ELEMENTS OF NORMAL SLEEP ACTIVITY - SLEEP SPINDLES

Shape
Group of rhythmic waves characterized by gradually increasing and decreasing amplitude.

Amplitude
Usually less than 50 µv, may decrease with age



Frequency / Duration
12-14 Hz / Duration more than 0.5 seconds

Distribution
They are characteristically frontocentral in location

Persistence
They may last up to few seconds, and are seen in mainly stages 2 and 3 of NREM sleep

Synchrony
After 2 years of age, they are bisynchronous and symmetrical

Miscellaneous

1. Sleep spindles are usually well developed by 3-6 months of age, appearing in prolonged runs lasting 8s or longer separated by interval of less than 10 s. After that time, the duration of spindle bursts decreases.
2. Spindles are commonly asynchronous over the two hemispheres until the age of 8 months in normal infants; continuously asynchronous spindles after 2 years of age are abnormal.
3. Spindle bursts are fairly asymmetrical in normal infants, but a marked and persistent reduction on one side may suggest ipsilateral cerebral dysfunction.
   

Reference:

1. Hughes JR. Sleep spindles revisited. J. Clin. Neurophysiol. 2: 37-44.


2. Jankel, WR and Niedermeyer, E. Sleep spindles. J. Clin. Neurophysiol. 2: 1-36.


3. Fisch BJ. Spehlmann’s EEG primer, Amsterdam: Elsevier, 3rd edition


4. Niedermeyer E, Lopes da Silva F. Electroencephalography: basic principles, clinical applications and related fields, Baltimore, Maryland: Williams and Wilkins, 4th edition