The Reward System and Mechanism of Addiction in the Brain. This video and similar videos are available for download, upon purchase of a license, on our website: https://www.alilamedicalmedia.com/en ©Alila Medical Media. All rights reserved. Voice by: Tatiana Bardisbanian All images/videos by Alila Medical Media have been prepared for informational purposes only and are not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare professional with any questions you may have regarding a medical condition. Addiction is a neurological disorder that affects the reward system in the brain. In a healthy person, the reward system reinforces important behaviors that are essential for survival such as foraging, reproduction, and social interaction. For example, the reward system makes sure that you seek food when you are hungry, because you know that after eating, you will feel good. In other words, it makes the activity of eating enjoyable and memorable, so that you want to do it again every time you're hungry. Drugs hijack this system, turning natural urges into drug urges. The brain is made up of billions of neurons, or nerve cells, that communicate through chemical messengers, or neurotransmitters. When a neuron is sufficiently stimulated, an electrical impulse called an action potential is generated and travels along the axon to the nerve ending. There, it triggers the release of a neurotransmitter into the synaptic cleft, a space between neurons. The neurotransmitter then binds to a receptor on the neighboring neuron, generating a signal that transmits the information to it. The major reward circuits involve the transmission of the neurotransmitter dopamine from the ventral tegmental area, VTA, in the midbrain to the limbic system and frontal cortex. Engaging in pleasurable activities generates action potentials in dopamine-producing neurons in the VTA. This causes these neurons to release dopamine into the synaptic gap. It then binds to the dopamine receptor on the postsynaptic neuron and stimulates it. This stimulation is thought to produce feelings of pleasure or reward. The dopamine molecules are then removed from the synaptic gap and transported to the sending neuron by a special protein called a “dopamine transporter.” Most drugs increase the level of dopamine in the reward circuit. Some drugs, such as alcohol, heroin, and nicotine, indirectly excite dopamine-producing neurons in the VTA so that they generate more action potentials. Cocaine acts at the nerve ending. It binds to the dopamine transporter and blocks the reuptake of dopamine. Methamphetamine, a psychostimulant, similarly blocks the reuptake of dopamine. Furthermore, it can enter the neuron, into the dopamine-containing vesicles and trigger the release of dopamine even in the absence of action potentials. Different types of drugs work in different ways, but the common result is that dopamine accumulates in the synapse in a much larger amount than normal. This causes a continuous overstimulation of the receptor neurons and is responsible for the prolonged and intense euphoria felt by drug users. Repeated exposures to high levels of dopamine caused by drugs eventually desensitize the reward system. The system no longer responds to everyday stimuli; the only thing that is rewarding is the drug. This is how drugs change the priorities in a person's life. After a while, even the drug loses its ability to reward and higher doses will be needed to achieve the rewarding effect. This eventually leads to a drug overdose.