Brain activity and state of consciousness
Electrical activity in the brain typically occurs in the range of frequencies from 0 to about 40 Hz. The frequencies 0 to 3 Hz are referred to as "delta" and occur in deep sleep. 4 - 7 hz are referred to as "theta" and occur in states of deep relaxation with vivid visual imagery. 8 to 12 hz are referred to as "alpha" and occur in states of moderately deep relaxation without much visual imagery. 13 to 28 hz are referred to as "beta" and occur in the normal waking state of everyday consciousness. 28 to about 40 hz are "gamma" and occur in states of wide-awake intense concentration.
Here it should be noted that at any given time, brain activity is a complex mix of all of these frequencies; a shift in state of consciousness occurs when there is a shift in the predominant frequencies. Think of this as similar to an election: the majority of the votes determine who wins. And, strictly speaking, there is far more to a state of consciousness than simply a given set of brainwave frequencies: emotions, which are largely chemical (for example neuropeptides); cognitive content, which is influenced by social and physical surroundings; other stimuli (pleasant or painful, etc.); and so on. Brainwave frequencies are only one element, but a significant one.
History of research
In the 1970s, much research was done in experimental psychology to explore the relationship between brain activity and states of consciousness. One of the more well-known outcomes of this was EEG biofeedback, which enabled individuals to learn to alter their brain activity, for example to induce states of relaxation by increasing the prevalence of brain activity in the "alpha" frequencies of 8 to 12 Hz (8 to 12 cycles per second). Individuals could also learn to increase the prevalence of brain activity in the "theta" frequencies (4 to 8 Hz), and thereby induce states of consciousness characterised by deep relaxation and vivid visual imagery.
A somewhat less well-known development was the discovery of the "frequency following response" (FFR) or "entrainment." Brain activity could be coaxed to follow audio signals and thereby induce the desired state of consciousness. That is, if you hear a sound that is in the range of frequencies in which the brain operates, a certain amount of your brain activity will tend to synchronize to this frequency and you will experience a change in your state of consciousness (perception, cognition, and emotion).
As I mentioned, alpha-frequency activity tends to correlate with relaxation; the alpha frequencies are 8 to 12 hz, so an audio signal at, for example, 9 hz, will tend to entrain brain activity to that frequency and you'll experience a relaxed state.
However, human hearing begins at approx. 20 Hz, i.e. most people can't hear sounds at frequencies lower than this. (For points of comparison, 20 Hz is the frequency that is also used to ring your telephone bell, and 60 Hz is the frequency that is used for your regular electrical power. 60 Hz is the familiar electrical hum, and 20 Hz sounds like a barely-audible low growl.)
Some of the more "interesting" changes in state of consciousness (relaxed states, creative states, hypnotic states, dreamlike states) involve brain activity in the range below human hearing, e.g. your alpha-frequency state of relaxation. So there arose the question of how to produce audible signals to entrain brain activity to these frequencies.
Audio and consciousness part one: beat frequencies
The answer was to use "beat frequencies." If you hear a tone at, for example, 440 Hz, (the musical note "A"), mixed with another tone at 448 Hz (a slightly de-tuned musical note "A"), you will also hear a "beat frequency" or modulation, at the difference between the two input frequencies. In this case, the beat frequency will be 8 hz. (the difference between 440 and 448).
Musicians make use of this for tuning instruments. Pluck a guitar string, tune it to a tuning fork; and then tune the other strings to that one at the appropriate frets. As you tune each string, the beat frequencies get "slower" as the string gets closer to the target frequency.
These "beat frequencies" can be used to make it possible to hear the "inaudible" frequencies of brain activity. That is, you can't hear 8 Hz directly, but you can hear 440 hz and 448 hz, and you can hear the beat frequency of 8 hz between them.
The same result occurs with any other combination of tones. For example, 300 hz and 310 hz, the beat frequency is 10 hz.
The same effect can occur binaurally. What this means is: You put on headphones, and on the left side is a tone of 440 hz, and on the right side is a tone of 448 hz. Now you hear the 8 hz difference as if it's coming from "inside your head," i.e. in a manner similar to a sound that's positioned at the "center" of an audio field in a stereo recording (technically it's not center stage but the explanation of this is a lengthy digression).
The way you hear the beat frequency in this case, requires that input from each ear is "mixed" in the brain: the signals from each ear are passed via the corpus callosum, which is the structure that connects the left and right hemisphere of the brain. When the left and right signals "mix" as they pass through the corpus callosum, the FFR (entrainment) effect is increased. By analogy, you have a two-lane road with traffic in each direction. A stall in one lane causes drivers to have to pass it by crossing lanes, thereby slowing traffic in the opposite direction as well. The corpus callosum is a "pinch point" where traffic from each side of the brain can affect traffic passing in both directions. The analogy is imprecise but it'll do for now.
So now we have two ways you can hear frequencies that are otherwise inaudible: as simple beats in either ear, on either side of the brain, or as binaural beats that occur through the interaction of separate sounds in each ear, via the neural equivalent of audio mixing mediated through the corpus callosum.
Audio and consciousness part two: using beat frequencies to alter consciousness.
Here's where we get to the issue of inducing altered states. As per my example, let's take a mix of 440 hz and 448 hz. The difference is 8 hz, an alpha frequency. If you sit there and listen to this for an extended period of time, rather than just tuning past it while tuning your guitar, your brain activity will tend to synchronize with it. That is, extended listening to this combination of tones will tend to cause more and more of your brain activity to lock in to the same frequency. As a result, you'll experience a shift in your state of consciousness: in the present example, 8 Hz, being an alpha frequency, will induce a state of pleasant relaxation.
Here I should note that the sound volume does not have to be high. As long as you can hear the signals, your brain can respond to them to some degree. In theory you could play the signals at normal conversational volume or at a whisper level, or embedded in music or with a white-noise background or by themselves; as long as they can be heard and the volume is not so loud as to be uncomfortable.
Now comes the interesting part.
Let's say you have data showing that a given state of consciousness correlates with a more complex type of brain activity. Let's say you want to try to use FFR to entrain that activity. What you do is use combinations of sounds. For example let's say you want to reduce verbal activity while increasing the awareness of spatial relations. The left ear is wired to the right hemisphere of the brain, which tends to be specialized for spatial relations. The right ear is wired to the left hemisphere, which tends to be specialized for verbal processes. So into your left ear, you play a combination of tones having a difference of 10 hz, which is a high alpha frequency, a reasonable choice for a state of "relaxed but alert." Your right hemisphere, spatial relations, will tend to remain alert. Into your right ear, you play a combination of tones having a difference of 3 hz, which is a delta frequency, a reasonable choice for "non-dreaming sleep." Your left hemisphere will tend to move toward a sleep-like state.
Now let's say you want to experiment with the ability of spatial information to translate to verbal terms. If you want to shut down the information transfer at the corpus callosum, so you play a tone in the left ear and another tone in the right ear, for which the difference is 2 hz, a slightly lower delta frequency. If you want to increase the transfer of information across hemispheres, you would do the opposite: play a tone in the left, and a tone in the right, for which the difference is a higher frequency, perhaps in the alpha or beta range.
For experimental psychologists, this type of thing opens up an enormous range of research possibilities. Consider any capability of human perception, cognition, or emotion, that correlates with a state of consciousness that in turn correlates with EEG frequencies, and sit down at the audio console and play around until you hit the right combinations.
This has in fact been done, extensively. One of the original applications was to study "out of body experiences" (OBEs), where an individual perceives that s/he has "floated out of the body" and can perceive from the perspective of, for example, "above him/herself on the operating table." This is remarkably common but was for a long time very difficult to study under controlled conditions. FFR/entrainment has made it possible to induce this condition in the lab, along with a number of other conditions that are of clinical or theoretical interest.
The most well-known application of FFR/entrainment is in the "relaxation tapes" and CDs that are sold freely. These typically consist of musical compositions with FFR patterns embedded in the audio: You listen to the music, and the FFR signals subtly nudge your brain into a pattern of activity that is more conducive to the desired state of consciousness. These tapes and CDs are available for a range of desired outcomes, including relaxation, concentration, access to creativity, reduction of anxiety, inducing sleep, and assisting meditation. The quality of these productions varies as with any other product you can buy: there are good ones and not-so-good ones. Generally the stuff you can buy "over the counter," is less "strong" than the examples that are used under controlled conditions, e.g. in the lab or in clinical psychology, because there are potential complications for certain individuals (e.g. persons with epilepsy can have seizures triggered by certain combinations of frequencies).
From bliss to barbarism:
In normal use, FFR/entrainment is entirely benign. People choose to use it to assist reaching cognitive goals of their own choosing, and for the most part the experiences are entirely pleasant.
Even where the experience is somewhat unpleasant, for example a psychologist using FFR to help a patient relax in order to better handle discussing a personal trauma, it's entirely voluntary. The patient knows that dealing with the trauma in therapy is going to be difficult and unpleasant: but it's still a choice freely made by a free person.
However, any tool can be abused for barbaric ends. Here's where the tool can be turned to torture:
If FFR/entrainment can be used to reduce anxiety, it can also be used to increase anxiety. If it can be used to improve concentration, it can also be used to impede concentration. If it can be used to increase awareness during meditation, it can be used to increase awareness during a period of stress. And if it can be used to help alleviate the awareness of pain, it can also be used to increase the awareness of pain. This is to say, the brain responds regardless, just as it responds to other stimuli. All one needs to do is determine the relationship between the desired outcome and the relevant brain activity, and then reproduce the desired frequencies in audio.
The effect is not 100% certain, in the manner of a psychoactive drug. If you are given a dose of a drug, it will almost certainly produce a characteristic response: stimulant, depressant, psychedelic, empathic, etc. If you are exposed to FFR signals, you can attempt to tune them out, for example by vividly imagining music or by concentrating on some other vivid internal process (memories, imagery, etc.), and thereby occupying "bandwidth" in your brain, reducing the "bandwidth" available for processing an external input.
But for individuals who have not been trained to recognize subtle changes in their internal states, or make use of latent cognitive abilities such as concentrative mediation or audio or visual imagery, tuning out FFR signals is like trying to tune out any other undesirable sensory input: for example, trying to tune out a loud radio that's playing while you're trying to immerse yourself in reading a book. For most people it's difficult enough under normal conditions, much less the conditions of confinement in a dungeon.
FFR/entrainment by itself could be used to produce emotional and cognitive states, such as anxiety, depression, and so on. A more complex case such as "the feeling of isolation" would depend on producing a more basic emotion and then "contextualizing" it appropriately: for example, simple depression, in the context of being confined in a dungeon, will produce a sense of isolation and hopelessness.
FFR/entrainment could also be used to heighten responses desired by the torturers. For example, it could be used in a "good cop / bad cop" situation to produce pleasant feelings when in the presence of the "good cop." In this manner it could be used to heighten responsivness or even alter personality. When you are alone, you feel hopeless. When you are with Interrogator A, you feel abject terror and every ounce of pain is magnified mercilessly. When you are with Interrogator B, you feel relief, relaxation, calmness, and thereby feel gratitude toward Interrogator B. After a while, you become highly responsive to Interrogator B's suggestions; perhaps even your fundamental desires and deeply-held opinions begin to change...
It could be argued that FFR/entrainment allows for a reduction in the barbarity of other methods of torture. After all, if you can produce a given level of pain without as much overt damage to the body, it could be argued that this is an "improvement" over the thumbscrew and rack and so on. But the point, nevertheless, is that this still involves the deliberate induction of pain, terror, dread, hopelessness: the deliberate and systematic breaking of the person, the fundamental violation of everything that a civilized society is supposed to stand for. As such, it's merely another form of "torture that doesn't leave marks on the body."
Note
The fact that entrainment can be used for torture should not become a rationale to condemn entrainment altogether. Most applications are, as I've said, benign: people choosing to use it to assist with a desired cognitive function such as relaxation or meditation. It's important to differentiate between the tool and the use to which it's put. Any of the common tools of the construction trades can be used as an implement of torture, but we're not calling for a ban on hammers and saws.
Meanwhile, the question remains: is this actually being done, i.e. is entrainment being used as an adjunct to torture? And the next question is, what are we going to do about it? International law and treaties ban the use of certain types of drugs on prisoners, but entrainment is a relatively recent discovery. Should it be banned from use in interrogation, in the same manner as certain drugs?
And politically: if this is going on, how can it be related to the overall issues of torture scandals and the transgression of law by the present Administration? Can this be framed in a manner that most Americans will understand? Can it be framed in a manner similar to using psychoactive drugs on prisoners? Or is it more useful to point out that if this is going on, it's part of an overall pattern of deliberate abuse of detainees?
Torture itself, and detention without habeas corpus, are clearly more severe violations of an individual than computerized wiretapping; yet so far the "snoopgate" scandal has apparently gotten more traction with Americans. In the same way, is there something about subtly tampering with an individual's brain, that is somehow more morally offensive than overt torture?
I can't answer these questions for others. What I've done here is provide the technical background so you understand what's possible. Now it's time for interested journalists to start digging and asking tough questions in the right places.
Perhaps this is a useful frame:
If they can tamper with your brain, nothing is sacred.
