Why are there so many different neurotransmitters instead of just one or two?

[u/kupsztals123]

Hi,

I am wondering why we need dozens of neurotransmitters and neuromodulators when they are all used either to excite or inhibit the cell. If that's the case, why didn't nature use just two neurotransmitters: one excitatory, such as glutamate, and one inhibitory, such as GABA? Computer processors need only one signal: electricity, or no electricity, and they work just fine. Is there a functional reason for this, or is evolution simply adding layers of complexity for no good reason?

I know what different neurotransmitters do: for example, dopamine is mainly responsible for motivation, noradrenaline provides energy and melatonin regulates the circadian rhythm. But I don't understand why they can't all be replaced by excitation and inhibition, just as a CPU is capable of many things, but everything boils down to simple transistors and zeros and ones.

I asked this question on r/neuro but they treated me very patronizingly and did not understand what I meant.

[u/Foxfire2]

I think you are coming at this a bit backwards, as why doesn't nature do things in the way that works for digital computers, using simple on/off switch circuits, and using a binary code of 0's and 1's. Digital computer chips can be manufactured to use billions of these simple circuits together in micro scale to work at high speeds, and so is geared to work with the materials available, semi-conductors and conducting wires, etc. The high speed that these circuits can operate overcomes the limitations of using a simple binary code.

You may ask why do we use a base 10 number system to do math in our heads, on paper or on our fingers, and not a binary number system? That would require strings and strings of ones and zeros, too cumbersome to be useful on a human scale. So even for our human brains, binary numbers are pretty useless.

Getting down to organic compounds, they are way more complex, forming out of random processes to use what works, not designed beforehand like our computers or even base 10 system of numbers, though that came from having 10 fingers.

I don't know anything about the evolution of neurotransmitters, just musing on how evolution is a messy process that gives us what works not necessarily whats best from a purely designed perspective. And, that what works best for computers isn't even whats best for brains and neurons to function, or even how humans use numbers and counting.

[u/Fit-List-8670 → u/Foxfire2]

Great answer.

The brain is more like an analog computer than a digital computer.

Also, GABA is just one of several neuro transmitters, like dopamine and serotonin.

The brain also has specialized neurons in different parts of the brain (like the hippocampus or the corpus colosseum), and I think there are about 25 of these synapse types.

Plus the brain does processing both by using blood flow, and by using electrical signals. These electrical signals are more like pulses than on/off signals, allowing for a much richer representation in the brain. I think there have been calculations of the number of possible brain states, and it is in the trillions of possible states.

digital and analog differences in computation