[Sleep spindles and physical parameters].

In 4 identical (Nos. 1-4) and 3 fraternal (Nos. 5-7) male twin pairs (mean age, 16 years), sleep spindles were analysed during sleep. The height, body weight, plantar length and chest circumference were measured, and the correlations between sleep spindles and these physical parameters were examined. The physical parameters showed concordance between identical twin pairs except one pair (No. 4) and one fraternal pair (No. 5) but discordance between two fraternal twin pairs (Nos. 6 and 7). Number of sleep spindles and sleep spindle density showed almost concordance between identical twin pairs and one fraternal pair (No. 5), while discordance between two fraternal ones (Nos. 6 and 7). Both number of sleep spindles and sleep spindle density were inversely correlated with body weight (r = -0.61, p less than 0.02; r = -0.62, p less than 0.02). These facts would suggest that sleep spindles rather reflect the individual development than genetic trait.