If you're like me, you probably catch at least one cold every winter. And, when that happens, you may feel as if your throat, nose, or head are about to explode. Actually, though, it is not those parts of the body that hurt. Rather, it is your brain that hurts.
Let me explain. Your brain, rather than external factors like viruses and stimuli, determines how painful or pleasurable something is. The extent to which we feel the intensity of different stimuli differs significantly from person to person; we're only beginning to figure out the mechanisms behind why that might be.
The pathway to pain or pleasure
When a stimulus interacts with our bodies, be that something sharp that pierces our skin or, indeed, a virus that causes inflammation in our throat, the sensory receptors located in our skin and tissues send a message to our spinal cord via nerve fibers and axons. From there, the message makes it's way to the brainstem and then to different areas of the brain — like the thalamus, hypothalamus, midbrain, and others, where it is processed. Once the brain reaches a verdict about the type of stimulus and its intensity, signals are sent back to the receptors and other parts of the body to respond to the event. At its most basic, this is the mechanism through which we respond to external stimuli and experience pain.
Conversely, we actively seek out pleasure because of a reward mechanism in the brain that motivates us to do so. In anticipation of an enjoyable event, the brain releases dopamine, a neurotransmitter that motivates us to pursue pleasurable things. After we complete the task — say, eating ice cream or having a glass of wine — the brain rewards us by releasing opioids, which, as you may have guessed, are similar to the active substances in recreational drugs and painkillers. We are designed to crave opioids. It is this craving that pushes some of us to pursue pleasure-inducing activities or substances repeatedly, giving in to addiction.
You might be tempted to think that pain and pleasure are as different from each other as they come. But in reality, neuroscientists discovered in the early 2000s that the same areas of the brain lit up during pleasurable and painful experiences when performing brain scans on patients. Furthermore, dopamine, the chemical that is responsible for our pursuit of pleasure, is also highly present in the bodies of respondents to pain, a study from the University of Michigan revealed, which helps to explain why people develop addictions during periods of intense stress and/or why they become addicted to pain medications.
Conceptually, we are wired to seek out pleasure or relief from pain and avoid pain because doing so is important to our survival. It is important to our survival to like food or sex and to dislike being bitten or hit. The feeling of pain causes our bodies to react in ways that safeguard our well-being. What would happen if we didn't feel pain when something burned us? We would likely burn to death or risk severe tissue damage. The mere gesture of removing our hand from the stove or a hot dish could help us avoid these dire scenarios.
In the rare instances when people aren't able to feel pain — like in the case of sufferers of a rare condition called congenial insensitivity to pain — they end up harming themselves unintentionally over and over again and having a lower average life expectancy than the rest of us.
Why so complicated?
That our brains are made up of a lot of neurons — around 86 billion of them — is a well-known fact. But a large number of neurons is only a small part of why our brains are so complex. The numerous connections among different cells and areas of the brain hold the key to our behavior, intellect, and the functioning of our bodies — in short, to our humanity. But these connections are still very poorly understood; how different parts of our brains encode information to then communicate it to other parts of the brain remains largely a mystery.
To complicate matters further, the knowledge that we do have about the brain is as fragmented as the studies from which it emerges. Study conditions, demography, methods, and sample size are only some of the factors that limit the validity of studies about the brain. That is to say, nothing about the fact that the only way researchers can access the brains of living people is through imaging, which is better at showing blood flows to the brain than at following the activity of individual nerve cells.
An illustration of the limitations of brain research is the case of two studies published in 2018. In an April study, researchers posited that adult brains contained equally as many new cells as young brains – which, the authors claimed, indicated that, contrary to long-held beliefs, old brains continued to make new cells. That would have been great news for those past their prime if it hadn’t been for the fact that, just a few weeks earlier, another paper claimed the exact opposite: that the human brain stops making neurons during childhood.
Therefore, our understanding of exactly how our brains process complex sensations like pain, pleasure, or fear remains limited. In practice, it is obvious that a multitude of types of information are at play when we experience external stimuli. Memory, environment, knowledge, and sensory information are just a few of the things that inform our reactions to the outside world. Past experience influences how intensely we respond to known stimuli.
For instance, if you’ve been afraid when walking down an alley at night at some point in the past, the fear you may feel when you’re faced with the prospect of walking down the same alley may be disproportionately higher than for someone who’s looking at the alley for the first time. And, if you’re anything like me, the memory of how the last ice cream you ate melted in your mouth might make you disproportionately excited about having another one. Sometimes only a few minutes after finishing the first one.