National Sleep Foundation

Glossary

T

Theta waves - Occur during stages 1 and 2 and are slower in frequency and greater in amplitude than alpha waves. As a person moves from stage 1 to stage 2 sleep, theta wave activity continues; every few minutes, sleep spindles (sudden increase in wave frequency) and K-complexes (sudden increase in wave amplitude) occur.

Tolerance - The need to provide increasing doses of medication to provide the same relief.

Total sleep time (TST) - The actual amount of time spent sleeping from sleep onset until awakening; TST includes all REM and NREM sleep.