Neural activity was recorded using a 64-channel Cheetah recording system (Neuralynx, Bozeman, MT, USA) as described previously (Johnson et al., 2007). This system's “plug board” allowed the simultaneous recording of unit and LFP activity, passed through different amplifiers. LFPs were continuously sampled at 1990.4 Hz, amplified 500 or 1000 times, band-pass filtered between 1 and 475 Hz (hardware filters, Cheetah recording system, Neuralynx) and recorded to disk, with at least one LFP recorded from each tetrode. When multiple LFPs were recorded from the same tetrode, only one was included for analysis. All LFP recordings were referenced against a reference electrode positioned in or near the corpus callosum overlying ventral striatal recording sites. Spiking activity was recorded and isolated using standard procedures, as described previously (van der Meer and Redish, 2009).
