Figure 4

Representative heat map images of (a): delta (δ) and (b) theta (θ) band power spectral densities (PSDs) obtained from the local field potential recordings with a 16-channel electrode representing 100–1600 μm cortical depths with the corresponding intensity scales (0-1) from an animal of the NMDA-treated group. (a) during hypercapnia, 5% CO₂ tended to increase δ in the superficial cortical layers, but activity diminished after switching to 10% CO₂ starting in the deep cortical layers gradually shifting upwards (arrow pointing up). After restoration of normocapnia, δ activity was also restored (arrow pointing down). NMDA, especially the higher dose strongly increased δ activity predominantly in the upper cortical layers (F_group = 1363.103 (1 mM NMDA); η² = 0.8614; p = 0.00001**). The second stimulation with graded hypercapnia showed a somewhat similar pattern, however, the δ depression during the deeper level of hypercapnia, and also the restoration of activity upon normocapnia was less clear-cut than before NMDA. (b) during hypercapnia, 5% CO₂ resulted in a quite widespread increase in cortical θ activity (F_group = 726.632 (5% CO₂); η² = 0.7623; p = 0.00001**) that was attenuated and reversed to depression after switching to 10% CO₂ similarly to the pattern observed for δ (arrows). NMDA (1 mM) resulted in an almost complete suppression of θ in all cortical layers. After NMDA, the second graded hypercapnia lacked the θ activation associated with 5% CO₂. BL: baseline.