Final answer:
Sleep spindles, occurring at 12-14 Hz with K complexes during stage 2 sleep, are absent in NREM sleep of patients with schizophrenia.
Step-by-step explanation:
The waves that are occurring at 12-14 Hz during stage 2 sleep with K complexes and are absent in NREM sleep in patients with schizophrenia are sleep spindles. Sleep spindles are characterized as a rapid burst of high frequency brain waves that are important for learning and memory. These are most prominent in stage 2 of NREM sleep. In contrast, alpha waves are characteristic of the early part of NREM stage 1 sleep, typically having a frequency of 8-12 Hz. Theta waves, with a frequency of 4-7 Hz, are dominant at the end of stage 1 sleep and carry into stage 2 sleep before sleep spindles appear. Beta waves, which have a frequency of 13-30 Hz, are characteristic during wakefulness. Lastly, delta waves signify deep sleep or slow-wave sleep found in stage 3 NREM sleep, with a frequency of less than 3 Hz and high amplitude. Considering these distinct characteristics, sleep spindles are the brain waves in question related to the absence in NREM sleep in schizophrenia patients.