We’ve all seen the heart machines in hospitals that beep in synchrony with a patient’s heartbeat. On the display, the spikes’ timing and amplitude provide information for the doctors and nurses to know how the patient’s heart is performing. This machine, called an ECG (electrocardiogram), detects the electrical signals pulsating through the heart. Since the 100 billion neurons in the brain also send electrical signals to each other, a similar device, called an EEG (electroencephalogram), can measure how a patient’s brain is performing.
The various spikes of electrical activity, which are produced in different regions of the brain, mean different things. For example, the back region, known as the occipital cortex, is largely responsible for vision, and the side regions, known as the temporal cortex, is largely responsible for hearing. Therefore, spikes in these areas indicate that the patient is seeing or hearing.
A lot more information can be unpacked from this electrical activity than just individual spikes. In fact, brainwaves can be divided into different frequency bandwidths, such as low-pitch and high-pitch, and they give clues into what a person is thinking and feeling. The slower ones can indicate feelings of being tired, slow, sluggish, or dreamy. The faster ones are related to feeling wired or hyper alert. Below is a diagram that shows the various frequency bands, their speed, which cognitive states they indicate, and how they look on the EEG.