In recent years, neuroimaging research has yielded important insights into emotional phenomena ranging from depression and anxiety to autism and prejudice. In some cases, such insights have begun to spur the development of treatments for emotional problems.
For the most part, the potential role that individual personality differences might play in the emotional brain has been largely disregarded. A new study, published in the February issue of APA's Behavioral Neuroscience (Vol. 115, No. 1), however, suggests that personality variables such as extraversion and neuroticism--known to be important to people's emotional experience but usually assumed to be irrelevant to measures of brain functioning--deserve greater attention in the neuropsychology of emotion.
"This is an important study," comments psychologist Elizabeth Phelps, PhD, who studies emotion in the brain at New York University. "In the past, if we haven't found a significant effect across subjects in a study, we just assumed it wasn't there. We don't usually think of individual variability as affecting our data that much. We talk about it as if that's not a significant factor. But this study suggests that it can be."
In their new research, Stanford University psychologists Turhan Canli, PhD, John D. Gabrieli, PhD, and colleagues used functional magnetic resonance imaging (fMRI) to measure the relation between brain responses to emotional stimuli and two dimensions of personality: extraversion and neuroticism.
While in an fMRI scanner, 14 female research participants viewed images that provoked strong positive or negative emotion. The images were presented in five alternating blocks of four positive, then four negative pictures.
Using a paper-and-pencil personality measure, the researchers also assessed participants' level of extraversion, or the tendency to be optimistic and sociable, and neuroticism, or the tendency to be anxious, worried and socially insecure.
The fMRI results indicated that participants who scored high on extraversion showed greater brain reactivity to positive stimuli, relative to negative stimuli, than did participants who scored low on extraversion. For participants who scored low on extraversion, no such correlation was found.
These associations between extraversion and neural activity in response to positive images were observed in several brain regions involved in emotion, including the frontal cortex, amygdala and anterior cingulate.
Similarly, neuroticism was strongly linked to brain reactions to negative stimuli--although the pattern appeared in fewer brain regions than did the association between extraversion and responses to positive stimuli.
"Depending on personality traits, people's brains seem to amplify some aspects of experience over others," explains Gabrieli. "All of the participants saw positive and negative scenes, but people's reactions were very different--one group saw the cup as being very full and the other group saw it as very empty."
'Pioneering' attention to individuality
The new findings may help account for why previous examinations of emotion and brain activation have sometimes turned up inconsistent results, suggests Canli, the study's lead author.
For example, he says, some studies have shown that the amygdala, a brain area known to play a role in emotional memory, is also important in shaping emotional experience, emotional face recognition and processing of visual, emotional stimuli. Other research appears to contradict those findings, however.
Canli speculates that one explanation for such inconsistencies may be that some studies included participants who happened to be more extraverted than those in other studies. "Those personality differences could lead to differing amygdala responses across studies," he says.
New York University's Phelps agrees that the results may shed light on previous results, including the amygdala research. But, she observes, because the Stanford study is the first of its kind, it's difficult to make general conclusions about the pattern of correlations that were found.
"With some of the data, we really don't know quite what it means," she says. "We're really just beginning to look at individual personality characteristics and emotionality."
Stephan Hamann, PhD, a psychologist at Emory University who also studies emotion and the brain, believes the study's most important contribution may rest less in the specific pattern of brain activation observed and more in its "pioneering" attention to individual difference variables in brain function.
"I think [this research] will change the way people conduct their experiments, in terms of collecting individual subject trait information," Hamann says.
That may be especially true in the field of emotion research, he indicates. "Emotional reactivity is intensely individual, and understanding that individuality in how the brain mediates emotions is important both theoretically and in practical ways."
For example, he suggests, as more is understood about personality differences in neural responses to emotional events, it will likely become increasingly possible to tailor treatments for emotional problems, such as depression and anxiety, to people's individual needs.
Phelps suggests a number of directions for future research. First, she says, studies that include male participants, who often show a different pattern of emotional responding than do women, may demonstrate a different pattern of results.
She also speculates that the new findings will prompt investigations of other personality variables, beyond extraversion and neuroticism. Finally, Phelps suggests, further research might address not only the effects of normal personality variability, but also what happens in abnormal cases, when personality goes awry.
Canli points out another question that remains unanswered. In the study, he notes, only positive and negative--but not neutral--images were presented to research participants. It's possible, he says, that the correlation observed between extraversion and reactivity to emotional stimuli represents not heightened responding to positive stimuli, but rather, muted responding to negative stimuli. Likewise, neuroticism may be linked not with stronger reactions to negative stimuli, but with weaker reactions to positive stimuli. Until research using neutral stimuli as a baseline has been completed, Canli acknowledges, that possibility can't be ruled out.
In addition, in experiments now under way, the Stanford group is examining how specific aspects of personality functioning affect emotional processing.
"In this study, we had people just view emotional pictures--they weren't asked to do anything in particular," Canli explains. "Some people may have been daydreaming, others may have simply felt emotions, and for others, the pictures might have brought up memories. We don't really know if the pattern of correlations really represents functions that truly go together, or whether it's just the sum of all the psychological processes that people may have been engaged in."
In follow-up work, the researchers are assigning participants more specific tasks to perform while viewing emotional stimuli, such as rating the emotional experience they're having, retrieving emotional memories or encoding the pictures into memory.
"By doing that," Canli says, "we begin to lay out a road map of how personality modulates our emotional processing in specific domains of functioning, such as attention, experience, memory and perception."
This article is part of the Monitor's "Science Watch" series, which reports news from APA's journals.