Substance Abuse Disorders

Question 1

Describe the positive reinforcement neural mechanism.

Answer 1

• Triggers the release of dopamine in the nucleus accumbens
  
  • Process of addiction begins in the mesolimbic dopaminergic system
  • Produce long term changes in other brain regions – starting with the ventral tegmental area (VTA)
  • Changes in the VTA lead to increased activation in a variety of regions that receive dopaminergic input from the VTA.
  • Synaptic changes that are responsible for the compulsive behaviours that characterise addiction occur only after continued use.
  • Most important changes occur in the dorsal striatum which is part of the basal ganglia
    The basal ganglia plays a critical role in instrumental conditioning.

Question 2

Describe negative reinforcement.

Answer 2

• Not a punishment rather the removal of something unpleasant
  
  • Tolerance - decreased sensitivity from continued use
  • Withdrawal symptoms - generally the opposite of the drug itself.
    ○ The body may have started to compensate for the disturbed homeostatic mechanisms
  • Potentially maintains addiction
    ○ Withdrawal symptoms are unpleasant, taking the drug removes them, producing negative reinforcement
  • Explanation for start of addiction in some scenarios
    Taking a drug to deal with stress or other problems

Question 3

Why can some people use drugs and not become dependent?

Answer 3

• Genetic and environmental factors influence whether someone is likely to take the substance in the first place and their likelihood of becoming dependent
  
  • There are both general factors and drug specific factors

Question 4

Therapy for drug abuse

Answer 4

• Immunotherapy
  ○ vaccines specific to the substance abused
• Deep brain stimulation (DBS)
  ○ DBS of the NAC has had some promising effects, however it is a high risk procedure.
• Transcranial magnetic stimulation (TMS)
  ○ TMS is less invasive and has shown efficacy in reducing tobacco use but the effects on nicotine use diminished over time.