The human brain is the most complex and important organ in the body. It is responsible for the coordination and performing of various functions in our bodies; from motor skills to vision, emotions, memory, breathing, and digestion among other processes. limbic system
This is done by transmitting signals back and forth to different parts of the brain. The signals are transmitted across billions of small cells in the brain, neurons, which release neurotransmitters to facilitate the flow of information.
Drugs interfere with the flow of this information by altering the way neurons send, receive, and process signals.
The chemical composition of some drugs may impersonate that of natural neurotransmitters and consequently, create a ‘false positive’ signal which activates the neurons to relay information through the brain’s network.
According to the National Institute on Drug Abuse, three major areas of the brain are affected by drug abuse; the brain stem, the limbic system, and the cerebral cortex.
This article will focus on how drugs impact the limbic system. However, before that, let’s look at how the limbic system functions.
The limbic system
The limbic system is the portion of the brain responsible for emotional, behavioral, and arousal responses.
Frankly, it controls our feelings, whether or not we feel hungry, or thirsty, the conscious and subconscious reflexes, and even the flight or fight responses.
This is made possible by sub-organs which make up the limbic system. They are:
Thalamus
It is responsible for processing all the senses in our body apart from the sense of smell. It detects and transmits to the suitable area in the brain where the appropriate response will be prompted.
Hypothalamus
It is responsible for the production of various hormones required in our bodies. the hypothalamus received messages from different organs of the body and works to keep it stable.
For instance, it controls our body temperature, blood pressure, mood, sex drive, hunger, thirst, and sleep.
Amygdala
Named from their almond-like appearances, the amygdalae are responsible for feelings of fear, anger, anxiety, and pleasure. They are two, each located in each hemisphere of the brain.
This is where our memories acquire an emotional attachment and determines how long they are retained in our minds.
Hippocampus
Like the amygdala and other parts of the brain, the hippocampus is located in each hemisphere resembling a seahorse. It is essentially the memory center of the brain.
Besides forming memories and associating them with specific senses (or triggers), the hippocampus is responsible for neurogenesis- the generation of new neurons from adult stem cells.
Basal ganglia
The basal ganglia perform three paramount roles; it controls the reward processing system, motor learning and control, and habit formation.
Now that we are aware of what the limbic system is in charge of, keep reading to explore how drugs of addiction act on the limbic system.
What happens to the limbic system during addiction?
Drug addiction is defined as a chronic, relapsing brain disorder that causes the inability to resist the urge of using a drug. This way, the user always feels the compulsive need to chase a ‘high’, effects which can linger long after consuming the drug.
Also known as substance use disorder, addiction alters the natural reward system in the basal ganglia by surging signaling compounds and neurotransmitters that produce dopamine and endorphins.
The link between reward pathway and drug addiction
Pleasure, in the brain, is registered the same way regardless of its cause.
Drugs, such as stimulants, nicotine, opioids, and sedatives alike, activate the reward circuit to produce dopamine– a hormone responsible for causing pleasurable feelings.
Naturally, once a pleasurable feeling is produced, our brains are wired to remember it. Dopamine signals induce neural activity which makes it easier to repeat that activity over and over.
After all, the activity still lingers in the human memory and so does the satisfaction it brings forth.
Research reveals that drugs can produce up to 10 times the amount of dopamine produced naturally. Therefore, drugs of abuse work by flooding the reward pathway with dopamine hence, the user feels more inclined to use the drug again.
Over time, the neurotransmitters are naturally desensitized and lesser natural rewards are processed successfully in the brain, that is, other pleasurable aspects of life do not produce dopamine.
As a result, such surges cause changes in the neural activity in the brain, causing it to be reliant on the substance and addiction develops.
Addiction is, therefore, a habit formed in the brain.
The same goes for other neurotransmitters such as:
- Serotonin – is a chemical responsible for mood stabilization, wound healing, sexual desire, and nausea.
- Norepinephrine – also known as the stress hormone, norepinephrine regulates energy levels, focus, and the fight or flight response. Its functions are similar to those of adrenaline.
- Gama-aminobutyric acid –is a natural tranquilizer that alleviates stress and lowers anxiety levels.
Why the need for more and more drugs over time?
As the motivation for substance use to increase the dopamine surges increases, the brain adapts a coping mechanism where less dopamine is produced.
This being so, larger amounts of the substance will be required to raise the dopamine levels to the new normal and hence, feed the addiction. Even more, will be needed to achieve the desired high. This is called drug tolerance.
Nonetheless, the likelihood of a drug-induced reward activity leading to addiction depends on the following factors:
- The speed with which the drug will stimulate dopamine release.
- The intensity of the dopamine release.
- Method of administration of the drug – drugs ingested intravenously will trigger a faster and stronger dopamine signal compared to those swallowed.
- The reliability of the drug to trigger a dopamine signal.
Click here to learn more about the brain recovery timeline from alcohol abuse.