Evolution of sleep spindles in childhood.

Twenty-six normal children (age range range 4-68 months) were studied during Stage 2 sleep which occurred within 20 min preceding or following the first three REM periods of the night. Sleep spindles were measured in Fp1T3. The number, length, and percent of sleep spindle activity were found to be maximal at 46 months of age. Beyond 6 months spindle activity decreased to reach minimal values by 27 months, remained fairly constant to 54 months, then rose again to higher values in the oldest subjects. The mean spindle-wave frequency was 1314 c/sec in subjects younger than 40 months, but was 12-13 c/sec in older subjects. Spindle onsets in Fp1T3 and Fp2T4 were more often concurrent in older as compared to younger subjects. Auditory stimulation (binaural clicks, 60 dB above hearing threshold) affected neither the incidence nor the length of spindles during sleep. Because sizable changes in sleep spindle activity are found between 3 months and 5 years of age, and because such changes are relatively consistent between subjects, it is concluded that sleep spindles recorded between frontal and temporal areas may serve as a useful index of neural maturation in the human subject.