Food intake and brain reward circuits
The dopaminergic system is involved in a large number
of behaviors including reward processing and motivated
behavior. Thus, all drugs of abuse increase the extracellular
concentration of dopamine (DA) in the striatum
and associated mesolimbic regions [7]. Di Chiara’s group
has extensively showed that addictive drugs (e.g. amphetamine
and cocaine) increase extracellular DA in the
nucleus accumbens (NAc), a primary site for reinforced
behaviors [7]. Likewise, microdialysis has shown that exposure
to rewarding food stimulates dopaminergic transmission
in the NAc [8].
Furthermore, neuroimaging studies show that our
brain response is similar in the presence of food and
drug abuse: increased cell activation in the NAc, the
brain’s pleasure center [9–11]. Neuroimaging studies in
humans have also shown similarities between obesity
and addiction. For example, both obesity and addiction
are associated with fewer D2 dopamine receptors in the
brain [12, 13], suggesting that they are less sensitive to
reward stimuli and more vulnerable to food or drug intake.
Thus, for example, individuals with the largest
body mass index (BMI) had the lowest D2 values [13].