| Previous research by Nader and Smith (2001) found a positive relationship between sleep spindle density and IQ for young adults (age 19–29). Normal sleep spindle activity and the relationship between spindle activity and cognition were investigated in 28 adolescent girls (ages 10–14). Several major differences between the adult population and the adolescent female population were found. One of the most striking findings in the adolescent sample was the existence of fast spindles (>16Hz) which accounted for 25% of spindle activity in these adolescents. These spindles have not been previously documented in an adult population, suggesting that they may be performing some developmental function. Furthermore, in contrast to adults, female adolescents showed no relationship between sleep spindles (11–16Hz) and their scores on either the WISC-III or the Wisconsin Card Sort Test (WCST). Two significant relationships, opposite to the predicted results based on adult performance, were discovered. A low spindle density in adolescent females was associated with higher scores on the Spatial Visualization subtest of the Matrix Analogies Test (MAT), and, a low density of fast spindles (>16Hz) was associated with a higher percentage of errors on the WCST. It appears that in females, a developmental shift occurs sometime between the onset of menarche and early adulthood. Five possible reasons for the differing relationships in adolescence and adulthood are discussed. One particularly appealing possibility is based on the work of Destexhe and Senjowski (2001) who have reported that spindles provide a physiological state in the brain which is ideal for synaptic growth and change. It is possible that the adult relationship between IQ and spindle density does not appear until much of this physical growth has occurred. |
