Lec 12/13 Flashcards
What does the term reward refer to?
refers to stimuli that are in some way desirable or positive and can affect behavior.
Examples: food, money, drugs.
Why do humans find certain activities naturally rewarding?
Humans, like other animals, naturally find certain activities to be rewarding. This is with good reason, as rewarding activities are usually critical to survival.
Examples: eating, sleeping, sex, exercise, etc.
Why is the reward stimuli different for everybody?
Rewarding stimuli can be different depending on an individual’s personal experience. Therefore, we learn to value more than just what we’re born liking.
The ability to learn new rewards is also valuable, because it teaches us to repeat successful behaviors
How was the reward system discovered?
- -Olds and Milner (1954) discovered the phenomenon of intracranial self-stimulation (ICSS) more or less by accident
- -James Olds accidently implanted an electrode the wrong way. He was supposed to implant it right above the reticular formation, but he didn’t wait for the substance to harden around the implanted electrode and he took out the rat’s head from the halo structure that holds it in place. This caused the electrode to slightly move. He noticed that the rat liked the stimulation and would repeatedly press the lever that caused the stimulation. He then realized that something is up and he opened the brain up and realized it was because it was in another area
What did the discovery of the ICSS show about addiction?
–Rats would press the lever thousands of times an hour, ignoring everything else that the experimenters could offer. Rats would ignore food, water, access to a sexually receptive female, and whatever other rat treats the experimenters could think of
–To researchers, this sort of behavior closely resembled the behavior of human drug addiction
They reasoned that the brain areas targeted by the electrodes must therefore be involved in drug addiction
What is the official name for the reward circuit and what does it mean?
- -mesocorticolimbic dopamine system
- -meso=middle (midbrain where VTA is)
- -cortico=cortex (where axons from VTA is projected)
- -limbic=limbic system (where axons from VTA is projected)
What main neurotransmitter is used in the reward circuit?
–dopamine
How does the reward system work?
- -It starts with the Ventral tegmental area (VTA) in the midbrain which contain neurons that produce dopamine
- -axons from these neurons project to the hippocampus, nucleus accumbens (NAc), and prefrontal cortex (PFC)
- -the VTA is tonically inhibited (GABA is coming from different regions to inhibit the VTA)
- -however, when a rewarding stimulus is detected, the VTA is disinhibited and it fires (releases dopamine) in the hippocampus, NAc, and PFC
- -Hippocampus: allows us to remember where in the environment we had the stimuli
- -NAc: the expectation and experience of rewarding stimuli. Unexpected rewards lead to especially large dopamine release
- -PFC: allows us to plan for it again in the future
- -together with the PFC and Hippocampus, it allows for the experience of reward, as well as the need to go after it again
- -in the case of natural, healthy, rewarding stimuli, this system is quite useful
What is the reward system on drugs?
–addictive drugs lead to supraphysiological dopamine. In other words, a dopamine release that is much larger than what would normally be seen with naturally occurring rewards.
What is addiction?
- -Addiction is a state of uncontrolled drug use that persists in spite of negative consequences associated with taking or procuring that drug
- -Negative consequences include: health effects, cost, family disruption, loss of (legal) employment, etc.
How does addiction develop?
- -Addiction develops over multiple exposures to addictive drugs. Users progress from least harmful (recreational) use to most harmful (daily/binge use)
- -Addiction is not an inevitable consequence of trying a drug, but repeated drug use does raise the risk of addiction.
- -only 4% of people who try drugs become addicted
How do we diagnose addiction?
–The definition of addiction remains controversial.
Addiction is not a diagnostic term
–DSM-5 now uses term “Substance Use Disorder”, and also includes behavioural addictions, diagnosed under “Addictive Disorders”.
–According to the DSM, patients must show 2 or more of 11 listed behavioural criteria (within the past year
–Like other disorders, individuals are scored on a spectrum, from mild, moderate to severe substance use disorder
What is drug tolerance?
- -Increased amount of a drug needed to achieve intoxication, or a diminished drug effect with continued drug use of the same amount of a drug
- -Can become tolerant to some aspects of a drug, but not to others
e. g., Alcohol: Tolerance to intoxicating effects achieved faster than tolerance to motor (cataleptic) effects and this is why you want to drink more even though you can walk or stand properly
Can have ___________ blood levels of drug and ____ appear intoxicated
–very high; not
What is drug withdrawal?
Behavioural and physiological symptoms that occur upon cessation of drug use
- —>Opposite to drug effects; compensation for drug effects on body
- —>Severity may change with characteristics of the user, history of drug use
- E.g., a hangover
- Muscle aches and cramps, anxiety attacks, sweating, nausea, convulsions, death
Why shouldn’t you take tylenol after drinking?
You shouldn’t take Tylenol (acetaminophen) because it is metabolized using the same group of enzymes that alcohol is. If you take acetaminophen in high doses regularly while drinking, the metabolic pathway will go to the alcohol and not the Tylenol so you could have dangerous levels of acetaminophen in your bloodstream
Advil is better
What is the technical definition of an addiction?
“A syndrome at the centre of which is loss of control over a reward-seeking behaviour”
Robert West, Theory of Addiction
What happens if a pregnant woman is a heroine addict?
If the mom is a heroin addict, the baby is not one either. It may show tolerance and withdrawal, but that doesn’t define addiction. There’s no loss of control over reward-seeking behavior (babies don’t really have much control over anything). The DSM 5 states in the beginning that ”the individual has shown problematic pattern of use leading to significant psychological distress over the last 12 months” so the baby does not demonstrate that.
Each drug has ___________
different brain targets
What is cannabis?
- -Most commonly used illegal drug in the world
- -Most controversial
- -Comes from the cannabis sativa and cannabis indica plant
- -Over 80 cannabinoids known
- —>Most common is Δ-9- tetrahydrocannabinol (Δ9-THC)
- —>Also contains cannabidiol (CBD)
Why don’t we use the term marijuana?
We don’t use the term marijuana anymore because it refers to a very specific product of the cannabis plant. We use cannabis instead because we can talk about all the cannabinoids, edibles, etc
What does psychoactive mean?
Psychoactive means it affects your brain cells –neurons and glia
What is the difference between THC and CBD?
- -CBD IS psychoactive (it binds to receptors on brain cells), but it is not intoxicating (won’t give you high)
- -THC is the main psychoactive ingredient; responsible for the “high” associated with use however pure CBD won’t
What is the inhalation administration of cannabis?
– 50% enters lungs, almost all of that enters body
Reaches brain in about 30 sec, peaks ~ 30–60 min., lasts 3–4 hours; subjective state for 12 hours
–Vaping – peak concentrations occur 10 min after administration
Distributed everywhere; likes to stay in fatty tissue
