The brain is a bio-chemical organ that emanates electromagnetic waves. That little, we do know. And brainwaves are linked to cognitive states from awareness and consciousness, to dream states. But what are their particularities? And are brain waves modulated by external frequencies?
Like any physical wave, neural oscillations are characterized by their
Action Potentials and Brain Waves
Rhythmic repetitive patterns of action potentials in the Central Nervous System (CNS) are driven by mechanisms within individual neurons, or the interactions between them.
It is worth noting that those processes in the human brain happen on a variety of physiological levels:
At the microscopic level, each neuron can generate action potentials resulting from changes in the electric membrane potential.
Neurons can generate multiple action potentials in sequence forming spike trains – those are the basis for neural coding and information transfer in the brain.
Groups of neurons can also generate oscillatory activity.
Through synaptic interactions, the firing patterns of different neurons can become synchronized and the rhythmic changes in electric potential caused by their action potentials will add up.
Neural oscillations can also arise from interactions between different brain areas coupled through the structural connectome. These connections form positive feedback loops.
At this macroscopic level, synchronized activity in a group of neurons can begin to get quantified.
Detecting Brain Waves with EEG
Neural oscillations are the result of electrical activity generated by large groups of neurons. This large-scale activity is quantified with electroencephalography (EEG).
Electroencephalography is a typically non-invasive investigative method that involves placing electrodes along the scalp. It records the spontaneous electrical activity of the brain.
The bioelectrical signals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex and allocortex of the brain. So, EEG can be used to help diagnose and monitor a number of conditions affecting the brain.
Electroencephalography is a powerful tool for tracking brain changes during different phases of life. EEG sleep analysis can indicate significant aspects of the timing of brain development, including evaluating adolescent brain maturation.
The drawback is that EEG poorly measures neural activity that occurs below the cortex (upper layers of the brain).
Nowadays, MRI (Magnetic Resonance Imaging) technology helps to explore the human brain and map its functions.
Quantifying Brain Waves – The Colour of Noise
Researchers have speculated that a fully functioning brain can generate as much as 10 watts of electrical power.
Even though this electrical power appears extremely limited, it behaves in very specific ways characteristic of the human brain.
Different colours of noise have significantly different properties. As audio signals, they will sound different to human ears. As images, they will have a visibly different texture.
Neural oscillations display a broad spectral content, similar to pink noise, indicative of an oscillatory activity in specific frequency bands.
Pink noise is a random signal, filtered to have equal energy per octave. And it sounds exactly like a waterfall.
Click below to hear pink noise:
In order to keep the energy constant over several octaves, the spectral density has to decrease as the frequency (f) increases.
As it is inversely proportional, it may be referred as “1/f noise” or “fractal noise”.
Pink noise is one of the commonest signals in biological systems.
Brain waves are linked to cognitive states, such as awareness and consciousness.
In fact, there is a plethora of neural oscillations.
Brain Waves and Their Frequencies
There are several signal categories. Below are just a few, ranging from the least active state to the most active:
- delta (1 – 4 Hz),
- theta (4 – 8 Hz),
- alpha (7.5 – 12.5 Hz) the best-known frequency band,
- beta (13 – 30 Hz),
- low gamma (30 – 70 Hz) and high gamma (70 – 150 Hz) frequency bands, linked to cognitive processing.
Delta Waves: Living/Sleeping
Delta brain waves have the greatest amplitude and the slowest frequency. At a range from 1.5 to 4 Hz (or s-1, i.e. cycles per second).
This signal never goes down to zero, which would otherwise indicate brain death.
But, deep dreamless sleep would take you down to the lowest frequency. Typically, 2 to 3 Hz.
Theta Waves: Daydreaming/Ideation
Theta waves underly different behavioural and cognitive aspects: learning, memory, spatial awareness.
They range from 5 to 8 Hz.
Someone who daydreams is often in a theta brainwave state. Someone who is driving on a freeway, and realises that they cannot remember the last five kilometres of their journey, is often in a theta state – induced by the process of motorway driving.
The repetitious nature of that form of driving compared to that on a country road would differentiate a theta state and a beta state in order to perform the driving task safely.
Motorway driving or running outdoors are often conducive to good ideas in a state of mental relaxation that is slower than alpha.
When in theta, people’s minds are prone to a flow of ideas. You may find this occurs in the shower or bath, while shaving or brushing your hair. It is a state of mind where tasks become so automatic that you can mentally disengage from them.
The ideation is often free flow and occurs without censorship or guilt – a typically very positive mental state.
Theta brain waves with a lower frequency range, usually around 6 – 7 Hz, are sometimes observed when a rat is motionless but alert.
Alpha Brain Waves: Meditation/Wakefulness
The next category of brainwaves in order of frequency is alpha waves.
Their frequency ranges from 9 to 14 Hz.
Alpha brainwaves are slower and higher in amplitude than beta waves.
Alpha waves can be detected from the occipital lobe of the brain, during relaxed wakefulness. They increase when the eyes are closed.
Someone who sits down to rest after activity, is often in an alpha state. Someone who takes time out to reflect or meditate, is usually in an alpha state. Someone who takes a break from a busy conference and takes a restorative garden walk, is often in an alpha state.
Alpha activity has also been connected to the ability to recall memories, lessen discomfort and pain, and reduce stress and anxiety.
Beta Brain Waves: Alertness
When the brain is aroused and actively engaged in mental activities, it generates beta waves.
These beta waves have a relatively low amplitude, and are the fastest of the four described brainwaves.
The frequency of beta waves ranges from 15 to 40 Hz.
Beta brainwaves characterise a strongly engaged mind.
Anyone engaged in active conversation would be in beta mode.
A person making a speech, or a teacher, or a talk show host would all be in beta when they are engaged in their work. A debater would be in high beta.
Gamma Brain Waves: Cognition
Gamma brain waves is a pattern of neural oscillation in humans with a frequency between 25 and 140 Hz,
The 40 Hz point is of particular interest.
Gamma rhythms are correlated with large scale brain network activity and cognitive phenomena such as working memory, attention, and perceptual grouping. It can be increased in amplitude via meditation, or neuro-stimulation.
Altered gamma activity has been observed in many mood and cognitive disorders, such as Alzheimer’s disease, epilepsy, and schizophrenia.
Whereas beta brainwaves represent a state of arousal, alpha waves represent non-arousal.
Consciousness and Unconsciousness
When we go to bed
We may read for a few minutes before attempting to sleep, and our brain waves are then most likely to be in low beta. Then, we put the book down, turn off the lights and close our eyes, our brainwaves descend from beta, to alpha, to theta…
When we Sleep and Dream
Eventually, we fall asleep, and our neural oscillations decrease further to delta.
Human beings dream in 90-minute cycles.
When this occurs, there is Rapid Eye Movement sleep.
This is called REM, or paradoxical sleep, and is a well known phenomenon. It bears physiological similarities to waking states, including rapid, low-voltage desynchronized brain waves.
When we Awake
When an individual awakes from a deep sleep in preparation for getting up, their brainwave frequencies will increase through the different specific stages of brainwave activity. That is, they will increase from delta to theta, and then to alpha and finally, when the alarm goes off, into beta.
When we hit the “snooze” button or Daydream
If that individual hits the snooze alarm button they will drop in frequency to a non-aroused state, or even into theta, or sometimes fall back to sleep in delta.
During this awakening cycle, it is possible for individuals to stay in the theta state for an extended period of say, five to 15 minutes, which would allow them to have a free flow of ideas about yesterday’s events or to contemplate the activities of the forthcoming day.
This can be an extremely productive time and a very meaningful period of creative mental activity.
Synchronized Brain Waves
From deep dreamless sleep to high arousal, those brain wave states are common to all human beings.
Brainwave patterns are always consistent, regardless of culture, ethnicity or country boundaries.
Men, women, children of all ages experience those characteristic brain wave patterns.
A Mix of Brain Waves
Although one brainwave state may predominate at any given time, depending on the activity level of the individual, the remaining three brain states are present in the mix of brain waves at all times.
Neuronal interactions can give rise to waves at a different frequency than the firing frequency of each neuron.
So, while someone in an aroused state exhibits a beta brainwave pattern, a component of alpha, theta and delta waves co-exist in that person’s brain, albeit at a trace level.
Understanding how brain wave states enhance a person’s ability to make use of the specialised characteristics of those states, including being mentally productive across a wide range of activities:
- feeling intensely focused,
- feeling relaxed,
- feeling creative and
- enjoying restful sleep.
Modulated Brain Waves
Billions of neurons communicate all at once. As those neurons fire, they can be affected by external interference around them.
Different levels of sound waves can cause different effects on the brain and its processes, affecting an individual’s thinking ability and sleep in different ways.
Environmental Noise Exposure
Exposure to high levels of noise (20 Hz to 20,000 Hz) has an impact on our language comprehension. And a 50 Hz and a 5,000 Hz sound appear equally loud to the human ear, if the 50 Hz signal is at a 95 dB level and the 5,000 Hz sound at a 76 dB level.
Noise can induce chronic stress, and increase the risk of heart attacks. It has been linked to the development of metabolic syndromes, such as obesity and diabetes.
Even exposure to low levels of environmental noise over long periods of time may affect our brain processes and mental health.
But what about the frequencies you cannot hear?
Under the normal lower threshold of human audibility is the infrasonic range, i.e. below 20 Hz and down to 0.1 Hz. Because of its low frequencies and long wavelengths, infrasound is capable of travelling long distances with little attenuation. As such, the infrasound energy will carry at considerable distances.
Human hearing decreases with frequency, so the sound pressure will need to be high enough for humans to perceive infrasound waves. When pure waves are produced at a very high volume, a human listener will be able to identify tones as low as 12 Hz.
Below 10 Hz, it is possible to perceive the single cycles of the sound, along with a sensation of pressure on the eardrums. At higher still intensities, it becomes possible to feel infrasound vibrations in the body.
Legal limits are set to prevent direct physiological damage. For a 24 hour exposure, levels of 120-130 dB are tolerable below 20 Hz.
Fear Frequency 18.98 Hz
Low frequency noises cause extreme distress to a number of people who are unfortunate enough to be sensitive to its effects. But the biological impact of very high levels of infrasounds is not fully understood.
The research so far has concentrated on using very high sound pressure to establish safe exposure limits.
However, there is growing evidence that low level, low frequency signals may indeed affect the nervous system by stimulating the vestibular system, producing an effect comparable to sea sickness, and may lead to a feeling of unease or visual disturbances that might be interpreted as ghostly apparitions.
The “Ghost frequency” or “Fear frequency” at 18.98 Hz is too low to be heard. Nevertheless, its effects can reportedly be felt by some individuals.
We know so little about the brain and the human mind workings yet, but neurologists are keen to find out more.
Brain waves create alternate states of awareness via the electrical, chemical and biological reactions they generate.
The question scientists ask is whether those reactions are purely biological functions, accidentally discovered by humankind, or are they truly mystical and spiritual capacities of our higher self or what we keep calling ‘consciousness’?
Several studies report an EEG surge in gamma brain waves as the body prepares to shut down.
Normally, gamma brainwaves signal consciousness – a state when the human brain is alert and very much awake.
As if that wasn’t strange enough, this boost in gamma brainwaves occurs in the area of the temporo-parieto-occipital junction of the brain, known as TPO, responsible for processing information from our senses, that is vision, touch, motor control and proprioception.
Scientists studied auditory and visual awareness of patients undergoing a cardiac arrest. Their findings appear to disprove the idea that an oxygen-deprived brain does not stay alive more than a few minutes. Bursts of activity in the full range of brainwaves occurred during cardiac arrest (CA), despite the patient being considered dead.
Beyond the brain’s resilience to lack of oxygen, the study showed synchronised spikes of gamma brainwaves confirmed the existence of a heightened lucid awareness, without any external signs of consciousness.
Theta and alpha waves are also coupled with low gamma oscillations following cardiac arrest, indicative of information coding, spatial and working memory, a feature of cognitive control in the mammalian brain.
During clinical death, the brain retains the potential for high levels of internal information processing. Somehow, it organises and executes a biological response that could be conserved across all species.
We can figure that much out. And yet, still, we don’t know why…