Comprehensive Study Notes on Social Behavior, Neurobiology, and Genetics

Defining Social Behavior and Social Psychology

Social Behavior: Broadly defined, animals act in ways that enhance their survival and reproduction. When these behaviors involve other members of the same species (conspecifics), they are defined as social behaviors.
Social Psychology: This is the subdiscipline of psychology that investigates how people impact the thoughts, feelings, and behaviors of others.
Cross-Species Study: While primarily focused on humans, social behavior is studied across various species and even between different species, such as the interaction between humans and dogs.
Internal and External Dynamic Loop: Understanding social behavior involves relations among genetic variants, gene expression, brain activity, and the environment.
    * Social environments can trigger gene expression and physiological activation within an individual’s body.
    * These biological changes produce thoughts, feelings, and behaviors.
    * These outputs then initiate biological processes and behaviors in others (reciprocity).
Examples of Bio-Social Cascades:
    * A smile or wink from a significant other activates a specific cascade of internal events.
    * Crying from a significant other triggers a different cascade.
    * Biological responses to these cues differ depending on the identity of the person providing the cue.
Behavioral Genetics Challenge: Characterizing how genetic variation plays a role in individual differences in response to social cues is considered one of the most difficult challenges in the field.
Three Categories of Social Behavior for Genetic Focus:
    1. Affiliation.
    2. Sexual behavior.
    3. Aggression.

Reciprocal Impacts: Genes, Brains, and Behavior

Figure 13.1 Dynamics: Social interactions impact brain function and gene expression across three distinct timescales:
    1. Physiological (Solid Line): Immediate responses.
    2. Developmental (Dotted Line): Long-term changes over the lifespan.
    3. Evolutionary (Dasherd Line): Changes occurring over generations via selection.

Individual Differences in Social Behavior: Developmental Context

Caregiver Relationships: The earliest and most critical social relationships are with caregivers (typically parents). Many species, including humans, have newborns incapable of survival without assistance.
Types of Care:
    * Maternal care: Provided by the mother.
    * Paternal care: Provided by the father.
    * Alloparental care: Provided by another conspecific who is not the parent.
Reproductive Strategies:
    * Short-lived/Unstable Environment Strategy: Species produce many offspring and invest minimal care (e.g., Drosophila melanogaster, which can lay approximately $500$ eggs with zero parental care).
    * Long-lived/Stable Environment Strategy: Species produce few offspring that mature slowly, requiring substantial care.
    * Mus musculus (Mouse) Example: Litter sizes range from $3$ to $8$ pups. Maternal care includes pup retrieval, nursing, licking, nest building, and defense.

Child Development and Childhood Maltreatment

Maltreatment: A risk factor for negative outcomes including depressive disorders, drug use, suicide attempts, sexually transmitted diseases (STDs), and risky sexual behavior.
Categories of Maltreatment: Physical abuse, sexual abuse, emotional/psychological abuse, and neglect.
Statistics: Approximately $10 \text{--} 15 \%$ of children worldwide experience childhood maltreatment.
Epigenetic Impact: Maltreatment can trigger epigenetic mechanisms like DNA methylation, influencing long-term gene expression patterns.
Attachment Theory: Developed by Bowlby and Ainsworth in the mid-20th century, characterizing the connection between child and caregiver:
    1. Secure: Seeks close contact and intimacy; able to regulate emotions.
    2. Avoidant: Actively avoids intimacy and suppresses emotions.
    3. Anxious-ambivalent: Seeks contact but has difficulty controlling/regulating emotions.
Social Cognition: Involves thinking about and communicating with others. Key components include:
    * Theory of Mind: Understanding that others have their own mental states and perspectives.
    * Facial Recognition: Identifying emotional states through facial expressions.
    * Empathy: Feelings for the plight of others.
    * Preferences: Valuing outcomes like fairness or cooperation.

Courtship, Agonistic Behaviors, and Dominance

Sexual Selection: Mate choice is a critical evolutionary feature. Preference for specific traits drives selection if those traits are partially genetically determined.
Drosophila Courtship: Involves complex multisensory communication and elaborate, species-specific genetically influenced rituals.
Agonistic Behaviors: Behaviors related to fighting, usually between conspecifics for limited resources (mates, food, territory).
Threat Displays: Because actual fighting carries a high risk of injury, species use displays (e.g., baring teeth) to intimidate opponents.
Example: Black-backed Jackal (Canis mesomelas):
* Submissive display: Crouching posture, ears lowered.
* Dominant display: Erect posture, ears upward.
Dominance Hierarchies: Social structures where rank determines access to resources. Sustaining high rank requires vigilance and risk of injury.

The Neurobiology of Social Behavior

Dynamics of Interaction: Social interactions consist of three reciprocal stages:
    1. Sensory Stage: Gathering information (humans rely on vision; rodents rely on olfaction).
    2. Decision Stage: Processing information based on internal states (memory, motivation, arousal).
    3. Execution Stage: Performing the behavior (e.g., choosing courtship over aggression).
Mouse Social Brain Circuits:
    * Input: Main olfactory bulb (olfactory cues) and Accessory olfactory bulb (pheromonal/vomeronasal cues).
    * Processing: Amygdala nuclei (integration of sensory info with memory/emotion).
    * Pathway: Signals go to the Bed Nucleus of the Stria Terminalis (BNST) or directly to the hypothalamus.
Hypothalamic Nuclei:
* Medial Preoptic Area (MPOA): Involved in parenting but NOT aggression.
* Ventromedial Nucleus: Involved in various social responses.
Behavioral Output: The periaqueductal gray (PAG) in the midbrain is critical for final behavioral decision-making.

Genetic Conditions Impacting Social Phenotypes

Turner Syndrome

Genotype: X-chromosome monosomy ( $45, X$ or $XO$ ).
Etiology: Mostly meiotic nondisjunction; some result from structural abnormalities or mosaicism (cells having different chromosome counts due to mitotic nondisjunction after fertilization).
Frequency: $1$ in $2,500$ live-born girls ( $4 \%$ of conceptions, but $99 \%$ are spontaneously aborted).
Social Deficits: Low social competence, shyness, low self-esteem, and difficulty recognizing emotional facial expressions (specifically fear and anger).

Sex Chromosome Trisomies

Prevalence: $1$ in $650$ to $1$ in $1,000$ live births.
Conditions:
    * Klinefelter Syndrome: $47, XXY$ (males).
    * XYY Syndrome: $47, XYY$ (males).
    * Trisomy X: $47, XXX$ (females).
Commonality: Subtle physical features but a shared difficulty in recognizing emotional facial expressions.

Williams Syndrome

Genotype: Deletion of $28$ genes in the Williams syndrome critical region on chromosome $7q11.23$ .
Mechanism: Non-Allelic Homologous Recombination (NAHR), where DNA repeats (Copy Number Variants) cause chromosomes to misalign during crossing over in meiosis, resulting in one chromatid having a deletion and the other a duplication.
Williams Syndrome Symptoms: Hyper-sociability, low social anxiety, outgoing nature. Physical markers: broad forehead, short nose, wide mouth, large earlobes. Risk of cardiovascular disease and hypothyroidism.
7q11.23 Duplication: Associated with high social anxiety, social phobia ( $47.8 \%$ of children tested), and increased risk for autism and schizophrenia.
Key Genes: $GTF2I$ and $GTF2IRD1$ . Both code for transcription factors that regulate genes for synaptic proteins.

Affiliation, Attachment, and Oxytocin

Oxytocin (OXT): A neuropeptide synthesized as an inactive precursor. The structural gene is on chromosome $20p13$ . It consists of three exons.
Oxytocin Receptor (OXTR): Encoded by a gene on chromosome $3p25.3$ . It has four exons and encodes a $389$ amino acid G-coupled protein receptor.
Physiological Roles: Uterine contractions during childbirth, milk-letdown reflex, and response to sexual stimulation/orgasm.
Social Recognition Memory: Fundamental to social interaction. Tested via the five-trial habituation-dishabituation test.
Mouse Knockout Findings:
    * $Oxt \text{--}/\text{--}$ and $Oxtr \text{--}/\text{--}$ : Impaired social recognition memory. They can approach social targets but cannot distinguish familiar from unfamiliar conspecifics.
    * The Bruce Effect: Wild-type females abort pregnancy when exposed to a new male. $Oxt \text{--}/\text{--}$ females show this effect even for familiar males if they were away for $24$ hours, indicating they forgot the partner.
    * Aggression: $Oxt \text{--}/\text{--}$ or $Oxtr \text{--}/\text{--}$ males born to knockout mothers show significantly higher aggression, even if cross-fostered to wild-type mothers.

Autism Spectrum Disorder (ASD)

Prevalence: $1 \text{--} 2 \%$ worldwide (boys are diagnosed $4 \text{--} 5$ times more often than girls).
Heritability: Estimated at $0.56 \text{--} 0.90$ .
OXTR Association: Meta-analyses show specific SNPs (e.g., $A$ allele of $rs237889$ ) are transmitted to offspring with ASD more often than chance.
GWAS: A study of $18,381$ cases and $27,969$ controls identified five loci at genome-wide significance.
De Novo Mutations: Contribute to $25 \%$ of cases in boys and $45 \%$ in girls; at least $24$ specific genes are implicated.

Sexual Behavior Mechanisms

Drosophila Courtship Dance Steps:
    1. Orienting: Using visual/olfactory cues.
    2. Tapping: Tasting pheromones with forelegs on the female's abdomen.
    3. Singing: Wing vibration producing a pulse song (bursts of silent intervals) and a sine song.
    4. Licking: Proboscis contact with female genitalia.
    5. Copulation: Mounting if the female spreads her wings.
The Fruitless (fru) Gene: A transcription factor in the sex-determination pathway. In males, specific splicing produces a protein that enables courtship. Mutations cause males to court other males or fail to court at all.
Human Sexual Orientation:
    * Prevalence: $3 \text{--} 10 \%$ report homosexual orientation.
    * Heritability Estimates:
        * Targeted sampling: Median $0.70$ .
        * General twin registry: Median $0.18$ .
    * UK Biobank GWAS ( $N=477,522$ ): Identified five loci. One ( $rs34730029; 11q12.1$ ) near olfactory receptors; another ( $rs28371400; 15q21.3$ ) related to hormone regulation.

Aggression and Brunner Syndrome

Types of Aggression:
1. Reactive: Impulsive, response to threat.
2. Proactive: Planned, goal-oriented.
Brunner Syndrome: First genetic variant for aggression identified in $1993$ . A rare mutation in the $MAOA$ gene (Monoamine oxidase A) results in an inactive enzyme, low breakdown of serotonin, and low levels of the metabolite $5 \text{-} HIAA$ .
Maoa Knockout Mice: Show high aggression, short attack latency, and easy startling. Brains show elevated serotonin, dopamine, and norepinephrine in pups.
Human Aggression GWAS: A meta-analysis of $17$ studies identified $10$ significant loci. Top pathways include G-protein coupled receptor signaling and axon guidance.

Questions & Discussion

Q: How might the reproductive strategies of different species impact interactions between parents and offspring?
* A: Short-lived species in unstable environments (like Drosophila) invest minimal care and have many offspring, while long-lived species (like humans and mice) have fewer offspring and provide substantial care such as nursing and protection.
Q: Compare and contrast attachment styles.
* A: Secure children seek intimacy and regulate emotions; avoidant children suppress emotions and avoid intimacy; anxious-ambivalent children seek contact but struggle with emotion regulation.
Q: What are agonistic behaviors and what purpose do they serve?
* A: These are behaviors related to fighting for resources. They serve to settle disputes over mates, food, or territory. Threat displays reduce the frequency of actual physical injury.
Q: What is Turner syndrome and what can it tell us about the role of genes in social behavior?
* A: It is an X-chromosome monosomy. It demonstrates that having the correct number of sex chromosomes is essential for social competence, facial emotion recognition, and typical social development.
Q: Explain non-allelic homologous recombination.
* A: This occurs when repetitive regions of DNA (copy number variants) cause homologous chromosomes to misalign during meiosis. Crossing over then results in an unequal exchange, causing deletions on one chromatid and duplications on the other.
Q: Summarize the evidence that genetic variation in OXTR is associated with individual differences in social phenotypes.
* A: Evidence comes from mouse knockouts (showing impaired social memory), meta-analyses of human candidate gene studies (linking variants to empathy and sociability), and transmission studies in families with ASD.
Q: What is Brunner syndrome and what can it tell us?
* A: It is a condition caused by a mutation in the MAOA gene. It demonstrates that neurotransmitter metabolism (specifically serotonin) is critical in regulating impulsive aggression.
Q: How is aggressive behavior measured in animal models?
* A: In mice, the resident-intruder paradigm; in zebrafish, mirror tests or conspecific introduction; in honeybees, hive-stinging targets; in fruit flies, food resource competition and video tracking of charging/boxing behavior.