Introduction

Humanity's relationship with nature, a never-dull affair based on both fear and attraction, spans more than 2 million years. Our ancestors grew to understand the natural landscape, figuring out over time how to maximize their ability to secure the factors that sustained life and minimize the multiple threats to it. They grew to respect nature, balancing the understanding that nature can bite, sting, poison, maim, and kill, with an awe and appreciation of what the natural world could offer to promote health of mind and body.

Throughout the ages, and across cultures, philosophers, poets, nature writers, and outdoor enthusiasts have extolled the mentally rejuvenating and uplifting power of nature. But what of the science? To what extent is the 2-million-year relationship with the natural environment imprinted in our neurons, and to what extent does nature immersion and deprivation work for and against the individual?

In our contemporary age of science and technology, researchers have finally turned their attention toward the evaluation of these enthusiastic claims related to the medical aspects of nature. What started as a trickle of scientific inquiry in the 1970s has transformed into a formidable body of research, with many of the most startling research findings published within just the last 36 months. Scientific researchers are investigating nature's role in mental health at a time when humans are more distanced from the natural world than ever before, an environmental context in which humans are increasingly becoming part of the machine. Humans have long demonstrated a pronounced ability to use technology to conquer, control, and adapt to our natural environments. Our earliest ancestors used fire and crafted cutting and hunting tools, clothing, and shelters. Since then, technology and man's mastery over the natural environment have developed at an astonishing rate. As far back as a century ago, writers were concerned that industrialization had placed a machine in the garden, one capable of dramatically changing our natural world. Today, not only has the machine taken over the garden but there are also legitimate fears that there is now only a bit of the garden left within the machine.

This should be of great concern: natural environments offer unbelievable benefits for our health. As neuroscience develops at a rapid pace, researchers are uncovering functional aspects of the intricate anatomy and physiology of the human brain, allowing them to have a clearer picture of the true depths to which environmental factors influence cognitive and mental health. So far, the results suggest that we have completely underestimated the way in which the human brain is influenced by its physical environment and, in particular, by the elements of the natural worlds of water, vegetation, and animals. (And for our purposes, this is what we mean when we refer to nature: the nonbuilt, nonsynthetic environment—sights, sounds, aromas, rivers, oceans, plants, animals, and light in as close a form as possible to that from which we evolved.)

Undoubtedly, technology has allowed for the strength and global spread of our species, and as such, it has largely escaped meaningful criticism and broad public discourse. But today's easy access and prolonged exposure to gadgetry is leading to nature deprivation, and what is lost through that might be far more detrimental than what is gained. We want to differentiate personal gadgetry—TVs, smartphones, tablets, and home PCs—from a long list of more meaningful technology, from life-saving medical technology to freshness-preserving refrigerators. While not anti-technology (or Luddites), and with the understanding that technology has increased safety and convenience in immeasurable ways, we are unabashed screen-time critics. Nature withdrawal is being driven, at least in part, by the lure of info-entertainment-rich commercial screens—the attraction of the screen and indoor video games, so-called videophilia, is very strong.

Less contact with nature, particularly in one's young years, appears to remove a layer of protection against psychological stress and opportunity for cognitive rejuvenation. Japanese research suggests also that nature deprivation may have wide-ranging effects on the immune system. In the big picture, our turn away from nature is associated with less empathy and attraction to nature and, in turn, less interest in environmental efforts related to nature. An obvious concern is that a massive withdrawal from nature will immunize us against empathic views of nature. Sustainability of the planet is not merely about being a good citizen and recycling; it is ultimately about maintaining an intimate relationship with nature. Research shows that in order to truly care about “being green,” one must actually have meaningful exposure to nature.

Your Brain on Nature offers readers a chance to more fully understand the impact that nature (or a lack of nature) has on individuals and society and suggests ways in which they can bring nature back into their lives. We present research showing that exposure to nature-based environments is associated with lower blood pressure and reduced levels of the stress hormone cortisol (and other objective markers of stress). And that exposure to nature is also responsible for higher levels of activity in the branch of the nervous system responsible for calming us down (the parasympathetic branch).

We introduce you to a variety of ways to help you reconnect with nature:

Finally, we round out the discussion by taking a look at the historical roots and current opportunities for change provided by ecopsychology and ecopsychiatry. Allied health professionals working under the umbrella term of “ecotherapy” are educating other health-care providers, the public, and influential leaders on the importance of mindful nature interaction for personal and planetary health. Ecotherapists, we believe, will be a driving force for broad change.

This is far from a pop-psychology book, and at times there is considerable depth to the discussions. (We examined thousands of sources, both historical and contemporary, and our detailed list of references is available online for your review at www.yourbrainonnature.com.) Although we try to keep the material as straightforward and readable as possible, there needs to be some depth to the discussions so that we can demonstrate why powering down and going outside has long-term implications for humans and the survival of the planet itself. Our in-depth analysis with historical perspective provides a true understanding of the mechanism through which nature contact can influence personal, community, and global health.

The combined authorship of a conventionally trained physician and a naturopath is uncommon; we hope that our differing trainings and backgrounds provide a unique and comprehensive perspective. Physician attention to this topic is rare, but the application of the healing power of nature (vis medicatrix naturae in Latin) should be embraced by all players in the health-care arena, conventional, complementary, or otherwise. As cities worldwide expand, the importance of green space in human health is an issue of common ground for all. We hope that this book serves as a template for shared discussion and decision making at a time when we are being overwhelmed with gadgetry. We can envision an optimistic future accompanying the inevitable bulging of global urban centers, and that bright future involves more green in more places.

Yours in health!

Eva M. Selhub, MD       Alan C. Logan, ND