Heritability
-proportion of the variance that is due to genetics (inherited)
-if we could find the genes we could treat 40% of the issue
Chronic Post Surgical Pain
-7% (2mil) of ppl get severe chronic post-surgical pain in canada per year
Individual Differences in Analgesic Response
-in a study of 3,170 postoperative patients (mostly orthopedic)
-morphine dose required for sufficient analgesia
(pain rating<30): 2 – 83 mg/kg
Organismic Reasons for Interindividual Variability
-genetic background
-sex
-psychological traits
-age
-circaidian rhythms
Environmental Reasons for Interindividual Variability
-past experiences
-gender
-psychological states
-diet
-social factors
Heritability in inbred Mice Strains
on average the mediate is just under 50% for inbred mice strains
HSAN’s
-the HSANs are all loss of function disorders (all congential insentitvities to pain)
–these are monogenic pain disorders, disorder caused by the dysfunction of a single gene
-monogenic pain disorders are incredibly rare
OPPERA Study (TMD)
-they got many ppl that were at the age to develop TMD but hadnt developed it yet and then waited for 5yrs, collecting their data and then compared data of ppl who went on to develop TMD vs those who didnt to see what differed
-biggest difference was high somatosization
-more somatosization lead to higher likelihood of developing TMD
Somatosization
paying an unusual amount of attention to stuff thats happening in your body thats weird (tickles, scratchyness), if you notice it, worry and ruminate on it
Sex Differences in Chronic Pain Prevelance
-Karen Berkley was the first to look into this
-underrepresentation of men bc they dont go to the doctor, women are more likely to report pain
-median between men and women is 5-10%
-could be bc women are more sensitive to pain then men
-maybe women are more susceptible to developing these conditions that have the side affect of pain
-sometimes studies are not statistically powered enough to see the sex difference
Experimenter Sex-Subject Sex Interactions
-looking at interaction of gender of participant and experimenter when reporting pain
-when reporting to opposite gender experimenters, men rate lower and women rate higher, probably due to gender roles
Sex Differences in Pain Mechnaisims (Von Frey Study)
-males and females had the same baseline level
-when a injury is inflicted, both experienced mechanical allodynia
-minocyclien is then given, blocks microglia, it blocks mechanical allodynia in male mice, does nothing at any dose for female mice
-can conclude that males use microglia to produce chronic mechanical hypersensitvity, females dont, they use t-cells (mice)
Ultimate Explanation
why a sex difference?
Proximate Explanation
how a sex difference?
Organizational Effects
developmental effects of gonadal hormones
Activational
post-pubertal, acute effects of gonadal hormones
Levels of Sex Differences
experiential
sociocultural
psychological
cellular (e.g., microglia)
Neurochemical
Neonates & Pain
-exaggerated and uncoordinated Flexion Reflexes in Neonates (newborn)
-in baby rats neuron firing is larger and goes for longer after poking
-when testing reflexes in babies, both knees will flex in very young infants
Elderly & Pain
-if ur a man living as long, you are probably very robust, so thats why pain goes down after peaking in men
-obv older ppl have more pain bc longer you live, more susceptible to injury
-elderly less sensitive to pain
Cultural Influence
-african americans report more pain and are more sensitive to pain than white ppl
-dk if its genetic or environmental
-there are huge racial disparities in pain care
-with the same presenting symptoms, over a 3rd of white children are offered opiates in the ER, only 12.2% of black children
Circadian Rhythms of Pain
-pain sensitivity peaks in the morning
-exception bc of arthritis which peaks in evening bc person has been walking all day
Lifestyle Factors
more pain attributed to
-poor diet
-high alc consumption
-low physical activity
-unemployment
-high labour exertion
-smoking
-high BMI
-lonlieness
- lower social class
-less education
Singer Study (didnt work)
-women seeing their boyfriends in pain activated the same intensity and areas as for when they experienced pain
-did not conduct the study the other way around
-but never actually measured their bahviour, didnt ask them directly
-tried again with mothers and children didnt work bc mothers were so happy to see their children in the video that it messed up imaging
Singer Study (worked)
-tired again by showing ppl a video of a fellow participant (confound) in pain, before seeing in him in pain, half were shown a video of him sharing a sad story, half were shown a him sharing a story that made him a jerk
-when they were tested for pain and did like the guy, they rated their pain higher, like his pain was adding to theirs
