Alpha Brain Waves

Alpha brain wave activity is generally associated with relaxed wakefulness, and alpha states are commonly described as tranquil and pleasant- sometimes accompanied by a "floating" feeling. Alpha frequencies are also indicative of a creative state of mind where free association is prominent. Alpha waves appear immediately and spread throughout the cortex when you close your eyes, which is part of the relaxation process leading to sleep.

Another interesting source of insight into the significance of alpha brain waves comes from extensive research that has found alpha to be a dominant wave length in the EEG scans of those who are actively meditating, and experiencing calm yet lucid, and sometimes "blissful" mental states, with minimal interruptive mental activity.

Beta Brain Waves

Beta is generally the mental state most people are in during the day, and usually this state in itself is uneventful. However, beta brain wave activity is significant to proper mental functioning, and insufficient beta activity can cause mental or emotional disorders such as depression, ADD and insomnia.
Broadly speaking, beta brain waves are associated with alert attentiveness and concentration- intense focus and problem solving are linked to beta activity. Beta waves can also be related to strong, excited emotions.
Medications that are designed to induce concentration and alertness, such as Ritalin or Adder-all, actually produce a beta brain wave state in most subjects.

Gamma Brain Waves

Gamma brain waves are the highest frequency brain wave type. A variety of studies have associated gamma with the formation of ideas, linguistic processing and various types of learning. Gamma waves have also been linked to the cognitive act of processing memories- the rate of the waves seems to correlate with the speed at which a subject can recall memories; the faster the waves, the faster the recollection.
Gamma waves have been shown to disappear during deep sleep induced by anesthesia, but return with the transition back to a wakeful state.
A recent Scientific American article discussed gamma waves in conjunction with long-term Buddhist meditation practitioners. It was found that the experienced meditators demonstrated self-induced, high-amplitude gamma oscillations during meditation. Researchers also noted that their gamma activity differed significantly from those in a control group, both during the meditation and before they even began. Interestingly enough, a similarly strong presence of gamma waves throughout the cortex has been observed in musicians listening to music, compared against a control group of non-musicians.
One current theory even suggests that gamma brain waves may play a role in creating the unity of conscious perception. Research into this theory is still ongoing, and the question is a difficult one to answer with certainty at this time. Though a further investigation is yet to be completed, the theory points to a very interesting possibility that gamma waves are involved in self-awareness.
The studies highlighted in the infographic above were cited in Dr. Tina Huang's landmark overview of brainwave stimulation, "A Comprehensive Review of the Psychological Effects of Brainwave Entrainment."
To be included in that review, articles had to be original, full-length journal articles in peer-reviewed journals, and the studies had to be of an experimental design, with outcomes measured using reliable and appropriate test procedures, and with statistical outcomes revealed.
That highly selective criteria means that these studies represent only a portion of all of the work conducted in this field, but are some of the most significant. Keep reading to learn more about the incredible results of this research.

Delta Brain Waves

Delta waves are the slowest of all brain waves, and are predominantly associated with Stage 3 and Stage 4 sleep.
However, researchers have found functions for delta stimulation beyond those related to sleep, as you have seen in the studies above. Stimulating delta in people who are wide awake has been shown to have additional benefits such as increasing relaxation and relieving certain types of pain.
The first two studies highlighted in the infographic above were cited in Dr. Tina Huang's landmark overview of brainwave stimulation, "A Comprehensive Review of the Psychological Effects of Brainwave Entrainment."
The third study, on improved sleep, was conducted by David Siever, one of the leading experts in the field today.

Theta Brain Waves

Theta brain waves (3-8hz) have been connected via extensive study to many different phenomena in the brain. Research on subjects as diverse as memory, emotion, neural plasticity, sleep, meditation and hypnosis have all drawn links to theta activity. A theta state is associated with stage 1 sleep- very light sleep from which subjects can easily be awoken.
Connections between meditation and theta activity have been researched and documented thoroughly, particularly in the case of both Zen and Transcendental Meditation. Meditative theta states are often associated with vivid mental imagery, peacefulness and generally pleasant experiences.
More recent research highlights the interesting role that theta may play in memory function. One theory proposed by Lisman and Idiart suggests that short term memories are constantly refreshed in order to retain their presence in the brain while they are being accessed. They suggest that individual memories are refreshed at the gamma rate, while the whole refresh cycle pulses at a theta rate. They believe that this may be why an average of 7 items can be held in short term memory by most people - per each 6Hz theta cycle, the 40hz gamma can cycle an average of 7 times. (Lisman, J.E. and Idiart, M.A.P. (1995) "Storage of 7 ^ 2 short-term memories in oscillatory subcycles." Science 267, 1512-1515)
On the significance of theta brain waves, Gabe Turow writes: "The links between the theta frequency and memory, emotion, and neural plasticity on a localized level provide relevant clues to questions on why visualizations of meditators in theta are so vivid, why meditators have such good memories, and why hypnosis can create lasting changes in the brain."