Serotonin For More Than Just Happiness

Serotonin is often known simply as the happiness hormone—which often gets it conflated with dopamine, which, like serotonin, is also a neurotransmitter strongly associated with pleasure.

For a deeper dive into the similarities and (important!) differences, see:

Serotonin vs Dopamine (Know The Differences)

And since serotonin also gets conflated with oxytocin (“the cuddle chemical”), see:

Neurotransmitter Cheatsheet ← four important neurotransmitters (the fourth being adrenaline/epinephrine), what they each do, and how to have more of them if you need more, and the downsides of having too much.

Today, we’re focusing on serotonin. Which, like 3/4 of the aforementioned neurotransmitters, is a targeted molecule in many antidepressants. In fact, selective serotonin re-uptake inhibitors (SSRIs) are perhaps the most commonly-used class of antidepressants in the world.

For more on that, see: Antidepressants: Personalization Is Key!

The lights are on…

Much like dopamine is associated with pleasure but is also critical for unrelated things such as motor skills and language faculties, serotonin does more than just make us happy.

It also makes us feel awake, and as such, is in many ways the counterpart of the closely-related hormone melatonin.

And, we now know, it’s also involved in decision-making!

Specifically, new research has shown that serotonin receptor (5-HT) neurons in the brainstem are interconnected, not acting independently as previously thought. The researchers used electrophysiology, cellular imaging, optogenetics, behavioral methods, mathematical modeling, and computer simulations, so we’ll not go into all the details (but we will link the paper in a moment).

What’s important about this is that they discovered distinct groups of serotonin neurons with specific activity patterns, each regulating serotonin release in different brain regions.

What’s important about that is that this goes against the traditional view of serotonin signaling as monolithic in a very binary sense, and supports a more dynamic, functionally competitive model among neuron groups, since high-activity serotonin ensembles can suppress the activity of lower-activity ensembles, affecting overall serotonin release.

To put it in less clinical terms: the ebb and flow of serotonin in our brain is not merely a matter of “more serotonin vs less serotonin”, but also a matter of where exactly in the brain that serotonin is more (or less) active.

For example (and with minimal use of clinical terms), the lateral habenula, a part of the brain involved in frustration and threat assessment, influences serotonin neuron activity, impacting binary decision-making (e.g. risk-taking vs safety-seeking choices).

This is big, because that was previously considered to be the sole domain of dopamine (in its role as “motivation molecule”).

For example: The Meds That Impair Decision-Making

Since this serotonin model allows for a lot more nuance, it could pave the way for new ways of treating conditions ranging from addictions to depression to anxiety and more.

You can read the paper in full here:

Nonlinear recurrent inhibition through facilitating serotonin release in the raphe

…and a pop-science article (with diagrams, taken from the paper) here:

Serotonin system’s hidden complexity may reshape understanding of day-to-day decision making

…which goes into more detail than we have room to here.

Want to learn more?

Check out:

The Gut Bacteria That Improve Your General Decision-Making In Life ← remembering that serotonin is not made in the brain like dopamine mostly is, but rather, is made in your gut, by your gut bacteria (so please look after those!)

Take care!