Detecting FFT Frequency Bands with EEG
Data on brain activity collected with EEG are often explained in terms of different frequency bands – how fast the brain is processing information and interacting with other brain regions. Of course there is a huge number of connections within the brain (trillions of trillions) and each specific interaction happens at its own pace. EEG observations can only be made when large numbers of neurons within the same region behave as part of a large scale activity which is characteristic of a particular type of activity, and it is quite normal for many different interactions of this kind to be taking place in the same part of the brain at the same time, therefore we often see significant activity on many frequency bands at the same time. Both the frequency of the interaction and the specific location of the activity provide information about the kind of activity inside the brain.
EMOTIV’s detection suites are based on the combined pattern of activity across the different regions using very detailed information including frequency bands, however most EEG researchers rely mainly on the band activity outlined below.
Theta (4 – 8 Hz)
Theta activity is seen in drowsiness, arousal and often during meditation. Dominant Theta activity is associated with relaxed, meditative, and creative states, memory recall and ‘flow’ states.
Alpha (8 – 12 Hz)
Alpha waves are the default ‘relaxed and alert’ mode of the brain. High Alpha values are often observed in the rear channels (occipital and parietal sensors) when the eyes are closed, indicating that the visual processing system is not currently engaged but is available and waiting for input. Similar conditions apply to other parts of the brain. High Alpha levels appear in the frontal lobes during relaxation and are suppressed when other activities take place. It is quite common in EEG analysis to compare the Alpha suppression between different regions in order to determine the functional areas which are currently in use. For example, linguistic processing tends to depress Alpha activity in the left frontal lobe, while abstract spatial thinking can suppress Alpha in the right frontal lobe. Trained meditators often produce much higher levels of Alpha activity during normal activities, especially in the frontal lobes.
Similar rhythms in the motor cortex (called Mu-rhythms, around the same frequency range) indicate muscle relaxation. Suppression of Mu-rhythms in the motor cortex in specific regions corresponds with activation of particular muscle groups. For example, clenching your right fist is directly associated with a dip in Mu-rhythm near the F3 sensor on the left side of the head.
Beta (12 – 25Hz)
Beta activity of multiple and varying frequencies is often associated with active, task- oriented, busy or anxious thinking and active concentration. The Emotiv API provides access to two sub-bands in The Beta zone – 12-18Hz and 18-25Hz, allowing the intensity and type of processing to be better understood.
Gamma (greater than 25Hz)
Gamma rhythms occur when different populations of neurons network together to carry out demanding cognitive or motor functions. Generally Gamma waves are observed in the frontal regions when fast, coupled processing is required, such as in fight/flight mode and when task switching during multitasking. In task switching, Gamma bursts are clearly evident when the current task is archived to short term memory and a new task is retrieved for ‘concurrent’ processing.