Final answer:
During the first stage of sleep, alpha and theta brain waves can be observed.
Step-by-step explanation:
In the first stage of sleep, known as stage 1 sleep, brain waves associated with both alpha and theta waves can be observed. Alpha waves have a frequency of 8-12 Hz and higher amplitude, while theta waves have a lower frequency (4-7 Hz) and higher amplitude than alpha waves.
Learn more about brain waves