Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics
in 2 minutes or less. In this installment I will discuss the reward system.
The reward system refers to a group of structures that are activated whenever we experience
something rewarding like using an addictive drug. When exposed to a rewarding stimulus,
the brain responds by increasing release of the neurotransmitter dopamine. Thus, structures
that are considered part of the reward system are found along the major dopamine pathways
in the brain. The pathway most often associated with reward is the mesolimbic dopamine pathway,
which starts in an area of the brainstem called the ventral tegmental area, or VTA. The VTA
is one of the principal dopamine-producing areas in the brain and the mesolimbic dopamine
pathway connects it with the nucleus accumbens, a nucleus found in a part of the brain that
is strongly associated with motivation and reward.
called the ventral striatum.
When we use an addictive drug or experience something rewarding, dopamine neurons in the
VTA are activated. These neurons project to the nucleus accumbens via the mesolimbic dopamine
pathway, and their activation causes dopamine levels in the nucleus accumbens to rise.
Another major dopamine pathway, the mesocortical pathway, also originates in the VTA but travels
to the cerebral cortex, specifically to the frontal lobes. It is also activated during
rewarding experiences and is considered part of the reward system.
Because dopamine is released whenever we use an addictive drug, researchers initially thought
dopamine must be the neurotransmitter that causes pleasure. More recent research, however,
suggests that dopamine activity doesn’t correlate exactly with pleasure. For example,
dopamine neurons are activated before a reward is actually received and thus before the pleasure
is experienced. For this (and other) reasons, it is now thought dopamine has roles other
than causing pleasure, such as assigning importance to environmental stimuli associated with rewards
and increasing reward-seeking.
Whatever the precise role of dopamine in reward is, the mesolimbic dopamine pathway is consistently
activated during rewarding experiences, leading it to be considered the main structure of
the reward system. Regardless, the actual network of brain structures involved in mediating
reward is much larger and more complex than just this dopamine pathway, involving many
other brain regions and neurotransmitters.