During which stage of sleep do delta waves begin to appear in EEG readings?

Delta waves begin to appear in EEG readings during Stage 3 sleep. This stage is characterized by the presence of high-amplitude, low-frequency delta waves, which indicate deep sleep. These waves play a crucial role in physical restoration and growth, as well as memory consolidation.

In the sleep cycle, Stage 3 is part of non-REM (NREM) sleep, and it follows Stage 2, where sleep spindles and K-complexes are more prevalent but delta waves are not yet significant. Delta waves become more predominant in this stage as the brain transitions into deeper levels of sleep.

Stage 4 is often considered a continuation of Stage 3 in some classification systems and may also show delta activity; however, the emergence of significant delta waves primarily characterizes Stage 3. This distinction is important in understanding the sleep architecture and the various physiological processes that occur during sleep.