Reward system

The reward system is a special group of parts in the brain that helps us feel motivated and happy. It is also called the mesocorticolimbic circuit. This system makes us want things we need or enjoy, like food, water, or affection from our parents. It also helps us learn by connecting actions with good feelings. For example, when we eat something tasty, our brain feels pleasure, which makes us want to eat again in the future.

This system is very important because it helps animals, including humans, stay safe and healthy. It encourages us to do things that help us survive, like finding food or taking care of our families. Over time, this system has helped animals live better by guiding them toward helpful actions and away from dangerous ones.

Sometimes, certain substances can overstimulate this reward system, making people want them too much. This can lead to behaviors that are hard to control. Understanding how the reward system works helps scientists learn more about how our brains guide our choices and feelings.

Definition

The reward system in the brain helps us learn from good experiences and feel happy. It controls things like wanting something we like and feeling joy when we get it. Activities that feel good, such as eating, playing, or spending time with friends, increase a brain chemical called dopamine. Dopamine helps us feel motivated and happy.

Rewards help us learn by linking actions with good results. They also help us decide what to do next and make us feel positive feelings, especially pleasure.

Neuroanatomy

Overview

The brain has special parts that help us feel happy and want things. These parts work together in a loop called the cortico-basal ganglia-thalamo-cortical loop. They use special messages, like dopamine, to tell our brain when something is good or helpful.

These parts include the ventral tegmental area, ventral striatum, dorsal striatum, substantia nigra, prefrontal cortex, anterior cingulate cortex, insular cortex, hippocampus, hypothalamus, thalamus, subthalamic nucleus, globus pallidus, ventral pallidum, parabrachial nucleus, amygdala, and more. They help us learn from good things, feel happy, and decide what to do next.

Key pathway

Ventral tegmental area

The ventral tegmental area is important for noticing when something good might happen. It sends messages to other parts of the brain to make us feel happy.

Striatum (Nucleus Accumbens)

The striatum helps us learn to do things that feel good. It gets messages from the ventral tegmental area to start actions that we like.

Prefrontal Cortex

The prefrontal cortex helps us decide what to do based on what might feel good. It talks to other parts of the brain to help us choose.

Hippocampus

The hippocampus helps us remember where and when good things happened, so we can do them again.

Amygdala

The amygdala helps us feel strong emotions and remember important moments that feel good.

Pleasure centers

Some parts of the brain make us feel happy when we get something good. These are called pleasure centers. They include parts of the nucleus accumbens, ventral pallidum, parabrachial nucleus, orbitofrontal cortex, and insular cortex. When these parts work together, they can make us feel very happy.

The Reward System during Adolescence

The brain's reward system keeps growing until we become adults, but it is especially active during teenage years. This helps teenagers learn and make decisions. During this time, the brain is very sensitive to new and exciting things, which can lead to trying new activities or taking risks. The way the brain processes rewards changes during adolescence, affecting how teenagers behave and learn.

Wanting and liking

Main article: Incentive salience

Incentive salience is all about "wanting" or feeling a strong desire for something that feels good. This happens thanks to a part of the brain called the nucleus accumbens shell, which gets messages from another area called the mesolimbic pathway.

People and even animals can feel like they want something without it feeling good to them, and vice versa. For example, sometimes we might really want chocolate even if it doesn’t taste as good as we remember. Scientists have found that the brain has separate systems for wanting something and for liking how it feels. Wanting is linked to certain brain messages, while liking involves other chemical systems in the brain.

Anti-reward system

Scientists have found that there is a special part of the brain that helps slow down our desire for things like food or fun activities. This part, called the anti-reward circuit, works like the brakes on a bicycle. It helps us not to want something too much.

This circuit includes parts of the brain such as the amygdala and the Nucleus Accumbens, along with certain signal molecules. It is also thought to help us handle stress and may play a role in habits that are hard to break. While the reward circuit gives us positive feelings at first, the anti-reward circuit later helps us feel bad when we can’t get what we want.

Learning

Further information: Associative learning

Rewards help us learn in two main ways: classical conditioning and operant conditioning. In classical conditioning, a reward can make us connect two things. For example, if you see a bell ring just before getting a treat, you might start to expect the treat when you hear the bell.

In operant conditioning, a reward makes us repeat actions that led to it. This helps us learn which actions bring good results. Some learned behaviors depend on the results they bring, while others become habits we do without thinking much about the results.

Different parts of the brain help us make these connections. Rewards play a big role in learning by helping us remember what leads to good things.

Disorders

Addiction

Main article: Addiction

Addiction happens when certain brain parts change how they work, making it hard to stop wanting something. This change is linked to a special protein called ΔFosB that builds up in a part of the brain called the nucleus accumbens. This protein helps make things feel really good and keeps people wanting more.

Drugs and some behaviors can make the brain release a chemical called dopamine, which makes us feel happy and want to do the thing again. This is why some things can be so hard to stop doing, even when they’re not good for us.

Motivation

Main article: Motivational salience

When the brain’s reward system doesn’t work right, it can affect how we feel motivated or happy. Some people might not feel much pleasure from things they usually enjoy. Others might feel a strong desire for certain things, like drugs.

In teens, the reward system is still developing, which can make them more likely to take risks or try substances. The brain area called the ventral striatum plays a big role in how we feel rewards and anticipate them.

Mood disorders

Some types of depression are linked to lower motivation and feeling less pleasure. Studies show that parts of the brain involved in feeling rewards might not work as well in these cases. Scientists are still learning more about how these brain areas change in depression.

Schizophrenia

People with schizophrenia often have trouble feeling motivated. They might still enjoy simple rewards, but have a harder time with more complicated tasks that need thinking. This is linked to changes in brain areas that help us process rewards and think.

Attention deficit hyperactivity disorder

Individuals with ADHD often find it harder to feel rewarded from everyday activities. They might feel a big boost of motivation after doing something very exciting, but then feel a quick drop in motivation afterward. This is connected to how dopamine, a brain chemical, works in their brains.

History

The first hint that the brain has a reward system came in 1954 from James Olds and Peter Milner. They found that rats would press a bar many times just to get a small electric pulse in certain parts of their brains. This is called intracranial self-stimulation or brain stimulation reward. The rats did this so much that they would press for hours, stopping only when tired. The researchers thought this stimulation activated the brain’s reward system, giving the animals a feeling of pleasure.

Later studies showed that a brain chemical called dopamine plays a big role in this system. In 2018, scientists also found that nutrients from the gut could trigger the reward system through a nerve in the neck. Earlier, Ivan Pavlov had studied how rewards help learning. He gave dogs food after a bell rang, so the dogs learned to connect the bell with food. Edward Thorndike also used rewards to study learning, by placing cats in boxes and letting them escape to get food. He found that the cats learned to escape even without the food reward.

Other species

Animals can learn to press a bar to get injections into certain parts of their brains. This shows they are motivated by rewards, just like humans. Research has found that animals and humans share similar reactions to pleasant and unpleasant tastes.

Studies have shown that the release of a brain chemical called dopamine affects how rewarding something feels. Even when dopamine is blocked, animals still show they enjoy sweet things, which suggests there is more to pleasure than just dopamine. Research also shows that changes in dopamine levels can affect how much pleasure people feel when listening to music. This helps explain why some people feel strong cravings for things even when they no longer enjoy them.