Episode 5: Happy Feelins in the Synapses
youresuchatardis asked: Why do humans feel emotions so strongly at times, and barely at others? Think about times of feeling very angry or very in love, ect and compare that to times of “meh”, as some of us would put it. I’m looking for the biological aspect, here.
Neurochemistry? Come on, you could have at least asked a hard question. (Seriously, though, biology was my worst subject in the sciences. I’m glad you asked this one — it’s something I’d like to learn more about, and I’d be happy to delve into it in further questions.)
Let’s start, as ever, by laying out some terms. Your brain is composed of a very large number of neurons, in the neighborhood of eighty to one hundred billion — these are cells that transmit information in your brain via electrical and chemical signals. This transmission occurs via synapses. In a literal sense, this is a neural network — neurons connected to nearby neurons. (I say that because the concept of a neural network also appears in artificial intelligence. That’s a complicated topic — I’d be happy to touch on that more in a future post.)
Emotions, in general, are regulated by the transfer of neurotransmitters between neurons via synapses. A neurotransmitter is a chemical signal, essentially. Nearby neurons will release these chemicals, which induce the neuron to behave in a certain way. Neurotransmitters come in two flavors: excitatory, which induce the firing of an action potential, and inhibitory, which block this.
Above: a neuron, center in the callout, connected by synapses, the thin tubes. The red dots are neurotransmitters.
Often, both excitatory and inhibitory neurotransmitters are released at the same time, competing for the neuron’s attention. Like bits in a computer, at any instant, a neuron either fires a message or doesn’t. But since neurons have the opportunity to fire messages many times a second, you end up with a gradient — how many times, and how many neurons, fire that message? The more times that happens to neurons that trigger an emotional response, the stronger the emotion.
Wouldn’t it be nice if that was the whole story? But this is biology and chemistry we’re talking about. Of course it’s not that simple. These chemical neurotransmitters don’t just disappear. If they’re still floating around in the brain, they’ll trigger the action potential of other neurons, again and again. So the chemical needs to be removed from the environment — it can be destroyed by enzymatic action, or be reabsorbed into the neuron that sent it, a process called reuptake.
To illustrate how these effects work, let’s look at a common case — prescription of anti-depressant drugs in depressed patients. The feeling of “happiness” is heavily influenced by a neurotransmitter called serotonin. Interestingly, serotonin’s primary function is to mediate the action of the gastrointestinal tract, but also perception of resource availability. In most cases this means food, but it also has a lot to do with perception of social standing; a socially superior animal generally has more access to resources. (When they say the way to a man’s heart is through his stomach, serotonin may well have a lot to do with it!) Intelligent animals, of course, have a lot more diverse resources to be concerned with.
Resources are delicious.
A commonly-prescribed medication for depression is a serotonin reuptake inhibitor, like fluoxetine (Prozac). By preventing reuptake, the speed at which serotonin is destroyed in the brain is reduced; this increases the frequency at which “happy feelings” action potentials are fired.
Another chemical believed to be involved with “happy feelings” is dopamine. Dopamine controls movement, emotional response, and the ability to feel pleasure and pain. More dopamine means stronger feelings; less dopamine, weaker feelings. L-DOPA, a precursor of dopamine, is converted by the brain into dopamine; this is frequently used in the treatment of Parkinson’s disease, which reduces dopamine available via the death of dopamine-generating cells in the brain. A class of drugs called amphetamines (like Adderall, for example) also serves to increase the production of dopamine and inhibit reuptake — but with some nasty side effects.
The third one is a hormone called norepinephrine. Norepinephrine is a neurotransmitter affecting the heart; increased norepinephrine triggers increased rate of contraction in the heart — a faster pulse. It has direct interaction with the body’s fight-or-flight response, as well as our reward system. Related: feelings of love and lust increase norepinephrine. The excitement you feel when interacting with the object of your affection is directly related; effects of norepinephrine include arousal (go ahead, get your yuks out now), as well as focused attention, increased energy, mania, and elation.
We’re still learning about neurochemistry — our ability to understand the brain is a very, very new thing, and there are surely plenty of triggers I’ve glossed over or that science hasn’t discovered — but as a vast oversimplification, you can think of the magnitude of happiness, therefore, as the number of action potentials triggered by serotonin, times the number of action potentials triggered by dopamine, times the number by norepinephrine.
And who said math made people sad?