The prefrontal cortex is used in system 2 thinking.

The prefrontal cortex (in red) is used in system 2 thinking.

by James Hubbard, MD, MPH

As I’ve mentioned multiple times, in emergency medicine, it is essential to memorize certain basic rules and techniques to the point that they become second nature—a reflex. “For a bleeding wound, apply direct pressure”; “cool a burn.”

The most obvious reason for this is quick action can prevent further damage. But there’s another reason I’d like to explain: Reflex-like thinking uses a different part of your brain than regular thinking. This allows you to multitask easily; you can treat the immediate problem while at the same time considering what to do next.

However, reflex-like thinking does have a down side. It can lead to incorrect assumptions. So the trick is not to let either type of thinking take over too much. Otherwise, you could get into major problems.

The two types of thinking are today called system 1 and system 2. Doctors use them every day. But you do too. And you can learn to use them for medical purposes.

System 1 Vs. System 2 Thinking

System 1 is reflex thinking. System 2 requires you to put on your thinking cap.

  • System 1 thinking happens in the limbic system—the same part of your brain that has a lot to do with emotions, memory and hunger. System 1 thinking involves things you do automatically, such as getting in a car, putting in a key, and turning on the motor. I expect many times, looking back, you don’t even remember taking the steps you took when you do this. It just happens.
  • System 2 thinking takes place in the prefrontal cortex. With this type of thinking, you take more time, mull possibilities, come up with solutions. So, maybe if the car doesn’t start, your system 2 goes into action and you try to figure out why. You jiggle the key, make sure the steering is locked. Check the battery light, check the gas gauge, or wonder if it’s the transmission.

Although system 1 thinking has many advantages at the start of emergencies, it’s not perfect. For instance, you may be convinced so strongly you know what’s going on that you neglect looking for other possibilities.

Here’s an example of how this works in medicine:

A middle-aged man comes into a clinic sweating, short of breath and complaining of a crushing chest pain. Because I’ve been trained to recognize the signs of a heart attacks and have seen many of them, my system 1 thinking immediately kicks in, and I assume—just for immediate, lifesaving purposes—that it’s a heart attack.

I go through the actions I’ve so often done in the past: I call for an ambulance and hook him up with oxygen. I get the equipment ready in case he has a cardiac arrest.

I may be wrong in my assumption, but I can worry about that later. This way of effortless thinking can save time, and lives.

So system 1 is quick and efficient. However, its drawback is assumptions aren’t always right.

What if this man is not having a heart attack after all? If I’m so focused on believing he is, I may miss that the fact that his oxygen is so low that his problem is more likely a collapsed lung. Or my thinking may delay me discovering it’s a blood clot to the lung.

So a balance between the two types of thinking is required.

System 1 Stumbling Blocks

Here are a couple of examples of how relying solely on system 1 thinking can lead you astray.

1. A groggy woman with a bleeding head is lying on the ground. She smells like alcohol, and there’s an almost empty liquor bottle in her coat. You assume she fell from being drunk and hit her head.

Most of the time you’d be right. But if help is not on the way it’s risky to assume. Instead you need to activate your system 2.

So what would you do?

In this instance, going through the AEIOU TIPS mnemonic of potential causes can help, along with just looking around for clues, both on the body and in the surroundings. Look for medicine bottles and ID cards that might suggest epilepsy, diabetes, drugs, etc. And treat according.

2. Your child has a rash, and you know that fifth disease is going around. He even has the red cheeks typically seen in this disease. So this is what you initially think it is.

But wait—the child looks sick and is running a fever. With fifth disease the rash doesn’t typically start until the fever has gone away, and usually the child is feeling fine. In fact, by rash time the child is no longer contagious and can go to school.

What to do?

Your doctor decides to check a strep test, and it’s positive. The doctor prescribes antibiotics and advises you to keep the child out of school a few days—two things that would not have been done if the diagnosis was fifth disease.

Doctors can fall prey to relying on system 1 too much too. There are even terms for this: anchor bias and framework bias. This is one reason you sometimes get two different diagnoses from two different doctors.

System 1 Benefits

While system 1 thinking has its downsides if overused, it also has some serious upsides. Quick action may save a life, but also, relying on system 1 for the initial response allows you to use system 2 thinking to start trying to figure out what happened and what you should do next.

For example, because I’ve done it so much, while I’m suturing a wound, I can be thinking of something else. Or when I’m treating one part of the body, I can be thinking about other problems I need to consider. So we doctors use both systems all the time.

But here’s a big likely difference between you me. Medicine is my life. For common health problems, I know what to look for and what to do. Health-related system 1 thinking comes easily.

That said, you can learn it too. You’ll just need to do some extra learning by reading, watching videos, and participating in hands-on practice.

How to Hone Your System 1 Thinking
How two types of thinking affect you in emergencies

The limbic system is used in system 1 thinking.

Memorization can help you develop your system 1 thinking, but hands-on training is often better.

Mnemonics can help with system 1 as well. A good example is CAB—compression, airway, breathing—for cardiac arrests.

However, since you only have so much time, you’ll have to limit the number of things you learn so well that they go into system 1 thinking. Therefore, I suggest focusing on two things for system 1:

  • The basic immediate treatments for the most common injuries
  • How to recognize and treat illnesses that you or family members have or are at risk for

You probably use system 1 thinking already in your own profession. To take a rather embarrassing nonmedical example of my own: Yes, I know medicine well, at the expense of not knowing some things any other person might think of as simple.

Many years ago I saw water on the floor. I looked under the sink, and a pipe was leaking. In fact, water was pouring out. Of course, I panicked. I did know enough to catch most of the water with a well-placed bucket, but that didn’t stop the flood I knew was to about to fill the house. So next, I called a plumber, thinking he would rush over and save the day. To my surprise he calmly started asking me questions.

Where was the leak? How bad was it? Had I tried turning off the water shut-off valve?

The what?

He explained there was a shut-off valve under the sink. If that didn’t work, there was one that turned off the water to the house.

To my amazement, there was the valve, and turning it off worked. Now an emergency became a nuisance.

The plumber came out later and fixed the problem. Now, if I have a leak, my system 1 tells me, turn off the valve. But I still depend on the plumber for system 2.

So what about you? Can you think of ways you use system 1 or times it may have failed you?


Prefrontal cortex image by: Polygon data were generated by Database Center for Life Science(DBCLS)[2]. (Polygon data are from BodyParts3D[1]) (CC BY-SA 2.1 jp), via Wikimedia Commons.