With almost 100 years of research validating the effectiveness of brainwave entrainment, it’s no wonder why it’s used by thousands of people all over the world. What does the future entail in this exciting field? With the adoption of smartphones, virtual and augmented reality, and advancements in technology reducing the cost of EEG and other forms of biofeedback devices, the entrainment possibilities are endless.

The Neuro Programmer website, as is typical, is full of testimonials and vague references to research. I tried to track down the research they referenced, but could not find anything published or peer-reviewed by the authors named or on the subjects indicated. For example, they cite one study by Thomas Budzynski, but the only thing published by him that is listed on Pub Med is a small study on biofeedback published in 1969. The 1999 study they reference is not listed. Also – Budzynski has connections to another company – Theta Technologies – which sells similar technology.  (The exact nature of his connection is not clear, he was at least a consultant. He is also listed as the director of research for another company, Synchromed, LLC.)  This looks like just another in-house worthless study to support the marketing of a product.

"Given the popularity and effectiveness of meditation as a means of alleviating stress and maintaining good health, there is a pressing need for a rigorous investigation of how it affects brain function," says Professor Jim Lagopoulos of Sydney University, Australia. Lagopoulos is the principal investigator of a joint study between his university and researchers from the Norwegian University of Science and Technology (NTNU) on changes in electrical brain activity during nondirective meditation.

Hello my name is Arvinder I really hope and pray u can help me I am really struggling I am 46 had serious insomnia aafter glandular fever at 23 since then been on all sorts of meds in the world for sleep five years back I did hypnosis while on the meds I felt really messed up and struggled to live I was on antipsychotic and sleep meds I tried to correct that mess and many many hypnosis sessions then I ended up on internet and listened to a deep sleep binaural beat music almost three years ago firer to

OK – so some of this is pretty common marketing hype. Consumers have become almost numb to such hyperbole. But still we see some of the common – almost ubiquitous – elements of pseudoscientific scams. The company claims that the device is “effort-free”, that the results are “rapid and long-lasting,” that it is the “most effective” method of its kind, and that it is useful for a broad range of applications (hey, why limit the market). I am used to such hype about dishwashing detergent, but find it intolerable when applied to a pseudoscientific device with medical applications.
Rudy's primary work is on Alzheimer's. In this disease, beta amyloid proteins form plaques in the brain and kill nerve cells eventually leading to dementia. Research from Washington University School of Medicine in St. Louis shows that when people's brains are in a Delta brain wave state, beta amyloid production in the brain ceases and the toxic material is cleared away. One thought is to explore the possibility of using brain entrainment technology to help treat Alzheimer's, but at this point all it is being used for is to help people meditate, relax and dream instantly and effortlessly.
Hi Et, In all the feedback and studies I’ve read and looked into over the years, I’ve seen lots of feedback from people talking about how they don’t like the sound of the tones, or they find them irritating in some way. Unfortunately, there doesn’t seem to be any particular reason why one person likes it and the next doesn’t. It’s a bit like normal music, one person’s sweet symphony is another person pneumatic drill. It’s common for people to find it weird and maybe annoying at first, which is how I felt in the beginning. But usually after a few listens you can start to get used to it and appreciate the sound, and especially the feeling it gives you. Personally, I think it can help if you try to embrace the sound, psychologically speaking beforehand. It can also help to have the sound playing at a very low volume, to begin with, then building it up as you get more used to it.

Complement C4 is a protein that is important for your immune function. It helps clear infections and protects against autoimmunity. Low levels increase the risk of various autoimmune disease, including lupus. High levels, on the other hand, mean that there is more inflammation in the body. They increase your risk of developing metabolic syndrome and […]

Let’s say you’re listening to a sound in your left ear that’s at a frequency of 132 Hertz (Hz). And in your right ear, you’re listening to a sound that’s at a frequency of 121 Hz. Your brain, however, gradually falls into synchrony with the difference — or 11 Hz. Instead of hearing two different tones, you instead hear a tone at 11 Hz (in addition to the two tones given to each ear).
There were no significant differences between the experimental and control conditions in any of the EEG measures. There was an increase of the Profile of Mood States depression subscale in the experimental condition relative to the control condition (p = 0.02). There was also a significant decrease in immediate verbal memory recall (p = 0.03) in the experimental condition compared to control condition.
Cortisol is an arousal hormone, stimulating alertness and attention. Cortisol levels rise and fall in connection to circadian rhythms—cortisol levels rise to their peak levels first thing in the morning, just in time for you to be active for the day. Too-high cortisol levels are associated with insomnia, as well as more time spent in light sleep, rather than deep sleep.
... The goal of the study was to observe the effect of exposure to BB on working memory capacity. As suggested by many studies, BBs corresponding to alpha brain waves can positively influence cognitive processing, namely attention, auditory sequential memory, working memory, working memory storage, and reasoning ability (Carter & Russell, 1993;Cruceanu & Rotarescu, 2013;Foster, 1990;Kennerly, 1994;McMurray, 2006). The results show that a BB of the frequency of 9.55 Hz – which is a representation of the alpha frequency range of the brain activity – had a temporary positive effect on working memory capacity in our sample of healthy, adult university students. ...

For example, if a 530 Hz pure tone is presented to a subject's right ear, while a 520 Hz pure tone is presented to the subject's left ear, the listener will perceive the auditory illusion of a third tone, in addition to the two pure-tones presented to each ear. The third sound is called a binaural beat, and in this example would have a perceived pitch correlating to a frequency of 10 Hz, that being the difference between the 530 Hz and 520 Hz pure tones presented to each ear.
Brainwave entrainment through the use of binaural beats is a scientific method that helps you go from alert to relaxed to asleep within minutes by using a process to alter your brainwaves. Sounds like something straight out of a science fiction novel, but brainwave entrainment is a very real and very effective way to help you sleep. Your alertness is linked to the dominant frequency of your brainwaves. So if you’re feeling alert and focused, your brainwaves are in the beta frequency but if you’re feeling relaxed, they’re likely to be in the alpha state. To sleep, your brainwave frequency needs drop to a slow delta. This can be hard, especially after a busy day. Your brain stays alert, preventing you from relaxing. By using Binaural Beats, you can quickly induce the frequencies associated with sleep in your brain within minutes.  Scientists discovered that the brain synchronises itself to a dominant frequency. So by inducing a new lower frequency with binaural beats, your brain begins to lower its own frequency to match this new frequency. It’s a powerful technology that I’ve been using myself for years with very good results.

Of course, meditation is actually quite a simple procedure, and one that can be practiced anywhere and at any time. There are no special requirements other than the need to have peace and quiet in a distraction-free environment for a few minutes. The trick is being able to switch off from whatever is going on around you and let your meditative state begin.

Using new scanning techniques, neuroscientists have discovered that certain areas of the brain light up constantly in Buddhists, which indicates positive emotions and good mood. "We can now hypothesize with some confidence that those apparently happy, calm Buddhist souls one regularly comes across in places such as Dharamsala, India, really are happy,"
Sleep issues are becoming much more of a common problem. I think it's great to look at alternative ways to help with insomnia and other sleep related issues, especially when they don't involve the need to take medication. Something proved to be effective is 'Sleepstation' a UK based organisation who use CBT techniques to cure insomnia. Their online sleep therapy course is brilliant and very convenient as it's delivered online. Their website is definitely worth a look if you're having sleep issues
Your brain cells reset their sodium & potassium ratios when the brain is in Theta state. The sodium & potassium levels are involved in osmosis which is the chemical process that transports chemicals into and out of your brain cells. After an extended period in the Beta state the ratio between potassium and sodium is out of balance. This the main cause of what is known as "mental fatigue". A brief period in Theta (about 5 - 15min) can restore the ratio to normal resulting in mental refreshment.  
Since the beginning of this year, I’ve been doing meditation with the help of audio-beat technology from a well-known brand, which I thought was a bit expensive. But, at least it gave me an insight into how the mind could and would give me an edge in solving most of my problems. From February, I decided to double the dosage to that which was recommended by the firm as I was desperate for a cure.
A therapy that slows brainwave activity, helping to produce low frequency waves, is likely to aid relaxation and sleep. But it’s not only lowering brainwave frequency that binaural beats may offer to sleep and relaxation. A small study (19 people) has found that exposure to binaural beats is associated with changes to three hormones important to sleep and well being:
There is a lot to like about this technology as a potential treatment for sleep problems. It’s low impact and non-invasive, it doesn’t rely on chemical drugs, it’s inexpensive and for most people likely easy to adopt and maintain. In this way, it’s similar to the other behavioral therapies for sleep that I like so much, including meditation and relaxation techniques, and other mind-body therapies.
One of the first pieces of research into using binaural beats as a sleeping aid was In a paper called “Tests of the Sleep Induction Technique” published in 1975 by Dr Arthur Hastings. He noted the effects of subjects who listened to a tape containing binaural beats starting from beta slowly descending to delta. Using an EEG machine he was able to monitor the subject’s brainwaves as they listened to the tape, becoming increasingly relaxed before falling asleep. He concluded; “patterns in the various stages suggested that the tape was influencing the subject’s state”.

Go behind the scenes of brainwave entrainment technology creation with Joseph Kao, developer of the extraordinary meditation tool Journey to the Center of the Self. Here, in an interview with John Dupuy, CEO of iAwake Technologies, Joe describes the amazing complexity of the brainwave entraining soundscape he created to both accompany his deeply inductive, 30-minute, guided meditation on the first track of Journey, and also stand alone as a music-only track that holds you in a profoundly relaxed, still, yet clear place on the theta/delta border. To find out all that went into the making of the inductive guided meditation on the first track of Journey, see A Guide to Transpersonal Meditation: Journey to the Center of the Self, part I of this interview.

There’s an aesthetic element to the music and there are a lot of drone-based sounds and time-stretched sounds, deep, rich bass sounds—there’s a spectrum of sounds within there—and what’s more, there’s a load of 3D processing that goes on to ensure that the mind doesn’t become habituated to them. There’s also a constant, subtle sense, a slow and gradual sense, of the sounds shifting around. And, there are layers of binaural beats.

If anybody would like to look over the scientific evidence concerning brainwave entrainment and isochronic tones, I’ve done a lot of research over the years which I’ve collected at the PubMed website of NCBI – a branch of the National Institute of Health – that provides access to a large library of medical journal articles. I’ve made my list public so you can look through the journal articles that were published concerning this topic. Here’s the link: http://www.ncbi.nlm.nih.gov/sites/myncbi/1tmDFOl0XtyA4/collections/51531796/public/. Most of the collection only gives access to abstracts or summaries unless you’re at some kind of educational institution that has a subscription to the particular journal that article is in, but I actually find abstracts really helpful. So have at it, read away. And if your psychiatrist/therapist thinks you’re nuts for feeling better after listening to isochronic tones, just whip out your 82-page collection of scientific journal abstracts written by her peers and give it to her to read. 🙂

... [9] While entrainment by binaural auditory beats in the alpha frequency has also been shown to enhance creativity, cognition, memory, and an improvement in intelligence tests and achievement tests in learning disabled boys. [10][11][12][13] The gamma-band activity has been shown to involve in a variety of functions such as attention, memory, and consciousness. Current literature suggests that entrainment by gamma beats promotes cognitive flexibility, modulates visual attention, and enhances creativity. ...
Eric Bartel is the creator of the Free Binaural Beats website and the sole creator of the audios found here. He specializes in creating binaural beats and isochronic tones along with relaxing ambient meditation music. From his home studio in the Black Hills of South Dakota, Eric is committed to bringing the healing power of binaural beats to anyone who wants to live a more peaceful, relaxed and fulfilled life.
Brainwave entrainment is a method to alter the frequency of your brainwaves by listening to audible tones containing the desired frequency. So if you want to sleep, you would listen to audio that begins at your current frequency and slowly descends to a delta frequency. By introducing these new lower frequencies, your mind begins to lower its own brainwaves to match this new frequency.
Brainwave Entrainment is the process of synchronizing the brain to specific frequencies and patterns embedded in audio tracks. These frequencies correlate to specific emotions, feelings, and even energy levels. Using nothing more than sound, Brainwave Entrainment can enhance creativity, change moods, and even alter behavior like sleep and energy levels.

There are five main categories of brainwave frequencies: Gamma (40Hz+), Beta (13 – 40Hz), Alpha (7 – 13Hz), Theta (4 – 7Hz), and Delta (<4Hz). Each category is associated with a different state of mind; so, for example, when you’re in a peak state of performance, your brain produces Alpha Waves, and when you’re in a deep sleep, your brain produces Delta Waves.
Monaural beats have similarities to binaural beats, but the two separate frequencies are delivered through a pulse pattern and mixed before they reach the listeners ears, resulting in the advantage of being audible without stereo headphones. However, using stereo headphones intensifies the effectiveness of monaural beats and is recommended for the best effect. 
Because the mind and body are a single system, changing our brainwaves and spending more time in harmonious, relaxed, and restorative mind-states also affects our physical health. Physical health then reinforces our mental-state, and a feedback loop of either positive or negative processes becomes established. Research studies have shown beneficial effects of using brainwave entrainment for treating migraine headaches, premenstrual syndrome, and for managing physical pain.
BrainwavePowerMusic has been the leaders of Lucid Dreaming, Astral Projection and Deep Sleep Music on Youtube for the last 5 years. The First Channel to focus on creating music specifically for dreaming and falling asleep. Unique music tracks dedicated to help you to fall asleep, getting a deep sleep that will leave you recharged and refreshed. Our astral and lucid dreaming tracks are all carefully formulated to make sure that you can achieve subconscious awareness and have helped millions of people to achieve a lucid dreaming state. Most of our sleep music mainly use Delta and Theta Waves. Mixing in soft instrumental music to help you achieve deep relaxation, and fall asleep fast. Our relaxing sleep music can be used as background music, meditation music, relaxation music, peaceful music and sleep music.
The binaural beats sleep package is a pack of four binaural beats audio sessions. It’s produced by the Unexplainable store, a popular binaural beats online store. They’ve been in business since 2007, selling a vast range of binaural beats for sleep relaxation and meditation. They have some real gems if you can look past the excessive new age marketing.
Hello, I am [name removed], from [city, state removed]. I would like to say thank you for making the CDs. They’ve really helped my friend get over years of abuse and the sadness of loosing the only good friend he had after he moved to [city removed]. I plan on getting the cds for myself, once I get to working, and seeing if they will help me with my problems caused by [condition removed]. But, if you had seen my friend before, and compared it to now you would be amazed.
The binaural-beat appears to be associated with an electroencephalographic (EEG) frequency-following response in the brain (3). Many studies have demonstrated the presence of a frequency-following response to auditory stimuli, recorded at the vertex of the human brain (top of the head). This EEG activity was termed "frequency-following response" because its period corresponds to the fundamental frequency of the stimulus (Smith, Marsh, & Brown, 1975). Binaural-beat stimulation appears to encourage access to altered states of consciousness.
... [9] While entrainment by binaural auditory beats in the alpha frequency has also been shown to enhance creativity, cognition, memory, and an improvement in intelligence tests and achievement tests in learning disabled boys. [10][11][12][13] The gamma-band activity has been shown to involve in a variety of functions such as attention, memory, and consciousness. Current literature suggests that entrainment by gamma beats promotes cognitive flexibility, modulates visual attention, and enhances creativity. ...
My name is [name removed] and I purchased the full Equisync set about 2 years ago and I’m very happy with this product. I still feel and notice euphoric and life changing effects to this day and I’m so grateful for this fact. I continue to follow the research on this subject and know that as science and technology advances a more quality product can be produced.
Your brain operates at certain levels of activity – the normal waking, active Beta, the meditative Alpha, the asleep-and-dreaming or deep meditative Theta, and the deep sleep/unconscious Delta. Beta is characterized by one thing we all want to get away from – stress.But that brainwave state has its place. It’s the action mode, and that’s the way it should be! If we’re not alert when we’re awake, bad things can happen, right?
Our relaxing music is perfect for Deepak Chopra Meditations, Buddhist meditation, Zen meditation, Mindfulness meditation, Kundalini meditation, Qi Gong Meditation, Zazen Meditation and more. Our music is influenced by Japanese meditation music, Indian meditation music, Tibetan music and Shamanic music. Our instrumental music has been designed to encourage and enhance relaxation, meditation, brain function and concentration, spa and massage therapy, and healing music therapy. In addition, we use binaural beats (Delta, Alpha and Theta Waves) to naturally reach a state of relaxation perfect for concentration, meditation or deep sleep. Our music playlists are perfect for your daily meditation and relaxation. Our music videos use soundscapes such as nature sounds, animals, oceans, rain sounds, thunder sounds and many more).
Binaural beats by themselves are dull for some people to listen to. But with nature sounds or ambient music, as well as either white noise, pink noise, brown noise, mixed in with the binaural beats it is more pleasant to listen to longterm. Normally it will take about 6 minutes for the brain to start becoming entrained by the binaural beats. But it is best to listen to binaural beat recordings daily that are any where between 10 minutes to an hour long.
I can’t thank you guys enough for saving my life. I tell everybody I know about your guys. I love you guys. I word of mouth advertise and give my testimony to the power of your technology almost everyday. I am only 30 years old, but since I was 17 teen years old my life was a miserable roller coaster ride. I ended up being diagnosed with fibromyalsia, bipolar disorder, adhd, manic depression, sever anxiety, severe depression, chronic fatigue syndrome, and you name it. Because of your product, I have never felt better in my entire life. I can cope and manage and more. I can finally sleep a full night without tossing and turning waking to knots in my back and stomach. I can finally stand straight and tall without feeling like I have a pinched nerve in my neck. I have energy again, and a renewed passion for life!
Binaural beats are created when two tones are played simultaneously, one in each ear. As long as the difference between the two frequencies is less than 30 hertz, the brain perceives the difference in the tones as a “beat” which, if listened to with enough focus, the brain will begin to follow (this is known as the “frequency following response”). By changing the difference between the two beats, the brain will change its wavelength and enter into different “states” of being.
In order to understand brainwave entrainment you first have to understand something about brain waves and electroencephalograms (EEG). Neurons are cells that communicate with each other through electrical conduction. When a neuron fires it creates a small electrical and magnetic field. These fields are far too small to measure by placing electrodes on the scalp, or even on the surface of the brain. The only reason we can detect the electrical fields of the brain is because many neurons are firing together – in synchrony. All brain waves that are measured by an EEG, therefore, represent a large group of neurons firing together.
When I first began, I thought I would just do 11 minutes, but I got so into it that I wanted to do it for the full 31 minutes. I experienced that it works in all the ways mentioned above and discovered more every day. I encourage you to practice this meditation and explore what it can do for you. It is good for beginners and seasoned meditators alike. One of the great things about basic Kundalini Yoga meditations is that no previous experience is required. Just tune in with ONG NA MO GURU DEV NA MO and go for it.
Really great stuff here, man. Well done! Without taking anything away from the article it would have been great to have under one “roof” similar information about hypnotherapy and subliminals. I invested quite a lot in buying binaural cd’s but after reading your material I think that for short term effects isochronic tones rather than binaurals are the technology to go for now. For longer lasting and possibly permanent effects I’m not sure whether I should go for hypnosis or subliminals (or both). An article as well written and comprehensive as yours but focusing on hypnosis vs subliminals would have completed the circle for me. The stuff I’ve read so far on binaurals vs isochronics hasn’t really done it for me. Any chance you could give it a shot?
The gentle pulsating rhythms of Brain Sync audio programs act in a similar fashion, yet because the frequencies are precise and consistent they can be targeted to induce highly specific and desired brain states. Just as you can tune a radio to get a particular station, with Brain Sync technology you can re-tune your consciousness – effectively dialing your mind into a wide variety of brain states.
Your brainwave activity during sleep is largely distinct from your brain activity when you’re awake. (REM sleep is one exception to this—during REM, your brain is active in ways very much like when you’re awake.) During non-REM sleep, the slower, lower frequency theta and delta waves dominate, compared to the alpha and beta waves that are prominent when you’re alert and active.
Long-term meditation practitioners have also shown to have a higher tolerance for pain.[15] This effect has been correlated to altered function and structure in somatosensory cortices and an increased ability to decouple regions in the brain associated with the cognitive appraisal of pain (anterior cingulate cortex and dorsolateral prefrontal cortex).[16]
Information on this website is provided for informational purposes only and is not intended as a substitute for the advice provided by your physician or other healthcare professional. You should not use the information on this website for diagnosing or treating a health problem or disease, or prescribing any medication or other treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Delta (3hz – 0.2hz) – Deep, dreamless sleep. Intuition. Empathy. Brainwave expert Judith Pennington calls it the doorway to Universal Consciousness and “A radar that scans the environment and psychically picks up information and energy.” According to British physicist C. Maxwell Cade “There have been reports that delta waves appear at the onset of paranormal phenomena.” (More information can be found in Cade’s book The Awakened Mind)
Slow Wave Sleep or SWS, is the deepest of sleep states and it plays a vital role in health and well being. During this phase of the sleep cycle, the brain begins producing very slow, large Delta waves. Even if your lifestyle doesn’t allow for the luxury of a full eight hours of sleep, a few hours of Slow Wave Sleep will trick your brain into thinking it’s had all the restorative sleep it needs.
** DISCLAIMER: I’m not a doctor or a scientist, just a nerd who loves meditation and experimenting with new things. I test every binaural beat track on myself and make sure I'm happy with the result before I make it public. Ultimately, every person is going to have their own unique experience. Using this track is done at your own risk -- if you start to experience any negative effects, STOP using it!
Meanwhile, the therapeutic benefits of listening to sound and music is a well-established principle upon which the practice of receptive music therapy is founded. The term 'receptive music therapy' denotes a process by which patients or participants listen to music with specific intent to therapeutically benefit; and is a term used by therapists to distinguish it from 'active music therapy' by which patients or participants engage in producing vocal or instrumental music.[37] Receptive music therapy is an effective adjunctive intervention suitable for treating a range of physical and mental conditions.[38]
Theta: This brainwave pattern is associated with deep relaxation and with some stages of sleep, including the lighter stages of non-REM (NREM) sleep. REM sleep itself is mostly composed of beta wave and other activity that’s similar to an alert, waking brain. Deep meditation produces theta waves, which are slower and lower frequency (between 5-8 hertz) than Alpha waves. That murky barrier between sleep and wakefulness, when you’re drifting in and out of sleep, and your thoughts feel dreamlike and difficult to remember? That’s a theta-dominant state of consciousness.

Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry[citation needed] into whether or not the synchronous electrical activity of cortical neural ensembles might not only alter in response to external acoustic or optical stimuli but also entrain or synchronize their frequency to that of a specific stimulus.[16][17][18][19]
It has been both a pleasure and an enlightening experience listening to the Equisync II CDs for the past month. As a 15 year stroke survivor, daily meditation has become a part of my life. Listening to these CDs reminds me of sitting alone in a forest during periods of rain, whether they be light, heavy, or in between. I am able to access my right hemisphere more readily and experience the feeling of nirvana that we all have within us. When I reach this point, my system reminds itself of all the compassion and connectedness we each have.
Meditation and its effect on brain activity and the central nervous system became a focus of collaborative research in neuroscience, psychology and neurobiology during the latter half of the 20th century. Research on meditation sought to define and characterize various practices. Meditation’s effect on the brain can be broken up into two categories: state changes and trait changes, respectively alterations in brain activities during the act of meditating and changes that are the outcome of long-term practice.

Hi. This article contains a lot of information about brainwave entertainment. Thanks. I have a question. I downloaded an Android app that plays isochronic tones. I like to use an Isochronic tone at 2.5Hz that is in Delta range and is supposed to help me get a deep and dreamless sleep. I use it without headphones and just keep the smartphone next to my pillow. But I do not know if I should keep the tone playing all the time while I sleep or put it on timer to shut off after some specified time. A custom timer is possible with the app. Can you please guide me.

With almost 100 years of research validating the effectiveness of brainwave entrainment, it’s no wonder why it’s used by thousands of people all over the world. What does the future entail in this exciting field? With the adoption of smartphones, virtual and augmented reality, and advancements in technology reducing the cost of EEG and other forms of biofeedback devices, the entrainment possibilities are endless.
Today, EEG machines are used for diagnosing epilepsy and sleep disorders, for determining dosages for anesthesia, and measuring the brain activity of people in comas or suffering from brain trauma. EEG machines also continue to play a role in researching and understanding brainwave entrainment and developing new and better methods for delivering the benefits of this form of brainwave modification. 

You listen to binaural beats using headphones. In each ear, you receive sound at a slightly different frequency (often accompanied by some relaxing background sounds). If your left ear receives a 300-hertz tone and your right ear receives a 280-hertz tone, your brain will process and absorb a 10-hertz tone. That’s a very low-frequency soundwave—one you can’t actually hear. But you don’t need to hear the sound for your brain to be affected by it.