The consumption of psychoactive substances is primarily hedonic before the development of addiction. To be reinforcing, drug-induced dopamine increases need to be fast and sufficiently large to stimulate low-affinity dopamine D1 receptors in addition to D2 receptors. D1 receptor stimulation in the nucleus accumbnes (NAc) by itself is sufficient to produce drug reward, whereas D2 receptor stimulation is not. While dopamine stimulation of D1 receptors in the direct pathway signals the expectation for the reward, dopamine stimulation of D2 receptors in the indirect pathway is more likely to sustain the motivation needed to procure and consume the reinforcer. The transition from controlled to compulsive drug taking has been associated with a shift in the involvement of striatal subregions, implicated in the rewarding response to drugs, to the dorsal striatum that is associated with habit formation. In addition to the reward system, an anti-reward system is involved. Positive reinforcing (pleasure/satisfaction) is more associated with impulse control disorder, negative reinforcing (relief from anxiety and stress) with compulsive disorders. Collapsing cycle of impulsivity and compulsivity results in an addictive cycle. The temperance limits (delays) the development of addiction in a vulnerable individual. Disturbed hedonic interpretations are associated, for example, with ambihedonia or parahedonia. lt would be interesting to scale the pathology of the quality of hedonia in substance induced disorders. The dark side of addiction is related to the development of allostatic changes. The extended amygdala (central nucleus of the amygdala, bed nucleus of the stria terminalis, and the NAc shell), lateral habenula, corticotropinreleasing factor (CRF), and norepinephrine are responsible for these allostatic changes. Upregulation of the dynorphin K-opioid receptor system (KOR) has been associated with the dysphoria and the increased sensitivity to stress during drug withdrawal. Perspectively, addiction treatment could focus on, among other things, reducing the reactivity with stress associated circuits.

Key words: anhedonia – ambihedonia – pseudohedonia – parahedonia – dyshedonia – alostase – addiction cycle – dark side of addiction