters fit into these receptors like keys in a lock. When the key gets inserted into the lock, the next neuron becomes stimulated and sends a signal down its body to the synapse, thereby stimulating the next neuron in the chain.
How Drugs Affect Communication in the Brain
Although different kinds of drugs operate on the brain in various ways, in nearly all cases drugs taken to alter one’s state of mind work by tampering with this communication system. For example, some drugs contain chemicals (such as THC in marijuana) which mimic the behavior of certain neurotransmitters. When THC is present in the brain, it stimulates the neurons in certain networks, causing abnormal levels of activation. Drugs like cocaine work by blocking the little pumps which then brings the neurotransmitter dopamine back into the neruon which released it. By blocking the reuptake of dopamine, cocaine causes increased levels of dopamine to be available in the synaptic cleft, and this leads to higher levels of stimulation in these neurons.
Tolerance and Addiction
When a particular drug is ingested repeatedly over time, the brain develops a tolerance to it. The primary way it does this is by adjusting the number of neuroreceptors on the neuron. So, for example, when a person develops a tolerance to cocaine, this is because the number of dopamine-specific neuroreceptors have been reduced. This means that there are less “locks” for the dopamine “keys” to be inserted into. Thus, even though cocaine would still block the reuptake of dopamine, the excess dopamine in the synaptic cleft no longer can stimulate the neuron at a higher rate because there are not as many neuroreceptors for it to bind with.
Tolerance will tend to increase over time, and this can ultimately lead to addiction. This occurs as a result of the damage caused by the severe and prolonged adjustment of neuroreceptors in the brain. For example, a person who has become addicted to cocaine has many fewer dopamine neuroreceptors than an average individual. This means that it takes significantly more dopamine than usual for these neurons to fire. Since dopamine is responsible for reward and happiness, cocaine-addicted individuals need to bring about abnormally-high levels of dopamine in order for their brain to properly produce certain positive emotions.
In response to this, the individual will become strongly motivated to ingest more cocaine in order to obtain a feeling of normalcy. At the same time, the brain will continue to downregulate dopamine receptors, making the drug less and less effective. The person will then need to obtain even more of the drug in order to achieve the same results as before.
The absence of cocaine will also produce physical withdrawal symptoms, where the body undergoes a series of unpleasant bodily sensations. In order to avoid withdrawal, the individual will become even more motivated to take more of the drug, thereby causing more damage to the brain.
Recovering from Addiction
The good news is that through seeking help, individuals suffering from drug addiction can recover. This process can take time, and involves many different components, but one of the most important processes occurs as the brain recovers from the addiction. It does this primarily by readjusting the number of neuroreceptors in the brain to their earlier numbers. By doing this, the brain is able to function properly again, and no longer needs the drug in order to be healthy.