What exactly are Brain Waves?
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Imagine your brain is a giant stadium full of people talking. Each person is a neuron. They’re all saying different things, and their voices all blur together, so it’s utterly impossible to make out what any person is saying (this is why it’s so hard to detect the activity of individual neurons using non-invasive methods).
Even though you can’t hear what any one person is saying, if the whole crowd (or at least a large fraction of them) is watching the same thing (e.g. a concert or a football game), you may hear changes in the overall sound as large numbers of people all get louder / quieter at the same time. That’s essentially what brain waves are. Slight changes in the activity of a large number of neurons all at the same time.
Brainwaves are the electrical signals we can detect through the skull (using an EEG machine) when large numbers of neurons are getting more/less active in sync with each other. These neurons don’t even have to be actually firing in order to generate brainwaves, they can just be getting more / less excited (like a person in the crowd talking a little louder / a little quieter). Because there’s a huge number of neurons (millions, or billions) involved, even very slight changes in their activity can add up to a signal strong enough to detect, if they’re all doing it at the same time.
They’re called brainwaves because, in practice, neurons tend to do this in a rhythmic pattern, switching between being more excited / less excited several times a second. We have different names for the patterns at different frequencies. If they’re switching back and forth around 2-4 times a second, that might be called a delta oscillation (delta waves). Up to around 7 times a second would be theta, then alpha up to around 12 times a second, then beta up to around 25, and above that is gamma, then “high / fast gamma”.
Importantly, the frequency is just one piece of the picture. Different parts of your brain (or even different brain cells in any one part of your brain) can have independent rhythms. Alpha waves in your visual cortex might mean something quite different from alpha waves in your motor cortex, which in turn means something different from alpha waves spread across most of your brain.
One leading theory for what brainwaves actually mean is that they’re a way of turning the flow of information between different brain areas on and off. There are many brain areas that have neurons connecting them (anatomical connectivity), but what goes on in one of those areas only affects what goes on in the other area *some of the time*, which we call functional connectivity. Sort of like how a landline phone is physically connected to basically the rest of the country, but most of those connections are inactive most of the time. The theory is that when the brain needs two brain areas to talk to each other, the brainwaves in those two areas becomes synchronized, and this allows information to flow between brain areas. In other words, brain areas may be able to control which inputs (from other areas) they accept and which outputs (to yet other areas) they send by literally ‘tuning in’ to the right frequency. (Note that just being on the same frequency isn’t enough, they must be in phase / in sync).
Source: did my PhD on neural oscillations
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