Brain Asymmetry and Affective Style

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As you are probably aware, the left and right sides of the brain are specialized, with asymmetry in the control of various psychological functions. One type of asymmetry that is receiving research attention is the relative amount of activity in the front part of the left and right brain hemispheres. The brain constantly produces small amounts of electrical activity , which can be measured on the scalp with sensitive electrical recording equipment. A recording of such electrical activity is called an electroencephalograph, or EEG. Moreover, such electrical activity is rhythmic and exhibits waves that are fast or slow , depending on neurological activation in the brain. One particular type of brain wave, called an alpha wave, oscillates at 8 to 12 times a second. The amount of alpha wave present in a given time period is an inverse indicator of brain activity during that time period. The alpha wave is given of f when a person is calm and is relaxed and is feeling a bit sleepy and not attentive to the environment. In a given time period of brain wave recording, the less alpha wave activity present, the more we can assume that part of the brain was active.

EEG waves can be measured over any region or part of the brain. In emotion research, particular attention has been directed toward the frontal part of the brain, comparing the amount of activation in the right and left hemispheres. Study results suggest that the left hemisphere is relatively more active than the right when a person is experiencing pleasant emotions and vice versa, that the right frontal hemisphere is more active than the left when the person is experiencing unpleasant emotions. For example, in a study by Davidson and colleagues (1990), they showed film clips to the partici pants in an attempt to amuse some of the participants and disgust the others. The participants were also videotaped while they watched the funny or disgusting films EEGs were taken while the participants looked at the films. When the participants were smiling at the amusing films, they had relatively more activation in their left than righ frontal hemispheres. Similarly, when the participants were exhibiting a facial expression of disgust (lower lip pulled down, tongue protruding, nose wrinkled), their brains were more active in the right than left hemispheres. These results are shown in Figure 7.6.

Similar results have also been obtained in very young children. Instead of using films, Fox and Davidson (1986) used sweet and bitter solutions placed in the mouth




Frontal alpha power

J Left J Right








Anterior temporal alpha power

J Left J Right



Figure 7.6

Results of Davidson et al. (1990) study.

of 10-month-old infants to produce pleasant and unpleasant af fective reactions. The infants showed relatively more left- than right-brain activation to the sweet solution and more right- than left-brain activation to the bitter solution. In another study of 10-month-old infants, the infants' mothers left them alone in the testing room, whereupon a stranger entered the room (Fox & Davidson, 1987). In this standard anxiety-producing procedure, some infants become distressed but some do not; some infants cry and fuss but others do not. The researchers divided their sample of infants into those who cried during separation from their mothers and those who did not cry . They found that the criers exhibited more right-brain activation, relative with the left, compared with the noncriers. These results suggest that this tendency to become distressed or not (and the associated brain EEG asymmetry) is a stable characteristic of infants. Fox and colleagues (Fox, Bell, & Jones, 1992) studied a group of infants at age 7 months and again at age 12 months and found that the EEG measures of hemisphere asymmetry taken at those two time periods were highly correlated, suggesting stability over time in frontal brain asymmetry . Similar results have been found with adults, showing that measures of EEG asymmetry show test-retest correlations in the range of .66 to .73 across studies (Davidson, 1993, 2003). These findings suggest tha individual differences in frontal brain asymmetry exhibit enough stability and consistency to be considered as indicative of an underlying biological disposition or trait.

Other studies suggest that EEG asymmetry indicates a vulnerability to pleasant or unpleasant af fective states. Tomarken and colleagues (T omarken, Davidson, & Henriques, 1990) and Wheeler and colleagues (Wheeler , Davidson, & Tomarken, 1993) examined the relation between individual dif ferences in frontal asymmetry and reactions to af fective film clips in normal participants. In these studies, EEG asym metry was measured while the participants were resting. Then the participants were shown either happy and amusing films or disgusting and fearful films. For the depen ent variable, the participants were asked to rate how the films made them feel. The hypothesis was that the participants with greater right-side activation at rest (measured before watching the films) would report more intense negative affective reactions to the fear and disgust films, compared with the participants with relatively mor left-side activation. The opposite prediction was made for the participants with greater left-side activation—they should report stronger positive emotions in response to the happy and amusing films. The predictions were essentially supported, with frontal asymmetry measures taken before the films were seen predicting the participants subsequent self-reported affective reactions to the films, with the right-side-dominan participants reporting more distress to the unpleasant films and the left-side-dominan participants reporting more pleasant reactions to the films


Assessing brain assymetry without an EEG. An EEG is not the only way to obtain an index of asymmetry in brain activation. Research suggests that a person's characteristic level of left- or right-sided activation may be indicated by the direction in which their eyes drift as they concentrate on answering difficult questions. When answering a difficult question (for example, "Make up a sentence using the words rhapsody and pleasure"), people's eyes drift one way or the other as they reflect on their answer (Davidson, 1991). Among right-handed persons, eyes drifting to the right signify left-sided activation, and eyes drifting to the left signify right-sided activation. If you ask a person several difficult questions (e.g., "How many turns do you make from your house or apartment to the nearest store?") and note which way his or her eyes usually drift, you may get an indication of whether they tend to be right- or left-sided asymmetric. Of course, this quick measure is not as reliable as an EEG. It nevertheless may be a rough gauge of whether a person is left- or right-side asymmetric.

Application (Continued)

Perhaps you could make some observations of a few friends or acquaintances, asking them several difficult questions and observing which way they move their eyes as they think through their answers. Most people will not show completely consistent patterns of going one way or the other. That is why it is important to ask several questions and see which way they usually move their eyes. You will also need to decide whether they are more vulnerable to positive or negative emotions. Persons who glance frequently to the right are more likely to be left-hemisphere dominant and should be more vulnerable to the pleasant emotions (e.g., happiness, joy, enthusiasm). Persons who frequently glance to the left while engaging in reflective thought are more likely to be right-hemisphere dominant and, by implication, should be more vulnerable to the negative emotions (e.g., distress, anxiety, sadness).

Certainly, many factors influence how people feel and which emotions they experience. The findings reviewed here suggest that the characteristic pattern of brain activation is one factor that may influence our affective lives by contributing to the likelihood that we will experience certain emotions.

Similar results have also been found with monkeys. Because monkeys cannot tell you how positive or negative they are feeling, researchers have used measures of cortisol to assess emotional reactivity. Cortisol is a stress hormone that prepares the body to fight or flee, and increases in cortisol mean that the animal has recently exp rienced stress. Davidson and his colleagues (reviewed in Kosslyn et al., 2002) have found that monkeys with greater right-sided activation had higher levels of cortisol. Identical results have recently been found with 6-month-old children. These researchers induced fear in the infants by having a male stranger enter the room, slowly approach the infant, and stare at the infant for two minutes. Those infants who had greater right-sided activation at baseline showed increased cortisol responses to the stranger . Also, those infants who showed the most right-sided activation during the stranger approach phase also displayed more crying and facial expressions of fear , and tried to escape more, compared to infants with less right-sided activation (Buss et al., 2003).

A study by Sutton and Davidson (1997) showed that dispositionally positive persons (assessed by Carver and White's (1994) BIS/BAS inventory) showed greater relative left frontal EEG asymmetry at baseline, in the absence of emotional stimulation. Sutton and Davidson (1997) explicitly draw on Gray' s theory to or ganize the literature on affective dispositions and brain function, illustrating the utility of Gray' s BAS and BIS concepts (e.g., approach motivation and withdrawal motivation, respectively) and their distinct activation. These results have recently been replicated using functional brain imaging techniques (Canli et al., 2001).

The importance of brain asymmetry research is that dif ferent portions of the brain may respond with pleasant or unpleasant emotions, given the appropriate af fec-tive stimulus. Fox and Calkins (1993) discuss this notion in terms of thresholds for responding. The person who displays a right-frontal-activation pattern may have a lower threshold for responding with negative emotions when an unpleasant event happens. It may take less of an af fective event to evoke negative feelings for right-dominant persons. For an individual who displays a left-frontal-activation pattern, the threshold for experiencing pleasant emotions in response to positive events is lowered. The concept of thresholds implies that persons with a left- or right-sided pattern require less of the af fective stimulus to evoke the corresponding emotion. A person's affective lifestyle may have its origins in, or at least may be predicted by , his or her pattern of asymmetry in frontal brain activation.

Recently, an unlikely collaboration has emer ged between the psychologist Richard Davidson, who runs the Laboratory for Affective Neuroscience at the University of Wisconsin, and Tenzin Gyatso, who is also known as the fourteenth Dalai Lama, the supreme leader of Tibetan Buddhism and winner of a Nobel peace prize. Dr. Davidson and other psychologists and researchers met with the Dalai Lama for five days in Dharamsala, India, in March 2000. D . Davidson measured the brain waves of one senior Tibetan monk, who turned out to have the most left-sided asymmetry that has ever been recorded. Was this a quirk, or is there something about the training of these monks that produces more left-sided brain activity?

To answer this question Davidson teamed up with Jon Kabat-Zinn, who founded the Stress Reduction Clinic at the University of Massachusetts Medical School. Dr. Kabat-Zinn uses a form of mindfulness meditation to teach people how to reduce stress. This form of meditation is loosely based on Buddhist meditation techniques. In this research, they obtained a sample of 41 workers employed in high-stress jobs in the biotechnology industry . Twenty-five of the workers were taught mindfulnes meditation and practiced it for eight weeks. A control group consisted of 16 workers from the same company in the same kinds of jobs. All subjects had their brain waves assessed before and after the eight-week period.

Before the mindfulness training, subjects tended toward a slightly right-sided asymmetry, suggesting chronic stress. After the training, these subjects, compared to the control group, showed a significant shift toward left-sided asymmetr . They also reported less stress, feeling more energized, more engaged in their work, and less anxiety. In a surprising finding, mindfulness meditation appeared to give the workers immune systems a boost. This was determined by the amount of flu antibodies the produced in response to a flu shot, with the mindfulness meditators showing a mor robust immune response to the flu shot (Davidson et al., 2003)

The Dalai Lama wrote a column in the New York Times (Gyatso, 2003) describing mindfulness meditation as a nonsectarian technique involving "a state of alertness in which the mind does not get caught up in thoughts or sensations, but lets them come and go, much like watching a river flow by . . these methods are not just useful, but inexpensive. You don't need a drug or an injection. You don't have to become a

Buddhist, or adopt any particular religion. Everybody has the potential to lead a peaceful, meaningful life." Indeed, it appears that practicing such mindfulness can bring about changes in biology , and that these changes in turn appear to promote more positive emotional traits.

In 2005 the Dalai Lama attended the annual meeting of the Society for Neuroscience, where he charmed an audience of 14,000 with a talk presenting meditation as an empirical way to investigate the mind. While many neuroscientists ar gued that a religious leader should not be given time at a meeting of scientists, most of those attending agreed with the Dalai Lama' s view that scientific evidence will persuade more people tha religious dogma. After his remarks, a symposium of several research papers examined the question of whether The Dalai Lama has been working with neuroscientists in an meditation can alter brain physiology and of fer health effort to understand the human mind. benefits. For example, Sara Laza , a psychologist at

Harvard Medical School, reported that areas of the brain associated with attention and sensory processing were thicker in persons who had been practicing meditation for many years than in subjects with no meditation experience. By encouraging scientific inves tigations of the brain, the Dalai Lama provides an interesting and current example of a physiological perspective on the mind.

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  • Eetu
    What were the results of the brain asymmetry and affective style?
    1 year ago

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