Chapter 3: Part III - Conditioned Drug Effects, Sensitization, Expectancy and Context

behavioural tolerance

through experience with a drug, an organism can learn to decrease the effect that the drug is having

classical conditioning

associating a neutral stimulus with a meaningful stimulus

operant conditioning

associating a behaviour with its consequence

what is classical condtioning

a neutral stimulus becomes associated with an unconditioned stimulus, which leads to a conditioned response

NS

neutral stimulus

US

unconditioned stimulus (naturally elicits a response)

UR

unconditioned response (naturally occurs)

CS

conditioned stimulus (formerly neutral stimulus)

CR

conditioned response (learned response)

what is operant conditioning

a behaviour followed by a consqeunce that increases or decreases the likelihood of that behaviour occurring again.

US for drug

effect of the drug on the brainU

UR for drug

compensatory reactions (opposite to drug effect)

CS for drug

novel stimulus paired with the drug

CR for drug

conditioned response (same as UR but to lesser extent)

in a novel environment

the CS is absent, so the CR is not triggered and full drug effect can lead to overdose

SR

spontaneous response

R+

reinforcement (increases behaviour)

R-

punishment (decreases behaviour)

tolerance occurs due to

increased UR

repeated pairings of CS and US

lead to compensatory responses (UR and CR)

the UR happens

when drug is present

the CR happens

even when no drug is present, body still processing as if it is

sudden loss of tolerance to heroin

due to taking heroin in unusual circumstance or environment

operation conditioning of drug effects demonstrated by

Campbell and Seiden 1973 study that used DRL: differential reinforcement of low rates of responding. animal is reinforced only if it waits for 17.5sec between responses

by the end of training in Skinner box

both groups of rats performed comparably - group 1 rats demonstrated tolerance to amphatamine

when group 2 rats given amphetamine prior to Skinner’s box instead of after…

they behaved as though they have never received amphetamine - no tolerance

sensitization also referred to as

reverse tolerance

drug sensitization

a progressive increase in the behavioural or physiological response to a drug after repeated, intermittent exposure - the opposite of tolerance

sensitization is well demonstrated with drugs that

increase activity in the brain’s dopamine reward system, such as stimulants

first exposure to cocaine

increased alertness, energy and locomotor activity

repeated intermittent exposure to cocaine

person takes cocaine on several separate occasions

later exposure to cocaine

same dose produces greater behavioural response - enhanced response is sensitization

drug sensitization occurs because

repeated drug exposure causes long lasting increases in dopamine responsiveness and neural plasticity in reward pathways

reward pathways with sensitization

dopamine/mesolimbic pathways become over-reactive and more easily triggered

long term neural changes occur where

in ventral tegmental area, nucleus accumbens, and prefrontal cortex

sensitization is amplified by

learning - over time just seeing a cue can activate circuits, making the response even stronger and faster

Bingel study

the effect of expectation on painful heat stimulation

conditions of Bingel study

1. baseline - saline solution

2. no expectation - drug presented but thought receiving saline

3. positive expectation - told drug was present

4. negative expectation - told drug was discontinued to investigate possible increase in pain

pain rating (greatest to smallest)

baseline > negative expectation > no expectation > positive expectation

placebo effect

change in person’s symptoms or physiological state that occurs because they believe or expect that a treatment will have an effect

nocebo effect

a change in persons symptoms or physiological state because they expect or believe that a treatment will have negative effects

summary of placebo

positive expectations can produce beneficial effects

summary of nocebo effect

negative expectations can produce unpleasant effects

what did brain imaging show

brain’s pain networks responded to different extents according to expectations at each stage and matched their reports of pain

brain areas involved in perception of pain

insula, thalamus, somatosensory cortex, anterior cingulate cortex, prefrontal cortex, amygdala, brainstem, cerebellum

pain perception process

1. nociceptors detect harmful stimuli and send signals via peripheral nerves to spinal cord

2. thalamus relays signal to multiple brain regions

3. somatosensory cortex processes the location, intensity and quality of the pain

4. ACC and insula adds emotional and unpleasantness components

5. prefrontal cortex provides cognitive evaluation and modulates the response (increase or decrease the perception)

descending pathways

regulate pain perception

the brain can send signals down to the spinal cord

that either decrease or increase transmission of pain signals

descending signals

decreased pain perception when releases serotonin, norepinephrine, or endorphins - increased pain perception when releases substance P and increases excitability