Brain, Hormones Behavior exam 3

Affiliation/ Prosocial behavior

brings individuals together

• pair bonding

• courtship

• parental behaviors

Aggression/antisocial behavior

keeps individuals apart

• territorial behavior

• dominance behavior

Territories in female meadow voles

• patterns of aggression and sociality can change seasonally in some species

• in summer, female meadow voles defend their territories from male and female conspecifics

• in winter, female meadow voles form strong same sex partner differences and behave more socially toward conspecifics

Why do animals form social bonds

• seems to have evolved from reproduction and parental behavior

• short term associations for mating have evolved into longer term social bonds

• some of the hormones and neural circuits involved in parental bonding have been co-opted for other social behaviors

Nonapeptide hormones in vertebrates

• hormones that promote affiliation are proximate mechanisms that facilitate monogomy

• alththough peptide sequences have evolved, functions have been conserved across vertebrate classes

Bonding in humans

• romantic and maternal love evoke similar brain activity

• images of one’s lover or one’s child induce activity in brain circuits involved with reward

• reward circuits also included brain areas rich in dopamine

• these areas also have high levels or oxytocin and vasopressin, which are involved in social attachment in non-human animals

Oxytocin and human bonding

• bonding facilitates cooperation

• also biases perception

  • e.g. parter attractiveness

Is affiliation adaptive?

• long-term pair bonds between mothers and fathers are necessary in some species to successfully rear young, so cooperation/affiliation has evolved

• pair bonding may also leas to more efficient mating, as there is no need to readjust behavior based on a new partner’s habits

Pair bonding is uncommon among mammals

• ~3% of all mammals

• ~15% of all primates

Monogomous voles

• prairie vole and pine vole

• pair bond

• social puberty inhibition

• males become aggressive towards intruders after mating

Polygamous voles

• meadow vole and montane vole

• no pair bond

• no puberty inhibition

• males are not around to assist with an intruder

Pair bonding in voles

• monogamous species prefer to spend time with their previous mate

• polygynous vole species show no social preference

Testosterone in social behavior of voles

• male prairie voles have about half the circulating T concentration as polygynous male voles

  • increasing T experimentally does not make them polygynous

• meadow and montane voles have high levels of circulating T

  • castration does not Mae them monogamous

OT binding differs across species

higher OTR in monogamous mice across brain except for the lateral septum (reversed pattern)

Female mechanisms for pair bond

Oxytocin antagonist into the nucleus accumbens and the prefrontal cortex prevents pair bond formation

Male mechanisms for pair bond

vasopressin 1a receptor antagonist (V1aRA) into the ventral pallium prevents pair bond formation

neurocircuitry involved in mating in prairie voles

VTA activation results in dopamine release, leading to reinforcement and reward learning

neurocircuitry involved in pair-bonding in prairie voles

• concurrent activation of neuropeptide and dopamine receptors in the reward centers during mating results in a conditioned partner preference, observed as a pair bond

• differential regulation of neuropeptide receptor expression likely explains species differences in the ability to form pair bonds

Dog and human bonds

• oxytocin in owners

• differences in face musculature and muscle physiology between wolves and domestic dogs

V1aR overexpression ______ social bonding

facilitates

types of aggression

• parental

• territorial

• intermale aggression

• predatory

most aggression is associated with males

• increases at puberty

• changes with seasons

• castration/replacement effects are predictable

male aggression

fight to increase reproductive success:

• gain and maintain resources

• defend females

• increase social status

Aggression and Testosterone

elevated testosterone

• grow and maintain antlers

• antlers regrow seasonally

• weapons for aggression

seasonal changes in male red deer

mating coincides with peaks in circulating T, male antler growth, and aggression in the population

Amputating antlers causes

a drop in social rank without influencing hormones

Exogenous T treatment can lead to male deer

maintaining antlers out of season. These males tend to rise in social rank

Testosterone can

• increase territorial aggression —> beneficial: access to resources

• decrease immune function, parental care, and deplete energy resources

Male mountain spiny lizards with T implants

• more aggressive

• more active during the day

• patrol more

• do more pushups

• use a third more energy than controls

• deplete energy supplies and die sooner

• spend much less time foraging

Top ranking wild baboons

are most stressed. Being second in the hierarchy may come with more benefits than being at the top

In some primate species, females compete for males

as ovulation approaches

Female Syrian hamster aggression

• live in burrows and fend off intruders

• estrogen and progesterone (estrus) inhibit aggression, which allows males to mate without injury

Effects of hormones on hamster aggression

• female Serbian hamsters are more aggressive during non-breeding periods (short days) than during breeding periods (long days)

• likely, estrogen and progesterone inhibit aggression during breeding conditions

_______ influences androgen concentration

Melatonin

• seasonal “switch”

• shift from gonadal to adrenal regulation of aggression

_________ modulates aggression in response to day length in females

estrogen

Effects of estradiol on aggression

• fast increase in aggression (20 min after treatment) —> non genomic effects

• no treatment effect on aggression during the breeding season

Behavior can influence hormones

• male Syrian hamsters that lose fights have reduced androgen levels for many days

• rhesus monkeys that are defeated by high-ranking males have reduced testosterone levels for weeks, while winners have immediate increases (up to 400%) in testosterone

• similar effects have been demonstrated in human athletic competition and even presidential races

The challenge hypothesis and testosterone

in some species (usually monogamous), challenges are met with temporary increases in circulating T

The challenge hypothesis

In polygynous species:

• males that experienced simulated territorial intrusions did not have higher testosterone levels than males that experienced no intruders

In monogomous species:

• testosterone levels do rise after simulated territorial intrusions

• usually have low testosterone levels except when competing with other males

Blood T concentrations in birds may reflect competition

• in some species, peaks in male T levels are tied to

  • territory acquisition

  • defense of fertile mates

• High T in males is sometimes incompatible with colony nesting

Components of a homeostatic system

• set point

• detection mechanism

• mobilization

• recognition

Homeostasis: physiology and behavior

• some systems regulated by physiology

  • body temp in endothermic species

• some by behavior

  • body temp in exothermic species

• some by both

  • fluid balance; feeding and body weight