Brainwaves are Frequency bands
Brainwavea are rhythmic or repetitive neural activity in the nervous system. Individual neurons can fire together (in groups of neurons) in rhythmic patterns, producing oscillatory activity.
If rhythmic activity happens 4 times a second it is called 4 Herz. This activity often happens in specific frequency bands . For example the frequency band called Alpha is between 7.5 to 12.5 Hz. These bands are not exacly defined. Some researchers define the beta-band from 13 to 30Hz and others from 13 to 38Hz. Some devide it into low, middle and high beta.
You can not just tell what brainwave mean and what kind of behavior and psychological state they are associated with. It dependands on the location (regio in the cortex) in which the waves show activity and/or the combination of different wave activity. Scientific studies do not always agree on there meaning and the brain-processes involved.
For example the prefrontal cortex has a role in attention and cognitive processes. And within that prefrontal region the EEG location F7 is located near centres for rational activities, and F8 is close to the sources of emotional impulses. In de anterior structures (prefrontal cortex) is the Sense of who am I. And in the posterior (back brain) is the body Sense of awareness.
Brainwaves in detail
Delta waves (0.2 to 3 Hz)
Delta brain waves are the ones with the lowest frequency and the highest amplitude.
They are primarily generated during deep and dreamless sleep (sleep stage 3 and 4) and in comatose states. The awareness of external stimuli is non-existent, and we are completely unconscious. Delta waves support healing and regeneration processes by releasing hormones such as dehydroepiandrosterone (DHEA), while decreasing the stress hormone cortisol. Infants spend a great deal of time in Delta wave activity. Delta waves have been shown to decrease across the lifespan. By the age of about 75, stage four sleep and delta waves may be entirely absent. Disruptions in delta activity is seen during intoxication, delirium and various neurological disorders. Sleep-walking occurs during periods of high delta wave activity.
Delta waves are apparently related to a unconscious state but some people who practice a type of deep meditation called Yoga Nidra (Sleep yoga) can remain conscious while in delta-sleep. In Advaita Vedanta, deep dreamless sleep coexists with wakefulness and dreaming in turiya, considered the background of the higher state of consciousness. If one can stay aware or conscious while in deepest dreamless sleep, a deep meditative state known as "jagrat sushupti" is said to be achievable. This may be linked to high cortical activity which happens during the delta-sleep.
High Delta values (on the Muse Headset
During eye movement there are electrical (non brain) signals that are registrated by elektrodes in the front. It is called artifact of electromyographic activity. This electrical data interferes with the brain data and may cause Delta to rise. If not filtered well enough the EEG equipement becomes an EMG rather than an EEG. The developper of Muse Monitor wrote : I believe Delta suffers from eye interference the most as it is the lowest frequency band and when you move your eyes it makes big slow (relatively speaking) arcs in the raw data from the eye muscle electrical signals, which you can see in the Muse Monitor raw data view. To get the cleanest brainwave data, try not to move your eyes, or move them slowly to minimise the effect. Once you eliminate the eye muscle interference, either with sophisticated
Theta Waves (3 to 7-8 Hz)
Theta in the cortical region is observed frequently in young children. Theta rhythms are strong during learning and memory retrieval, especially the episodic memory. In the morning while we are still sleapy there are more so called hypnogogic events (dreamlike imaginations) accompanied by more theta. Theta also tends to appear during meditative, drowsy, or REM sleep states. Studies in (self) hypnosis show significant higher theta activity. With Theta our senses focus on the world within and are withdrawn from our surrounding. In some way they are the keeper of subconscious desires and fears. In neurofeedback traing of theta waves is used in accessing of painful or repressed memories.
Alpha Waves (7/8 to 12/13Hz)
The characterization of Alpha waves is a wakeful, but relaxed and peaceful state, which we experience while falling asleep, waking up, when daydreaming and upon self-introspection.
They get stronger while relaxing, letting go of judgement, letting go of trying to control things, not thinking about anything with a goal, or being without an active task. Not being busy with a mental task but still alert to your senses.
Closing the eyes immediately stimulates alpha waves. Alpha may be a kind of bridge between our conscious and subconscious, needed to bring something to our concious attention.
p.s. Alpha can be usually observed better in the posterior and occipital regions. Alpha of occipital origin are the strongest source of neural signals in the EEG.
Beta Waves (12/13 to 32/38 Hz)
Beta brain waves are connected to our waking state with mental activity, such as concentration, logical and analytical thinking, attentiveness and the focus on cognitive tasks. Since our waking state is so extensive with different forms of activity, the Beta range has been divided into three further sections.
Low amplitude beta waves with multiple and varying frequencies are often associated with active, busy or anxious thinking and active concentration. Bursts of beta activity are associated with a strengthening of sensory feedback. People with (more than average) low Beta waves may report a lack of energy and the inability to concentrate.
Beta waves in the middle section (Beta 2 with 15 to 22 Hz) create a clear focus with a harmonic energy level, whereas Beta waves with a high frequency (Beta 3 with 22 to 38 Hz) may generate high excitement, restlessness and anxiety.
Gamma Waves (32/38 to 100 Hz)
Gamma is higher if we are concentrated and have a strong focus of attention on a specific task. The progression of the Relative Spectral Power (RSP) of Gamma can be a index for concentration.
Experiments conducted by Rodolfo Llinas supports a hypothesis that the basis for consciousness in awake states and intrinsic activity during dreaming is 40-Hz oscillations throughout the cortex. What characterizes Gamma waves is a neural synchrony throughout the brain (temporal synchrony) The hypothesis is that synchronization of neuronal discharges underlie the selection of perceptually and behaviorally relevant information. This synchronization of different brain areas is needed for the creation of ideas and language.
Gamma and learning
The more gamma waves the more AHA experiences we get. They are needed for a our language ability.
Gamma oscillations were maximally coherent during slow-wave sleep. This may be related to lucid dreaming (dreaming while knowing that you are dreaming).
Meditation and mystical experiences
As investigators agree, temporal synchrony is needed for conscious awareness. Experiments on Tibetan Buddhist monks have shown a correlation between transcendental mental states and gamma waves. When the monks were told to generate an objective feeling of compassion during meditation, their brain activity began to fire in a rhythmic, coherent manner, suggesting neuronal structures were firing in harmony. This was observed at a frequency of 25 to 40Hz, the rhythm of gamma waves. These gamma-band oscillations in monks were the largest seen in humans. Gamma waves may relate to peak performances, and expanded (non dual) consciousness.