Neuromodulators, Benefits and Side-effects

In the real world, “raw” signals are not continuous. Wind, water flow, stronger smells etc can all make signals short-lived. If a living thing were to only rely on such signals, it would give up way too soon.

 

It is to address these real-world constraints that certain neuromodulators arose, explains Max Bennett in A Brief History of Intelligence. Neuromodulators tune the neural activity across the entire brain, not just in neighbouring neurons. Not surprisingly, they have side-effects.

 

Dopamine is the neuromodulator that says “Keep going” even though the signal that initiated the action is no longer present. The principle behind it is as follows: if the animal got a whiff of food, it is probably nearby. If the signal soon stopped, it is probably because of a change in wind direction or other such variable. Continuing to look makes sense.

 

Dopamine, however, is not about liking something. It is all about wanting something. It is easy to understand this with an example. When scientists would flood the brains of rats with dopamine, it would keep consuming food even though its body language, after a point, did not convey any pleasure from eating. The rat just keeps wanting food, whether or not it is liking it anymore. This, says the author, is why we humans can keep scrolling our phone feeds endlessly (the want) even though it is not giving us any pleasure beyond a point (no like)!

 

The opposite neuromodulator is serotonin. It is a signal of “Enough”, no need to continue reacting to signals on that front. So the animal doesn’t keep reacting to signals of food if it has already eaten.

 

Then there is adrenaline, the famous fight-or-flight neuromodulator. It is an all systems go signal. The animal goes in full heartedly, and it is hard to stop either the fight or the flight. This made sense – giving up half-way would mean precious energy had been expended with no purpose achieved, so best to go all in. At this point, the body diverts energy to the muscles and away from everything else (reproduction, immune system etc). If overdone, it leads to acute stress. Animals tend to over-eat in this stage because they anticipate future threats and possible food scarcity.

 

To address the stress problem, evolution found other anti-stress chemicals, to signal the “end of the war”. Opioids are an example of such a chemical. (No, they are not produced from poppies; the body produces them internally). They also help restore the adrenaline and serotonin levels to normal levels and also reactivate the on-hold systems like digestion, immune system and reproduction. This is why opium like drugs are so dangerous – they trigger all these changes in excess and without control.

 

What if some threats and situations are inescapable? Spending a lot of energy against such situations is just a waste. So animals evolved a safety valve mechanism to not react if the situation felt futile. This was OK for animals whose backdrop kept changing. Unfortunately, with humans often the backdrop does not change for extended periods, so it can lead to depression.