Recording of single units and local field potentials in the hippocampal CA1 region of freely behaving mice.

(A) The characteristic oscillations confirm the recording happened in the hippocampal CA1 region of a representative control mouse. The top panel shows a representative channel of local field potential (LFP) recorded during sleep, and the filtered LFP shows high-frequency ripple (100–250 Hz). The lower panels show the raw LFP and LFP_theta (4–12 Hz) recorded when the animal was active exploring. Scale bar: 0.5 mV and 0.1 sec. (B) Sharp wave associated ripple (top panel) and theta oscillations (bottom panel) were also observed in the CA1 of the knockout mouse hippocampus. (C-D) Automatic spike sorting was performed with KlustaKwik method and followed by manual cutting and merging in MClust program. Spike clusters for a typical stereotrode were shown with the energy of the two channels of a stereotrode. The stereotrode waveforms of each unit are shown in the inserts. Stable recordings were confirmed as judged by the distribution of spike clusters and spike waveforms of each individual unit at the beginning (C) and end (D) of the recording whole session. L-ratio and Isolation distances were used to quantitatively measure the quality of sorted units. The L-ratios of the four units shown here were 0.2077, 0.0233, 0.1987 and 0.1220, respectively, and the Isolation distances were 21.0224, 63.8598, 25.2531 and 31.7989, respectively.