Recordings made during a 7-day retreat in September 2015 suggest that the average EEG power in beta and gamma frequency bands at the forehead (FP1 and FP2) increase uniformly during individual 20-minute meditation periods. Further, the maximum levels reached near the end of the periods grows gradually during the course of the seven days. During this particular sesshin, beta and gamma power reached maximum on the fourth day and remained relatively high during the remainder of the retreat.
Starting the day before the meditation retreat began (Day 0) and continuing through the final day of a 7-day sesshin at Tahoma Zen Monastery, I recorded my brain waves during 20 minute sittings after the close of formal meditation. I used the same meditation technique for all sessions: eyes open, counting exhalations from the start of the period.
Below are the results for beta and gamma bands for left front (FP1) and right front (FP2) sensors on Day 0:
While there is an indication for a slight increase in beta and gamma on the left side, it’s not very pronounced.
Below are the corresponding results for beta and gamma bands on Day 3. Note that a uniform upward trend is clearly evident in all four graphs, a trend that was absent on Day 0:
The fact that the average power is increasing over the entire meditation period suggests that assigning a single mean power value to the whole period does not convey what’s really going on.
Let us now focus on a single meditation period at the end of Day 3, by creating an animation of radar charts of the absolute band power for all five frequency bands. Each frame of the animation represents the mean power values over 8 successive intervals of 120 seconds each (16 minutes total).
We see a steady growth in beta and gamma power over the course of this period.
To examine changes over the course of the 7-day retreat, we plot average absolute power values for 2-minute intervals taken from the beginning and the end of each meditation period. First we have the left front sensor:
Next we have the right front sensor:
The average band power of the two front sensors looks like this:
Beta and gamma power at the front sensors FP1 and FP1 reached their maximum mid-week and stayed higher than their initial values at the beginning of the retreat.