November 5, 2019
Written by: Rebecca Somach
You walk into a room and sit down as a strange device is placed on your head. You are told to think about a meeting you had last week, or maybe to look at a picture of a friend very closely. After several minutes, you are told that “your beta brain waves have a high power, that means you are concentrating well.” No, this scene isn’t taking place on an alien spacecraft, or in the middle of a psychic’s studio. Instead, a scientist in their lab is examining your brain waves using an electroencephalogram, or EEG. While the concept of ‘brain waves’ sounds like something made up for a new age religion, they are actually real.
Scientists have known about these waves for a long time, as far back as 1875 when recordings were made in animals and the 1930s when recordings were made in humans. EEG recordings have been used to monitor sleeping and test for sleep disorders, test if a patient is deep under anesthesia, and diagnose some conditions such as epilepsy, brain tumors, stroke, or brain death. Recording brain waves with EEG is a good way to look at brain activity because it does not take long to put on and it is not invasive (Figure 1). Other common methods of measuring brain activity, such as Magnetic Resonance Imaging (MRI), can take significantly longer than just putting on an EEG cap. EEG’s also don’t require surgery so scientists and doctors can observe brain waves from anyone.
So what are these ‘brain waves’, where do they come from, and how can they teach us about the brain?
To record brain waves from an EEG, several electrodes are placed on the scalp (Figure 1). Underneath the scalp, the brain has many neurons that are communicating with each other using electrical signals. Each electrode can detect the electrical signals from neurons under that one part of the scalp. Each individual signal is quite small and would be hard to detect by itself. However, when many neurons are active at the same time, their signals get large enough that an EEG electrode can record them as a brain wave. More than that, if the neurons all fire together, there will be bigger waves. If these neurons are firing together, they are said to be ‘synchronized’ in their firing1 (Figure 2). Being ‘more synchronized’ isn’t better than being ‘less synchronized,’ it just reflects the activity of the neurons. For instance, epilepsy is a condition where lots of neurons are firing together at the same time. That can be seen in an EEG as large waves of activity. Having a balance in activity is important for brains to be healthy.
To understand how scientists study brain waves, we have to understand how waves in general work. There are two main properties of all waves. Waves can have different spaces between their peaks. Each time a wave goes from peak to peak (or from the bottom of the wave to the next bottom of the wave), that is called a cycle. When scientists measure waves, they will measure them in the number of times in one second you will see a full cycle. This ‘cycles per second’ is also called the frequency of the wave, measured in hertz (abbreviated as Hz). The other part of the wave that can be measured is how big the wave is, or the amplitude of the wave (Figure 3). This is true for all waves, not just brain waves. For instance, sound and light are also waves and can be measured in a similar way.
Some waves are very easy to analyze: they have just one frequency and a single amplitude. However, most waves are more complicated than that, including brain waves. If you were to look at an EEG recording, you wouldn’t see nice waves, you would see a big mess (Figure 4). However, trained scientists can recognize and analyze these signals. To understand complicated signals, scientists make a wave simpler by breaking it down. Often, they will use a method called Fourier analysis. This method takes a complex wave, like a recording from the brain, and divides it into more basic waves. Breaking down the original brain wave into these simpler waves makes the original brain wave pattern much easier to understand and study. When you add the simple waves back together, they should combine to make the original brain wave (Figure 4).
In the brain, neuronal activity produces waves with several characteristic frequencies (Figure 5). These waves were given names to help distinguish them. Delta waves are slow, at 0.5-4 Hz and happen during the deepest parts of sleep. Theta waves are in the 4-8 Hz range and are thought to be important for memory. Alpha waves have a frequency between 8-13 Hz and are seen when a person is quietly awake. Beta waves are in the 13-32 Hz range and are seen when a person is concentrating. Finally, gamma waves are the fastest at 32-100 Hz and are thought to be local signals and are also thought to play a role in memory processing.
EEG data used to be useful for diagnosing different diseases. Scientists are now trying to understand brain waves on a deeper level. Scientists now have much more powerful ways to analyze the large amounts of data generated from recording brain waves. They want to understand if the waves in the brain are doing something, or if they have no importance. For example, they are currently investigating how brain waves might be involved in information processing. Different parts of the brain have groups of neurons that fire at different frequencies. It is thought that if different groups of neurons can coordinate their firing, this can help with memory formation. For example, if one part of the brain has a short gamma rhythm, but it always happens at the same time during a different brain region’s theta rhythm, that might help coordinate activity between these two regions (Figure 6).If one group of neurons always fires at the same time during the theta rhythm and that theta rhythm is linked to making a memory, that could mean that group of neurons is always going to be associated with that memory2. Scientists are still trying to figure out what this coordination might mean for making new memories.
While scientists continue to study why these rhythms are important, there is a market for trying to use the power of brain waves to do all sorts of things. There are now commercial headsets that let people do common tasks with “the power of their mind”. There are apps that can help with ‘brain training’ to help people concentrate or calm down. There are also remotes that let people control RC cars or even change the channels on a television. The way that most of these products work is with a headset that will take EEG recordings and try and translate those into computer commands. These products prove that people are definitely intrigued by brain waves. A lot of scientific terms might sound silly, or made up but brain waves are definitely real. Whether it is for health, research, or fun, brain rhythms have become an important part of our understanding of neuroscience. When we understand where they come from and why they are important, we understand how medical doctors can use them to diagnose disease, how researchers can use them to learn more about the brain, and how people want to use them to try and have a bit of fun.
- Bear M., Connors B. , Paradiso M., Neuroscience: Exploring the Brain Fourth Edition. 2016 Wolters Kluwer
- Colgin L., Theta-gamma coupling in the entorhinal-hippocampal system. Current Opinion in Neurobiology
Cover Image by geralt via Pixabay. https://pixabay.com/illustrations/brain-wave-awareness-compassion-4372153/
Figure 1: Image by ulrichw via Pixabay. https://pixabay.com/photos/eeg-integration-2680957/
Figures 2, 3, 4, 5, and 6 created in Microsoft Powerpoint.