The First Scheduled Nap Opportunity
A 20-minute window to fall asleep, lights out, electrodes on.
- 20 min: Nap duration offered (per trial, lights out)
- ~1.5–3h: First nap start (after morning wake time)
- Dark, quiet: Room condition (controlled bedroom)
- EEG/EOG/EMG: Recording channels (stage-scoring montage)
Lights out, clock starts
The patient reclines and stops trying to stay awake.
What latency measures
Time from lights-out to the first epoch of any sleep stage.
Why the first nap matters
Sets the baseline curve the remaining four naps build on.
Second Nap — Latency and REM Onset Recorded
Two hours after nap one, the same 20-minute trial repeats.
- 2 h: Inter-nap interval (fixed spacing between trials)
- ≤15 min: SOREMP window (REM onset after sleep start)
- 30 sec: Scoring epoch (standard PSG epoch length)
- 2 of 5: Trial count so far (naps completed)
Consistent spacing
Every nap starts exactly two hours after the last.
Watching for early REM
REM within 15 minutes of sleep onset flags a SOREMP.
Between-nap wake rule
Patient stays awake and upright between trials.
Third Nap — Pattern Continues
Midday trial, SOREMP tally updates after each scored nap.
- 3 of 5: Naps completed (running total)
- ≥2: ICSD-3 SOREMP threshold (across all naps)
- ≤8 min: Mean latency threshold (supports narcolepsy)
- Required: Overnight PSG lead-in (night before testing)
Running tally
Each completed nap adds to the SOREMP count live.
Circadian dip
Early afternoon naps often show shorter latencies.
Consistency check
Technologists watch for stable scoring across trials.
Final Two Naps Complete the Series
Late-afternoon and early-evening trials finish the protocol.
- 4–5: Total naps in protocol (per AASM guidance)
- ~6:00 PM: Final nap time (typical end of testing day)
- After nap 4: Early termination rule (if 2 SOREMPs already seen)
- ~7–8 h: Total test duration (across the testing day)
Closing the series
Naps four and five mirror the earlier trials exactly.
Early stop option
A fifth nap may be skipped once criteria are already met.
Data lock
All five latency and REM values are now finalized.
Mean Sleep Latency Calculated
Averaging all trials turns raw timings into a diagnosis.
- Σlat / n: Mean latency formula (across completed naps)
- ≤8 min: Narcolepsy cutoff (mean sleep latency)
- ≥2: SOREMP cutoff (plus PSG REM ≤15 min substitute)
- >15 min: Normal alertness (typical mean latency)
Averaging the naps
Every completed latency value feeds the mean.
Reading the SOREMP count
Two or more SOREMPs point toward narcolepsy.
Final call
Mean latency plus SOREMP count yield the MSLT verdict.