Chapter 9 - Neurobiology of Drug Addiction

Addiction Model

Thought of as a cycle with 3 stages: the 3-stage model

Preoccupation with anticipation stage

preoccupation with obtaining the drug, persistent physiological problems, the idea of taking the drug becomes stronger

Binge Intoxication Stage

Escalated drug usage/frequent intoxication

stems from a persistent desire for the drug, typically resulting in larger doses of drug

Withdrawal Negative Affect Stage

Stopping the drug, but experiencing negative side affects as a result of abstinence, tolerance, compromised social/occupational/recreational activities, ect

consists of bad mood, physical pain, enhanced desire for drug, ect

Reward Citcuit

Pathway in the brain that mediates the acute rewarding and reinforcing effects of most recreational drugs

Mesolimbic DA Pathway

VTA to the Nucleus Accumbens, almost all drugs activate this pathway either by enhancing VTA firing or increasing extracellular DA levels in Nacc

Abused Drugs Firing?

Mimics burst firing

DA receptors

D2 has a higher affinity for DA; therefore only elevated levels will activate D1

D1 is more important for reward than D2, but both play a role in addiction

Incentive Sensitization Theory of Addiction

the distinction between liking versus wanting a reward (the incentive)

Incentive Salience

having the desire to take the drug when in the presence of strong stimuli, despite not wanting the drug

Psychostimulants & Dopamine

DA is necessary for the rewarding effects of psychostimulants

Other drugs and Dopamine

DA is a contributing factor to reward, but not required

Reward-Prediction Error

DA signal the difference between prediction of receiving a reward and actual occurrence of reward

Kyperkatifeia

Negative emotional state evoked by drug withdrawal, proposed to be a core feature of addictive disorders

Within-System Adaptations

results in progressive down regulation of activity

Natural reward is harder to satisfy

Between System Adaptations

Gradual recruitment of antireward system (amygdala)

• put a limit or break on reward

• Activates aversive effects like stress, sadness, pain, ect

Brain Images of Addiction

Shrinks w/ addiction

Dysfunctions in PPFC plays into drug craving, leads to intrusive thinking of drug

Insula implicated with motivational regulation

Thalamus relays drug-induced stimuli to insula

Cue-Induced craving

correlates paired stimulus (drug) with activation of PFC

Behavioral Control Brain Areas

Shifts from striatal areas (pleasure related) to habitual areas (habit)

Ventral striatum to dorsal striatum

“Go” System

motivates and activates learned responses

Inital drug use to addiction invokes an enhancement of the GO system; tunrs from goal directed to behavioral habit

“Stop” System

system that stops the habit

dysfunction of this system, which includes to PFC components

• Leads to intrusive thinking, drug craving, and loss of impulse control

Recovery

Varies in individuals, random cravings can return due to long-lasting changes in the brain that alter gene expression/changes in synaptic plasticity/reward/antireward

Desensitized Gene

expression changes via methylation

Chronic use results in the gene desensitized.

Repressed Gene

Acetylation or Phosphorylation leads to chromatin opening “primed” genes for expression

With too much drug, the gene for specific pathways can be reperssed

Synaptic Plasticity

After 1 exposure of a drug, the brain was changed and maintained it for 5 days

Disease (medical) model

views addiction as a disease, based on evidence for dysregulation of brain function

Moral Model

Addiction was seen as a sign of personal and moral weaknesses

Criticisms of Disease Model

Brain alteration does not prove addiction as a disease

No single diagnostic test to confirm the disorder

empirical evidence raises doubt that heavy drug usage is outside of users control

Non Disease Theories

Argues that addicts choose the drug because it serves a purpose; alleviating pain, lack of positive reinforcement, provides motivation

Contingency Management

Rewarded when tox screen is negative