Among her many talents, my granddaughter Sophie, who has just turned 2*, has a clear vision of what would make her happy, coupled with the persuasive skills and executive function to make it happen. "Slide?" she says, cocking her head to one side, meaning the nearby park in New York City, which has slides, swings, and a sandbox. I'm tired and would really rather not, having planned a quieter evening of baby-sitting her, with books and toys. I try to distract her but to no avail. "Slide," she repeats, forgoing the questioning tone and nodding her head repeatedly, as if to hypnotize me into agreement. To remove all obstacles, she fetches her sand pail, wedges her shovel and ball neatly into it, and repeats, even more assertively: "Slide, Tayta" (i.e., Grandma). "Go to slide." She brings me my shoes and my purse and waits expectantly at the door. Of course, I succumb.

At the park, we hit the sandbox first. Sophie is delighted except for a pesky problem--the sand getting into her sandals, seeping between her toes. Intermittently, she stops her play to clean it off. A teachable moment, I think--if you can't get rid of it, embrace it! I persuade her to take off her sandals and dig her feet into the sand. She is hesitant at first but humors me and then starts wiggling her toes and laughing. She pours a bucketful of sand over her feet with glee. "Tayta, take off shoes," she commands, with the repeated nodding. "In for a penny," I think to myself, and off come my shoes. Of course, I'm persuaded to stick them in deeper as Sophie pours her bucketfuls onto them. Amazingly, the sand feels great on my tired feet. I would have never imagined sitting in the middle of New York City, wearing black business pants, with my feet bare, burrowed into the sand. But it makes her happy, I think to myself, with a smile. It makes me happy, I realize! Then I have an odd thought--where is "happy" in my brain?

Having worked on emotions for many years--pain, stress, anxiety, depression--in the midst of a strong emotion, I can think about specific brain circuits being activated. It's a little trick I use to put things in perspective--"Yeah, my amygdala is going a little crazy right now." As I control myself, I can imagine my frontal cortex gaining the upper hand. But these are all negative emotions, stressful. Remarkably, they all share some common neural circuitry and have correlates we can measure in blood--an increase in stress hormones, for example.

But what is the counterpart of these mechanisms when Sophie is screaming with joy as she hurtles down the spiral slide or bubbling with laughter when we play peekaboo? Of course there are some molecular candidates out there--dopamine for reward, for instance. But scientific scrutiny typically rewrites their role, for example, implicating dopamine in salience--attending to what is important--rather than simple reward. More importantly, should reward and joy be equated? Is there a biological concept as broad as stress that connotes not neutrality but feeling great, experiencing joy or happiness? And do we know its neural correlates?

As far as I know, this knowledge does not exist in modern neuroscience. The recently developed field of positive psychology emphasizes the study of factors that enable individuals to lead more fulfilling lives, be it more enjoyable (the pleasant life), more engaged in helping others (the good life), or more purposeful (the meaningful life). But it is remarkable to me that as a neuroscientist interested in emotion, I, along with my colleagues in affective neuroscience, know so little about the neurobiology of positive emotions.**

I recently challenged my laboratory staff to think of animal models that could teach us about the biology of joyfulness, if not long-lasting happiness. My student, Javier Perez--possibly because he was in a joyous stage of life, having just completed a Ph.D. and fathered a beautiful little girl--rose to the challenge. He initiated studies on the impact of music alone or music coupled with an enriched environment (a space filled with toys) on the emotional responses of rats and associated changes in their brains. Although these studies are currently being run in adult animals, I have a feeling that we will shortly move to very young animals to determine whether such experiences have a long-lived effect on the brain and how. I am betting that the repercussions will last far beyond the momentary enjoyment, that such fun and positive activities will not only enhance positive responses in adulthood but also protect against stress and modify coping strategies. Science will tell.

On that day in the park, I realized that Sophie knows something essential that we adults tend to forget: Having fun is important! It entails unexpected sensations, novel situations, body contact, and physical challenge (as long as these are not extreme or threatening). I imagine that the motor and sensory stimulation and the ensuing exhilaration are doing something special to her young brain, possibly much more important than reading a book. I know with even greater certainty that playing with her--experiencing the simple joy of being silly and making her happy--is wonderful for my brain. It lifts my spirits while inspiring my research. I can feel that circuit of happiness crackling, wherever it might be.

* This article, which will appear shortly after Sophie's 2nd birthday on 24 July, is my present to her, along with some handmade wooden toys that remind me of the simple fun of my own childhood. Sophie, may your life always be joyful!

** A notable exception: the creative research carried out by Dr. Jaak Panksep, who also coined the term "Affective Neuroscience."

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Huda Akil is a research professor and codirector of the Molecular and Behavioral Neuroscience Institute in the Department of Psychiatry at the University of Michigan, Ann Arbor. Her research focuses on the brain biology of stress and depression and the biology of endorphins and other molecules related to substance abuse.

Huda Akil is a research professor and codirector of the Molecular and Behavioral Neuroscience Institute in the Department of Psychiatry at the University of Michigan, Ann Arbor. Her research focuses on the brain biology of stress and depression and the biology of endorphins and other molecules related to substance abuse.
10.1126/science.caredit.a0900093