After ten years as a psychologist practicing , I reclined on the couch of my own analyst feeling burdened by my chosen work. After a day of seeing patients, I was drained. I had been trained to listen at many levels—words, emotions, disclosures—and I took all of that in and sorted it out in my mind. I was good at helping others discover and pursue what they wanted out of life. But at day's end I had no resources left to do it for myself.

Then I heard myself say: "I don't like being a therapist." Pause. "I never have." I loved the study of psychology. I didn't love seeing patient after patient. I was perpetually overstimulated, busy decoding everything I took in. Plus, I wondered why I couldn't tolerate the large caseloads my colleagues took on willingly.

Suddenly I felt free, loosed from expectations that never fit. And just as suddenly, I felt I could say no to the demands of others. I could even say no to being a therapist.

As a card-carrying introvert, I am one of the many people whose confers on them a preference for the inner world of their own mind rather than the outer world of sociability. Depleted by too much external stimulation, we thrive on reflection and solitude. Our psychic opposites, extraverts, prefer schmoozing and because such activities boost their mood. They get bored by too much solitude.

Over the past two decades, scientists have whittled down to five those clusters of cognitions, emotions, motivations, and behaviors that we mean by "personality" factors. , and by inference , is chief among them, along with , , , and —psychology's so-called . Although introverts and extraverts may seem like they come from different planets, introversion and extraversion exist on a continuous dimension that is normally distributed. There are a few extremely extraverted folk, and a few extreme introverts, while most of us share some extravert and some introvert traits.

Although there is no precise dividing line, there are plenty of introverts around. It's just that perceptual biases lead us all to overestimate the number of extraverts among us (they are noisier and hog the spotlight). Often confused with , introversion does not imply social reticence or discomfort. Rather than being averse to social engagement, introverts become overwhelmed by too much of it, which explains why the introvert is ready to leave a party after an hour and the extravert gains steam as the night goes on.

Scientists now know that, while introverts have no special advantage in , they do seem to process more information than others in any given situation. To digest it, they do best in quiet environments, interacting one on one. Further, their brains are less dependent on external stimuli and rewards to feel good.

As a result, introverts are not driven to seek big hits of positive emotional arousal—they'd rather find meaning than bliss—making them relatively immune to the search for that permeates contemporary American culture. In fact, the cultural emphasis on happiness may actually threaten their mental health. As American life becomes increasingly competitive and aggressive, to say nothing of blindingly fast, the pressures to produce on demand, be a team player, and make snap decisions cut introverts off from their inner power source, leaving them and depleted. Introverts today face one overarching challenge—not to feel like misfits in their own culture.

Introversion in Action

On the surface, introversion looks a lot like shyness. Both limit social interaction, but for differing reasons. The shy want desperately to connect but find socializing difficult, says Bernardo J. Carducci, professor of psychology and director of the Shyness Research Institute at Indiana University Southeast. Introverts seek time alone because they want time alone. An introvert and a shy person might be standing against the wall at a party, but the introvert prefers to be there, while the shy individual feels she has no choice.

Introverts don't necessarily hide. Beth Wheatley is very much in the public eye as director of public relations for The Nature Conservancy. Yet she scores squarely as an introvert on personality tests. She was led to her work by her love of nature. She runs daily, not just for the physical exercise but because running allows her time to think through the events of her day. She prefers talking with one person at a time. She usually opts out of after-work social events.

"My number-one strategy is to stay under the radar screen. I stand next to a wall and put an invisible barrier around me so that I'm not bombarded and can think about my next move," she confides.

It's often possible to spot introverts by their conversational style. They're the ones doing the listening. Extraverts are more likely to pepper people with questions. Introverts like to think before responding—many prefer to think out what they want to say in advance—and seek facts before expressing opinions. Extraverts are comfortable thinking as they speak. Introverts prefer slow-paced interactions that allow room for thought. Brainstorming does not work for them. Email does.

Introverts are collectors of thoughts, and solitude is where the collection is curated and rearranged to make sense of the present and future. Introverts can tolerate—and enjoy—projects that require long stretches of solitary activity. Extraverts often have to discipline themselves for bouts of solitary work, and then they prefer frequent social breaks.

While extraverts spend more time overall in social activities than introverts do, the two groups do not differ significantly on time spent with family members, romantic partners, or coworkers. Moreover, extraverts and introverts both report a mood boost from the company of others. For introverts, however, the boost may come at a cost. Researchers have found that introverts who act extraverted show slower reaction times on subsequent cognitive tests than those allowed to act introverted. Their cognitive fatigue testifies to the fact that "acting counter-dispositionally is depleting."

Too Fast, Too Loud, Too Much

Like individuals, cultures have different styles. America is a noisy culture, unlike, say, Finland, which values silence. Individualism, dominant in the U.S. and Germany, promotes the direct, fast-paced style of communication associated with extraversion. Collectivistic societies, such as those in East Asia, value privacy and restraint, qualities more characteristic of introverts.

According to the personality test administered to two randomized national samples, introverts make up 50 percent of the U.S. population. The MBTI definition of introversion—a preference for solitude, reflection, internal exploration of ideas vs. active engagement and pursuit of rewards in the external/social world—correlates closely with the Big Five description. But the results still surprise; if every other person is an introvert, why doesn't the cultural tone reflect that?

It's not just that we overestimate the numbers of extraverts in our midst because they're more salient. The of individuals is reinforced in the media, which emphasize the visual, the talkative, and the sound bite— immediacy over reflection.

"In verbal cultures, remaining silent presents a problem," report Anio Sallinen-Kuparinen, James McCroskey, and Virginia Richmond, who have studied communication styles in the U.S. and Finland. Perceptions of competence tend to be based on verbal behavior. An introvert who is silent in a group may actually be quite engaged—taking in what is said, thinking about it, waiting for a turn to speak—but will be seen in the U.S. as a poor communicator.

When psychologists Catherine Caldwell-Harris and Ayse Ayçiçegi compared U.S. and Turkish samples, they found that having "an orientation inconsistent with societal values" is a risk factor for poor mental health. The findings support what the researchers call the personality-culture clash hypothesis: "Psychological adjustment depends on the degree of match between personality and the values of surrounding society." To the extent that introverts feel the need to explain, , or feel guilty about what works best for them, they feel alienated not only from society but from themselves.

Enough Stimulation Already!

Solitude, quite literally, allows introverts to hear themselves think. In a classic series of studies, researchers mapped brain electrical activity in introverts and extraverts. The introverts all had higher levels of electrical activity—indicating greater cortical arousal—whether in a resting state or engaged in challenging cognitive tasks. The researchers proposed that given their higher level of brain activity and reactivity, introverts limit input from in order to maintain an optimal level of arousal. Extraverts, on the other hand, seek out external stimulation to get their brain juices flowing.

Neuroimaging studies measuring cerebral blood flow reveal that among introverts, the activation is centered in the frontal cortex, responsible for remembering, planning, , and problem solving—the kinds of activities that require inward focus and . Introverts' brains also show increased blood flow in Broca's area, a region associated with speech production—likely reflecting the capacity for .

But extensive internal dialogue, especially in response to negative experiences, can set off a downward spiral of affect. And indeed, and are more common among introverts than extraverts. In general, says Robert McPeek, director of research at the Center for Applications of Psychological Type, introverts are more self-critical than others—but also more realistic in their self-assessments. Call it depressive realism.

The biological difference between introverts and extraverts is most evident in the way they respond to external stimulation, observes Colin DeYoung, assistant professor of psychology at the University of Minnesota. "The levels of stimulation extraverts find rewarding can be overwhelming or annoying for introverts." He cites studies showing that, when learning, introverts do best in quiet conditions and extraverts do better with more noise.

DeYoung traces the differences to brain sensitivity to rewards and positive emotions, which is orchestrated by the neurotransmitter . In fact, introverts and extraverts can be distinguished by differences in the size of brain structures responsible for sensitivity to rewards, such as the medial orbitofrontal cortex, which codes the reward values of incoming stimuli.

The dopamine-driven search for rewards shows up in characteristic extravert behaviors such as talkativeness, , and enthusiasm. Notes DeYoung: Such behaviors are reinforced in American society, where "there certainly seems to be a cult of extraversion."

To Hell With Happiness

In the united states, people rank happiness as their most important goal. That view has a special impact on introverts. Happiness is not always their top priority; they don't need external rewards to keep their brains in high gear. In fact, the pursuit of happiness may represent another personality-culture clash for them.

In a series of studies in which subjects were presented with an effortful task such as taking a test, thinking rationally, or giving a speech, introverts did not choose to invoke happy feelings, reports Boston College psychologist Maya Tamir. They preferred to maintain a neutral emotional state. Happiness, an arousing emotion, may be distracting for introverts during tasks. By contrast, extraverts reported a preference to feel "happy," "up," or "enthusiastic" and to recall happy memories while approaching or completing the tasks.

At this year's meeting of the Society for Personality and Social Psychology, Tamir, along with Iris Mauss of the University of Denver, presented a paper entitled, "Come On, Get Happy: The Ironic Effects of the Pursuit of Happiness." The two did not specifically study introverts or extraverts. What they discovered is that, for all people, the pressure to be happy actually reduces happiness.

"We found that when we prime people to value happiness more, they become more unhappy and depressed," reports Mauss. "Our findings offer an intriguing explanation for the vexing paradox that even in the face of objectively positive life circumstances, nations generally do not become happier."

The effect seen in the study parallels the social priming introverts experience in everyday life. Although introverts like pursuing frontal cortex functions associated with the exploration of meaning, "there are cultural pressures that could make one feel guilty for not wanting to be as happy as the culture dictates," says Tamir. As a result, introverts are hit with a double whammy—feeling less happy, then feeling guilty and inadequate for feeling that way.

With a biological makeup that enables them to see positive emotional stimuli as a distraction when they are focused on another task, introverts are good at resisting all distraction. Using functional brain imaging, Stanford biopsychologist Brian W. Haas measured the reaction time for introverts and extraverts when they tried to identify the color in which an emotionally provocative word was printed. Introverts proved more able to focus on the task of color identification while disregarding the emotional content and had significantly better reaction times. Concludes Haas: Introverts, who exhibit a higher resting state of arousal, "don't need the same kind of outside entertainment."

Inner Life to External Success

Award-winning Los Angeles architect John Bertram identifies himself as an introvert. "I enjoy solitary activities or those with few people. I am not a joiner and do not meet new people nor make new friends easily. I have trouble making small talk. I have never played on a sports team, joined a club, or gotten in a fight." But, he admits, it's not easy being an introvert in L.A.

"Los Angeles, like New York, is full of type A people whose success depends upon their coercive powers and being comfortable with and conflict. Unless I am careful I can easily be manipulated and coerced."

Bertram loves researching, designing, drawing, and producing specifications. "In the practice of architecture, one is rarely called on to develop ideas or solutions on the spot. Conflicts and challenges that arise can typically be dealt with in private at my leisure. I liken it to the difference between speaking extemporaneously and speaking from a prepared text. The former tends to leave me hopelessly confused because I find it difficult to think on my feet and under pressure. I am the person who thinks of a witty retort minutes or hours after the situation has passed."

Many introverts require a wake-up call to see the effects of cultural extraversion on their lives and to become more fully themselves. Some speak of a defining moment that crystallizes what they already know about themselves. PT Blogger Nancy Ancowitz was working on Wall Street as a manager with a top financial organizations. "The culture included back-to-back meetings, many lasting several hours," she recalls. The common approach was to "shout it out, say it again, say it louder—to use verbal sharp elbows to get a point across."

Then the company gave everyone in her department the MBTI. One look at the results helped explain the stress she was feeling. I tend to think first before I share my ideas. Check. I get tired by attending meeting after meeting. Check. I like to dive deeply into topics. Check. Hardest was feeling judged—and judging herself—for how she was wired. Others would nudge her: "Just say what you think." Being reflective was not appreciated or encouraged.

Ancowitz is no longer attending serial meetings. She works for herself as a business communication coach. "I know everything that's coming—no surprises. She frequently gives speeches. "I craft my message in advance, and it's a very efficient use of my energy." She gets up, presents her material to a large group of people, then goes home to take a nap.

Ancowitz is author of Self-Promotion for Introverts, in which she shares what she learned as an introvert in the business world. "Since visibility is often crucial to getting ahead, my goal in writing the book was to help introverts get the opportunities, promotions, and raises they desire. We can do that by using our quiet strengths such as rooting around for competitive intelligence on the Web, reading, writing, and listening attentively—activities that extraverts have less patience for."

As for me, after that pivotal session with my analyst, I started moving in a new direction—which really turned out to be an old direction. I had been writing since I was a child, but I had never explored the possibility of doing it professionally. Five books later, I sometimes feel like a transcriber: I've already written the book in my head. And I teach small-group seminars to help people find the book inside.

While my therapy skills are primarily directed at books, my psychology practice continues to thrive. I have exactly two patients. I've finally discovered the perfect caseload.

Crossed Signals "X" and "I" in dialogue

Conversation between an introvert and an extravert can involve a series of misunderstandings. As the introvert struggles to follow multiple conversational threads and sort out his own thoughts, he remains quiet and appears to be just listening. The extravert reads that as engagement, a cue to keep talking. The introvert struggles with the continuing flow of input and soon starts to shut out the extravert, while nodding or smiling, or even trying to stop the exchange.

Even a simple opener of "Hello, how are you? Hey, I've been meaning to talk to you about X," from anyone can challenge an introvert. Rather than bypassing the first question or interrupting the flow to answer it, the introvert holds onto the question: Hmm, how am I? (An internal dialogue begins, in which the introvert "hears" herself talking internally as the other person speaks.)

Even if the introvert responds, "I'm good," she's probably still reflecting on how she is: Good? That's not quite right. I really have had a pretty crummy day, but there isn't a quick way to explain that. She wants to first work out privately her thoughts and judgment about the day. She also may evaluate the question itself: I hate that we so often just say 'good' because that's the convention. The other person doesn't really want to know. She may even activate memories of how the question has struck her in the past.

While the introvert is evaluating the question on at least two levels (how she is feeling and what she thinks about the question, perhaps also what this says about our society), the speaker is already moving on to sharing something about his day. The introvert must take the incoming message from the speaker and tuck it into working until she can get to it, while more information keeps flowing in that demands tracking, sorting, searching, and critical analysis.

The cognitive load becomes increasingly difficult to manage, as the internal talk competes with the external conversation. Moreover, while trying to keep the conversation going, introverts may miss social cues, which can make them appear socially inept. The conversation is also anxiety-provoking, because the introvert feels she has too little time to share a complete thought. She hungers to pull away and give time to the thoughts her brain has generated.—Laurie Helgoe, Ph.D.

What Not to Say to an Introvert

Introverts, those quiet creatures that walk among you, are not as mild-mannered as made out to be. They seethe and even will lash out at those who encroach upon or malign their personal comfort zones. Here are a few emotional buttons to avoid with your introverted companions.