Friday, March 18, 2011

EEG 101

I've got this EEG. It tells me gamma/beta/alpha/theta/delta readings. I think learning more about EEGs and the corresponding greek lettered names would be useful.

First of all, what are these? My understanding: your brain gives off electrical impulses in regular wavey patterns. We classify these waves based on their frequency. (I think EEG folks don't talk much about "where" the wave occurs because you don't get much spatial resolution. You just know "there's 20hz going on in your brain as a whole." Seems weird! Wouldn't a 20hz wave in lobe A be potentially way different than in lobe B? Dealing without spatial resolution seems like trying to decide what to wear tomorrow when you only have a national weather report. "There's rain somewhere!" But that's all we get.)
Gamma waves (30-100hz) are really quite interesting! There's evidence that they point to the origination of consciousness itself (whatever that means) or the Binding Problem (whatever that means) or at least transcendental states in expert Tibetan meditators (whatever that means). Well! Okay, so this is super interesting but not as well understood; let's move on to waves that we know more about:
Beta waves (12-30hz) are common when you're awake, particularly when you're alert, jumpy, anxious.
Alpha waves (8-12hz) are common when you're awake and relaxed, calm, peaceful, and creative, or when you're REM sleeping.
Theta waves (4-7hz) happen when you're drowsy, sleeping (not super deep), or meditative.
Delta waves (0-4hz) are deep sleep waves.

People sometimes call the deeper, slower states "synchronized" and the shallower, faster states "desynchronized".

For a discussion of what parts of the brain cause different brain wave frequencies in sleep, this Scholarpedia article on the neurobiology of sleep and wakefulness has been pretty helpful (though also pretty dense). I don't think I'll rehash this here; it seems not super critical to me now.

I think I'll follow up with another post talking about EEGs and sleep, because that alone could fill a bookshelf.

A couple other notes/thoughts I want to jot down here so I don't forget:
- According to Wikipedia, Zen meditators produce more alpha waves. A little googling reveals a page about a study. The study is... just a citation? I don't know where the full text is. There seem to be a few papers about meditation and EEGs, like this and this, which I haven't read yet.
Ole Jensen says: alpha waves in an area indicate inhibition, gamma waves indicate engagement. (this hypothesis is also right on his group's front page.) Their group uses MEG, which offers more spatial localization. (MEG is also more expensive and large.)
- What could this mean? There seem to be all kinds of parallels here. Zen meditation -> concentration -> alpha waves, Tibetan meditation -> mindfulness -> gamma waves? I think it is important not to get too carried away jumping to conclusions. But it's interesting!

No comments:

Post a Comment