I studied the brain as if it were an island. It isn't.

I am an engineer by training — electrical engineering, then nuclear engineering, then information and communication, and a doctorate in mechatronics. I spent those years learning to think about systems: circuits, signals, the way a fault in one place reveals itself somewhere else entirely. Then I became fascinated by the most complicated network ever assembled, and for almost three decades I have worked as a neuroscientist, building tools that read the brain's faint electrical signals to catch the early fingerprints of stress, anxiety and depression.

I was trained to find the signal. Show me a brain and I will find you the marker for depression — one organ, one measurement, one answer. Without quite noticing, I had absorbed the deepest assumption of modern medicine: that the body is a collection of separate departments. I studied the brain the way a cardiologist studies the heart.

It is not an island. The brain I was scanning was in constant conversation with the gut, syncing its rhythms to the pulse, shaped night after night by sleep, flooded or starved by what the person had eaten, lifted or pressed down by whether they had spoken to someone they loved that week. The depression I was hunting for in the electrical signal was very often not starting in the brain at all. I had been handed a fault in the network and told to study the one wire where it happened to show up.

That changed the question. I had spent a career trying to detect illness earlier and earlier — a good aim, but detection is still a response to something already breaking. The real prize is further upstream: understanding the whole system well enough that the disorder never takes hold. Less treatment, more prevention. It is what I now say in every lecture hall I am invited into.