Psychiatry and Clinical Neurosciences (2001), 55, 305–310

Proposed supplements and amendments to ‘A Manual ofStandardized Terminology,Techniques and Scoring
System for Sleep Stages of Human Subjects’, theRechtschaffen & Kales (1968) standard
SLEEP COMPUTING COMMITTEE OF THE JAPANESE SOCIETY OF SLEEPRESEARCH SOCIETY (JSSR): TADAO HORI, YOSHIO SUGITA, EINOSUKE KOGA,SHUICHIRO SHIRAKAWA, KATUHIRO INOUE, SUNAO UCHIDA,
HIROO KUWAHARA, MASAKO KOUSAKA, TOSHINORI KOBAYASHI,
YOICHI TSUJI, MASAYOSI TERASHIMA, KAZUHIKO FUKUDA, NORIKO FUKUDAINTRODUCTION
In 1967, the Association for the PsychophysiologicalStudy of Sleep (APSS) chartered a committee ofsleep researchers to establish a standard system forvisually scoring stages of sleep. The Committee’s
terminology and scoring system (edited by Alan
Rechtschaffen and Anthony Kales, co-Chairpersonsof the Committee) were quickly adopted after its
1968 publication under the auspices of the UCLA
Brain Information Service as ‘A Manual of Standardized Terminology, Techniques and Scoring System for
Sleep Stages of Human Subjects’. The manual and its
recommendations have been well accepted and thesystem has spread across the world.
The proposal to standardize recording techniquesand scoring criteria was intended to increase thecomparability of results reported by different investigators. Researchers who have applied the systemcorrectly have increased the reliability of their sleep
stage scoring. In the several decades since its publication, however, a number of serious areas of unreliability in the 1968 standard scoring system have been
identified. In particular, researchers developing computer-based automatic sleep staging systems haveencountered numerous vague and ambiguous areas in
the current standard.
At the 15th Annual Meeting of the JapaneseSociety of Sleep Research (JSSR) in 1990,

Correspondence address: Tadao Hori, Department of Behavioral
Sciences, Faculty of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan.
Email: tdhori@hiroshima-u.ac.jp

Terashima’s report from the Japanese Conference forSleep Analysis emphasized the need to re-examine
the definitions of sleep stages when developing computer staging systems based on the standard scoring
system. The results of multiple comparisons among
institutes and laboratories using methods for automated sleep staging based on the standard scoring
system were unexpectedly poor. The lowest level ofcongruence between automation and records staged
visually using the 1968 standard system was found forStage 1 sleep, with the second worst agreement (stillless than 70%) for sleep Stages 3 and 4.
To increase both the within- and betweenresearcher agreement in sleep stage identification andto foster the development of computer algorithms forautomatic analyses of sleep, a need for additional definitions was recognized. In 1991, the Subcommittee
for Automatic Sleep Staging (SASS) was formed by
the JSSR. The Subcommittee comprised 53 investigators and seven project leaders selected for their skillin scoring sleep records: S. Sugita (Chair), M. Okawa(co-Chair), T. Kobayashi, T. Hori, A. Miyasita, S.
Shirakawa and Y. Atsumi. In 1995, based on their
5 year discussions, the Subcommittee proposed
supplementary definitions and amendments for theStandard Scoring System to the JSSR. These proposals were reported in the JSSR Newsletter (1996; No.
13, February 1, pages 5–13).
In 1997, at its 22nd Annual Meeting, the JSSR
restructured the SASS to form the Sleep Computing
Committee (SCC). The SCC working group has now
formalized Supplements and Amendments to theStandard Scoring System based upon the 1995 SASS
proposals. The Committee has met several times
for discussion and to test their new definitions using

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carefully selected representative polysomnographic
recordings. The final JSSR Sleep Computing Committee proposals have been published in Japanese as
the ‘Learning Manual of PSG Chart: Polysomnogram,
Sleep Stage Scoring, Interpretation’. The Committee
has now prepared the English language version of
their proposals for evaluation and empirical testing by
sleep researchers all over the world.

SUPPLEMENTARY AND AMENDED
DEFINITIONS FOR INTERNATIONAL
CRITERIA FOR SLEEP STAGE SCORINGThe JSSR’s proposals to supplement and amend thecurrently used criteria for sleep staging (A Manualof Standardized Terminology, Techniques andScoring System for Sleep Stages of Human Subjects,
Rechtschaffen A, Kales A (eds). BIS/BRI Universityof California, Los Angeles, 1968; hereafter, the‘standard criteria (SC)’) are detailed below.

Definition of alpha waves
Alpha waves are electroencephalographic waves witha frequency of 8 Hz or more but less than 13 Hz.

Definition of a vertex sharp wave (V-wave)
A vertex sharp wave is a sharp waveform distinguished from background activities at or near Cz (C3,
C4), with an amplitude of 75 µV or greater, and with afrequency of at least 5 Hz but no more than 14 Hz.

Slow eye movements
Slow eye movements (SEM) can be difficult to detectin recordings that were not made using long time constants. The following definitions are considered toapply for recordings made under recommended conditions. Slow eye movements waveforms do not manifest
saccade-like sharp, abrupt, movements. Rather, SEM
are smooth sinusoidal eye movements with amplitudesof 100 µV or more, and 10 s or less in duration.

Movement time: MT
When research purposes are not met by the SC, different movement time criteria may be used. However,in such cases, the modified criteria should be clearlystated and the degrees of modification should notexceed those in the following examples.

Example 1
MT is judged following the SC, with the addition ofscoring parts of the recording with higher muscle
tones and degrees of artifact as ‘gross movement’ or‘movement with duration more than 50% of an
epoch’, and the number of such segments is reported.

Example 2
Even when an epoch fulfils the SC definition of MT,
the epoch may still be scored as a stage of sleep using
additional criteria (below). In this case, an SC-defined
epoch of MT can simultaneously be defined as anepoch of sleep and a body movement epoch.
Examples of criteria: (i) MT epoch is scored as thesame stage as the preceding epoch and (ii) MT epoch
is scored as the same stage as the following epoch.

Judgement of sleep Stage 1
The following supplementary definitions are used forscoring a transition from stage wake to Stage 1 sleep.
Stage 1 is not necessarily defined as a sleep onset(sleep onset is defined below).

Time constant: Longer time constants of 1.5 s or moreare recommended to minimize deformations of SEM
signals and to enhance the detection of SEM.
Amplification: Amplification of 200 µV/5 mm is recommended. This amplification allows observation ofsubtle eye movements without appreciably increasing
the likelihood of signals saturating the amplifier.
Derivation: Monopolar recordings from both outercanthi are recommended to distinguish eye movements from contamination such as superimposition ofelectroencephalographic (EEG)waveforms.
Supplements for poor alpha wave subjects: For
subjects whose central EEG alpha waves duringresting wakefulness occupy less than 50% of theanalysis epoch when the eyes are closed, one of thefollowing criteria should be used to judge Stage 1 sleep.
When using these exception criteria, the resting wake
EEG should be recorded both before bedtime and after
awakening from all-night sleep recording along withobservations to confirm that subjects are behaviorally
awake.
1. In subjects whose occipital EEG alpha activity
occupy more than 50% of the analysis epochduring wakefulness with eyes closed, SC should beapplied.
2. Electroencephalogram of various frequencies but
less than 8 Hz and 20 µV or more in amplitude,

Proposed supplements and amendments

which is considered as EEG, suggesting lower
vigilance level comparing resting wake with eyes
closed condition, occupies more than 50%. In theabsence of true alpha band activity, alpha-like
activity in EEG frequencies below 8 Hz may be
used to suggest lower vigilance levels when it isof 20 µV or greater amplitude, increases duringresting wakefulness with the eyes closed, and occupies 50% or more of an epoch.
3. When the preceding criteria (2) are applied, confirmation of SEM activity is also recommended.

Judgement of sleep Stage 2
The following supplementary definitions of the Kcomplex should be considered.
1. The K-complex waveform begins with the abrupt
onset of a negative sharp wave, which is immediately followed by a high amplitude positive slow
wave. Polyphasic (notched) negative-positive waves
are sometimes observed just before the onset of thenegative K-complex sharp wave. The duration of a
K-complex must be longer than 0.5 s. Its peak-topeak amplitude must be greater than 200 mV. Waveforms must be visually distinct from background
EEG activities; and a waveform should not be identified as a K-complex if it occurs within 5 s preceding or following high voltage delta waves (defined
below). The K-complex waveform may or may not
be accompanied by sleep spindle activity (defined

Figure 1. Onset and termination of K-complex

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below). Termination of a K-complex is identified by
the peak of a trailing negative wave, which follows
the major positive component, neglecting otheroverlapping waves (Fig. 1).
2. Sleep spindles are defined as trains of 12–16 Hz
waves of 10 mV or greater amplitude, composed ofat least six consecutive waves, or a train duration
longer than 0.5 s. The appearance of the waveform
train is not specified in the definition (i.e. a‘spindle’ shape is not a requirement for identification as a sleep spindle). Although the mean frequency of a single train of waves can be used as asingle descriptor for identified sleep spindles, its
use must be clearly reported. Similarly, if a different amplitude threshold is used to identify sleep
spindle activity, the threshold value must be clearlyreported.

Definition of sleep onset
Sleep onset may be defined as necessary for research
purposes, but should include the first epoch scored as
one of the standard sleep Stages (1, 2, 3, 4, or REM)
after the lights are darkened or a subject goes to bed.
Researchers must report their definition of sleep
onset. Researchers are expected to specify the sleep
stage criteria used for the judgement of sleep onset,
including all criteria for the duration of sleep stage(s),its (their) duration, and the time course of sleep etc.
as in the following examples.

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1. In this example, the first epoch judged as one of
the sleep stages is defined to be sleep onset.
However, if the first stage is Stage 1, the epoch canbe judged as sleep onset only if it is followed byconsecutive epochs of sleep stages 2, 3, 4 or REM.
2. In this example, the first epoch judged as one of
the sleep stages is defined to be sleep onset.
However, if the first stage is Stage 1, the epoch is
judged as sleep onset on the condition that Stage 1or the other stages continue for a specific length oftime (e.g. 3 or 5 min).
3. In this example, the first epoch judged as sleep
Stages 2, 3, 4, or REM is defined to be sleep onset.
(A definition to attach importance on the appearance of Stage 2.)
4. In this example, the first epoch judged as sleep
Stages 2, 3, 4, or REM is defined to be sleep onset.
However, the epoch is judged as sleep onset on thecondition that sleep Stages 2, 3, 4 or REM, follows
for a specific duration (e.g. 3 or 5 min).
5. The expressions of ‘Stage 1’ or ‘Stage 2’ in theexample definitions can be modified to use ‘vertex
sharp wave’ or ‘sleep spindle’ criteria as desired.

Judgement of Stages 3 and 4
If slow waves with frequencies below 2 Hz and withamplitudes greater 75 mV occupy between 20 and 50%of an epoch, that epoch is judged as Stage 3 sleep. If
the slow waves occupy more than 50% of an epoch,that epoch is judged as Stage 4 sleep. However,
because these definitions do not contain any descriptions of complex composite waveforms, it can often be
difficult to judge Stages 3 and 4 under the SC.
1. We add the following supplements to the definitionof high amplitude slow waves given above.
(i) When the combined period of two contiguous
EEG waveforms is 0.5 s or longer (i.e. thefrequency of the composite wave is 2 Hz or
lower), that wave complex can be scored as
one slow wave if the amplitudes of thetwo waves satisfy the requirement B ≥ A/2(Fig. 2).
(ii) When fast waves appear superimposed on aslow wave, the amplitude of the slow wave is
still measured from peak-to-peak, including
the superimposed waves.
(iii) The onset of an individual slow wave must
follow a trough satisfying the requirement B £A/2 (Fig. 3).
2. When bursts of slow wave activity precede or
accompany an arousal response or high amplitude
EMG (e.g. body movements), those bursts should

Figure 2.

Figure 3.

not be considered slow waves for EEG stage
scoring, but as one form of the arousal response.
Such portions of a record should be consideredpart of the preceding or following epoch when
stage scoring. Furthermore, the terms ‘movement
arousal’ or ‘EEG arousal’ are recommended overthe general term ‘arousal response’, following thedefinition of American Sleep Disorders Association (EEG arousal: scoring rules and examples.
Sleep 1992; 15: 173–184).

Judgement of stage REM
Addition of the following supplement to thedefinition of rapid eye movements (REMs)
The same time constant, gain, electrode placements
and montage can be used to record both SEM and
REM. The REM waveform must appear as a saccadic
movement, with rapid changes in angular velocity
at the onset and termination of eye movement. Since
small eye movements often appear during the transitions to and from REM sleep, a low amplitude criterion of 40 mV or greater (1 mm pen deflection underabove-mentioned recording condition) is recommended. In recordings at 15 mm/s (or the equivalent
digital display), REM activity should be identifiable asa 45° or greater angular departure from the baseline.
Researchers should specifically report any modifications to the above-mentioned criteria.

Addition of the following definition of twitches(phasic EMG activity)
A twitch is defined as a skin-recorded EMG discharge
with duration shorter than 0.5 s, or the EMG dis-Proposed supplements and amendments

charge accompanying the contraction of a single
muscle unit. The term ‘these transient changes may bedisregarded’ in the standard manual (p. 8) is ambiguous. Therefore, the muscle activities satisfying theabove-mentioned definition of twitch may be disregarded, while a transient increase in tonic EMG notsatisfying the definition may be regarded as a sign ofmovement arousal.

Supplements and modifications for distinguishing
the end of and interruptions of stage REM
Rechtschaffen and Kales (1968) discussed the difficulty of identifying the onset of REM sleep:
A special case frequently arises where a movement
arousal interrupts the continuity of stage REM, themental-submental EMG quickly reverts to thestage REM level following the movement arousal,
the EEG remains relatively low voltage, mixed frequency, and there is a resumption of REMs orchange to stage 2 one or more epochs following
the movement arousal. The problem is whether toscore the interval following the movement arousal
and the resumption of REMs or change to stage 2
as stage 1 or stage REM. (p.10, Part C).
The general guidelines for distinguishing between
Stage 1 and stage REM support little more thanscorer judgement. The following partially modified
guidelines have been arranged to aid the discrimination of Stage 1 from REM sleep.
The following cases justify scoring as stage 1:(i) epochs follow long or intense movement
arousals;(ii) epochs contain slow eye movements;(iii) epochs contain persisting alpha activity following a movement arousal;(iv) epochs contain well-formed vertex spikes;(v) epochs contain waveforms similar to, but not
fulfilling the definitions of sleep spindles or Kcomplexes. Such cases may be considered as
supporting evidence that the interval between
the movement arousal and unambiguous Stage
2 or REM has been Stage 1.
The following case justifies scoring as stage REM:(i) epochs contain well-formed saw-tooth waves.

Definitions of sleep parameters
The following definitions of sleep parameters frequently used in sleep science and sleep medicine arelisted for reference.

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1. Total recording time (TRT): The duration of timefrom the start to the end of a recording.
2. Time in bed (TIB): The duration of time from‘lights out’ to final awakening.
3. Total sleep time (TST): The amount of actual
sleep time in a recording.
4. Sleep efficiency (SE): The ratio of total sleep time
to time in bed (i.e. (TST ∏ TIB) ¥ 100).
5. Sleep period time (SPT): The duration of timefrom sleep onset to final awakening.
6. Time spent in each of the sleep stages based on
total recording time (TRT).
TS1: Time spent in Stage 1.
TS2: Time spent in Stage 2.
TS3: Time spent in Stage 3.
TS4: Time spent in Stage 4.
TSR: Time spent in stage REM.
7. Percentage of the sleep stages.
(i) Percentage of the sleep stages based on sleep
period time (SPT).
%SW: Percentage of stage W.
%S1: Percentage of Stage 1.
%S2: Percentage of Stage 2.
%S3: Percentage of Stage 3.
%S4: Percentage of Stage 4.
%SR: Percentage of stage REM.
(ii) Percentage of the sleep stages based on total
sleep time (TST).
%S1: Percentage of Stage 1.
%S2: Percentage of Stage 2.
%S3: Percentage of Stage 3.
%S4: Percentage of Stage 4.
%SR: Percentage of stage REM.
8. Wake time after sleep onset (WASO), intermittent awakening: The total time spent awake
during sleep period time (SPT).
9. Number of arousals: The number of arousals
occurring in sleep period time (SPT).
10. Number of stage shifts: The number of occasionsof sleep stages shifting from one to another.
11. Sleep latency: The duration of time from ‘lights
out’, or bedtime, to the onset of sleep.
12. REM sleep latency: The interval from sleep onset
to the first appearance of stage REM sleep in arecording.
13. REM activity: REM activity is identified as one ormore REM in a unit of time and often expressedas the total number of such units.
14. REM density: REM density is a function that
expresses the frequency of eye movements perunit of time during stage REM.
15. Number of REM episodes: The number of REM
episodes that appear during sleep period time. If
REM sleep continues with interruptions by wake310

or other sleep stages, such REM episodes are considered as a single REM episode when the interruption is less than 15 min.
16. Sleep cycle: The first sleep cycle is the period
from sleep onset to the end of the first REM
sleep episode. Later sleep cycles are definedas the periods from the end of a REM sleep

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episode to the end of the subsequent REM sleep
episode.
17. REM sleep interval: The REM sleep interval is
the interval between the end of a REM sleep
episode and the beginning of the subsequent
REM sleep episode. Time awake is generally
excepted from the interval.