The reward pathway
Dopamine neurons projecting from the ventral tegmental area to the nucleus accumbens and prefrontal cortex reinforce behaviours such as eating, sex and social contact. Nicotine, alcohol, cocaine and opioids raise dopamine there far more strongly and quickly than natural rewards.
Tolerance and withdrawal
- Tolerance: neuroadaptation such as fewer or less responsive receptors means larger doses are needed for the same effect.
- Withdrawal: without the drug the adapted brain loses balance, producing anxiety, dysphoria and physical symptoms such as alcohol tremor or opioid pain.
George Koob links this to opponent processes and stress systems such as CRF, so use shifts from seeking pleasure to escaping distress.
The three-stage cycle
Koob and Volkow describe a cycle of binge/intoxication (basal ganglia), withdrawal/negative affect (extended amygdala) and preoccupation/anticipation (prefrontal cortex), with weakened prefrontal control making impulses hard to resist.
Incentive sensitisation
Robinson and Berridge argue that addicted people come to want drugs more without liking them more, so drug cues trigger intense craving and relapse.
Behavioural addictions
DSM-5 lists gambling disorder with addictive disorders and internet gaming disorder as a condition for further study, while ICD-11 (2019) includes gaming disorder. Evidence on other behaviours, such as smartphone overuse, is still debated.
References
- Koob, G. F., & Volkow, N. D. (2016). Neurobiology of addiction: A neurocircuitry analysis. The Lancet Psychiatry, 3(8), 760-773.
- Robinson, T. E., & Berridge, K. C. (1993). The neural basis of drug craving: An incentive-sensitization theory of addiction. Brain Research Reviews, 18(3), 247-291.
- Volkow, N. D., Koob, G. F., & McLellan, A. T. (2016). Neurobiologic advances from the brain disease model of addiction. New England Journal of Medicine, 374(4), 363-371.
- American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). APA.