Sciences de la Santé
Amygdala
Hippocampus
Pre-frontal cortex
Ventral
tegmental area
Lateral
Hypothalamus
Nucleus
accumbens
Figure 1 - The reward circuit
stimulus) that had not been predicted. In contrast, a
decreased level of dopamine would signify that the
reward is absent or less than expected. Finally, if the
reward is just as expected, the dopamine neurons re-
main at the basal firing rate.
In terms of behavior, these results actually
mean that, as long as there is no change in the envi-
ronment (i.e. the reward is exactly as expected), there
is nothing to learn and no need to change the behav-
ioral response. In contrast, when the response is not
as expected, the changes in dopamine level influence
future responses to stimuli to focus on bigger rewards
and avoid fruitless pursuits of non-rewarding situa-
tions.
Addictive drugs action fundamentally differs
from that of natural reward as they cause DIRECT do-
pamine release in the reward circuit, no matter what.
Therefore, according to the theory above, the brain
would always interpret this signal as a reward bet-
ter than expected, or if you prefer, a really rewarding
reward...Thus influencing behavior toward maximum
drug-seeking and drug-taking.
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Été 2018
This is just the beginning of the process. As
the drug consumption continues for a long time, pro-
gressive plasticity and changes in the neuronal cir-
cuits occur, specifically in the prefrontal regions and
their associated circuits. This results in a serious im-
pairment of higher functions, like self-regulation, de-
cision making, flexibility and error monitoring. Thus,
the addicted person loses control over drug use and
becomes focused only on drug taking, dominating all
other pursuits despite serious negative consequences.
These effects explain why the persons can be sincere
in their desire and intention to stop their addiction
and yet simultaneously unable to do that.
Finally, memory also plays a major role in ad-
diction. All the drug related cues, including environ-
ments in which a drug has been taken, persons with
whom it has been taken, and the mental state of a
person before it was taken are stored in memory. Any
exposure to these cues can awaken the crave of con-
sumption even years after drug abstinence. Some-
times, it can even reproduce the same euphoric state
independently of drug consumption. This explains