The Biological Basis of Behavior: Unit III



The Biological Basis of Behavior: Unit III

Biological Psychology Studies

Study 1

Some individuals who use drugs become drug abusers - they continue taking drugs even though doing so causes serious problems in their lives. Others avoid abuse or addiction. By studying patterns of drug use in pairs of twins, NIDA-supported researchers are beginning to clarify the role that genes play in predisposing individuals to drug abuse.

|[pic] |

|If genes influence the risk for drug abuse, identical twin pairs, who share the same |

|genes, will tend to be concordant-that is, both will abuse drugs or both will not abuse|

|drugs.   |

"Twin studies explore the roles and interrelationship of genetic and environmental risk factors in the development of drug use, abuse, and dependence," says Dr. Naimah Weinberg of NIDA's Division of Epidemiology, Services, and Prevention Research.

In twin studies, researchers interview both members of identical (monozygotic) and fraternal (dizygotic) twin pairs, who typically are exposed to common environmental influences. If genes influence their risk for drug abuse, identical twin pairs, who share the same genes, will tend to be concordant-that is, both will abuse drugs or not abuse drugs. Fraternal twin pairs, on the other hand, are no more similar genetically than non-twin siblings, and so will be less concordant - there will be more pairs in which one twin abuses drugs and the other does not. By comparing the degree of concordance in identical and fraternal twins, researchers can estimate the extent to which genes influence vulnerability to drug abuse.

Marijuana and Cocaine Abuse Among Female Twins

NIDA-supported researchers Dr. Kenneth Kendler and Dr. Carol Prescott at the Medical College of Virginia in Richmond have examined the patterns of marijuana and cocaine use by female twins and found that genetic factors play a major role in the progression from drug use to abuse and dependence. The researchers interviewed 1,934 twins, ranging in age from 22 to 62, recruited from the Virginia Twin Registry, a database compiled from Commonwealth birth records.

|[pic] |

|Percentages of pairs in which both twins used, abused, or were dependent on |

|marijuana or cocaine were higher in identical twins than in fraternal twins.   |

In the study, drug "use" involved at least one nonprescribed use of a drug; "abuse" was based on the definition provided in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), which includes symptoms such as recurrent use in situations where it presents a physical danger, failure to meet obligations at work or school, or recurrent social or interpersonal problems caused by effects of the drug; and "dependence" was based on the DSM-IV definition and included characteristics such as physical symptoms of tolerance or withdrawal, taking larger amounts of the drug or using it over a longer period than intended, or spending large amounts of time seeking, obtaining, and recovering from the effects of the drug.

"Our research supports other studies that indicate family and social environmental factors are influential in determining whether an individual begins using these drugs," Dr. Kendler says. "But our findings suggest that the progression from the use of cocaine or marijuana to abuse or dependence was due largely to genetic factors."

In addition, Dr. Kendler says, the study found that concordance rates-both twins using, abusing, or being dependent on drugs-were higher for identical than fraternal twins (see chart). For cocaine use, concordance was 54 percent in identical twins and 42 percent in fraternal twins; for abuse, 47 percent in identical twins and 8 percent in fraternal twins; and for dependence, 35 percent in identical twins and zero for fraternal twins.

"Abuse and dependence are highly heritable," Dr. Kendler says. "For both cocaine and marijuana, genetic factors are responsible for roughly 60 to 80 percent of the differences in abuse and dependence between fraternal and identical twin pairs."

The Biological Basis of Behavior: Unit III

Biological Psychology Studies

Study 2

The human brain is wired with natural checks and balances that control negative emotions, but breakdowns in this regulatory system appear to heighten risk of violent behavior, according to findings of a study by UW-Madison psychologist Richard Davidson.

As part of a special report on violence in the July 28 issue of the journal Science, Davidson and colleagues analyzed brain imaging data from a large, diverse group of studies on violent subjects and those predisposed to violence. The studies focused on people diagnosed with aggressive personality disorder, those with childhood brain injuries and convicted murderers.

Researchers found common neurological threads among these more than 500 subjects in the brain's inability to properly regulate emotion. The study focused on several interconnected regions in the prefrontal cortex of the brain, areas defined in Davidson's previous work as an essential control mechanism for negative emotions.

A similar brain process has been implicated in a number of mental health problems, including depression and anxiety disorders. Davidson says this newfound connection between violence and brain dysfunction opens a new avenue for studying and possibly treating violence and aggression.

"We are placing the question of violence right in the middle of our basic research on the neurobiology of emotion, because our previous insights in this area give us tremendous leverage to understand the root causes of violence," Davidson says. "There never has been a theoretical framework to make sense of this before."

One of the core findings, Davidson says, deals with the interplay between several distinct brain regions, namely the orbital frontal cortex, the anterior cingulate cortex and the amygdala. The orbital frontal cortex plays a crucial role in constraining impulsive outbursts, while the anterior cingulate cortex recruits other brain regions in the response to conflict. The amygdala, a tiny but highly influential portion of the brain, is involved in the production of a fear response and other negative emotions.

Davidson and colleagues Katherine Putnam and Christine Larson found that normal brain activity in the orbital and anterior regions were blunted or entirely absent in many of the study groups, while the amygdala showed normal or heightened activity. The inability of the two brain regions to effectively counteract the response of the amygdala may help explain how threatening situations can become explosive in some people.

A major strength of the research is in the range of people studied and the consistency of the results, Davidson says. The researchers found dysfunction in common brain regions in reviews of brain imaging data from 41 murderers, from a study group suffering from aggressive impulsive personality disorder, and from a group diagnosed with antisocial personality disorder.

They also reviewed data from two individuals who suffered early damage to the two regions of the brain in question. Those individuals, injured early in life, both showed histories of verbal and physical abusiveness and intermittent, explosive bursts of anger.

The research paper also described a large group of subjects who have a genetic deficit that causes a disruption in the brain's serotonin levels. The serotonin system employs many of the brain regions described earlier and a disruption of the system has been linked to increased aggression. Davidson's analysis showed that these emotion-controlling brain regions showed less activity in the individuals who carried this genetic abnormality.

Davidson stresses that the research points to both genetics and poor environmental history as potential contributors to impulsive violence, and together they present a "double whammy" that put people at much greater risk. "These parts of the brain are particularly responsive to experiential shaping," Davidson says.

The study may recast the way society looks at impulsive violence, by defining it as a mental health issue. "Emotion regulation is extremely significant for a whole constellation of problems people encounter," he says.

The long-term implications of the study will be in the realm of new treatments, Davidson predicts, that will combine targeted behavioral interventions with drug therapies, in much the same way depression and anxiety disorders are treated.

"Given what we know about brain plasticity and the fact that the brain really can change in response to experience, we have good reason to expect that these treatments may, in fact, have beneficial consequences," Davidson says.

While the research points to emotion regulation deficits as a "smoking gun" in impulsive violence, Davidson cautions that science is a long way from developing any preventive strategy for at-risk populations. Davidson's future studies will explore this complex brain process in much greater detail, through the use of imaging technologies such as magnetic resonance imaging (MRI) and positron emission topography (PET) used in tandem for high-resolution, real time images of brain function.

Davidson is director of the Wisconsin Center for Affective Science and directs the W.M. Keck Center for Functional Brian Imaging. His research is supported by the National Institute of Mental Health.

The Biological Basis of Behavior: Unit III

Biological Psychology Studies

Study 3

Women with higher levels of testosterone are more attracted to masculine looking men like celebrity beefcakes Russell Crowe and Daniel Craig and men with raised levels of the same hormone are more attracted to feminine looking faces like those of Lost star Evangeline Lilly and the actress Natalie Portman.

These are the findings of the University of Aberdeen's Face Research Laboratory which reveal that changes in testosterone levels affect the extent to which men and women are attracted to different types of faces.

It has been assumed that people are attracted to other people because they are drawn to particular types.

But Drs Ben Jones, Lisa DeBruine and Lisa Welling have shown that testosterone levels appear to be the key.

Theirs is the first study to reveal the role the hormone plays in making certain women attractive to certain men.

The researchers asked male and female volunteers to complete short face preference tests in which they were shown pairs of masculine and feminine faces. Participants were asked to choose which face from each pair was more attractive.

Men and women completed four different test sessions that were each a week apart. In each session, volunteers also provided a saliva sample which was used to measure testosterone levels.

Dr Jones, a Psychology lecturer, said: "People preferred different types of face in the session where their testosterone level was highest than in the session where it was lowest.

"When men's testosterone levels were high, they were more attracted to feminine women. When women's testosterone levels were high, they were more attracted to masculine men.

"Since masculine men and feminine women are thought to produce the healthiest children and sex drive is higher when testosterone levels are also high, these findings suggest that men and women in hormonal states where their interest in sex is highest, show stronger attraction to high quality – or healthy – mates."

Dr Welling added: "We tend to think that attraction is relatively stable over time. However, our research shows that attraction is affected by fluctuations in testosterone levels."

The Biological Basis of Behavior: Unit III

Biological Psychology Studies

Study 4

Men have long been accused of judging women on looks alone, but even the plainest Jane can get their hormones raging, a study has found.

Research involving a group of male students found that their levels of the hormone testosterone increased to the same extent whether they were talking to a young woman they found attractive – or to one they didn't fancy much at all.

After 300 seconds alone in the same room as a woman they had never met before, and in some cases did not find particularly attractive, the men's testosterone levels of the hormone had shot up by an average of around eight per cent.

The study's authors believe the rise in testosterone may be an automatic and unconscious reaction that has evolved in man when faced with a woman, to prepare him for possible mating opportunities.

The rising levels may then fuel more visible changes in male behaviour that occur in the presence of a woman, including a squaring of shoulders, an upright posture, and greater use of hands - and even, it is suggested, a flaring of the nostrils.

The rise in the male hormone may also be the reason why men are more likely to tell women exaggerated stories about their job, career, education and earnings, the researchers believe. The study, published in the journal Hormones and Behaviour, involved 63 male students aged 21 to 25 who were not aware of the purpose of the study.

Their testosterone levels were measured with saliva samples and they were then taken to another room by a researcher under the guise of being there to solve a sudoku puzzle.

In the same room another man or a woman appeared to be solving a similar puzzle, but he or she was in fact acting as the so-called stimulus.

The women were chosen on the basis of being moderately attractive for the student population.

The researcher then made the excuse that he did not have the correct puzzle for the participant and left the room to get it. The two were then left alone to wait together for five minutes. The stimulus people were told to engage in friendly conversation in a natural manner, or allow long pauses if the man elected not to talk.

After five minutes, the experimenter returned with the correct puzzle, and then left the room with the stimulus person.

Fifteen minutes later, the experimenter returned to collect the puzzle from the man, and to take a second saliva sample. Comparison of the saliva tests showed that testosterone levels rapidly increased by an average of 7.8 per cent after the five minute contact with a woman.

Men who were rated as more aggressive or dominant types had gone up even higher. The results also show that testosterone levels did not change when they were in the room with another man.

The men were also asked to rate the attractiveness of the woman in the room, and the results show that the testosterone increase was not influenced by the perceived attractiveness of the women.

Leander van der Meij, who led the study at the University of Groningen in Holland, said: "We found a testosterone increase after only five minutes of exposure to a woman. Our results suggest that the increase in testosterone levels that we found, may be an automatic male response that activates receptors in organs and the nervous system to prepare the human body for mate attraction."

The researchers believe the results suggest that one of the ultimate functions of testosterone may be to attract mates. One way it may do that is by orchestrating changes in appearance and behaviour that may increase their attractiveness.

This idea is supported by evidence that dominance behaviours of men increases their desirability as a date and by research showing that men who exhibit more dominant-like behaviour make more frequent successful contact with women.

Mr van der Meij added: "We showed that testosterone levels increased in men after contact with women. This increase is probably an important mechanism through which men acquire partners.

"Testosterone levels rose motivating men to seek mating opportunities. That in turn triggers changes in unconscious behaviour designed to attract a mate. The rise in levels of the hormone bring about changes in way men display themselves.

"Once levels have risen, they can display more dominant behaviour. They talk more with their hands, there is more eye contact, their posture is more upright, and they are more likely to tell stories designed to impress the woman. We known that women can be attracted by these kinds of things. All this, we believe, may be fuelled by the rise in testosterone that we have found."

The Biological Basis of Behavior: Unit III

Biological Psychology Studies

Study 5

The Biological Basis of Behavior: Unit III

Biological Psychology Studies

Study 6

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