Biological Approach Case Studies

Meyer-Lindenburg et al., 2008

AIM: To see how differences in the MAOA gene affects brain activity when exposed to threat.

METHODS: 2 groups analyzed: 1 with high-expressing MAOA gene, while another had low expression of gene, which is coorelated with aggressive behavior. Brain activity was measured during “emotional arousal” by showering angry and fearful faces.

RESULTS: When viewing angry & fearful faces in fMRI, MAOA-L group had increased acitivity in amygdala, reduced activity in PFC, and reduced cognitive control.

CONCLUSION:

• MAOA-L carriers may be prone to impulsive-reactive aggression and link between MAOA-L and violent behavior.

APPLICATIONS:

• Techniques to study the brain (fMRI)

• Genes and behavior (MAOA gene)

RESEARCH METHOD: Natural experiment

ETHICAL CONSIDERATION: Informed consent

Baker et al., 2007

AIM: To examine to what extent antisocial behavior is genetically based.

METHODS: Over 1,000 MZ & DZ twins and triplet kids studied. Multiple tests used to measure levels of antisocial behavior including self-report, teacher and caregiver questionairres. ASBs included levels of aggression, psychopathic traits and disordered conduct.

RESULTS: Heritability was ~50%, so differences in antisocial behavior (including aggression) in children is ~50% due to other factors.

CONCLUSION:

• Use of twins shows that antisocial behavior is a combination of genetics and the environment.

APPLICATIONS:

• Genetic similarities

• Genes and behavior

• Twin and kinship study

RESEARCH METHOD: Correlational study

ETHICAL CONSIDERATION: Informed consent

Ahs et al., 2009

AIM: To investigate connections between phobias and activation of the amygdala

METHODS: 16 Swedish females identified as having a fear of snakes or spiders. Placed in a brain imaging machine (PET) and shown various images of snakes or spiders and other neutral stimuli.

RESULTS: Activity in the amygdala was higher when perceiving images of stimuli they were afraid of (snakes, spiders) than perceiving neutral images.

CONCLUSION:

• Amygdala plays an important evolutionary role in fear as it helps activate fight/flight response when we see threatening stimuli

APPLICATIONS:

• Localization

• Evolution

• Techniques to study the brain

• Role of amygdala w/ fear

RESEARCH METHOD: True experiment

ETHICAL CONSIDERATION: Informed consent

Radke, 2015

AIM: To see how an increase in testosterone may affect the amygdala when people are responding to a threat.

METHODS: 54 female participants were injected with either testosterone or a placebo. They were placed in an fMRI and viewed images of angry or happy faces. Participants were told to approach or avoid the face by moving a joystick to make the image bigger or smaller. Approach/avoid task is designed to replicate what happens in real life when presented with a threat.

RESULTS: Testosterone injection increased activity in the amygdala when participants approached angry face, but not when avoiding it.

CONCLUSIONS:

• Testosterone biases the amygdala towards dealing with and reacting to social threat. Could explain why testosterone is linked with aggression.

• Testosterone increases amygdala activity which facilitates aggressive reactions to social threat by increasing physiological and emotional arousal (key in aggression).

APPLICATIONS:

• Hormones

• Brain and behavior

• Techniques to study the brain

RESEARCH METHOD: True experiment

ETHICAL CONSIDERATION: Informed consent

Ehrenkranz et al., 1974

AIM: To investigate correlations between testosterone and aggression in criminals.

METHODS: Participants were prisoners in USA. Divided into 3 groups: 1. Chronically aggressive behavior 2. Socially dominant w/out physical aggressiveness 3. Not social dominant or physically aggressive. Testosterone levels of all were measured.

RESULTS: Average testosterone levels were higher in Chronically aggressive and socially dominant than not dominant or aggressive. Aggressive had almost 2x testosterone levels of nonaggressive.

CONCLUSION:

• Testosterone levels linked with aggressive behavior and social dominance in human males.

APPLICATIONS:

• Hormones

RESEARCH METHOD: Correlational study

ETHICAL CONSIDERATION: Anonymity

Pucilowski, 1985

AIM: To see how increasing serotonin in the amygdala affects aggression

METHODS: Rat study. Experimental group was injected with serotonin in amygdala. Control group had no injection. Conducted a resident-intruder test to measure aggression.

RESULTS: Serotonin injection increased the time of attack latency- reduced aggression.

CONCLUSION:

• Aggression may be caused by lack of serotonin in amygdala

• Serotonin may reduce aggression

• Could explain correlations found in human studies between serotonin dysfunction and aggression.

APPLICATIONS:

• Neurotransmitters

• Brain & behavior

RESEARCH METHOD: True experiment

ETHICAL CONSIDERATION: Animal welfare & justification

Feinstein et al., 2011

AIM: To see if the amygdala plays a role in the experience of fear.

METHODS: “SM” is patient w/ bilateral amygdala damage due to genetic condition. Researchers tested fear response via exotic pet store, haunted house, scary film clips. Questionnaires & interviews used to gather data on life experiences relating to fear.

RESULTS: SM displayed no fear response. She could display other emotions, like happiness & excitement. SM found herself in dangerous situations in life as well.

CONCLUSION:

• Role of the amygdala is to cause a fear response, and this is healthy evolutionary adaptation.

APPLICATIONS:

• Localization

• Evolution

• Techniques (MRI)

RESEARCH METHOD: Case study

ETHICAL CONSIDERATION: Anonymity

Wedekind, 1995

AIM: To see if MHC genes influence attraction through sense of smell.

METHODS: Men and women. Men wore t-shirts for 2 days. Female participants smelled the shirts and rated them from 1-10 in terms of intensity, pleasantness, & sexiness. 3 t-shirts were worn by men w/ similar MHC genes, and 3 w/ dissimilar MHC genes. Women smelled t-shirts during second week of menstrual cycle around ovulation.

RESULTS: Women preferred scents of t-shirts worn by men who had the MHC genes that were different from their own. NOT the case if they took oral contraceptives.

CONCLUSIONS:

• Attracted to smells of ppl with opposite MHC genes because provides us with healthiest offspring.

• Pheromones in sweat could explain the results. This suggests that mate selection may have a biological basis linked to genetic compatibility.

APPLICATIONS:

• Pheromones and behavior

RESEARCH METHOD: Natural experiment

ETHICAL CONSIDERATIONS: Informed consent

Luby et al., 2013

AIM: To see if socioeconomic status (SES) is correlated with brain development

METHODS: Studied 145 kids over 10 years. Questionnaires, observations, and MRIs measured correlations between poverty, stressful life events, and parent-child interactions with hippocampal volume.

RESULTS: Lower SES coorelated with lower hippocampal and amygdala volume. Positivie parent-child interactions correlated positively with hippocampal volume. Parenting and stressful life events were mediating variables.

CONCLUSION:

• Neuroplasticity: SES affects neuroplasticity b/c stress increasing affects brain development

• Neural pruning: Stress may accelerate neural pruning, which reduces volume of hippocampus.

APPLICATIONS:

• Techniques to study brain (MRI)

• Neuroplasticity

• Neural pruning

RESEARCH METHOD: Correlational studies

ETHICAL CONSIDERATION: Anonymity