Inside the brain, every moment, there is plenty of bioelectric activity. A lot of signals go from one neuron to another carrying precise information. Some of these signals can be registered and reported on an electroencephalogram (EEG).
From the late 1800s, it was clear that some brainwaves of EEG represent particular brain activities. Today, the electroencephalography is central in the neurological field because it allows analysis of sleep and many cerebral diseases.
Different brainwave types
In a normal EEG, there are four different bands of brainwaves, and each one is specific for some conditions.
During the last years of the 19th century Hans Berger, a German doctor, proposed the association between brainwaves and brain activities.
When someone is awake, with his eyes closed, the EEG is dominated by the α (alpha) band. This type of waves is characterized by a frequency of 8-13 Hz and a normal width <50 microvolts (μV).
If the subject opens his eyes, α waves disappear and another wave type becomes evident: the β (beta) type. These brainwaves have a higher frequency (30-35 Hz) and a width of 25-30 μV.
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In those moments between sleep and being awake and in some sleep’s phases the θ (theta) waves are evident, with a frequency of 4-8 Hz.
When the subject is sleeping we can see the δ (delta) waves. Those brainwaves have the lowest frequency (<4 Hz) and a high width (200 μV).
A particular rhythm with a very high frequency (40 Hz or more), called γ (gamma) activity, is considered to be the base for perception and consciousness.
Where do brainwaves come from?
As we have seen in the previous article about neurons, these cells communicate with each other by electrical signals.
Dendrites of each neuron receive many excitatory (EPSP) and inhibitory (IPSP) signals.
Now, imagine that we are looking at a dendrite and we have the possibility to give it an EPSP. In the region in which we give the EPSP, we’ll induce depolarization and this region will be electronegative. Then, the electric current will flow through the dendrite until it will go out from it. In the exit point, we’ll have an electropositive region.
We formed a dipole.
When many neurons are synchronized we have the formation of very strong dipoles and we can register them through the scalp.
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Brainwaves come from cortical neurons, above all, from those neurons that are in the external part of the cortex.
The utility of brainwaves
Electroencephalography is central in the neurological field. Being able to evaluate the cerebral activity, allows us to identify some characteristics of disease. EEG can be very useful in the study of epilepsy, for example. Even Alzheimer’s disease and schizophrenia have their own EEG alterations.
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Last, but not least, EEG can evaluate the absence of cerebral activity. An EEG flat for 30 minutes and repeated twice is one of the elements that physicians use to certify cerebral death and this judgment allows to extract organs from the body.