118 — Theta and alpha oscillations are traveling waves in the human neocortex

Alpha and theta waves have been studied for nearly a century; these functions of constructive electrical activity in the brain can be easily studied with basic EEG hardware. These waves, researchers hypothesize, correspond to synchronization events that coordinate brain activity at large scale across disparate regions. Even though these signals appear to be propagating waves when measured with a stationary probe, up until recently there was no definite proof that these oscillations were actually literal travelling waves across cortex.

This study looked to 77 human patients undergoing invasive procedures, where tissue was already going to be exposed to air. The researchers used electrode probes to monitor 2–15 Hz (alpha and theta waves) for activity while the subjects performed different tasks. The electrode-based measurements suggested that the bands of oscillation propagation were around 2 to 5 cm wide, and moved at about half a meter per second. For comparison, action potentials along myelinated axons propagate at ~10 m/s, and APs along slow, C-fiber axons involved in nociception move at around 2m/s.

When the subjects performed well in their memorization and memory retrieval tasks, the waves were found to move at more consistent speeds and direction. When the subjects performed poorly, the propagative waves were less focused and less refined.

This work reconfirms that brain oscillations are a propagation of activity across cortex, and that this coordination of activity represents task-based focus and fluency. Moreover, it shares a model of thes brain waves as a “network of coupled oscillators” — essentially showing that these waves propagate across cortex in the same way as a vibration would propagate across a network of springs.

This talk of high-level brain region coordination reminded me of the superficial patch system seen in visual cortex of many mammals. I wonder if these superficial structures are responsible for other, unrelated types of brain synchronization, or perhaps the systems are related.