PSY1EFP Lecture Notes - Lecture 6: Functional Magnetic Resonance Imaging, Nucleus Accumbens, Sympathetic Nervous System
18 Jun 2018
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EFP Lecture 6 Session 1 – Brain Behaviour Relationships (6)
People Use and Abuse Many Psychoactive Drugs
Drugs have been used throughout history to create altered states.
-Around 317 million people use illicit drugs each year (United Nations Office on Drugs and Crime, 2013b).
-Other widely used drugs include alcohol, prescription medications, caffeine, and nicotine.
Drugs are useful in the treatment of many medical conditions, but recreational drug use can have negative
consequences.
- Addiction: drug use that remains compulsive despite its negative consequences
Pleasure Centres
Intracranial self-stimulation: self-administered shock to pleasure centres of the brain
Starving rats prefer ICSS to food over 80 percent of the time
The neural mechanisms underlying both ICSS and natural reward appear to use the same neurotransmitter:
dopamine
This suggests dopamine serves as the neurochemical basis of positive reinforcement in operant conditioning
Interfering with dopamine eliminates self-stimulation as well as naturally motivated behaviours
Dopamine activity underlies reinforcement
Positive reinforcement works in two ways:
-provides the subjective experience of pleasure
-increases wanting for the object or event that produced the reward
The neurotransmitter dopamine is involved in addictive behaviour and plays an important role in reinforcement
Dopamine and Reward
The nucleus accumbens is a subcortical brain region that is part of the limbic system
More dopamine is released under deprived conditions than under nondeprived conditions
-Do you have the intuition that food tastes better when you are hungry?
Dopamine appears to be especially important in wanting a reward
Love really is like a drug
Tests on 15 American students who admitted to being in the passionate early stages of a relationship showed
that feelings for their partner reduced intense pain by 12% and moderate pain by 45%.
In the study, researchers at Stanford University showed eight women and seven men photographs of their
partners while delivering mild doses of pain to their palms with a hot probe. At the same time, the students had
their brains scanned by a functional magnetic resonance imaging machine. At the end of each test, the students
were asked to rate how much pain they felt.
Feelings of love, triggered by a photo of their partner, acted as a powerful painkiller. Brain scans revealed that
these feelings caused more activity in parts of the brain that are also triggered by morphine and cocaine. Looking
at an image of an attractive friend rather than their partner had only a mild analgesic effect.
"One of the key sites for love-induced analgesia is the nucleus accumbens, a key reward addiction centre for
opioids, cocaine and other drugs of abuse. The region tells the brain that you really need to keep doing this."
People use and abuse many Psychoactive drugs
Psychoactive drugs: mind-altering substances that change the brain’s neurochemistry (marijuana, opiates)
Stimulants are drugs that increase behavioural and mental activity and activate the sympathetic nervous system.
-Amphetamines, methamphetamine, and cocaine are potent stimulants.
-Nicotine and caffeine are mild stimulants.
-Some stimulants work by interfering with the normal reuptake of dopamine.
Depressants: reduce behavioural and mental activity by depressing the central nervous system
-Alcohol is the most widely used depressant.
-Anti-anxiety drugs, such as benzodiazepines
Opiates, sometimes called narcotics
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-Heroin
-Morphine
-Codeine
Opiates have been used to relieve pain and suffering for hundreds of years.
Hallucinogens: sometimes called psychedelics, produce alterations in cognition, mood, and perception.
-The most common hallucinogen is lysergic acid diethylamide (LSD).
-Peyote cactus and psilocybin mushrooms produce hallucinogenic effects.
Amphetamines and Methamphetamine
Long history of use for weight loss and staying awake
Seldom used for legitimate medical purposes
-Methamphetamine: The National Survey of Drug Use and Health for 2012 estimates that over 4 percent of
the U.S. population ages 12 and older have used methamphetamine.
Increases dopamine production; blocks reuptake
Causes considerable physical damage
Composite brain scan highlighting areas damage due to Methamphetamine
This image is a composite of brain scans from 29 methamphetamine addicts. The red and yellow areas represent
the brain damage that typically occurs in the frontal cortex as a result of methamphetamine abuse. Such damage
may explain the cognitive problems associated with methamphetamine use.
Icestralia
Ice causes hallucinations, aggression, paranoia, delusion and impaired memory
The number of 15 to 24-year-olds dependent on the drug has more than doubled from 0.4% in 2009-1-0 to 1.14%
in 201314
Cocaine
Stimulant derived from the leaves of the coca bush
-Users experience increased alertness, confidence, and sociability.
-Increases concentration of dopamine levels at synapses
-Habitual use of cocaine in large quantities can lead to paranoia, psychotic behaviour, and violence.
Coca-Cola
Alcohol
Alcohol produces its effects by activating GABA receptors.
-Through its effects on GABA receptors, alcohol inhibits neural activity, which may be why it is typically
experienced as relaxing.
-GABA reception may also be the primary mechanism by which alcohol interferes with motor coordination
and results in slowed reaction time and slurred speech.
-Alcohol is a factor in about one-third of fatal accidents.
Marijuana
Most widely used illicit drug
-Not easily categorized as a stimulant, depressant, or hallucinogen
-Produces a relaxed, contented mood and more vivid perceptions
-The psychoactive ingredient in marijuana is tetrahydrocannabinol (THC).
-Operates at the cannabinoid receptors. Heavy long-term use of marijuana is associated with a smaller
hippocampus and amygdala, brain regions involved in processing emotions.
Medical use of marijuana is controversial.
MDMA
“Ecstasy” (MDMA) has gained in popularity since the “raves” of the 1990s.
-High school students’ use increased from 3.7 to 4.7 percent between 2009 and 2010 (National Institute of
Drug Abuse, 2010).
-Users feel energized and may hallucinate. Lowers dopamine; more serotonin activity
In animal studies, MDMA caused damage to a number of brain regions, particularly the prefrontal cortex and the
hippocampus.
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