Children play. Nobody has to show them how to do it; they're just born knowing. 

But as adults, we become so disconnected from it that we forget what it is and how to do it. Psychiatrist Stuart Brown, who founded the nonprofit organisation National Institute of Play in California, says: 'Play is an ancient, voluntary, inherently pleasurable, apparently purposeless activity or process that is undertaken for its own sake, and that strengthens our muscles and social skills, fertilises brain activity, tempers and deepens out emotions, take us out of time, and enables a state of balance and poise'. 

Play is happening when you are so engrossed in something you enjoy that you lost all sense of time and don't want it to end. It's where that inner critic finally shuts up, self-consciousness fades away, and we can open up to new possibilities.

When we're depressed, play can seem like a foreign concept.

In this state of 'flow', while there may be a goal, the activity is its own reward. The degree of difficulty is just enough to keep you interested but not so difficult that you're tempted to give up. 

Play opens up a more flexible mind, beckoning us to seek out novel thoughts and actions in response to the task at hand. Play builds physical, emotional, social and intellectual development. As we continue to play, we become more flexible and creative in the way that we approach things and therefore helps us foster a resilient mind. 

This balance of play is a feeling of engagement and satisfaction - the opposite of depression. The depression loop is fueled by negative emotions, self-judgments, disengagement, helplessness and isolation. 

Play inspires the exact opposite qualities and takes away this fuel. When we're depressed, play can seem like a foreign concept. Sometimes when I ask my depressed clients what they envision when I say the word 'play' they look at me with a blank stare.

So I set about asking people what play meant to them. I found that many people I spoke with had a hard time conceiving what play is for grown-ups, because it's different from child's play, which was the only kind of play they knew. 

In fact, in a culture that prizes productivity, adult play seems to be defined as a negative, unproductive, self-indulgent activity. I believe that we need to update our definition of play. My questioning led me to believe that play means different things to different people. 

For example, after my kids go to bed, I enjoy playing around in the kitchen making homemade granola - but my wife would see this as a decidedly unplayful chore. One of my clients revealed that her 'guilty pleasure' was lying down in her pyjamas and immersing herself in Game of Thrones, a purposeless yet pleasurable activity.

In order to rediscover play in your life, it's helpful to look back in your past.

She was surprised to identify that as a moment of play for her, and she no longer felt guilty about it. She had redefined what play was.

In order to rediscover play in your life, it's helpful to look back in your past and see how you played and what gave you joy. Your experiences from childhood are stored as encoded memories that inform your perceptions today. 

Recalling them can provide clues to what gives you joy now, as an adult. Take a moment to think about how you played as a kid. Was it alone or with friends? What did you enjoy most? Maybe you engaged in imaginary play with dolls or invisible friends. You may have spent hours building Lego castles. Or maybe life felt most enjoyable when you were outside playing sport. Whatever you choose, make sure that it gives you a sense of release from your day to day life.