What is the characteristic of delta waves during sleep?

Delta waves during sleep are characterized by low frequency and high voltage. These brain waves typically oscillate at a frequency of about 1 to 4 Hz and are associated with deep sleep stages, particularly during non-REM sleep. The high voltage of delta waves indicates a synchronized activity of neurons in the brain, which reflects the restorative processes that occur during this phase of sleep. This stage is crucial for physical recovery and aspects like memory consolidation, making delta waves an important marker of healthy sleep patterns.

The other options do not accurately describe delta waves. High frequency is more characteristic of beta waves, which are present during wakefulness and alert states. Medium frequency waves can relate to alpha or theta waves, which are not indicative of the deep restorative sleep associated with delta activity. Rapid fluctuations would typically be associated with beta waves, which are characterized by quick changes in voltage and frequency, again distinct from the low frequency and sustained nature of delta waves.