I’m rereading the book that really set me off on the journey of understanding neuroscience: Antonio Damasio’s “Descartes’ Error.” The book has a section that kind of introduces the basic functionality of the brain and reading it today led me to an interesting rumination.

We understand the brain as a series of interconnected wires (neurons.) These neurons can only fire in one direction. Additionally, these neurons can receive input from numerous other neurons, not just one. (I think 5000 inputs is about average.) So, you can envision a very complex wiring system with of all these neurons overlapping each other and sending signals across the circuitry. It’s very easy to presume, as some scientists do, that the ethereal thing called consciousness merely arises as a kind of emergent property from all this complex circuitry.

But something struck me about this today. Let’s consider that point that neurons are unidirectional. This means even if you have a signal that is following a complex path through the brain, going through hundreds of neurons, it had to start somewhere. Where? Well, the obvious answer is our sensory nerves — the nerves in our eyes, skin, tastebuds etc. A photon hits a nerve in my eye, and that fires off a signal which goes to my brain and contributes to my sensation of sight. A salt molecule stimulates a nerve in my tongue which also goes my brain, culminating in taste.

So that would explain our brain’s processing of our sensory experience. But what about our internal life? What about thoughts? They seem to arise out of nowhere. What is the initial event that fires them off?

Now, I’m the first to admit that I don’t know. Maybe nobody knows, or maybe this is well understood in neuroscience and I’m just not aware of it. But I can offer a couple ideas. One is that a lot of thoughts ultimately do arise from some kind of external sensory stimulation. You find yourself thinking about your ex-girlfriend named Rose, but as you trace the origins of that thought, you realize that you just passed a guy who had a nose ring, and Rose had a brother who had a nose ring. So this seemingly random rumination actually had an external source. (There’s a parallel to this in dreams. You’ll have a strange dream where a unicorn starts playing Paganini on a violin, and when you wake up it occurs to you did see an ad for a Paganini record sometime last week. This observation has just been filtering around in your unconscious, waiting to be expressed in a dream.)

Is there anything else that could set off trains of thought? It seems possible that our body processes might lead to the creation of thought. For instance, your stomach starts rumbling, and this reminds you of the last time your stomach rumbled and how you solved the problem by eating cheese and crackers and boy you sure like cheese and which is better? Cheddar or Swiss? My point here being that your stomach rumbles and suddenly you’re on train of thought. And your stomach rumbling has nothing to do with external stimulation*, but internal, visceral. (Again, we have a parallel in dreams. I recently had the experience of eating something that disagreed with my tummy, and I had nightmares.)

*Not entirely true. Your stomach rumbles because you haven’t eaten, which could be thought of as external simulation (or the lack thereof.)

But this opens up a more interesting question. I’m alleging that all brain processing (thoughts) ultimately needs some kind of stimulus, either from the external world or our internal body processes. What happens if that stimulus never comes in? Does the great and powerful Oz, er, I mean brain (a construct some have called the most complex thing in the universe) fall silent? Maybe, I don’t know. Certainly it’s noticed that minimizing your stimulation — through meditation, immersion tanks or just going to the park and staring at the lake — seems to eliminate some of the chaos of brain activity and provide a certain peace.