Final answer:
Different patterns of brain waves can be observed in various stages of sleep and wakefulness, with their frequency and amplitude indicating different states of brain activity. The total absence of these waves is a criterion for brain death.
Step-by-step explanation:
There are different types of brain waves that can be observed using an electroencephalogram (EEG). The absence of brain waves is a medical criterion to determine brain death. In a living individual, brain wave patterns change in frequency and amplitude across different stages of sleep.
During wakefulness, beta waves, which are of the highest frequency (13–30 Hz) and lowest amplitude, dominate brain activity. As one transitions into sleep, particularly non-REM (NREM) stage 1, alpha waves emerge with a frequency of 8-12 Hz. These then give way to theta waves and ultimately delta waves as a person moves into deeper stages of sleep. During REM sleep, the brain exhibits wave patterns similar to wakefulness, and this stage is where dreaming often occurs. The analysis of these brain wave patterns is not only useful for studying sleep, but also for evaluating brain function in various conditions.