Fig. 8: Hypothetical schematic of direct and indirect septo-hippocampal pathways mediating tSCs in the CA1.

In this schematic, we depict the direct and indirect pathways between the MS and the CA1 implicated in controlling distinct CA1 supra-theta oscillations. Color codes for MS projections, including anatomically identified MS neurons, are shown on the left. Cortico-hippocampal and intrahippocampal pathways are color-coded by their dominant tSCs: tSC1, blue; tSC2, green; tSC3, purple; tSC3, green; tSC4, orange; tSC5, gray. i We suggest that direct GABAergic MS-CA1 projections (dark red curve) contribute to tSCs1-4. ii Orchid cells (teal) are likely important determinants of tSC3-4 in CA1 via their projections to PrS and EC. iii Teevra neurons (magenta) contribute to tSC1-2 through the CA3. iv LRNs (mustard) also form part of the tSC1-2 network via their projections to CA3 and DG. v Further indirect MS-EC-CA3/DG-CA1 pathways probably also contribute to the control of tSC1-2 components in the CA1. vi Local processing in the CA1 strongly contributes to fast gamma (tSC5) oscillations. vii Hippocampo-septal feedback by somatostatin-expressing GABAergic neurons (brown) could control tSC generation by negative feedback. MS, medial septum; EC, entorhinal cortex; PrS, dorsal presubiculum; DG, dentate gyrus; LRN, Low-rhythmic neurons; str. py., stratum pyramidale; str. rad., stratum radiatum; str. lac. mol., stratum lacunosum moleculare.