EEG has four types of waves alpha,beta,theta and delta.
Consider a family where mother has passed away leaving 3 children in the protection of father.The father will be the head of family(consider him as alpha), next comes the son who is a college student(Beta), the third child is younger 6 years(theta), the youngest child is an infant(delta).
- Most prominent wave of EEG with frequency of 10-12Hz.
- Most marked in the parieto occipital area
- Seen in humans who are awake but at rest with mind wandering and eyes closed.
- Seen in stage 0 and 1 of NREM sleep.
- Asynchronous waves of higher frequency of 18-30 Hz but lower amplitude.
- Most marked in frontal area.
- Seen in human when awake persons attention is directed to some specific mental activity
- Not seen in any stage of sleep,replace alpha waves when an awake person at rest opens his eyes.
- Frequency of 4-7 Hz and large amplitude
- Most marked in parietal and temporal region in children
- They occur normally in children and in stage II and III of NREM sleep.
- Slow waves with a frequency <4Hz and a very large amplitude.
- Seen in infancy and serious organic brain damage.
- Seen in stage III and IV of NREM sleep(deep sleep).
- Sleep spindles and K complexes occur in stage II of NREM sleep.
- Sleep spindles are short spindle shaped bursts of alpha waves that occur periodically in NREM sleep.
- Frequency decreases and amplitude increases as we proceed from alpha to delta, the only exception is beta(highest frequency).
Relation with sleep
Stage 0 -alpha- close eyes beta-open eyes
stage 1 -alpha +theta
stage 2- theta waves spindles k complexes
stage 3- delta theta and spindle
REM sleep-all frequency of waves
Alpha waves (8-11 Hz) are slower and larger. They are associated with a state of relaxation and basically represent thebrain shifting into idling gear, relaxed and disengaged, waiting to respond when needed. If one merely closes his or her eyes and begins picturing something peaceful, in less than half a minute there will be an increase in alpha brainwaves. Alpha is present typically when one feels at ease and calm or in a position to change one’s mind efficiently and effectively in order to accomplish a task.
Sensory Motor Rhythm (12-15 Hz) measured over the sensorimotor cortex are brain waves associated with mental alertness and readiness for action, combined with behavioural stillness.
Beta waves (16 Hz and above) are small, faster brainwaves associated with a state of mental or intellectual activity and outwardly focused concentration. Beta waves are present when one is thinking, problem solving, processing information, or anxious.
Delta brain waves (1-3 Hz) are the slowest, highest amplitude brainwaves, and are present primarily during sleep or when in an empathetic state. Excess delta activity in the awake state is usually indicative of dysfunction.
Theta waves (4-8 Hz) are present when daydreaming or fantasising. At the same time, creativity and intuition are also associated with theta waves. This contrast occurs because theta waves occur at two levels: The lower range of theta (4-5 Hz) basically represents the twilight zone between waking and sleep. It is a profoundly calm, serene, floaty, drifty state. In this range, conscious intellectual activity is not occurring. It is also the range of frequencies produced in excess by children and adults with ADHD.