Figure 1. Periodic Limb Movements During Sleep Demonstrated By Polysomnography. Periodic limb movements during sleep are displayed as demonstrated by periodically occurring (every 20–30 seconds) activations of anterior tibialis electromyography. Also noticeable in this schematic are activations of electroencephalography, in the form of synchronous cortical firing (K-complexes) and acceleration of heart rate as evidenced by shortening of the R-R interval on electrocardiography.