Figure 3. The firing of the different neuronal subtypes reflects phase selectivity relative to the cortical slow oscillations.

A–C, phase relationships between a typical ECoG (above A) and the activity of PPN neurons (average spikes per bin), and single representative cases of their corresponding spike-triggered averages of ECoG waveforms (right, AvWv). A, most cholinergic PPN neurons fired preferentially during the active component of the slow oscillations and, thus, phasic increases in gamma oscillations (n = 6). Large error bars are due to the low firing rate of some of the cholinergic neurons in this group. In contrast, non-cholinergic neurons (B, n = 8) and a minority of cholinergic neurons (C, n = 3) fired preferentially during the inactive component of the slow oscillation. D, traces from the ECoG and the firing of three different neurons (represented as events) recorded simultaneously using high-density multi-electrode arrays. E, the representative spike-triggered averages of ECoG waveforms show the phases of the cortical slow oscillation in which they preferentially fire, allowing the comparison with the juxtacellularly labelled neurons (left), and thus their identification as putative active component-locked cholinergic neurons (ChATa, red), putative non-cholinergic neurons (Non-ChAT, blue) or putative inactive component-locked cholinergic neurons (ChATi, grey). F, even though their firing was timed with different components of the slow oscillation, they all show a peak of oscillation at ∼1 Hz, as shown by the Lomb periodograms (dashed lines in top and bottom panels represent level of significance).