Understanding brainwaves

Neurofeedback & Brainwaves

Neurofeedback training is based on the principle of operant conditioning, which involves rewarding an individual for inhibiting certain brain waves and increasing others, depending on their levels of cortical arousal. An audio or visual stimulus is used for reinforcement during most NF training protocols.

Certain frequencies of brain waves are inhibitory, whilst others are excitatory. This means that the stimulation of certain wave bands may be responsible for characteristics associated with over-arousal (e.g. fidgeting, hyperactivity and feelings of agitation), whilst others lead to features of under-arousal (e.g. poor concentration, spaciness, and day-dreaming)

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Delta Waves (1-4 Hz) are slow brainwaves, which begin to appear in stage 3 of the sleep-cycle, and by stage 4 dominate almost all EEG activity. At this stage, healing and regeneration are stimulated, and are considered essential for the restorative properties of sleep. An excess of delta waves when a person is awake may result in learning disabilities and ADHD, and make it extremely difficult to focus. It has been found that individuals with various types of brain injuries produce delta waves in waking hours, making it extremely difficult to perform conscious tasks. Sleep walking and talking tend to occur while delta production is high.

Research suggests that cortical circuits generate delta <1Hz, whereas higher-frequency delta rhythms are an intrinsic property of thalamacortical cells and intracortical network interactions. Importantly, delta may also reflect general neurotransmitter activity, specifically dopamine and acetylcholine. Because delta is active within brain networks that connect the cortex and insula with the hypothalamus and the brainstem, delta is closely involved with the physiological interface between the brain and the body. During delta wave sleep, neurons are globally inhibited by gamma-aminobutyric acid (GABA).

Normal Occurrence of Delta Waves

  • Delta waves are slow EEG waves that oscillate from about .5 to 4 times per second.

  • Newer classifications may call Delta 5-2Hz activity and some may classify Delta as 1–4Hz

  • Delta waves tend to be large in amplitude.

  • Delta waves are rarely seen in the healthy waking adult EEG but are prominent and normal during sleep, especially of infants, children, and young adults.

  • Delta waves are common in infants most of the time (Imagine a baby and how they often nap and doze)

  • Delta waves are common in stage 3 & 4 sleep in adolescents and teenagers

  • Delta waves begin to disappear from the sleep records of adults after age 45 and tend to be almost entirely absent from those older than age 75.

Abnormal Occurrence of Delta Waves

  • Delta should generally be absent from the waking EEG records of adults.

  • If Delta appears in the waking EEG record, it may indicate the presence of…

  • Head trauma such as might occur in a car accident or bad fall.

  • Exposure to toxins such as heavy metals, pesticides, etc.

  • Cognitive impairment that might be the result of liver disease or degenerative brain diseases like dementia or Alzheimer’s disease.

  • Focal Delta may be the result of a lesion or tumor or may indicate damage from a stroke.

Physiological Origin of Delta Wave Rhythms

  • Most Delta that is recorded from the scalp in routine EEG is cortically generated and seems to be an intrinsic property of the pyramidal neurons that are primarily responsible for generating the scalp recorded EEG (the cortex is the surface of the Brain).

  • Cortical Delta can also be generated by the Suprachiasmatic Nucleus which plays a role in regulating Circadian Rhythms (Sleep / Wake Cycles).

  • The Thalamic nuclei also have a role in generating Delta rhythms especially during sleep (the Thalamus is one of the primary pace makers of the brain resulting in the oscillating rhythms seen in the EEG).

  • Delta activity during wakefulness in adults is inhibited by the ascending cholinergic neurons from the reticular activating system.

Role of Delta Waves in Having a Healthy Brain

  • Delta during sleep is involved in triggering the release of hormones that help the body heal and recuperate.

  • Delta during sleep plays a role in transferring new learning and memories into long-term memory storage.

  • Interruption of Delta activity during sleep is linked to a variety of disorders including…

  • ADHD

  • Schizophrenia

  • Anxiety & OCD,

  • Night Terrors & Sleep walking

  • Type 2 Diabetes

  • Parkinson’s disease

  • Autoimmune disorders such as Juvenile Rheumatoid Arthritis


Theta waves (4-8 Hz) are particularly involved in day-dreaming and sleep. Cortical theta is observed frequently in young children, but in older children and adults, it tends to appear during meditative, drowsy, or sleeping states (but not during the deepest stages of sleep). When we are awake, excess theta levels can result in feeling scattered or day-dreamy, and is commonly reported in ADHD. Too much theta in the left hemisphere is thought to result in lack of organisation, whereas too much theta on the right results in impulsivity. Theta in people with attention disorders is often seen more towards the front of the brain.

Frontal Midline Theta: Sinusoidal and high in amplitude (1-10 second bursts), generally occurs in response to events (ie. an ERP). This midline theta is associated with opening the sensory gate to the hippocampus for intermediate storage of episodic information. The frequency of frontal midline theta varies from 5-7.5 Hz, with an average of 6Hz. This rhythm is associated with working memory, episodic encoding and retrieval. It also appears during hypnosis and deep meditation. Frontal midline theta is thought to originate from the anterior cingulate. It mainly appears when one is performing a task requiring focused concentration, and its amplitude increases with the task load. It is mainly concentrated around Fz. When anxious and restless, the signal is reduced or even eliminated. When anxiety is medicated, the signal is restored. This suggests that the anterior cingulate cortex is involved in regulating the emotional state from restless anxiety to focused relaxation.

Hippocampal Theta: Has been found in the posterior cingulate, entorhinal cortex, hypothalamus and amygdala. Often more tonic and diffuse, and elicits and coordinates memory.

Normal Occurrence of Theta Waves

  • Theta waves oscillate about 3.5 – 7.5 times per second (Hz).

  • Some consider Theta to be from 4 – 8 Hz.

  • Theta is normal in small very amounts in the healthy waking adult EEG.

  • Theta in the adult waking EEG should be symmetrically distributed.

  • Theta is more prominent and considered normal in the raw EEG’s of children & adolescents unless there is clear indication of pathology.

  • Theta at the scalp surface in the adult EEG is normal as part of the early stages of drowsiness.

  • Theta may occur in some individuals who are day dreaming.

  • Some individuals produce a frontal-midline Theta (FZ) under task conditions that can be recorded at the scalp and is dependent on task difficulty and reflects transfer of information to long-term memory / memory functions

Abnormal Occurrence of Theta Waves

  • Excessive Theta activity in the waking raw EEG of adults is considered abnormal. It can represent reduced metabolism cortical grey matter (too little oxygen uptake).

  • Theta that is asymmetrically distributed in the waking adult EEG is considered abnormal (more on one side than the other)

  • Spike and slow wave complexes that occur in seizure disorder often occur in the Theta frequency range.

  • Excessive Theta on quantitative analysis is often seen in conditions such as…

  • ADHD

  • Learning disabilities

  • Head injuries or brain lesions

  • Certain neurological disorders

Physiological Origin of Theta Wave Rhythms

  • Cortical Theta generation in humans is projected to the cortex via Thalamo-cortical projections and is influenced by GABAergic / Cholinergic inhibitory & excitatory inputs from the Reticular Activating System.

  • Cortical Theta is essentially a slowing of the Alpha rhythm but may also be influenced by limbically generated (septo-hippocampul) Theta as described below.

  • Sub-cortical Theta Rhythms are prominent in the Hippocampus & Limbic system and result from alternating inhibition / disinhibition between the septal nuclei & hippocampal nuclei.

  • Limbic Theta oscillations are caused by alternating inhibition / disinhibition of GABAergic & Cholinergic neurons.

  • The hippocampus is part of the “Papez Circle” including the Hippocampus (HIP), Entorhinal Cortex in Temporal Lobes, Sensory areas of the Temporals & Parietals, the Mammillary Bodies of the Hypothalamus, and the Thalamus that are involved in memory consolidation.

Role of Theta Waves in Having a Healthy Brain

  • Hippocampal & Limbic Theta are highly involved in the encoding of meaningful events into long-term memory.

  • Cortical Theta likely represents a “binding rhythm” that ties functionally related neural networks together in time for coordinated processing of memory storage functions.

  • Inducing a Theta state via hypnosis or neurofeedback may aid in anxiety reduction and the processing of traumatic memories such as may occur in PTSD


Alpha waves (8-12 Hz) dominate during moments of quiet thought, and similar meditative states. Alpha is considered the “power of now”, being here and in the present of the moment. It is the resting state for the brain, not unlike a car idling at a stoplight. Alpha waves aid overall mental co-ordination, calmness and alertness, mind/body integration and learning. Alpha tends to be highest in the right hemisphere, and too little alpha in the right hemisphere correlates with negative behaviours such as social withdrawal. This is also seen in people with depression, particular with too much alpha frontally. Alpha is involved in active and adequate inhibition of the irrelevant sensory pathways.

Alpha is related to resource allocation in the cortex, and is produced as a result of a resonance process between the thalamus and the cortex. If we consider the thalamus the gateway to the cortex, alpha can be thought of as the mechanism by which the sensory gate to the cortex can be closed.

Alpha appears to be closely involved with reticular activation, and participates in binding mechanisms and resource allocation in regards to orientation and task sequences.

Alpha diminishes during sleep onset, while focusing on tasks, and is also a normal consequence of ageing. When alpha slows and theta increases in frequency, it is often an indicator of pathologically slowed high-amplitude alpha, which is associated with Parkinson’s disease and cognitive decline. This indicates degradation of myelination and cell death in the cortex, and reflects growing metabolic inefficiency.

After completing a task and given feedback, the high functioning brain shows increased levels of alpha. This is associated with consolidation of the task events, called post reinforcement synchronisation (PRS). This represents and alpha burst in the brain when the brain is consolidating information.

Normal Occurrence of Alpha Waves

  • Occipital Alpha is the dominant rhythm in relaxed wakefulness in 85% of healthy adults with closed eyes (Occipital = Occipital lobe at the back of the head).

  • Alpha activity may spread to temporals and parietals in some people and this is considered normal.

  • 85% of adults have a resting Alpha rhythm between 9.5-10.5 Hz.

  • Some people have Alpha variants (slower or faster) that are generally considered normal if localized to the occipitals & attenuating (diminishing) with eye opening.

  • Alpha may appear in polymorphic complexes mixed with Theta or Beta especially in drowsiness.

  • Mu Rhythm (usually localized to C3 / C4 in scalp recorded EEG is considered an Alpha-like Rhythm & reflects motor system activation.

  • Some individuals have an Alpha asymmetry over non-dominant hemisphere up to 50% greater and this is considered normal.

  • Alpha activity generally attenuates (diminishes) with eye opening, mental activity, and drowsiness.

  • Alpha activity may be present in REM sleep with a frontal / central distribution & may be related to periods of increased brain activity during sleep.

  • Alpha may also be present with Delta in slow wave sleep

Abnormal Occurrence of Alpha Waves

  • Frontally prominent & persistent Alpha may indicate hypometabolism (reduced blood flow) & abnormality.

  • Alpha that fails to attenuate (diminish) with eye opening may be due to drowsiness or other pathology, including abnormalities in the visual system.

  • Decreased Alpha peak frequency may reflect disease or brain injury such as TBI, dementia, medication effects, and age-related cognitive decline.

  • Alpha peak frequency below about 8.5 Hz at PZ in the Adult waking record is considered slow.

  • Alpha peak frequency above about 11 Hz at PZ in the Adult waking record is considered a fast variant.

  • Absence of Alpha in one hemisphere or asymmetries between hemispheres greater than 50% are considered abnormal.

  • Slowed Alpha rhythms may reflect neurological diseases such as dementia, Alzheimer’s, head injuries, or other conditions that can cause reduced cognitive abilities.

  • Excessively fast Alpha can be associated with anxiety and OCD symptoms.

  • Alpha that is frontally prominent may relate to depression and attention problems.

Physiological Origin of Alpha Wave Rhythms

  • There are cortical generators of Alpha that act as “epicenters” where Alpha starts and spreads via cortico-cortical connections across the cortex.

  • Alpha may also be generated by alternating GABAergic inhibition & Glutaminergic excitation of Thalamic “pace maker” neurons in the Reticular Nucleus.

  • Cortical & Subcortical Alpha generators interact to cause the scalp recorded Alpha rhythm.

  • Alpha amplitudes are influenced by cortical metabolism. Increased arousal usually = less Alpha.

  • Alpha frequencies are influenced by the degree of Reticular Nucleus Neuronal Depolarization. More Activation / Depolarization = Faster Alpha Frequencies.

Role of Alpha Waves in Having a Healthy Brain

  • The posterior Alpha rhythm is one of the best indicators of cognitive functioning.

  • Alpha can be thought of as your brains “sampling rate” and indicates how your sensory system is interacting with your environment.

  • Maintaining a healthy Alpha speed (@10 Hz for adults) is an important measure of cognitive functioning. If the Alpha begins to slow due to aging, head injury, toxic exposure, etc., cognitive problems can be expected.


Beta waves (12-38 Hz) represent our normal waking state of consciousness when attention is directed at cognitive tasks and the outside world. Beta is ‘fast wave‘ activity and dominated when we are alert, attentive and engages in problem-solving, decision making and focussed mental activity. Low beta (12-15 Hz) is thought to be ‘fast idle’, or musing thought, Beta (15-22 Hz) is high-engagement and actively figuring things out, and finally, High Beta (22-38 Hz) is highly complex thought, integrating new experiences, high anxiety or excitement. Continual high frequency processing is not an efficient way to run our brains , and can result in tension and difficulties relaxing, and if present at night, can result in difficulties settling the mind and falling asleep. Beta waves tend to dominate in the left hemisphere, and too much beta on the right can be correlated with mania.

There are discrepancies regarding how the three levels of beta and gamma divide their territory in the brain. While it is widely agreed that higher beta frequencies are more correlated with arousal, some convincingly suggest that they are mostly a result of muscle artefact. For example, Helleter et al. found that anxiety was highly correlated with elevated right hemisphere beta, and more recent work has found that insomnia is correlated with higher temporal lobe frequencies of beta, and migraines are associated with central high beta.

Normal Occurrence of Beta Waves

  • Beta waves oscillate between about 13 and 35 times per second.

  • Beta waves are prominent during states of concentration and problem solving.

  • Beta waves are common in the EEG’s of most waking adults but may also be present during drowsiness.

  • Beta waves tend to be more visible in the EEG when the patients eyes are open.

Abnormal Occurrence of Beta Waves

  • Beta asymmetries are usually pathological over the side with reduced amplitude, especially if the asymmetry is greater than 50%. However, other frequency asymmetries should be considered before determining abnormality (is there also reduced Alpha / increased Theta, etc.).

  • Interhemispheric Beta Asymmetries can be due to remote infarcts or subdural collections (bruises, swelling, etc.).

  • Bi-laterally increased Beta can be due to previous craniotomy (Breech Rhythm).

  • Elevated Beta amplitudes in posterior leads is more unusual than Beta in central / frontal leads.

  • Lack of Beta desynchronization with difficult tasks may be abnormal.

  • Spindling Beta generally reflects increased cortical irritability and is most likely seen in clinical conditions such as…

  • ADHD

  • Epilepsy

  • Psychoses including during hallucinations

  • Anxiety disorders

  • Excessive Beta activity on quantitative analysis can relate to symptoms of brain over arousal such as anxiety, obsessiveness, sleep difficulties, hyperactivity, etc.

  • Deficient Beta activity on quantitative analysis can relate to symptoms of brain under aroused such as difficulty concentrating, problem solving, etc.

Physiological Origin of Beta Wave Rhythms Two Types of Beta Rhythms

  • Sensory-Motor Beta (Rolandic) is localized to the motor strip (center of the head) but distinct in morphology, speed, & location from Mu rhythm. It has peak frequency @ 20Hz. It becomes less rhythmic with motor action or motor planning and more rhythmic following motor actions. Sensory-motor Beta reflects the resting and resetting of the motor system following information processing. The more frequently Beta rhythms synchronize (the faster the rhythm) the more excitable the cortex (surface of the brain).

  • Frontal Beta is localized to front of the head and it is composed of irregular rhythms generally less than 20 Hz. Frontal Beta tends to become more rhythmic and synchronized several hundred ms post-processing of stimuli that require assessment, cognitive evaluation, and decision making. This synchronization may be preceded by Beta desynchronization. The amount of frontal Beta desynchronization and rebound synchronization in response to a cognitive task is proportional to the difficulty of the task. Increasing Task Difficulty = Increased Beta Desynchronization.

Role of Beta Waves in Having a Healthy Brain

  • Beta Power (and Alpha Power) is a good indicator of how much activity and metabolism is occurring in your brain.

  • Beta tends to become less rhythmic when you are concentrating on something that is mentally challenging. This correlates with increased blood oxygenation and metabolism in the brain.

  • Some neurofeedback seeks to increase Beta in the 12-18 Hz range or to reduce the Theta / Beta ratio to aid in attention.

  • NFB to inhibit excessive Beta can be helpful in reducing anxiety, OCD, and the high beta subtype of ADHD.


Gamma brainwaves have the highest frequencies of any brainwave, oscillating between 30 (ish) to 100 Hz. They are associated with peak concentration and high levels of cognitive functioning. Low levels of gamma acitivity have been linked with learning difficulties, impaired mental processing and limited memory, while high gamma activity is correlated with a high IQ, compassion, excellent memory, and happiness.

Gamma is currently of limited clinical value, as it is argued that it cannot be effectively measured using current EEG technology, due to muscle contamination. While promising research has suggested that Gamma training can be successfully implemented to enhance intelligence, it will not be of proper clinical use until this issue of technology is resolved.

Gamma and theta work together to recruit neurons which stimulate local cell column activity. As such, it is associated with cortical processing related to cognitive functions, and is also potentially related to meditative states, although research on this relationship is vague.

What is EEG? How is it generated?

The EEG is recorded from the surface of the head. Measurable surface potentials (microvolts) are produce by neurons in the brain in the top layer of the cortex. The cortex contains the outer information processes of the brain. The main EEG signals are produced by pyramidal cells as these are oriented in a manner than produced measurable voltage. The brains electrical sources are dipoles, which is a charged entity that had a positive and negative side (similar to a battery). The EEG is a epiphenomenon (side effect) of the brain’s activity, but is not a direct measure of information processing such as a recording of action potentials.


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