TY - JOUR T1 - Deciphering the Contribution of Oriens-Lacunosum/Moleculare (OLM) Cells to Intrinsic Theta Rhythms Using Biophysical Local Field Potential (LFP) Models JF - eneuro JO - eNeuro DO - 10.1523/ENEURO.0146-18.2018 SP - ENEURO.0146-18.2018 AU - Alexandra P. Chatzikalymniou AU - Frances K. Skinner Y1 - 2018/08/22 UR - http://www.eneuro.org/content/early/2018/08/22/ENEURO.0146-18.2018.abstract N2 - Oscillations in local field potentials (LFPs) are prevalent and contribute to brain function. An understanding of the cellular correlates and pathways affecting LFPs is needed but many overlapping pathways in vivo make this difficult to achieve. A prevalent LFP rhythm in the hippocampus associated with memory processing and spatial navigation is the theta (3-12 Hz) oscillation. Theta rhythms emerge intrinsically in an in vitro whole hippocampus preparation and this reduced preparation makes it possible to assess the contribution of different cell types to LFP generation. We focus on oriens-lacunosum/moleculare (OLM) cells as a major class of interneurons in the hippocampus. OLM cells can influence pyramidal (PYR) cells through two distinct pathways: by direct inhibition of PYR cell distal dendrites, and by indirect disinhibition of PYR cell proximal dendrites. We use previous inhibitory network models and build biophysical LFP models using volume conductor theory. We examine the effect of OLM cells to ongoing intrinsic LFP theta rhythms by directly comparing our model LFP features with experiment. We find that OLM cell inputs regulate the robustness of LFP responses without affecting their average power and that this robust response depends on co-activation of distal inhibition and basal excitation. We use our models to estimate the spatial extent of the region generating LFP theta rhythms, leading us to predict that about 22,000 PYR cells participate in intrinsic theta generation. Besides obtaining an understanding of OLM cell contributions to intrinsic LFP theta rhythms, our work can help decipher cellular correlates of in vivo LFPs.Significance Oscillatory local field potentials (LFPs) are extracellularly recorded signals that are widely used to interpret information processing in the brain. Theta (3-12 Hz) LFP rhythms are correlated with memory processing, and inhibitory cell subtypes contribute in particular ways to theta. While a precise biophysical modeling scheme linking cellular activity to LFP signals has been established, it is difficult to assess cellular contributions in vivo to LFPs because of spatiotemporally overlapping pathways that prevent the unambiguous separation of signals. Using an in vitro preparation that exhibits theta rhythms and where there is much less overlap, we build biophysical LFP models and uncover distinct inhibitory cellular contributions. This work brings us closer to obtaining cellular correlates of LFPs and brain function. ER -