The Neurobiology of Social Memory & Pair-Bonding

Question 1

OT and AVP are released in the brain as

Answer 1

NT/neuromodulators

Question 2

OT and AVP are released from the posterior pituitary as

Answer 2

neurohormones

Question 3

Accessory olfactory system. Describe the anatomy of the vomeronasal olfactory system using a block diagram. Begin with the vomeronasal organ and trace the flow of information from the organ into the brain, and then to the structures of the telencephalon and diencephalon. What is the main target of the accessory olfactory bulb (AOB)?

Answer 3

AOB: main target is MeA
OB: main targets are piriform cortex and CoA
But OB also has direct projection to MeA and indirect influence on MeA via CoA
Both systems influences social & reproductive behavior via their projections to amygdala.
Amygdala then carries olfactory information to BNST & MPOA.

Question 4

How do we know OT is important for maternal behavior? Describe at least 3 types of experimental evidence that OT is important for maternal behavior in rats and mice. Hint: Experimental evidence includes lesion studies (of what structure?), injections of OT (where?) and the use of genetically altered mice.
Describe the reproductive & maternal behavior of female mice lacking the gene for the OT receptor (OTR KO)

Answer 4

OT from PVN or SON may act on OT receptors throughout the brain to promote maternal responsiveness
lesions of the PVN result in a near complete loss of brain oxytocinergic system and delay in onset of maternal behavior in naive rats
OT injected into a pregnant and virgin wild house mice also increases maternal behavior towards pups
OT receptor antagonist injected into MPOA and VTA inhibit maternal behaviour by progesterone withdrawal
OT knockout mice show grossly intact maternal behaviour
in semi-naturalistic conditions, OT knockout mice reveal pervasive social deficits
Peg3 knokckout mouse has reduced OT neurons in the PVN and has a profound deficit in maternal behaviour such as absense of nest building, pup retreval and crouching behaviours
in the wild type animals, peg3 is present in brain areas involved in maternal behaviour such as MPOA, BnST ,
pvn, medial amygdala
suggest that peg3 activity may be upstream of OT and other genes involved in the neural circuitry of maternal behaviour and peg3 may contrivute to the developmental organization of the behaivour

Question 5

Where do sensory stimuli from pups, e.g. odors, act to promote maternal responsiveness?

Answer 5

olfactory bulb

Question 6

What is pair-bonding? Describe 3 lasting changes in behavior that follow the 1st mating in prairie voles.

Answer 6

Bonding: a relatively permanent increase in preference for contact with a particular individual.
3 lasting changes after 1st mating in prairie voles:
partner preference (most studied)
mate guarding: aggression towards strangers
parental behavior: both male and female participate

Question 7

In female prairie voles, what causes OT release in the brain during mating, and where does OT act to produce partner preference?

Answer 7

Breast stimulation, e.g. nursing
Genital stimulation
vagino-cervical stimulation during parturition (birth)
relevant to mother-infant bonding in sheep, care of pups in rodents
vaginal stimulation during copulation
relevant to pair-bonding in prairie vole

These stimuli produce OT release from the posterior pituitary, but also within the brain.

Question 8

The mating-induced increase_______ maintains the bond by promoting aggression toward strangers.

Answer 8

in DA1 R in NAcc

Question 9

A ________ blocked pair bonding in mated males.

Answer 9

D1 agonist into NAcc

Question 10

What neural changes are responsible for the bond?

Answer 10

Reorganization of DA Rs in NAcc is a candidate.

Question 11

Injection of a _______ of paired males blocks aggression toward strange female.

Answer 11

D1 antagonist into NAcc

Question 12

Mechanism for Pair-Bond Formation

Answer 12

VTA axons release DA in NAcc.
PVN axons release OT into NAcc and MeA
MeA neurons release AVP:
in LS to facilitate olfactory memory of the mate.
in VP to promote approach to mate.

Question 13

PP in male voles depends on AVP acting in _______

Answer 13

ventral pallidum (VP).

Question 14

What is the VP?

Answer 14

VP carries part of the output of a forebrain network for reward.
Parallel Reward Pathways
DA  dorsal striatum (caudate/putamen)  globus pallidus  output (motor & other)
DA  ventral striatum (NAcc) 
ventral pallidum  output (motor & other)

Question 15

maternal behavior, mood, attention, arousal

Answer 15

cingulate cortex

Question 16

modulates central amygdala, modulates visual processing via projections to inferior temporal lobe cortex.

Answer 16

basolateral amygdala

Question 17

output of amygdala to many areas important for emotions, including anxiety & fear, participates in all types of emotional responses.

Answer 17

central amygdala

Question 18

maternal behavior, male sexual behaviour

Answer 18

MPOA

Question 19

female sexual behavior

Answer 19

VMN

Question 20

OT acts here to dampen emotional arousal

Answer 20

NST

Question 21

In human fMRI studies, activations are seen in various cortical areas representing the visual stimulus, and components of the mesotelencephalic DA pathway:

Answer 21

VTA and both dorsal & ventral striatum.

Question 22

What are the two brain sites in which an oxytocin R antagonist blocked the formation of partner preference in female prairie voles?

Answer 22

In female, an OTR antagonist injected into either the NAcc or prefrontal cortex, but not the caudate, blocks PP.

Question 23

In what brain site did a vasopressin R antagonist block the formation of partner preference in male prairie voles?

Answer 23

In male, a V1aR antagonist into the ventral pallidum, but not thalamus or amygdala, blocks PP.

Question 24

It has been proposed that the formation of a pair-bond between a mating pair of prairie voles is based on a specific kind of learning. What is this learning-based explanation for pair-bonding (or at least partner preference)? What is learned, and what is the reinforcement for this learning?

Answer 24

A reward (mating induced DA release) is paired with an odor (of the mate) to produce a conditioned olfactory preference.
DA release into NAcc is critical, just as it is for other conditioned preferences, e.g. drug reward.

Question 25

Brain changes in pair bonding

Answer 25

Reorganization of DA Rs in NAcc is a candidate.
a D2 agonist injected into the NAcc promotes bond formation in unmated male prairie voles.
A D1 agonist into NAcc blocked pair bonding in mated males.
Activation of D2 & D1 Rs in NAcc has opposite effects on bond formation.
This change in the balance of D1 vs. D2 R expression may be part of the mechanism that maintains the bond
Stimulation of D2 Rs promotes bond formation, while stimulation of D1 Rs inhibits it.
One of the ways the bond is maintained is via selective aggression against strangers.
Selective stimulation of D1 Rs promotes this aggression.
Mating produces a permanent change in prairie voles: aggression against strange voles, or mate guarding, appears following mating in both sexes.

Question 26

What is the evidence for the idea that dopamine release in the nucleus accumbens is necessary for the formation of a partner preference?

Answer 26

The mating-induced increase in DA1 R in NAcc maintains the bond by promoting aggression toward strangers.

Question 27

According to the learning-based explanation, where do dopamine release and oxytocin converge to produce partner preference? Where do olfactory information and oxytocin converge to produce partner preference?

Answer 27

VTA axons release DA in NAcc.
PVN axons release OT into NAcc and MeA
MeA neurons release AVP:
in LS to facilitate olfactory memory of the mate.
in VP to promote approach to mate.

Question 28

genital stimulation during mating activates two brain areas that project to the PVN. Projections from these areas then activate PVN neurons, which release OT. What are the names of these two areas that respond to genital stimulation?

Answer 28

MPOA/BnST

Question 29

In rodents, the sensory modality most important for social interaction is

___________________, while in humans social interactions depend more on

___________________ and auditory (voice) stimuli.

Answer 29

smell

visual

Question 30

How did the authors identify brain activation that represented love for the romantic partner?

Answer 30

studied using photographs of the loved one, i.e. visual (not olfactory) stimuli.
Participants were recruited using a newspaper ad asking, “Are you still madly in love with your long-term partner?”
scanned while viewing photographs of their partners or old friends.
The subtraction method was used to measure activation specific to romantic love.

Question 31

The authors found that when participants viewed photographs of their partners’ faces, activation was seen in the VTA and the NAcc/caudate. They also found that the degree of activation was correlated with measures that represented the strength of the bond. What was activation in the right VTA correlated with? What was activation in the NAcc/caudate correlated with?

Answer 31

correlation b/t activation in right VTA and “inclusion of other in the self” (IOS) score.
said to measure “closeness” within the relationship.

correlation b/t activation in the right hemisphere NAcc/Caudate and years married.