The one neuron model5 min read

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As I will likely parrot in most of the things I write, physicists think ‘bottom up’. That is, to find some fundamental equation that underlies the whole of whatever it is describing, even if it itself does not give a very accurate portrayal of reality. Think of those classical problems in school physics lessons of a 2D ball being launched by some force at a specific angle. I’m sure some of you have nightmares after the mere mention of SUVAT equations (apologies).

But these Newtonian equations describe the fundamental physics of classical objects travelling along a trajectory really well. To then accurately describe the forces (wind resistance, spin, friction etc.) acting on a 3D real-life ball flying through the air, terms and perturbations are added to the fundamental equations. Importantly, however, terms are never taken away.

It is the same through all areas of physics: E=mc² in special relativity, the Einstein field equations in general relativity or Schrodinger’s equation in quantum mechanics, to name a few. These simple fundamental equations provide the foundation to build higher levels of complexity.

I have found that this bottom-up approach helps in most walks of life. It is simply how things are, from simplicity to complexity.

During my various mental illness ailments, I have found the models others have in their heads of how a brain works to be pretty insufficient at explaining what the heck was going on with me. It was all generalisations, usually without referencing the brain in any shape or form. For example, see the following description on the NHS website on Anxiety:

 “Anxiety is a feeling of unease, such as worry or fear, that can be mild or severe.

Everyone has feelings of anxiety at some point in their life. For example, you may feel worried and anxious about sitting an exam, or having a medical test or job interview.

During times like these, feeling anxious can be perfectly normal.

But some people find it hard to control their worries. Their feelings of anxiety are more constant and can often affect their daily lives.”

I have no idea what the above actually means. It doesn’t seem to convey any information about the condition, why it happens or how it happens. It just seems to suggest that anxious people are worried more often.

I suspect anyone with an anxiety condition will tell you that the above description is a load of crock. My anxiety feelings have a different flavour to what I believe ‘normal’ people feel. There is a tremendous sense of loss of control, in thoughts, feelings and behaviours¹.

I think I have hopefully come up with a more helpful model. It does not portray the reality very well at all, but I believe it is perhaps closer to the fundamental first step of thinking about not only anxiety, but most mental health conditions.

I imagined the brain as a single neuron. Just one. A single neuron does one thing and one thing only, it either fires off a little jolt of electricity (called an action potential) or doesn’t. Think of a light switch being turned on and then very quickly off again. I know there are all different types of neurons in different shapes and sizes and the ‘not firing’ part is actually a pretty complex picture of inhibition and excitation by neurotransmitters. But I believe the fundamental ‘on’ or ‘off’ picture still holds.

So, what would ‘normal’ look like on this single neuron? Well, neurons in the brain are in this persistent re-firing process. If they fired all at once, all the time, we would be having chronic seizures. If they didn’t fire at all, we would be dead. Therefore, it follows that normal would look like something in between, close to a single frequency of firing: on – off – on – off. Like a ticking clock:

Tick (on)……….(off) ………. Tock (on) ……………….Tick……….……….Tock……………….Tick……….……….Tock … etc.

I think anxiety in this model would be an increase in the firing frequency in this single neuron. i.e. Imagine the clock ticking faster:

Tick …Tock … Tick …Tock…etc.

Most symptoms of anxiety are in some sort of heightened state, on alert, feeling like thoughts are rushing, a feeling of too much energy etc. i.e. some neurons are firing faster than they normally would.

Depression on the other hand is the slowing of this ticking clock:

Tick……….……….……………….Tock……….……….……….……….Tick……….……….……………….Tock … etc.

Symptoms tend to be low and slow. Loss of pleasure, an increase in lethargy, hopelessness etc. For me, it was like I had lost access to large parts of my brain. Some neurons are firing slower than they normally would.

Bipolar disorder would be a quickening of the clock then over time a decrease to normal continuing to slow but after a while then speeding back up to a quick ticking. Imagine the ticking going faster and slower like waves coming into shore from the ocean:

Tick …Tock …… Tick ………Tock…………Tick……………Tock ……………… Tick …………………Tock……….……….

………..Tick…………………Tock ……………… Tick…………… Tock ………… Tick …… Tock … Tick … Tock… etc.

In my ignorant position, it may provide a simple picture of how mood stabilisers like Lithium might work. Modulating the firing frequency of neurons so that they return to a stableish pattern. Probably not though.

In schizophrenia, there is a literal classification of ‘positive’ and ‘negative’ symptoms. Many of the positive symptoms seem to correspond to a faster firing of our single neuron (hallucinations etc.), the negative slowing (anhedonia etc.).

The same can hopefully be applied to symptoms of other conditions. Some likely easier to do than others with some, I suspect, likely not to fit at all.

Despite the examples I have given above, I have not found this model to be useful to help explain the disease I have. You will perhaps notice that ‘excitement’ and ‘stress’ both seem to fit under the higher frequency end of the spectrum. Probably highlighting the spatial characteristics of brains. Further, every neuron does not fire at exactly the same rate. Different areas of the brain will naturally fire quicker and slower as time progresses. Models of mental health conditions will be way, way… way more complex than thinking of them as a single neuron. 

I have however found it useful to classify my symptoms and help to keep my mind at ease during the coming and going of symptoms. For instance, I was ill recently, which meant that I suddenly got depressed, seemingly from nowhere. Since inflammation typically slows neurons down, it put my mind at rest that this depression was likely going to only last as long as the cold and that it wasn’t a sign that my medication had stopped working.

It may also help when thinking about deep breathing, calming and meditative exercises. Instead of the generic “it helps you to relax from stress”. You could think of it as slowing down your breath slows down the frequency of certain neurons, helping you to feel less anxious. It is probably not anywhere near that simple, but it helps me to see the fundamental picture of what is likely happening.

Simple, but probably unrealistic models, give a starting point to go on and try to tackle complex realities. These models make me feel less lost in my world of chaos. They sometimes helped to keep me grounded in what was really going on, rather than grasping at whatever explanation was nearby. I don’t know if this particular model will help anyone else. You’ll have to let me know!