<p>Hypnagogic Hypersynchrony (HH) is the pattern seen in infants and children during the transition from drowsiness to sleep. It consists of high amplitude, paroxysmal, bilateral, rhythmic bursts of 3 to 5 Hz waves. Unlike, POSTS, which live in the occipital leads, HH is a diffuse pattern, tending towards anterior dominance. It may emerge as early as 4 months but is seen in the majority of infants between 6 to 8 months old. HH may be continuous from ages 8 to 12 months but as the child ages a more paroxysmal type of HH is seen. The pattern begins to dissolve by age 2 years and is usually gone by age 12 years. Since this is only a transition pattern, it will disappear once N2 sleep is reached. At three months, the distinctive pattern of hypnagogic hypersynchrony emerges replacing the high amplitude 2 to 3 Hz rhythm seen during drowsiness. This high amplitude bisynchronous rhythmic 3 to 6 Hz activity can be paroxysmal or continuous for several minutes either at the beginning or end of the sleep cycle.</p><p>After 3 months of age, all NREM and REM sleep stages show maturation as well as development of new patterns. REM now only occupies 25% of the total sleep time. During NREM sleep, patterns reach mature formations. Sleep spindles are fully developed, synchronous, and symmetrical by 2 years. The amplitude and incidence of V-waves and K-complexes decrease at 3 to 4 years until the adult waveform is attained.</p><p style="text-align: center;"><img src="@@PLUGINFILE@@/hypnogogic-hypersynchrony.png" alt="Hypnogogic Hypersynchrony" width="603" height="386" class="img-responsive atto_image_button_middle"><br></p><p style="text-align: center;">Figure : Hypnogogic Hypersynchrony<br></p>