Figure 3.

Layer 5 RS neurons produce theta-frequency spike outputs. A, Example trace showing a layer 5 LFP recording of delta activity. Spectrum shows a tight, single modal peak at ∼2 Hz as in Figure 2. B, Example recordings from a non-accommodating, FS interneuron in layer 5. Response to step injection of +0.2 nA current for 200 ms demonstrates the intrinsic spiking behavior. Top trace shows sporadic bursts of spike generation at resting membrane potential phase locked to the concurrently recorded field (A). Note also predominant theta-frequency spike generation. Top histogram shows mean spike incidence at theta frequency. Bottom trace shows membrane potential at −70 mV (mean) revealing small, slow, regular depolarizations interspersed with more rapid but smaller, faster EPSPs with large events occurring at theta frequency. Bottom spectrogram shows mean power of EPSPs onto FS cells had a bimodal peak at delta and theta frequency. Lines plotted show means of each of the three cells recorded. C, Example recordings from an RS neuron in layer 5. Step depolarization with 0.2 nA (200 ms) reveals the RS behavior of this cell type. Top trace shows spontaneous spike generation at resting membrane potential is dominated by single or double spikes per delta period (note that these traces were not concurrently recorded with the example field in A). Top histogram demonstrates mean spike incidence approximately at theta frequency. Middle trace shows a recording from the same neuron held at −70 mV (mean) revealing small compound EPSPs occurring at delta frequency (from mean power spectrum on the left). Bottom trace shows activity in the same cell held at −30 mV to reveal IPSP inputs. IPSPs were complex, consisting of both delta- and theta-frequency components. Note the absence of the runs of fast IPSPs seen in the FS cell in Figure 2. Calibration: 200 μV (field), 20 mV (resting membrane potential), 10 mV (−70 and −30 mV recordings), 0.5 s.