Thread by @RGottliebSmith

1/🧵
Ever look at an #EEG & wonder what the 🧠 squiggles mean?

This #twEEGtorial is for you

#MedTwitter #NeuroTwitter #EEGTwitter #Tweetorial

2/
Let’s start with some background:

💡 #EEG = electroencephalogram
💡 What an EEG does: records electrical activity in the 🧠

3/
You might then 🤔: how does the 🧠 create ⚡️?

A bit of neuroscience: 🧠 cells called neurons generate ⚡️ through the flow of charged ions (sodium & potassium) across their membranes

An EEG on the scalp can't detect the ⚡️ of a single neuron, but can when neurons are in sync

4/
💡 Electrodes = small metal discs that are ⚡️ detectors - for millions of neurons!

To understand the 🧠 squiggles, we first need to understand how the electrodes are set up for an EEG recording

📷 of a standard EEG set-up: commons.wikimedia.org/wiki/File:21_e…

5/
What's going on with the 🔤 soup?
◾️ A = auricular (ear)
◾️ C = central
◾️ F = frontal
◾️ O = occipital
◾️ P = parietal
◾️ T = temporal

& the 🔢s?
◾️ Odd = left
◾️ Even = right
◾️ z = midline

6/
So how does that translate into the 🧠 squiggles?

On the 💻 are EEG montages = arrangements of electrodes

2 major types:
1⃣ bipolar: compares ⚡️ between 1 electrode & the next in a chain
2⃣ referential: compares ⚡️ between each electrode & a reference point

7/
Let's look at an example of the popular bipolar longitudinal = "double banana" 🍌🍌 montage

Each electrode compared to 1 behind it

Chains (example for L):
◾️ Outer temporal: Fp1➡️F7➡️T3➡️T5➡️O1
◾️ Inner parasagittal: Fp1 ➡️F3➡️C3➡️P3➡️O1
◾️ Central

8/
Here's what the bipolar longitudinal 🍌🍌 montage looks like on the big 💻

👉 Organization is typically LEFT over RIGHT

9/
Some EEG basics:
💡 Amplitude is the height of the squiggle (waveform), measured in microvolts
💡 Frequency is the number of squiggles per second, measured in hertz (Hz)
💡 When electrode 1⃣ in a pair is more (+) than electrode 2⃣, you get a downward deflection - & vice versa

10/
Now that we've gotten the orientation & some basics, let's 👀 at some normal EEG findings

👇 a normal EEG in an awake, relaxed state with eyes closed

📒 Symmetric
📒 Normal "anterior posterior gradient" = 🔽 frequencies, 🔼 amplitude in the back [AKA "party 🎉 in the back"]

11/
In fact, you can actually quantify the 🎉: the posterior dominant rhythm (PDR) is the resting frequency of the 🧠 in the occipital regions

👉 Adults: 8.5-12 Hz
👉 Increases as kids develop: ~8 Hz by age 3

12/
The PDR goes away with eye opening (red box)

How can you tell the eyes are open (in addition to the note at the bottom 😉)?

When you blink, the eyes move up ➡️ the corneas (with a (+) charge) get closer to the frontal electrodes, causing a downward deflection

13/
So why am I emphasizing "awake?" What about 😴?

It's a whole different ⚾️game w/ 4⃣ sleep stages...

...& a whole other #twEEGtorial. I nominate @JulieZiobro to write it. 😉

👇 📷s of stage II sleep w/ sleep spindles & K complexes as a teaser - can you guess where they are?

14/
Summary:
◾️ EEG records 🧠 ⚡️
◾️ There’s a method to the 🔤 🔢 madness: standard EEG set-ups & montages
◾️ One popular EEG montage = bipolar longitudinal 🍌🍌
◾️ Some normal awake EEG findings: eye blinks, anterior posterior gradient, PDR with eyes closed

Thanks to @AvrahamCooperMD for the #EEG #tweetorial idea & @JulieZiobro for the EEG 📷s!

Interested in how EEG was discovered? Check out this great 🧵 by @OligoclonalBand:

& to learn about abnormal EEGs, check out cases of the day from @RebeccaFasanoMD & @TheNotoriousEEG and Q's of the week from @vumcpedepilepsy