Because the experience of pleasure is fleeting, the pursuit of pleasure can all too easily spiral out of control, sometimes tipping into dangerous risk taking and addictions. But if kept under control, experiencing pleasure is the spark that strengthens the circuits and networks that make up the sunny brain. And one of the great benefits of the sunny brain is the optimistic mindset it nurtures, which is not only about feeling joy and happiness, or even just about feeling good or thinking positively about the future, but also about sticking with tasks that are meaningful and beneficial. Our sunny-brain circuits help us to stay focused on the things that bring us rewards, and this keeps us engaged on important tasks.

This is a central insight, backed up by anatomical evidence, of how our sunny brain works. Optimism is about more than feeling good; it’s about being engaged with a meaningful life, developing resilience, and feeling in control. This dovetails nicely with psychological research showing that the benefits of optimism come from the ability to accept the good along with the bad, and being prepared to work creatively and persistently to get what you want out of life. Optimistic realists, whom I consider to be the true optimists, don’t believe that good things will come if they simply think happy thoughts. Instead, they believe at a very deep level that they have some control over their own destinies.

Thinking positively or negatively is important, but there’s much more to dispositional optimism than wishful thinking. Journalist Barbara Ehrenreich in her book “Smile or Die” presents a devastating critique of what she sees as the cult of positive thinking that pervades contemporary society. She realized how mindless this cult had become when she was diagnosed with breast cancer and was immediately deluged with positive messages on how this would “make her,” would allow her to “find meaning in life,” would even help her to “find the divine.” Faced with a devastating illness, she was horrified at the suggestion that she should be grateful and that all she needed to do to get better was think happy thoughts. With a clear-eyed view, Ehrenreich demolishes the notion that the power of positive thinking is the solution to all of our problems. She’s absolutely right. The scientific research tells us that optimism often has more to do with what people do and how their brain responds, rather than what people think at a superficial level.

What’s perhaps most surprising is just how optimistic we are. Survey after survey confirm that, even in the darkest moments, people are usually positive about the future. Take the following findings from a survey conducted by the United Kingdom’s National Lottery in 2009. Overall, 75 percent of the British people questioned described themselves as optimists, while 58 percent said that being around optimists was infectious and made them feel happy. The United States is no different. Following the election of Barack Obama as American’s first African American president in 2008, a wave of optimism swept across the nation, according to newspaper reports. Even though the country was in one of the deepest economic crises it had ever experienced, national polls reported that 71 percent of Americans believed that the economy would soon start to improve. In terms of their own personal financial situations, 63 percent of Americans thought that things were about to get better, and an impressive 80 percent said that they were strongly optimistic about the next four years.

What is the reason for such irrepressible optimism, especially in the face of so many global problems? The answer is both complex and intriguing. One part of the puzzle is that our brain is wired to ensure that we remain hopeful for the future. As we have seen, our sunny brain also plays an important role in keeping us engaged with ultimate rewards. Optimism is a crucial survival mechanism, honed by nature, to keep us going even when everything seems to be going wrong. Psychologists call this the optimism bias, and almost all of us have fallen prey to its appeal at some point.

Because the optimism bias is so common, it must have been highly adaptive, and, from an evolutionary perspective at least, there must be some survival benefit to this mindset. Science gives us several clues as to how the optimism bias might be of benefit. Take the tendency of men to overestimate how appealing they are to women to see how this adaptation works. Frank Saal, a psychologist from Kansas State University, paired up forty-nine males and forty-nine females who hadn’t previously met and got them talking to each other individually for a few minutes. Following this interaction, other groups of men and women observed the conversations on videotape. Women almost always said that the woman in most of these interactions exuded an air of general friendliness, but the men usually thought the woman was displaying sexual interest. In two subsequent studies, where male managers interacted with their female employees, or male professors interacted with students, men consistently mis(interpreted) female friendliness as a sexual come-on.

Martie Haselton, a psychologist from the University of California, Los Angeles, claims that these effects are predictable. He and David Buss developed the error management theory, in which they argue that because men are limited in the number of people they can mate with from an evolutionary perspective, there’s a high cost to missing out on an opportunity, while the pain of rejection is short-lived and not overly costly. Therefore, it pays for men to overestimate how appealing they are to women, and so the seeds of optimism—realistic or otherwise—are sown.

An inbuilt optimistic bias has real benefits in our everyday life as well. For one thing, our belief that things will be good in the future makes us feel happier and more satisfied with life at the moment. Countless surveys, such as those conducted by the University of Illinois psychologist Ed Diener, have shown that people say they are happy and satisfied with life most of the time. Diener and his colleagues developed the simple Satisfaction With Life Scale (SWLS) back in 1985, which is still used to see how content we are with our lives. In agreement with international surveys on optimism, Diener finds that most of us say we are fairly satisfied and happy with most areas of our lives.

While there has been much unsubstantiated hype, there are many scientific studies that suggest that a positive mindset, like optimism, is associated with better health and well-being. This is almost certainly due to the link between an optimistic mindset and beneficial actions rather than any magical power of thoughts. Most dramatic of all is the assertion that optimism can make us live longer.

The fact that people who are buoyantly optimistic also tend to be resilient in the face of adversity provides one clue as to how optimism is associated with longevity. Barbara Fredrickson, a psychologist at the University of North Carolina, has found that resilient people use optimistic thoughts and positive emotions as a way to cope with difficult situations. She explains why this is effective with her “broaden and build” theory. The central concept is that positive emotions broaden the range of ideas we have for dealing with adverse situations. In a typical experiment people were given a temporary boost of “positivity”: they were given a bag of brightly colored candy or shown funny video clips. When then asked to write down what kinds of things they would like to do if they had a spare half hour, those in a positive mood came up with far more ideas than those who had watched a scary movie. This makes sense, since one of the functions of negative emotions like fear is to narrow our attention down to a potential threat. In contrast, positive emotions tend to expand and widen our attention, and they generally lead us to more creativity. The message here is that if you want a successful brainstorming session, get people into a happy and relaxed mood first, and the ideas will flow far more easily.

This broadening effect of positive emotions can be very useful in helping us deal with difficulties in a more creative way. This can be seen in the burgeoning of compassion and togetherness that occurred in the aftermath of the September 11 attacks in New York City. Fredrickson interviewed several people immediately after the attacks and found that, while there was grief and sadness, there was also a profound thankfulness to be alive. Indeed, she noticed that people who were able to express at least some positive emotions were more resilient and far less likely to slip into despair than those who were overcome by negativity.

Given optimists’ greater persistence, it comes as no surprise to find that optimism is also linked with success. In the business world, optimism is advantageous, since the ability to deal with failures is often required. While it might seem strange to link optimism with failure, without optimism it’s virtually impossible for budding entrepreneurs to put their plans into action. Setting up a business is all about maintaining a belief that things will work out, even though there are likely to be many hurdles and obstacles to overcome. Former British prime minister Winston Churchill, no stranger to adversity himself, said, “Success is the ability to go from failure to failure without losing your enthusiasm.” This is why Thomas Edison, whose optimism was magnetic to those around him, constantly encouraged his workers to never give up. On one occasion, having realized that he had tried out more than 10,000 different ways to develop an electric lamp, he famously proclaimed: “I have not failed. I’ve just found 10,000 ways that won’t work.”

Excerpted with permission from “Rainy Brain, Sunny Brain: How to Retrain Your Brain to Overcome Pessimism and Achieve a More Positive Outlook” by Elaine Fox. Available from Basic Books, a member of The Perseus Books Group. Copyright © 2012.