Polysomnography & Sleep Scoring

John ShawLancaster University

ProcedureBefore they turn up

• Instructions to participants– Try to have a relaxed day- No daytime sleep– Wash their hair!

• Prepare the material– Prep gel– Electrodes– Gauze/tape– Hair clips– Computer set up

10 - 20 System

• Widely used, standardised system of electrode placement• Electrodes placed at specific intervals along the head• Each spot has an identifying letter and a number.

• F- Frontal• T- Temporal• C- Central• P- Parietal• O- Occipital• z- Mid line• Odd Numbers- Left Hemisphere• Even Numbers- Right Hemisphere

Landmarks

10 – 20 System

• Nasion- depressed area between the eyes

• Inion- prominent projection of occipital bone

10 – 20 System

• FPz- 10% above the Nasion

• Fz, Cz, Pz and Oz at 20% interval

• Leaves 10% between Oz & the Interval

10 – 20 System

• Measure between the two preauricular points across Cz

• 10% up from Ax is Tx, 20% up from Ax is Cx

10 – 20 System

• Circumference of the head is measured through Fpz, Oz, T3 and T4

10 – 20 System

• Circumference of the head is measured through Fpz, Oz, T3 and T4

• 5% from Fpz is Fp1/Fp2• 10% from Fp1/Fp2 is

F7/F8• 10% from F7/F8 is T3/T4• 10% from T3/T4 is T5/T6• 10% from T5/T6 is

O1/O2• 5% from O1/O2 Is Oz

5%10%

10%

10%

10%5%

10 – 20 System

• Longitudinal distance from Fp1/Fp2 through C3/C4 to O1/O2 is measured either side at 25% intervals

25%

25%

25%

25%

10 – 20 System

• F7 through to F8, passing through F3, Fz, and F4 at intervals of 25%

25%25% 25%

25%

• Got the key 6 points• A1 & A2 are positioned on the

ear lobe or the mastoid

• Ground electrode placed on FPz

10 - 20 System

Electrode Application

• Prepare the Electrode site– Thorough cleaning to remove

dirt/debris/dead skin cells– Use of Electrically conductive

prep solution• Preparing the Electrode

– Sterilized after the previous study

– Filled with electrically conductive paste, filling the cup

Electrode Application

• Placing the Electrode– Placed in the exact location

of the mark• Hair clips are useful

– All sides of the metal cup should be in contact with the skin

• Applying the Electrode– Place gauze diagonally over

the cup with small amount of tape holding it down

Impedance Checks

• Impedances are measures of electrical resistance

• High impedance = signal distortion

• Maximum electrical impedance should be 5000 Ohms– If over this, remove sensor and go through the steps again

Sleep Scoring

Sleep Scoring

• Monitor the 8 channels outlined earlier– F3– F4– C3– C4– O1– O2– M1 (Reference)– M2 (Reference)

• Paper speed of 10mm/Sec, defined as an Epoch

Sleep Scoring

• Rechtschaffen and Kales (1967)– Introduced a manual for sleep scoring for different stages

Sleep Stages

• Stage W• NREM (70-80%)

• Stage 1 (10-12%)• Stage 2 (45-55%)• SWS (15-20%)

• REM (20-25%)

• Sleep starts with NREM, enters REM sleep after about 60 mins– NREM-REM cycles every 90 mins– Typically 4-6 cycles per major sleep episode– Sleep qualitatively changes during the night

Sleep Scoring- Stage W

• Participant is awake

• Movement artifacts obscure most behaviour

• Occipital channels display alpha activity when eyes are closed

Sleep Scoring- Stage N1

• Low voltage, mixed frequency EEG pattern, typically 4-7Hz

• First sleep stage entered from Wakefulness

• The ‘Transitional stage’– People can still hear noises in the room and think they are awake

Sleep Scoring- Stage N2

• Comprises about 50% of total sleep time in healthy adults

• N2 is characterised by the presence of sleep spindles and K complexes and begins at the first instance of sleep spindles or K complexes

• Absence of slow waves

Sleep Scoring- Spindles & K-complexes

• Spindles– Brief bursts of activity appearing in the central channel– Most commonly associated with Stage N2 sleep– Associated with transference of memories from the hippocampal

store to the neocortex in consolidation of skills• K-complexes

– Sharp negative wave followed by a slower positive component

Sleep Scoring- Stage N3

• Replaces delta sleep (Stages 3 & 4) from Rechtschaffen & Kales

• Epoch is scored as N3 when at least 20% contains slow waves

• Typically be between 0.5-2Hz in frequency, prominently seen in frontal/central locations

• Most often seen during the first third of the night, reducing progressively

Sleep Scoring- Slow Waves

• Low Frequency, high amplitude waves typically seen in the frontal region

Sleep Scoring- Stage R

• REM sleep is highly beneficial for memory restoration.• Typically occurs 90 mins after sleep onset• Initially quite short but progressively gets longer as night

progresses• Presents similar frequencies to N1

– Sawtooth waves typically 2-6Hz

• After 1 instance of Stage R, all subsequent epochs are coded the same until spindles/K-Complexes are present

Polysomnography & Sleep Scoring

John ShawPsychology DepartmentLancaster University