Seven days of daily EEG: what the sittings actually produced

Result

Tl;dr: I managed to get consistent readings over the past week. I got nine sittings over seven days, and every single time, the alpha rhythm at the back of my head got stronger when I closed my eyes. On average it was about twice as strong with my eyes closed. In my first test on 1 November, it was about 1.7 times.

O1, Oz and O2 are the three sensors at the back of my head. Each number is how much stronger the 8–12 Hz rhythm was with my eyes closed than open. The last column is the sensor at the front of my head (Fz): how much stronger a slower 4–8 Hz rhythm was while I was counting backwards than while I was staring at a spot.

So what do these numbers actually mean?

• Anything above 1 means the effect showed up. Every number in the first three columns is above 1, and most are around 2. Closing my eyes roughly doubled the rhythm, every day.
• All three sensors agree. They mostly rise and fall together. My strongest sitting (6 November) was top on all three, and 7 November was near the bottom on all three. That’s a good sign. If one sensor was loose or picking up noise, I’d expect it to go off on its own. The middle sensor (Oz) was usually the strongest, in 5 of 8 sittings.
• It moves around day to day, from about 1.5 to 2.75. I checked whether sleep or coffee explained that, and nothing jumped out. My strongest sitting (6 November) and my weakest (10 November) both came after coffee and a short night, so those two don’t explain it on their own.
• Counting also changed the back of my head. While I was doing the maths, the rhythm at the back got a little weaker again, by up to about a fifth, even though my eyes were open the whole time. That happened in all seven counting sittings, though only just on 9 November.
• The front sensor is the one that’s changing. In the last column, above 1 means a slower rhythm at the front got stronger while I counted. It started at about 1.7 and has drifted down to just under 1. More on that below.

What I recorded

• 9 sittings, 7 days in a row, from 5 to 11 November. I didn’t miss a day, though I did take a few days off after the first test.
• The first one (5 November) was the short version of the test, with 20 seconds for each step. I left it out of the table so I’m comparing like with like.
• The other 8 are my new daily routine: a minute with my eyes open, a minute closed, then a minute open again. I also added a sensor at the front of my head. On 7 of those days, I added a minute of counting backwards by 7 in my head.
• All 9 passed my basic check (the main sensor was actually picking up a signal), so I didn’t have to throw any out.
• The sensors stayed in the same spots every time, as far as I can tell. The back ones are easy to find. Getting the exact same spot each day for the front one (Fz) and the one just above the back row (POz) has been trickier, so those two could be off a little from day to day.

What this does and doesn’t show

The rhythm stayed put. Most days it peaked at about 9.3 Hz, the same as my first test. A few readings came in a notch lower, at 8.8 Hz. My setup can only tell frequencies apart in steps of about half a hertz, though, so I’d just call it “about 9 Hz, every day”.

The numbers are higher than my first test, but it’s not a fair fight yet. The daily sittings are three times longer. I also only started filtering out the hum from the wall socket on 8 November. And on one day (10 November), O1 actually came in a little lower than my first test.

The counting test is the interesting bit, but it’s early. For the first six sittings, a slower rhythm at the front of my head was stronger while I was doing the maths than while I was just staring. But that number has been sliding all week, from about 1.7 down to just under 1 on 11 November. That last one was also the latest I’d ever done the test: late afternoon, 10 hours after I woke up. The Fz sensor might also not be in exactly the same spot each day, which could be part of it. With only seven readings, and my sleep, coffee and timing all over the place, I can’t say what’s behind it yet.

I’ve been less good at the notes. After each sitting, I answer a few questions about sleep, caffeine, exercise and so on. Here’s where I slipped:

• I never filled in exercise, and that’s mostly on purpose. I don’t want to be sweaty when I put the electrodes on, and I have to shower right after anyway to rinse the paste off. So fitting a workout right before or after a session is tough right now. That also means I can’t see whether exercise changes anything yet.
• I only started noting where I was on 8 November. That’s what tells the software which wall hum to filter out.
• I only wrote down anything unusual three times: a thunderstorm, a bad night’s sleep, and the late-afternoon session.
• I haven’t tried a proper before-and-after yet, like one sitting before coffee and one after.

What got in the way? Not much, honestly. Nothing failed. There’s one mystery, though. The board has three inputs with nothing plugged in, and they should stay flat. They do, except on 8 and 9 November, when all three showed almost the same signal. I haven’t worked out why yet.

This is just me, on a board I put together myself. None of it is medical.

The code is on GitHub at agteo/diy-eeg-mac. More on the build is on Things I’m Building.