How Fever Dreams Work

What are fevers anyway? Why do our bodies suddenly turn up the heat when we get sick? Typically, our internal temperature is 98.6 degrees Fahrenheit (37 degrees Celsius). That can vary by a degree up or down depending on the time of day. Often it goes down a degree just before sunrise and up a degree sometime after lunch.

That's a pretty stable interior climate zone. But it can change. If your immune system stumbles across trouble somewhere in your body, it sounds the alert. Biochemical materials called pyrogens start flowing through your bloodstream. Both body tissues and certain pathogens produce these pyrogens. The "pyro" in pyrogen is not a coincidence. "Pyro" comes from the Greek word for "fire." When these pyrogens reach the base of the brain, they run into the hypothalamus, which happens to be in charge of your body's temperature settings.

Detecting pyrogens, the hypothalamus dials up the heat and tells the body not to let it out. Luckily the viruses and bacteria that make us sick are heat-sensitive. The idea is to make things hot enough to cook the bacteria or viruses until they're dead. Seems like a good idea as long as our internal organs don't get baked along with the pathogens. That's actually a possibility. Sometimes in its efforts to get rid of the stuff that's making us sick, our immune system can make us even sicker. If our temperature tops 105 degrees Fahrenheit (40.5 Celsius) for too long, we can be in danger of side effects such as seizures and tissue breakdown [source: Nalin].

Kids tend to have higher fevers that spike more quickly because their immune systems are young and inexperienced. Think of your childhood hypothalamus as a trigger-happy rookie cop and your grown-up hypothalamus as a jaded old hand who does the minimum necessary.

So much for fevers. What about dreams?

What's in a dream? Or, more specifically, what in the name of Morpheus is a dream? Why have them? Are they, as the ancients thought, a mode of communication with the gods? Or was Sigmund Freud right when he posited that they represent repressed desires? Maybe Carl Jung was on to something when he suggested that dreams tapped into a collective unconscious.

Neurologists, of course, aren't into dream interpretation. They think all that stuff is poppycock. In fact, for a long time, many scientists were convinced that dreams were just an accidental byproduct of our synapses randomly firing while we sleep. They had a name for it — "activation-synthesis hypothesis" [source: van der Linden]. The idea was that during the rapid eye movement (REM) stage of sleep, a bunch of disconnected images bump and thump through our brains. When we wake up, we automatically string the images together into a semi-coherent sequence. We come up with a dream story because that's just how our minds work.

But more recently, a series of innovative studies using electro-encephalography (EEG) and magnetic resonance imaging (MRI) point to a different way of thinking about dreams. Italian researchers used EEG technology to study the dreaming process for a cohort of subjects. They put some people in a sound-proof room, hooked them up to EEG machines, and, after they'd drifted off, woke them up at different points and had them write down what they'd dreamed [source: van der Linden].

We go through five stages of sleep and different combinations of brain waves show up at each stage. There are four different kinds of brain waves: alpha, beta, delta and theta. Each one moves at a different speed. We dream the most during REM sleep stage, which features a mix of brain waves very similar to our waking state. The study participants who remembered their dreams best were the ones who had the highest quantity of theta waves in their frontal lobes. Theta waves are low-frequency. The researchers were intrigued because there's another instance when theta waves are present in the frontal lobes, and that's when we're building and recalling memories. So there appears to be a close link between dreaming and remembering.

A separate study conducted with MRI equipment found a relationship between dreams that are particularly graphic, weird and highly emotional, and the parts of our brains known as the amygdala and the hippocampus. The amygdala is linked to how we deal with emotions while the hippocampus is involved in processing memory.

A third study discovered that our dreams are channeled through, and possibly even originate in, the lingual gyrus, an area of the brain related to emotion, memory and visual activity. Putting all this together, it seems that dreams use the memory system to help us deal with raw emotions. Turning intense emotions into memories helps neutralize them, reducing stress and anxiety. If this is true, it would help explain why people deprived of REM sleep for too long can often develop mental health issues [source: van der Linden].

Now that we've got a handle on fevers and dreams, let's put them together. What is it about fevers that makes our dreams so horrible? If, under normal circumstances, our dreams are supposed to help us neutralize difficult emotions, why do they terrify us when we're sick?

Remember that dreams occur in your brain, and your brain is quite different from the rest of your body. While it makes up just 2 percent of your total body mass, it needs 20 percent of the oxygen you breathe. Plus, neurons, the main component of the brain, are high-wattage cells; they require a lot of power to get the job done. In fact, a single neuron needs anywhere between 300 and 2,500 times more energy than the average body cell [source: Kiyatkin].

All that energy dissipates as heat, and to run well, the brain, like a computer, must be careful not to get too hot. That can be a challenge since the temperature in your gray matter tends to go up higher and faster than the rest your body when dealing with any kind of challenge (like a fever). Certain recreational drugs (e.g., meth, ecstasy and MDMA) are known to raise brain temperatures, which is one of the main reasons they can be toxic to your neurons [source: Kiyatkin].

We know that all forms of mental activity are highly sensitive to temperature changes. One study even showed that when we're exposed to higher temperatures our ability to make smart decisions decreases significantly [source: Ward]. That doesn't mean that people in hot climates make bad decisions — given enough time, our bodies can adjust to higher or lower temperatures. But an unusually hot day could be a bad time to choose a data plan or bet on the ponies.

As discussed earlier, our bodies are remarkably adept at controlling our internal temperatures. But that's not always true. It turns out that during REM, your interior thermometer tends to develop technical difficulties [source: Science Focus]. Add a fever to that and throw in the fact that your brain's temperature spikes faster and higher when the body is challenged, and then mix in the adverse effects of heat on brain function, and you've got a recipe for disastrous dreaming.

Remember the amygdala, that part of the brain closely linked both to dreams and the processing of intense emotions? It's particularly associated with negative emotions like terror and anger. Specialists think the amygdala is the culprit behind your garden variety nightmare [source: McNamara]. It would seem that it goes especially haywire under the fever-plus-REM scenario and just starts shooting out horrific dream matter willy-nilly like some misfiring grenade launcher. The result: fever dreams.

Is there anything nice we can say about fever dreams? We've established that while fevers induce misery, they mean well. They're just trying to help. Maybe they overdo it sometimes and start to roast you from the inside out, but that's just because your hypothalamus is ruthlessly committed to nuking any and all invaders.

And we know that dreams are probably an important part of how our brain preserves our mental health. We need our dreams to help us process our emotional experiences into harmless memories. If we can't dream, we can become overwhelmed by stress and anxiety. So both of the components of fever dreams, namely fevers and dreams, have a purpose. Does that hold true in any way when they're combined?

Probably not. Fever dreams are essentially turbo-charged nightmares. While the occasional nightmare could be caused by nothing more exotic than an overly spicy meal, recurrent nightmares are probably caused by something else. If you've got some stuff you need to deal with and try to avoid facing it all day, it could very well bubble up during REM. And your dream machine might not be able to handle the bubbling. Some specialists believe that when your dreams are overwhelmed by intense emotions and can't convert them into safe long-term memories, they start cracking up and turning into nightmares [source: McNamara].

So fever dreams are probably just the result of your dreams having a breakdown under pressure from overheating. The only thing they're telling you is what the rest of your body is saying — slow down, relax, rest, eat well. If you don't, your febrile amygdala is going to continue to plague you with visions of headless cyborgs, geysers of blood, warped space-time, murder, dismemberment anddeath. So, you know, get well soon.