2-Minute Neuroscience: Reward System


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.

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