Your brain actively constructs your experiences. Every morning, you wake up and experience a world around you full of sensations. You might feel the bedsheets against your skin. Maybe you hear sounds that woke you, like an alarm buzzing or birds chirping or your spouse snoring. Perhaps you smell coffee brewing. These sensations seem to sail right into your head as if your eyes, nose, mouth, ears, and skin were transparent windows on the world. But you don’t sense with your sensory organs. You sense with your brain.

What you see is some combination of what’s out there in the world and what’s constructed by your brain. What you hear is also some combination In much the same way, your brain also constructs what you feel inside your body. Your aches and jitters and other inner sensations are some combination of what’s going on in your brain and what’s actually happening within your lungs and heart and gut and muscles and so on. Your brain also adds information from your past experiences to guess what those sensations mean. For instance, when people haven’t slept enough and are fatigued or low energy, they may feel hungry (because they’ve been hungry before when their energy was low) and may think that a quick snack will boost their energy. In fact, they’re just tired from lack of sleep. This constructed experience of hunger may be one reason why people gain unwanted weight.