AHL Biological Studies

Question 1

Describe Meaney’s Study

Answer 1

Determine effect of glucocorticoids (stress hormones) on memory

Independent samples design: rats randomly allocated to ½ conditions
Treatment group:
Newborn rats handled daily by researchers for 3 weeks
Taken from mothers for 15 mins & placed in plastic container lined with paper towel
Brushed for intense 15 mins, simulating grooming of mother - reducing stress
Control group: taken from mother but no handling from researchers
Tested effect of elevated rates of stress hormones over lifetime, 2 year old rats placed in pool of milky water with a platform
Researchers tracked route of rats as sought out platform based on memories of previous attempts to escape water

High levels of glucocorticoids in early life of rat resulted in changes that affected rats in old age
Increased exposure to glucocorticoids accelerated hippocampal neuron loss, worse memory & cognitive impairments in ageing
Extra stroking led to activation of genes responsible for reaction to stress response
Epigenetics: grooming turns on genes which help young rat to cope with stress, leading to longer & healthier life

Grooming leads to gene expression which helps with stress regulation, leading to lower cortisol levels in the life time, so that they have less of an effect on memory impairment later in life

Questionable how much we can generalise findings from rats to humans
Artificial study - lacking ecological validity
Research led to new theories on role of stress in cognitive function
To measure hippocampal volume, rats had to be killed, ethical concerns, animals may be used in cases where using human subjects deemed unethical

Question 2

Describe Dorries et al’s Study

Answer 2

Investigate if female pigs are more sensitive to androstenone (chemically related to androstadienone - male pheromone) than male pigs

Pigs individually housed in pens & fed daily but water restricted for 10 hours prior to training or testing to encourage them to seek reward of sugary water
Training phase: Pigs trained to go to different drinking ports associated with different odours as researchers cannot ask pig which odour they detected
Over time pigs learned via operant conditioning which odours were associated with certain drinking ports, if detected certain odour, would walk to certain drinking port to be rewarded
Testing phase 1:
Pigs approached apparatus which triggered a mist created by bubbling liquid nitrogen & mixing it with an odour
Pigs exposed to mist for 1 sec then given 10 secs to approach correct drinking port
Pigs rewarded for correct answers: if exposed to AND, they were rewarded with sugary water when approached correct drinking port had learned to associate with AND
So, researchers could understand if pigs had correctly identified odour
Testing phase 2: Descending odour concentrations used to test sensitivity of males & females to AND

Male & female pigs equally effective in distinguishing between 3 odours in high concentrations
Female pigs 5x more effective at detecting AND than male pigs

AND detection is sexually dimorphic, it may have a specific role for different sexes, female pigs are specifically able to identify & respond to AND

Questionable how much we can generalise findings from pigs to humans, especially as yet to find human pheromone
Artificial study - lacking ecological validity

Question 3

Describe Krakenberg et al’s Study

Answer 3

Study conducted using a 5-HTT knockout mouse model
Knockout mouse = a laboratory mouse in which researchers have inactivated an existing gene by replacing it or disrupting it with an artificial piece of DNA
5-HTT knockout mice either lacked 5-HTT gene homozygous or heterozygous
Male wild type (15), heterozygous - 1HTT gene(14) & homozygous - 2HTT genes(11) knockout mice used
Experimenter blind to genotypes of mice during experimental phase
4 behavioural tests performed for anxiety-like & exploratory behaviours e.g. Elevated Plus Maze Test

Homozygous 5-HTT mice displayed lowest levels of exploratory locomotion & highest levels of anxiety like behaviour
Heterozygous mice didn’t show this behavioural change

Anxiety like behaviour highest when there is no 5-HTT gene present

All ethical guidelines followed, study approved by relevant authorities
Reduced number of mice used
Triangulation: multiple different behavioural tests used
Higher degree of control possible than with humans