We’ve mentioned brain waves a lot on this blog, but we’ve never gone into detail about them. So we’re going back to basics today, and talking about what exactly a brain wave is. Consider this a “Brain Waves 101” post.
To start off, the brain is made up of neurons, which are specialized cells that communicate with each other via chemical and electrical signals. The neuron is an excitable cell, meaning its membrane potential (the difference in voltage between the inside and outside of the cell) changes upon stimulation. When a neuron receives enough stimulation to fire, it experiences an action potential, which is a brief, rapid change in membrane potential along the axon.
In short, when a neuron is activated, it fires an electrical impulse.
Diagram of the neuron: Signals are received by the dendrites, and a rapid change in voltage fires down the axon, triggering the release of neurotransmitters from the terminal.
Neurons do not fire continuously, but at regular intervals. The frequency of firing depends on the incoming stimulus, and the same neuron can fire at a high or low frequency at different times. It is this periodic firing, also called neural oscillation, that is recorded by electroencephalography (EEG). On the display, the oscillation is displayed as waves of activity and rest. EEG is completely non-invasive, as it measures electrical activity using electrodes on the surface of your head. It records this activity from relatively large areas of the brain, so brain waves are a representation of the general neural oscillation in the brain.
Brain wave frequencies
Brain waves can occur at different frequencies, which correspond to different states of mental activity. Frequencies are measured in Herz (Hz), or cycles per second. The following table outlines the names and mind states associated with different brain wave frequencies. Keep in mind that the boundaries between different frequency bands are approximations, and may deviate by a few Herz.
|Frequency Range||Name||Associated With:|
|> 40 Hz||Gamma (γ) waves||Higher mental activity, including perception, problem solving, fear, and consciousness|
|13-39 Hz||Beta (β) waves||Active thinking and concentration|
|8-12 Hz||Alpha (α) waves||Relaxed alertness, pre-sleep drowsiness|
|4-7 Hz||Theta (θ) waves||Deep relaxation, REM sleep, dreaming|
|< 4 Hz||Delta (δ) waves||Deep dreamless sleep|
So what does a brain wave tell us? It essentially tells us how active our brain is at different times and in different areas. Different EEG headsets have different numbers of electrodes, which record brainwaves from multiple sites on the scalp. These numbers can range from one electrode to over sixty electrodes. And since the brain is functionally organized, we can place them accordingly, and get a better understanding of the functions of different brain areas.
Measuring brain activity
EEG is just one of many possible ways to measure brainwave activity. Other techniques employed include magnetic resonance imaging (MRI) and magnetoencephalography (MEG), which measure electromagnetic activity, and near infrared spectroscopy (NIRS), which measures blood flow. Here at InteraXon, we use EEG because it’s the most practical solution for real-world applications that anybody can use anytime, anywhere. No unwieldy machinery, no mishmash of wires, and no jumble of electrodes. In fact, the NeuroSky MindSet headsets we use simply resemble a pair of headphones, with a single frontal electrode. More robust brain imaging tools are ideal for laboratory and medical settings, but our priority is making the technology accessible to you.