Brain waves are a thing that appear with increasing frequency in pop-psychology and business blogs, as hackable features of the brain. So, there's this from the HBR which equates the stress of not taking breaks with greater beta-wave activity. Reducing that pesky beta-band activity, it is implied, will help you build a top-performing team. Or there's this HBR article which tells you that music at 60bpm will produce alpha waves, and thus reduce stress.
As far as I can tell, this is more-or-less the same confidence game people play when they're talking about neurotransmitters. Take more breaks and listen to slow music and you'll be less stressed is far less sexy to say than taking breaks and listening to slow music fucks with your brain waves and you'll be less stressed, even though the informational content is identical.
The main bands that pop-psychologists care about are, in fact, alpha and beta. Typically, alpha waves are described as being associated with states of relaxation and calmness, because when you close your eyes and concentrate less, alpha waves increase. On the other hand, the harder you concentrate, the higher beta-wave activity tends to be. So, if you're trying to hack your brain, it makes sense that you'd want to up alpha when you're being creative or trying to relax, and up beta when you're trying to get things done.
Gamma waves and theta waves are less popular, but also appear from time to time. I'd imagine they're less popular because they are described in confusingly similar terms as alpha and beta. Theta, when it appears in blogs and whatnot, is usually associated with creativity and daydreaming. Gamma is associated with problem-solving and consciousness. It's sort of hard, from a high level description, to tease these out from alpha and beta.
As a heuristic to get people to behave in ways that are more productive or relaxing, there's no particular harm in this. Call it brain waves, or limbic hijack, or broaden and build mode. Adding sciencey-sounding jargon into your common-sense advice is always going to make your advice go further.
But brain waves have slightly more value, I think, when they're explored for their actual behavioural correlates than this new wave of pseudo-scientific self-help.
What are brain waves?
Brain waves are just the measurement of electrical or magnetic energy coming out of the head. Neurons fire, producing magnetism and electricity as a byproduct. If you place a few electrodes or magnetic sensors around the scalp, you'll pick up these signals as waves---faster waves when the neurons are firing faster, and slower when the neurons are firing more slowly. The more neurons firing at the same rate, the stronger the waves; the less, the weaker.
So, then, we can talk about two aspects of these waves, their speed and their strength. Speed is measured in frequency---hertz (Hz), or how many times the wave could fit in a second. The strength corresponds to the amplitude of the wave---how tall or short it is.
More importantly, any given brain signal will be comprised of multiple waves at once. You're typically measuring across billions of neurons, all of which are going slightly different speeds. So you take those signals, do some fancy math, and you can pull out all the different frequencies and strengths of wave that exist.
What we've then found is that certain bands of frequencies, or groups of waves, seem to loosely correspond to certain kinds of behaviour.
Delta Waves (0.5-4ish Hz): large scale processes
Delta is the slowest band. Mostly they're associated with sleeping or unconscious people, though they're also seen during deep meditation. We might assume, then, that they're involved in or reflecting the processes of integration and restoration that go on when we're sleeping or meditating. This seems even more sensible when we consider that, as the slowest waves, they're also the longest. If we assume that neurons firing at the same rate are doing similar stuff, then we might assume these super long, slow waves are reflecting long-range communication between regions of the brain that are far apart---essentially reflecting large-scale processes.
Interestingly, delta waves are common in infants and young children while they're awake. So we might start to make assumptions about the kind of processes going on in children related to their growth and development through the integration across the brain of lots of information. It seems reasonable to assume that we do similar integrative stuff while we're asleep as adults. We need to do it less than children, but we still need to do it.
Delta isn't limited to sleep and unconscious processes though. Delta activity has been observed during tasks requiring high levels of attention and working memory. For example, the phase of delta oscillations (i.e. the timing of the waves) in the prefrontal cortex has been associated with timing and decision-making processes. This is particularly true during tasks requiring cognitive control, like maintaining and updating information in working memory. We also see delta waves in subcortical regions like the thalamus, with oscillations that seem coordinated with cortical activity. Again, not so surprising---long slow waves might be reflecting some process of holding onto information over time, while it's passed all over the brain to be integrated at the places that it's needed.
So, delta waves seem to be about large-scale processes, the most obvious of which are those that have to do with the kinds of integrative, development-related stuff that we assume happens during sleep.
Theta Waves (4ish-8ish Hz): probably memory stuff?
Theta is the next slowest band. When we thought delta waves were about sleep, it seemed useful to distinguish the next set of waves that seemed more about wakefulness. But of course, with delta being more frequently found in awake adults doing tasks, it starts to seem like a less sensible delineation. It won't surprise you that these waves are involved in very similar stuff---daydreaming and memory-processes mostly. It's notable that the main place we seem to see these signals are the hippocampus---an important memory-related structure. We make the jump from there to assuming that theta rhythms reflect a process of consolidating memory and learning.
Theta, like delta, is also present during deep meditation, but unlike delta is more common during lighter sleep stages and the transitional state between being awake and falling asleep (hypnagogia). Again unlike delta, we're more likely to see theta frequencies during emotion-related tasks, and in areas of the brain commonly active during emotional processing. This is actually not particularly surprising. If theta is also a product of large-scale integrative processing, but is more memory-related, then it might well reflect the coupling of memory with the emotional valence of those memories.
Of course, like delta, theta is messily involved in more complicated processes. They've been involved in tasks requiring cognitive flexibility and the maintenance of attention over task transitions. For example, studies have found an increase in frontal-midline theta activity during tasks requiring executive control and complex problem solving. Increased theta activity is also observed when people make mistakes during tasks, suggesting a role in performance monitoring and the subsequent behavioural adjustments needed.
The idea that these long, slow waves are reflecting large-scale processes by long-range communication is better supported in the theta range than the delta range. We often observe a mechanism known as "phase coupling," where the phase of a theta wave in one region of the brain begins to appear across other distinct regions is usually taken to be a sign that the initial theta activity is syncronising these other regions in service of some particular brain function or function. Even more interestingly, theta waves have been found to interact with other frequency bands through cross-frequency coupling, particularly with gamma-band activity. This means that the phase of a theta wave can sometimes be seen to influence the amplitude of the faster gamma waves, and vice versa. The obvious conclusion to make here is that the long, slow theta waves across big swathes of the brain are influencing and being influenced by the fast, short waves produced by functions that are happening more locally in small bits and pieces of the brain.
Alpha Waves (8ish-12 or sometimes 14 Hz): noise suppression?
The pop-psych notion of alpha waves have them reflecting how relaxed and calm we are. This is mainly because the pre-eminent alpha response is that it gets stronger when we close our eyes, and weaker when we have them open. Alpha is also often common when we're resting and meditating, like all the slower waves, and they get weaker when we are engaged in a focused task. So we might be led to think, like your average business blog, that by fostering alpha wave activity we'll improve creativity and problem-solving.
This wouldn't be quite right. Alpha happens primarily occipitally. This back part of the brain is where your eyes plug in. Alpha gets stronger not only when we close our eyes, but also when we're trying to suppress irrelevant visual information. For example, if I ask you to ignore what's going on in your left eye and concentrate on the right, we'll see alpha shoot up in the bit of brain that corresponds to your left eye.
There is a similar finding in the part of the brain that is associated with your senses and coordination of actions. We call this the Mu rhythm, but it's the same frequency band, and seems to be also reflecting suppression, but in this case the suppression of motor activity.
This probably isn't all alpha does, but it really is the main set of findings and it certainly doesn't really scream 'relaxing' to me. Rather, what it looks like alpha (and mu) is commonly reflecting is some kind of noise-suppression system. When you need to ignore stuff, it 'whites out' the thing you need to ignore so it doesn't distract you. This is made more salient by the fact that alpha spikes in the transitional time periods between active engagement and more restful states---perhaps some kind of soft reboot of systems, blanking them out in preparation to receive new information. Like an etch-a-sketch.
Beta Waves (12 or 14-somewhere between 30 and 40 Hz): task-related processing
Complicated by the fact that we're looking now at a range of frequencies that is larger than the previous three combined, beta is usually fairly clearly related to the tasks people are doing. It gets stronger when we are more focused on or stressed by a task, and it is weaker when the tasks are easier or we're distracted. A major finding is beta activity over the motor cortex, and it appears particularly to predict our responses. For example, a larger beta response will occur in the part of the brain responsible for the left hand than the right hand when we're about to press a button with our left hand and not with our right. Another major finding is that the strength of the beta response scales with the evidence of a task. If I show you a noisy image, where the thing you're supposed to respond to is hard to see, then beta will correspond to how noisy the image is---more beta when its easier to see and less beta when its harder. While the higher frequencies in the beta band are sometimes linked to stress and anxiety, basically beta seems to more or less reflect ordinary brain function when you're trying to do things.
This is a more reasonable conclusion when we consider that we're now really looking at a range of shorter and faster waves. If the long, slow waves are doing long-range communication for large-scale processing, then the short fast waves are probable doing short-range communication for local processing on a smaller level. Beta probably captures all sorts of brain functions that happen when we're doing things. It makes sense then that abnormal beta activity is associated with various neurological and psychiatric conditions, such as Parkinson's disease (where there is excessive beta synchrony) and schizophrenia (where there may be disrupted beta activity).
Gamma Waves (everything faster than beta): ?
Everything else gets shoved into the gamma bucket. From 30-40Hz to, usually, somewhere around 140 or 150Hz. Some people go higher, and some are interested in high-frequency oscillations that can range up to 500Hz or more. But this isn't really standard.
One difficulty before we even start interpreting gamma is the fact that it not only overlaps electrical signals produced by muscles (around 80-100Hz), it also overlaps the signal produced by the electricity that flows through the rooms you'd be measuring in (either 50 or 60Hz depending on your country, which then produces 'harmonic' signals at 100/120, 150/180, etc). There are ways of mitigating or removing these artifacts, but they're far from clean.
That aside, the gamma band refers to the fastest (and shortest) brain waves. It's a huge range of them, of course, so it seems likely that as with beta we're talking about an enormous range of things. But similar to beta, it might be that any given brain function doesn't perfectly occupy a single wavelength, but can sometimes be a bit faster or slower.
Gamma waves are typically seen to reflect local circuit processing in tight neuronal networks, and these frequencies can be synchronised across many different regions of the brain. The general idea is that this these fast oscillations allow for precise timing of neural firing, which we think is pretty important for coherent and integrated brain activity. But also, we'd assume gamma reflects local coordination, for example within cortical layers where fast, reciprocal interactions between different types of neurons occur.
Gamma is also seen very frequently to interact with the other brain-waves---becoming stronger or weaker in response to the phase of oscillations in other bands. This is true of all bands, but more regularly observed in gamma. Basically, gamma is probably very similar to beta but even more specialised, reflecting the activity of more precise functions and/or tighter neural regions. Perhaps the most interesting proposal for gamma is the idea that gamma wave synchronisation is related to conscious awareness. The idea is that by bringing disparate neural activities into a shared time window, gamma waves might be essential for the subjective experience of a unified perception.
What we can take away from brain waves for behaviour
We can always use brain waves to sort of handwave at mental functions. We can talk about alpha instead of relaxation if it makes people listen better, or talk about beta instead of concentration. But I think understanding the frequencies better gives us an opportunity for a little more depth when we see studies that talk about these things.
Slower, longer brain waves like delta, theta, and to a lesser extent alpha, probably have something to do with large-scale coordination and long-range communication. Faster waves like beta and gamma have shorter ranges and probably reflect the local circuit coordination related to more local brain functions. When we see them acting together, we are seeing the brain communicating what is going on in some regions of the brain to other regions of the brain. So for example, when we learn that magic mushrooms reduce slow wave activity, we can assume that what the mushrooms are doing is reducing the amount of global processing and allowing more disconnected local processing. This helps us understand why tripping makes colours and other sensations more intense and weird, while at the same time at higher doses we can forget our sense of self (i.e. something that requires some global stability). On a more general level, we can think about what we're probably doing when we're engaging in an activity that encourages more slow, or fast brain wave activity. Are we encouraging global integrative processing? Or are we prioritising local, task-related activity?
Another interesting insight is that, while oscillations for the most part probably aren't doing anything, they probably are doing some things. It doesn't seem that likely that the rate of neural firing is making you sleep or something like this. Rather, the slow waves are simply reflecting the fact that you are asleep and the activity going on as a consequence. But at the same time, it's very conceivable that the firing rate that produces alpha and mu rhythms are acting like a noise suppression mechanism---blanking out bits of your perception with noise so you can ignore stuff that is distracting you. We can use this to think about things too. So, if we can find an activity that strengthens alpha, we might think to use it not merely to relax, but specifically to help us relax in situations where the world is too noisy. Indeed, if that HBR article I linked up top is to be believed, then music at 60bpm isn't helping you relax so much as its helping you drown out certain kinds of noise. This is the kind of nuance that's actually quite helpful. For example, a colleague recently demonstrated that, if you make images flicker at the same rate as alpha activity, then the amount of distraction it produces in the brain when it appears on the screen is reduced. This kind of thing isn't so much interesting for its potential for relaxation as it is for its potential to improve task performance. It makes you start to wonder just how much the flickering lights, or the flicker from your screen refresh rate is influencing your thinking. More speculatively still, individuals with ADHD often exhibit abnormal theta/beta ratios. If there is some kind of problem with the communication of whatever is going on in the beta activity by the longer theta waves, then neurofeedback training that aims to normalise these ratios could potentially lead to better-focused attention. In general, it seems like we can use these oscillatory frequencies to tune the way our brain works.
One final, related, thought I've had relates to the generation of insight. I've written before that creative insights seem to happen when old rigid ways of thinking bump into unusual patterns of thought. Sort of implied in this dance between long, slow waves and short, fast waves is a dynamic balance between stability and flexibility in cognitive processes. Stable neural patterns, where the frequencies of neural activity are well-synchronised within their respective bands is something we take to indicate reliable and efficient performance, particularly when a task is routine or well-learned. But of course, too much of this stability is going to hinder our ability to adapt to new information or unexpected situations---cognitive rigidity. On the other hand, flexibility would seem to require that we disrupt these stable patterns to allow us to make associations between things we wouldn't normally connect together. This would, it would seem, to be reflected by the desynchronisation of brain waves across different bands as we shift tasks or attention. Anything that alters the balance between these synchronised and desynchronised patterns might encourage either more stable patterns of activity for those times we need to be consistent and efficient, or promote flexibility when we need to be creative and adaptive. We could probably get after this with activities known to produce these effects. More, thinking about how things like brain stimulation and neurofeedback could help us achieve this kind of influence seems like an interesting pursuit (although so far there isn't much promise here).
None of this is quite as satisfying as saying that doing x thing increases alpha and so we relax better. But it certainly gives you the tools to think a little bit more about that finding you heard about, what it might be doing, and how (or even if) you could use it. At a minimum your little confidence game will sound a little less trite.