05. Psychobiology Motivation

AUD vs SUD

Alcohol Use Disorder vs Substance Use Disorder

Phytochemistry

Chemicals synthesised by plants, humans have exploited these for years

E.g. nicotine, caffeine, alcohol, cocaine etc.

Implications of Substance Abuse

• May be an inheritance of evolutionary past, used for survival advantages and adaptive benefits

• Most cultures have consumed substances for health or ritualistic reasons

Oral ingestion

• Drugs dissolve in the stomach and are carried to intestine, where they are absorbed into the bloodstream

• Some pass through the stomach wall and act sooner, some are metabolised by the liver reducing concentration

Implications of Oral Ingestion

• Somewhat safer than other methods

• Effects can be unpredictable, delayed action

• Rate can depend on other factors like food in stomach

Injection

• Drugs can be injected into fat under the skin, muscle or a vein

• Blood takes the drug directly to the brain

Implications of Injection

• Fast and predictable

• Little to no opportunity to counteract the effects of overdose, impurity or allergic reaction

Inhalation

Some drugs can be absorbed through capillaries in the lungs

Implications of Inhalation

• Difficult to regulate the dose

• Causes lung damage

Mucous membranes & Implications

• Some drugs can be absorbed through mucous membranes in the nose, mouth and rectum

• Can cause damage to membranes

Drug penetration

• Following administration, drug will enter the bloodstream

• Drugs must cross the blood-brain barrier to exert an effect

• Psychoactive substances typically have small molecules that can pass through easily

Drug action

• After passing the BBB, drugs then influence the nervous system

• Some drugs act on lots of different membranes throughout the CNS

• Others are more specific and bind to synaptic receptors

Tolerance

A state of decreased sensitivity to a drug that develops because of repeated use, and a greater dose is now required to produce the same effect

Withdrawal

Sudden elimination can trigger adverse reactions, dependent on duration and degree of drug use and speed of elimination

Developments of an A/SUD

• Experimental drug use

• Casual drug use

• Heavy drug use (abuse/misuse)

• Compulsive drug use (dependence)

• AUD/SUD

Cost-benefit analysis of drug use

• Benefits: pleasurable high, increased alertness, social aspects

• Costs: hangover, illness, death

Addiction as a Disease (Leshner, 1997)

• All abuse of drugs affect a pathway deep within the brain (directly or indirectly)

• Drug use causes changes in brain structure and function

• The ‘addicted’ brain is different than the non-addicted brain in structure and function

‘Reward systems’ in the brain

• Mesocorticolimbic pathway: the M pathway, changes with SUDs

• Mesolimbic dopamine system: the VTA and areas that project to and from it

• Mesolimbic pathway: VTA to the limbic forebrain

• Mesocortical pathway: VTA to the prefrontal cortex

Dopamine

Dopamine release can mean an experience of pleasure or reward, triggered with drug-related cues as well as natural rewards

Incentive Salience (Robinson & Berridge, 1993; 2003)

• Repeated drug use leads to a sensitised spike in DA activity in the Mesolimbic pathway

• Also found when presented with drug related cues

• Exaggerated dopamine response manifests as incentive salience

Wanting and Liking

• Wanting and liking drugs are served by different neural systems

• Drug wanting increases while drug liking can decrease

Incentive sensitisation theory: withdrawal and relapse

• Sensitisation process lasts a long time, even after negative effects of withdrawal are gone, the brain’s neural system underlying ‘wanting’ is sensitised

• Long-term risk in relapse, even after years of abstinence, due to this ‘want’

IST & Learning

• Associative learning processes increase the likelihood of wanting a drug when in the place where you associate taking that drug

• Classical conditioning and relating a reward to taking a drug can lead to sensitisation

• Drug addicts show cognitive impairment, affecting executive function, decision making and inhibitory control

Inhibitory Control

• Self-control becomes diminished, while drug salience, learned responses and motivation to obtain the drug increase

• IC allows people to inhibit dominant behavioural responses

Role of Inhibitory control

Poorer IC predicts hazardous drinking, relapse, escalation of heavy drinking, and alcohol involvement in adolescence