What Are Brainwaves?

Much of our knowledge about brainwaves and brainwave entrainment stems from research on electroencephalography. This article provides a brief overview of electro-encephalography as it applies to brainwave analysis and some common waveforms that are used in brainwave entrainment.

What is Electroencephalography?

Electroencephalography (EEG) is the science of recording neuronal electrical activity at the scalp surface. It has diagnostic medical applications, particularly for investigating abnormal electrical activity evident in epilepsy and other brain disorders. The first human scalp EEG was recorded in 1924 by Hans Berger, a German physiologist, however recordings from exposed monkey and rat brains date to the work of Richard Caton in 1875. While some notable early EEG research occurred in the first half of the 20th century, the importance of the EEG as a scientific tool really only commenced in the second half of the 20th century following the first international EEG congress in 1947.

Some of the early EEG research focused on exploring waveform patterns during sleep. It is now known that there are a number of phases during normal sleep including a phase of very deep slow wave sleep so named because of the preponderance of slow delta waves (< 4 Hz or 4 cycles per second). Rapid Eye Movement (REM), which occurs during dreaming, reveals a similar EEG profile to the awake EEG.

Common EEG Waveforms

While a normal human EEG generally reveals a broad range of waveforms affected by a number of factors including artefacts and the site of the brain that is recorded, useful data is described in terms of rhythmic activity which is divided into various frequency bands. A cursory glance at the literature establishes that there is no official listing of brainwave frequencies, although there is considerable consensus that there are at least five bands – gamma, beta, alpha, theta, and delta – which correspond with subjectively different, reportable or inferred mental states. There is less actual agreement as to the specific frequency cut-offs for each of these bands. For instance, many research studies report that there are up to three sub-bandings within each brainwave type, which for alpha brainwaves would include alpha 1, alpha 2, and alpha 3. The basis for these apparently arbitrary subdivisions in research seems mostly for the purpose of statistical analysis of findings rather than reflecting different types of subjective states corresponding to different waveforms.

There is also some disagreement as to where each band starts and stops although there seems to be some consensus for the band frequencies given in Hertz (Hz; cycles per second) in Table 1. A one second waveform sample of each wave is also provided in Table 1.

Table 1: Consensus band frequencies and one second sample waveforms (click on each image for a larger view)

 

Band

 

Freq.(Hz)

 Waveform Sample [1]

 

 Gamma

 

 > 30

 

 

gamma waveform

 

 

  Beta

 

 13 – 30

 

 

beta waveform

 

 

  Alpha

 

 8 – 12

 

 

alpha waveform

 

 

  Theta

 

 4 – 7

 

 

theta waveform

 

 

  Delta

 

< 4

 

 

delta waveform

 

 

Subjective Correlates of Brainwave Frequencies

The correlation of various frequency bands with subjective phenomenological states is moderately consistent across research. There is also a wealth of anecdotal evidence supporting subjective correlates of various brainwave frequencies. Table 2 provides a brief overview of subjective states that may be experienced in one of the five bands indicated above and naturally eliciting factors for these brainwave states.

Dominant brainwave bands tend to shift across the lifespan, with lower frequencies appearing to be dominant in earlier stages of life and higher frequencies characterising adult and later life. This finding raises a number of questions that have hitherto been left unanswered. What we do know is that there is a movement towards reduced stress and improved health with lower frequency delta brainwaves. Research has confirmed that delta waves coincide with the release of hormones that preserve life and a reduction of hormones that are dangerous when in excess. This occurs during slow wave sleep and also with delta entrainment. It is most fascinating that a developing human foetus is, for the entirety of its existence in utero, exposed to a very strong delta pulse due to the mother’s heartbeat, which is approximately 1.3 Hz (80 heart rate beats per minute). Even before the baby develops sensory organs enabling it to hear, the pulsing of the mother’s heart would be ‘felt’ by the baby. In a literal sense, the baby is fully immersed within a delta rhythm whilst in the womb and research establishes the delta waveform is the dominant waveform in infancy also.

Table 2: Subjective states and naturally eliciting factors to five waveform bands

Band

Subjective State and Naturally Eliciting Factors

Gamma

Improved whole brain thinking and mental processing. Improved sensory awareness and cross model sensory processing. Improved short-term memory. May enhance IQ, self-control, and compassion. May have natural antidepressant properties.

Beta

Active concentration, logical and critical thinking, problem solving, increased focus and motivation. May enhance IQ and productivity. In excess may be experienced as excitement, nervousness, anxiety, and stress. More common in adults and often the dominant rhythm in adults. Tends to increase with age.

Alpha

Relaxed, introspective, but alert mental and physical state. Stress and arousal reduction. Improved immunological function. May be conducive to creative states and peek athletic performance. Has been implicated in ‘super learning’ and inhibition control. Occurs naturally after closing eyes for a few minutes. Elicited by meditation and substances including tobacco smoking and consuming green tea (L-theanine). Common in children.

Theta

Experienced as drowsiness in adults. Can be associated with mystical or spiritual experiences. Present moment awareness and heightened creativity. Emotional attunement and intuition, subconscious awareness and heightened suggestibility. Has been linked with heightened creativity and ‘super learning.’ Theta is the dominant waveform in younger children.

Delta

Adult Stage 3 and 4 slow-wave sleep with complete unconsciousness. Release of growth hormone and melatonin, body restoration, reduction in the stress hormone cortisol. Associated with deep empathy and mystical experiences. Delta is the dominant waveform in babies.



[1] 2005 Hugo Gamboa. Used under GNU Free Documentation and Creative Commons Licensing.