The overall density of sleep spindles did not show significant correlation with IQ, neither in the ANT (r = 0.139, p = 0.682 for slow and r = 0.029, p = 0.932 for fast sleep spindles, N = 11), nor in the MD (r = 0.311, p = 0.497 for slow and r = -0.523, p = 0.229 for fast sleep spindles, N = 7). Furthermore, the association of fast spindle density measured on the scalp with IQ did not reach the specified alpha level (r = 0.399, p = 0.225, N = 11). However, when thalamic sleep spindles were separated according to their associations with and without ripples, positive correlations were observed between IQ and fast SP(ripple) density in the ANT (r = 0.778, N = 11,p = 0.0055) and slow SP(ripple) density in the MD (r = 0.808, N = 11, p < 0.028).