I've been reading Jonathan Sadowski's The Empire of Depression. It's a book about the history of depression.

Reading this book has helped me think about the kinds practical applications for wearable, non-invasive brain activity monitors. The historical context is helpful to see how ambiguous tracking and defining "depression" still is.

Why is it hard? Because we still don't know what it is.

One debate mentioned by Sadowski is where to draw the "illness" line for depression. When is a person's mood or reaction to an event normal and expected and when is it not normal and therefore an illness?

My take is that we should draw a line at the extremes, and over time with research and better understanding of the brain, mark new lines towards the more common experiences that we currently label as "depression".

I think we should mark the line whenever someone is considering taking away their life or the life of someone else.

Suicide and homicide are, in my opinion, reflections of brain activity that are worth labelling as states needing support and attention.

How can we create brain activity monitors that make it easy for people to see their emotional state?

How can brain activity monitors help in the prevention, diagnosis, and treatment of suicide?

What mental states do people contemplating suicide exhibit?

What is the brain activity map of suicidal ideation? What does it look like?

What set of emotions and emotional intensity marks a person contemplating death?

How would people contemplating suicide even consider wearing a brain activity monitor? How could we help those people who are silently dealing with suicidal ideation?