Histograms of links strength in the brain-chin network during different sleep stages.

<p>Group averaged links strength are obtained using the TDS measure, where each link represents the interaction of the chin with a given brain area through a specific frequency band. Links are separately grouped by brain areas (Frontal, Central or Occipital), and are arranged in order from low-frequency (<i>δ</i> and <i>θ</i>) to high-frequency (<i>γ</i>₁ and <i>γ</i>₂) bands. A consistent frequency profile of links strength is observed for all brain areas—strongest links mediated through the highest-frequency <i>γ</i>₂ band, a gradual decrease in link strength for the lower-frequency bands (<i>γ</i>₁, <i>β</i>, <i>σ</i>, <i>α</i>, <i>θ</i>), followed by a slight increase in link strength for the lowest-frequency <i>δ</i> band. The sleep-stage stratification observed for the links strength in the brain-chin radar-charts (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0142143#pone.0142143.g009" target="_blank">Fig 9</a>) is consistently observed for all frequency bands and brain areas as shown in the histograms—stronger links during W and LS, and weaker links during REM and DS. Note the strong symmetry in the links strength distribution between the left and right hemisphere that is present for all sleep stages.