Figure 5.

Layer 5 RS neuron theta spiking is only nested within delta rhythms over a narrow range of membrane potentials: outputs coincide with superficial layer field potential theta transients. A, Example traces (left) from a layer 5 RS neuron held at mean membrane potentials varied from −65 to −60 mV. Note at more hyperpolarized levels that the neuron fires only once on each delta period, whereas at more depolarized membrane potentials, firing is continuous at theta frequency. Example traces (right) show spiking behavior in three model layer 5 RS cells in which the population received a range of tonic drives. Note the neuron with highest drive spikes continuously at theta frequency, whereas the neuron with lowest drive fires only single spikes at delta frequency. Graph shows mean spike probability, from experiments, during a field delta period (10 ms bins) from seven layer 5 RS neurons held at −65 mV (blue), −62 mV (black), and −60 mV (red). Calibration: 20 mV, 0.75 s. B, Brief bursts of theta-frequency activity are manifest in superficial layer LFPs but not those from layer 5. Example traces show concurrently recorded fields from layers 2 and 5 along with corresponding spectrograms showing the theta bursts nested within the dominant delta rhythm. Calibration: 50 μV, 0.5 s.