Computational model predicts local networks of IB neurons and GABAB receptor-mediated inhibition are necessary and sufficient to generate delta rhythms. A, Model layer 5 LFP (inverted sum of all synaptic inputs to IB neurons). B, Example simulation of the behavior of an IB neuron demonstrating delta activity as periodic bursts of action potentials (top trace). The quiescent period between bursts is composed of an initial AHP from the IB neurons (a compared with Fig. 2C) and a later GABAB-mediated IPSP (b). Bottom trace shows an example simulation of the periodic GABAB receptor-mediated conductance in layer 5 IB neurons. C, FS neurons in layer 5 were modeled as two types receiving different profiles of excitatory inputs from layer 5 pyramidal cells (see Materials and Methods). Those receiving greater tonic excitation (FS2, modeled as neurogliaform-like cells) demonstrated more intense spike bursts interspersed with theta-frequency single spikes (compare with Fig. 3B). D, Example trace of activity in non-tufted, layer 5 RS cells from the same simulation as A–C. Note the absence of delta-frequency bursts, being replaced by doublet spikes with interspike interval reflecting theta period, occurring every field potential delta period. Calibration arbitrary (field and IB GABAB): 50 mV (spike behavior examples), 0.5 s.