The lowest frequencies are delta. These are less than 4 Hz and occur in deep sleep and in some abnormal processes also during experiences of "empathy state". Delta waves are involved with our ability to integrate and let go. It reflects unconscious mind.
It is the dominant rhythm in infants up to one year of age and it is present in stages 3 and 4 of sleep.
It tends to be the highest in amplitude and the slowest waves. We increase Delta waves in order to decrease our awareness of the physical world. We also access information in our unconscious mind through Delta.
Peak performers decrease Delta waves when high focus and peak performance are required.
However, most individuals diagnosed with Attention Deficit Disorder, naturally increase rather than decrease Delta activity when trying to focus. The inappropriate Delta response often severely restricts the ability to focus and maintain attention. It is as if the brain is locked into a perpetual drowsy state.
Another way to look at Delta is to imagine you are driving in a car and you shift into 1st gear....you're not going to get anywhere very fast. So Delta would represent 1st gear.
Delta (0.1-3 Hz):Distribution: generally broad or diffused may be bilateral, widespread
Subjective feeling states: deep, dreamless sleep, non-REM sleep, trance, unconscious
Associated tasks & behaviors: lethargic, not moving, not attentive
Physiological correlates: not moving, low-level of arousal
Effects of training: can induce drowsiness, trance, deeply relaxed states
The EEG pattern changes throughout the night. These changes can determine when dreaming occurs. The chart below is an average sleep cycle during those eight hours.
[sleep cycle diagram]
Stage 1 is the drowsy period of sleep, characterized by what is known as sleep spindles (spindle-alpha).
Stage 2 is a sleep state where response to external and/or internal stimulation can occur. This stage is characterized by what is known as K-complex waves.
Stage 3 means you are on your way to Stage 4.
Stage 4 is deep sleep. It is also delta state and is not associated with dreaming. REM state (Rapid Eye Movement) is where most dreams occur.
Notice how an individual spends most of the first part of the night in State 4 sleep. The later part of the night is spent mostly in REM sleep. Therefore, most dreams occur toward the end of the night's sleep. When deprived of REM sleep, temporarily personality changes occur with other psychological changes. When lost sleep is made up, the person spends more the sleep cycle in lighter REM stages. In a sense, this makes up for that lost dream time.
Although there is a lot of variable data on EEG changes with age, there is a basic curve that shows the usual rate of development and change with time. Primarily the EEG frequency of a person starts very low, about 1-2 cps in a newborn infant, gradually increasing in frequency until the age of 19, where the normal adult rhythm, while awake, is about 20 cps.