Figure 1. Right-sided surface EEG and LFP from right GP of case 1 in the three states of vigilance (awake, N2 and N3).

A, wakefulness: a regular α-rhythm of ∼9 Hz is present in Pz–O2, while in F4-C4 frequencies in the β-frequency band dominate with interspersed waves in the α- and to a minor extent θ-band. LFPs from GP compared to surface EEG (see box for LFP amplified a further 3 times) are of very low amplitude and show similar frequencies as seen in fronto-central leads. B, N2: both surface EEG traces consist of K-complexes, sleep spindles between 13 and 17 Hz and waves in the θ-frequency range. Activities in Pz–O2 and F4–C4 are partially synchronized. K-complexes can also be identified in the GP-LFP. Boxed area as in A. C, N3: low frequency δ-waves (∼1 Hz) are of higher amplitudes than in N2 (note that δ-waves here are smaller than the 75 μV required for N3 according to Rechtschaffen & Kales (1968), because a bipolar lead is used in contrast to the usual contralaterally placed ear reference). Both surface EEG traces appear to be more synchronized than in N2. In addition to sleep spindles in the range of 13–17 Hz, ∼10 Hz spindle-like waves are also present in F4–C4, but not in the parieto-occipital lead. In GP both sleep spindles as well as the ∼10 Hz activity are present, mostly in synchrony with F4–C4. Boxed area as in A.