The reinforcement mechanism Reward circuits The reward system short-circuit Reward, memory, and learning
The reinforcement mechanism
We are faced with the so-called
positive reinforcement: a useful behavior is rewarded to encourage repeating it in the future. Negative reinforcement is the opposite: we tend to avoid repeating unpleasant experiences. Sometimes reinforcement can come from external sources: a material reward, expressions of
affectionWhat is affect according to science? Affect represents one o... More, or compliments are excellent motivators. But the nervous system can provide its own rewards to reinforce behaviors via the reward circuits. How does our brain evaluate and deliver rewards, and why are they particularly important for learning?
Reward circuits
The reward system involves both the frontal cortex and deeper parts of the brain, such as the ventral tegmental area, substantia nigra, nucleus accumbens, and
hippocampusThe hippocampus is a part of the brain located in the inner ... More. Neurons in the ventral tegmental area and substantia nigra are the main producers of
dopamineA neurotransmitter found in the brain and central nervous sy... More. Dopamine is
a neurotransmitter whose release underlies the sensation of pleasure and behavioral reinforcement.
For evolutionary reasons, performing advantageous actions increases our survival capabilities. Thus, the human and animal nervous system has gradually associated performing beneficial actions with the experience of pleasure, mediated here by dopamine. From the ventral tegmental area, dopamine travels through the mesolimbic pathway, a neural circuit inside the brain, to the nucleus accumbens. This area is responsible for encoding motor actions into repeatable processes: it effectively converts motivationMotivation: a scientific perspective Motivation is a fundame... More into repeatable actions.
A second, more “external” circuit, the mesocortical pathway, runs from the ventral tegmental area to the prefrontal cortexThe prefrontal cortex plays a fundamental role in numerous p... More, an area involved in decision-making and evaluating choices, where the association between emotion and reward is consolidated. Finally, dopamine release also strengthens synapsesA synapse is a term used in neuroscience to describe the fun... More in memoryMemory is a fundamental cognitive function that consists in ... More and learning centers, like the hippocampus, and in emotion management areas such as the amygdala"The amygdala is a gray matter structure named after its cha... More.
The reward system short-circuit
The reasons that associate stimuli with pleasure and satisfaction are the same
underlying the effects of common psychoactive substances. The intake of alcohol, nicotine, opioids, and cocaine stimulates dopamine production, creating an association in our brain between the use of these substances and pleasure. This can lead to
substance dependence and, over time,
tolerance, requiring increasing amounts to replicate the effect.
It’s not only about drugs: even if less harmful, “dopamine addiction” can occur with everyday stimuli. Social media, video games, and sugary foods can bombard us with constant rewards, sometimes intentionally designed to do so, and we must be careful not to overuse them. Emotional imbalances or attention deficits can also negatively affect the reward system, dissociating positive behaviors from rewards or linking them to negative ones.
Reward, memory, and learning
Because the reward system circuit is closely linked to memory, it’s no surprise that rewards are fundamental for learning. So-called
associative learning consists in establishing a link between a behavior and a positive outcome, consolidating it via memory. Interestingly, it is more effective not for the reward itself, but for
our expectations about it:
learning occurs when the reward does not match what we anticipated.
If the reward exceeds expectations, we are pleasantly surprised, and dopamine release increases. If it falls short of expectations, so does dopamine release. We are disappointed by the outcome, and a negative association forms in our brain, making us unlikely to repeat the experience. A reward matching our expectations does not alter dopamine release, positively or negatively: we learn nothing new, and the experience has less impact both memorably and emotionally.
These mechanisms can be applied to stimulate learning in children, both at home and in school. Studies in U.S. primary schools on “token economies” seem to support this. In these systems, points, symbols, or small objects (tokens) are given by teachers to reward certain behaviors. Pro-social behaviors (being tidy, not fighting, paying attention, etc.) are rewarded, rather than academic performance itself. Tokens can later be exchanged like currency for prizes or special activities, though sometimes the act of receiving tokens is rewarding enough. Receiving a reward is highly motivating, often more than the reward’s actual value.
- Ewa Galaj, Robert Ranaldi, (2022), Neurobiology of Reward-Related Learning, NeuroscienceThe human brain is one of the most complex and fascinating s... More & Biobehavioral Reviews, Volume 124, May 2021, Pages 224-23
- Ji Young Kim et al, (2021), Systematic Review and Meta-Analysis of Token Economy Practices in K-5 Educational Settings, 2000 to 2019, Behaviour Modification, Volume 46, Issue, https://doi.org/10.1177/01454455211058077
