20. social neuroscience

12 01neurLecture 20; November 21, 2013Social neuroscience

NEUR%1201%%Fall%2013%%Harry%MacKay%

Book recommendation

The World Until Yesterday Jared Diamond


What is social neuroscience? The human brain may be the most complicated

single object in the universe (that we know of).

If that is true, then surely a society of human brains would be exponentially more complicated than a single brain in isolation.

That being said, often times humans become easier to understand and explain in a social context. It seems that the more people are involved, the

easier it is to understand the behavior of the group as a whole.

Social neuroscience is a field of study concerned with understanding how social interactions aect the brain, and how the brain directs social interactions. Social neuroscience is considered a relatively new

field of study, but as we will see, some of its most important tenets have been known for a long time.


The importance of social neuroscience Much of the work of early (and present day) neuroscience

has assumed that then brain can be accurately studied in solipsistic isolation. This isnt due to ignorance or laziness, rather its caused by

practical considerations, and the perfectly reasonable assumption that the brain is a general information processor concerned with the objective reality.

However, almost every activity of the human brain has some degree of social interaction, and understanding these interactions is especially important for understanding mental illness. Many mental illnesses have a social component. They may

affect social behaviors, or they may be caused/exacerbated by adverse social environments (trauma, bullying, etc.,)

This complicates matters for researchers. While rats and mice have very interesting social lives, it is not clear whether or not their behaviors tell us much about human socialization. Instead, researchers must resort to using primate models like

chimpanzees, bonobos and baboons. It is also difficult to recreate social situations in a laboratory

environment.


What does social neuroscience study?

How the social environment can aect brain development.

How social relationships can influence the brain.

How neurobiological and neuroendocrine factors control social motivation and behavior.

How ones social life may protect them, or put them at greater risk of mental illness.

The mechanisms of social cognition how does the brain allow complex social behavior. Social cognition is disrupted in autism spectrum disorders, thus we

will focus on that topic in the autism class.


Social neuroscience and mental illness Very few mental illnesses are even 50% genetic -

when genetic risk factors exist, they usually account for less than 50% of the risk for an illness.

In other words, it is possible to have the genes for a certain mental illness, but never actually develop that condition.

What else, aside from genetics can be blamed? As we are beginning to see, the social environment has a profound influence on mental health. Early-life social conditions program the HPA axis, and

re-shape the brain in a way that makes mental illness more likely.

Adverse social circumstances like rejection, bullying, etc., all affect the brain and also increase the risk of mental illness.


Social development influences the brain The stress response and HPA axis are

controlled by the brain, and new research is suggesting that the development of these control systems can be aected by exposure to early-life stress. This has already been demonstrated in

rodents (see epigenetics lecture).

Of course, ethics prohibit exposing humans to experimental early-life stress.

Two areas of investigation are especially popular in this field: Adults/teens that had been subjected to child

abuse. Adults/teens that had grown up in Eastern

European orphanages.

Conditions in Romanian orphanages were deplorable during the communist regime (they still are pretty bad). Children who survived this experience provide a way to study the effects of early-life stress.


Social development and the HPA axis It is fairly well established that survivors of child

abuse (and other early-life trauma) show hypersensitivity of the HPA axis. This can lead to increased risk of stress-related mental

illness.

A recent study looked at post-mortem brain tissue from suicide victims that either had or hadnt been exposed to abuse as children.

The authors of this study found that suicide victims that had been exposed to child abuse showed increased DNA methylation on the glucocorticoid receptor gene in the hippocampus. This means that less of this receptor was being

transcribed.

Since glucocorticoid receptors in the hippocampus mediate the negative feedback loop that controls the HPA axis, this finding explains the altered stress responses of abuse survivors.

--

-

Hypothalamus!

Ant. Pituitary!

Cortisol!

CRH (reduced)!

ACTH (reduced)!

Reminder of the negative feedback loop that shuts down the stress response (see stress lecture)

Hippocampus!


Social development influences the brain Children who spent the first ~2 years of their lives in

an Eastern European orphanage had increased amygdala volume. Interestingly, the time that the children spent in the

orphanage was positively correlated with amygdala volume. Kids who were adopted early had normally sized amygdalae.

A recent study of teenagers that had experienced childhood abuse found that they had reductions in the volume of the orbitofrontal cortex (OFC). The OFC is located directly above the eye socket (the

anatomists call this the orbit) The magnitude of this reduction correlated with the

degree of abuse the more abuse the children had suffered, the more smaller their OFC. Location of the human orbitofrontal cortex (OFC)

Amygdala volume in later-adopted post-institutionalized children.


Social neuroscience and relationships Having a good number of close social

relationships is known to improve health. This, of course, has been known forever on

a common sense basis, but emerging epidemiology research is showing that it has a scientific basis.

Socially connected individuals live longer relative to isolated individuals, and show increased resistance to diseases such as heart disease and cancer.

Loneliness (self-perceived social isolation) predicts poorer health outcomes in a variety of diseases.


Social relationships and health

The quantity and quality of ones social relationships have a huge eect on mortality.


Social neuroscience and relationships How could social relationships impact health?

Humans are social animals, and we may be genetically programmed to require social access to other humans.

The strength of ones social relationships seems to aect a variety of brain systems. Ultimately, these work to aect physical health through the HPA axis. Remember that the immune system can also be

affected by the HPA axis. This also ties social function to health.

Unfortunately, the quality and quantity of social relationships in industrialized countries is decreasing. This is often attributed to increased social mobility,

delayed marriage, dual-career families, and more single-residence households


Social relationships and health Why should social relationships aect mental function,

stress, and health? In other words, why would our brains have evolved the ability to

cause a stress response when were lonely.

Humans, like many animals, evolved to function best in small social groups. Living in small, close-knit communities has characterized the

typical form of human interaction for millennia.

Having adapted to this way of life, we seem to have developed extensive neural circuitry dedicated to monitoring the behavior of other humans, the health of our social group, and our social status.

Since all of those factors can influence our survival, we may have come to interpret loneliness and social isolation as a survival threat. We thus respond to it using the same neural and hormonal

systems that we use to respond to any threat namely the HPA axis and associated brain regions.


How to study social rejection Since its dicult to socialize naturally inside an fMRI

machine, researchers have had to create clever imitation social scenarios.

This typically involves some kind of simulated social rejection. In one model, participants play a virtual ball-tossing game

where they toss a ball with two other people (actually computerized opponents).

After a little while, the computerized opponents exclude the participant from the ball tossing. This is said to be representative of social exclusion.

Other models of social rejection: Participants engage in an online chat with a confederate.

After the chat, the participant is given the choice of meeting their partner in real life. They are then told that the partner was offered the same choice, but chose to not meet the participant.

Participants can also be recruited if they are in the middle of a breakup, or some other kind of social rejection.


Social rejection hurts A recent study (2011) recruited participants

who had just experienced a romantic breakup.

The researchers found that brain activity was similar when participants viewed pictures of ex-lovers and when participants were subjected to a minor painful stimulus.

Areas such as the Insula and dorsal Anterior Cingulate Cortex (dACC) are involved in processing the emotional components of pain. We are now beginning to see that both physical

and social pain activate these areas.


Social rejection hurts

Activation of the Insula and dACC by both physical and social pain.


The neuroscience of social (dis)connection

Social disconnection and rejection are processed in dierent circuitry from social connection. The latter tends to use reward circuits.

Areas involved in social connection !

AmygdalaPAG

Dorsal Anterior

Cingulate

Areas involved in social disconnection!

Anterior Insula

Ventromedial PFC

Ventral Striatum/

Septal Area


Hormonal regulation of social behavior Hormones such as vasopressin and oxytocin are

known to aect social behavior in both humans and animals.

Vasopressin is a peptide hormone secreted by the brain. When it was first discovered, researchers found that it could increase blood pressure and reduce urine output. For this reason, it used to also be called Anti-Diuretic

Hormone (ADH).

Oxytocin (quick birth G.) was originally identified as a hormone involved in beginning the process of childbirth. Oxytocin, or drugs that are chemically related to it, is

often given to induce labor.

Both of these hormones were identified for their roles in functions having nothing to do with socialization.

People are now getting tattoos of the oxytocin molecule.


Adventures with voles

Voles are small rodents. Prairie voles engage in monogamy they mate for life (usually). Meadow voles, on the other hand, engage in polygyny males mate with many females.

Aside from these dierences in behavior, the two types of voles are very similar genetically and structurally.

Prairie voles! Meadow vole!


Adventures with voles Male prairie voles will form a pair-bond with a

female after mating. This is due to the release of vasopressin. Interestingly, if vasopressin is administered to male

prairie voles artificially, it re-creates the same post-mating pair-bonding behaviors.

Female prairie voles also form pair-bonds with males after mating, but this depends on oxytocin. Giving females oxytocin artificially causes them to

pair-bond with a nearby male, even if they havent mated.

Importantly, both of these eects depend on the brains of prairie voles having receptors for vasopressin and oxytocin in reward and hypothalamic regions of the brain. Meadow voles do not have these receptors, and

thus oxytocin and vasopressin do not produce the same effects in them.

A picture I found on then internet that accurately describes the situation.


Oxytocin and vasopressin in humans Oxytocin and vasopressin promote pair-bonding in

monogamous prairie voles. Do these hormones have similar eects in humans?

Yes! Oxytocin and vasopressin can both be administered to humans intranasally.

Psychological experiments have shown that intranasal oxytocin causes men to be more trusting, generous, and willing to cooperate. Studies of romantic partners have shown that

discussions of relationship conflict are improved when the men are given oxytocin.

Vasopressin action in humans is less understood, but evidence suggests that it can increase cortisol release in response to social stressors in men.

Both of these hormones may have clinical potential, though they raise a lot of questions as well

Oxytocin can be administered as a nasal spray.


Final thoughts Since it devotes so much of its processing power to the

social life, we cannot understand the human brain without taking social factors into account.

Because the brain can be so focused on social matters, we might have to re-evaluate some of our favorite nuggets of advice: Saying ignore what other people think may be asking the

impossible. Our brains seem hard-wired to care about what others thing.

The human brain was shaped by many thousands of years of living in close-knit hunter-gatherer (or nomadic) communities. Modern society is totally dierent, and so we may have another case of mismatched environment

20. social neuroscience

Documents