Multi electrode recording system

Neuronal ensemble recordings were made using a multi-electrode recording system (Plexon, Dallas, TX). Putative single neuronal units were identified on-line using an oscilloscope and an audio monitor (Plexon, Dallas, TX). Plexon Offline Sorter was used to analyze the signals after the experiments were completed, and to remove artifacts. Spike activity was analyzed for all cells that fired at rates above 0.1 Hz. Principal component analysis (PCA) and waveform shape were used to sort spikes. Analysis of neuronal activity and quantitative analysis of basic firing properties were carried out using the NeuroExplorer software (Nex Technologies, Littleton, MA) and custom routines available in the MATLAB suite. In each animal, one electrode with minimal neuronal activity was reserved for local referencing, so that 15 electrodes per animal were available for spiking activity. Putative neurons were classified as either medium spiny neurons (MSNs) or fast-spiking interneurons based on waveform peak-to-trough ratio and half-peak widths^{50 (link)}. MSNs were identified from these parameters by Gaussian mixture clustering in MATLAB (fitgmdist.m). Because significantly fewer fast-spiking interneurons were identified, we restricted our analyses to MSNs.

Neuronal ensemble recordings were made using a multielectrode recording system (Plexon, Dallas, TX). In each animal, one electrode without single units was reserved for local referencing, yielding 15 electrodes per animal. Offline Sorter (Plexon) was used to analyze the signals after the experiments and to remove artifacts. Spike activity was analyzed for all cells that fired at rates above 0.1 Hz. Principal component analysis (PCA) and waveform shape were used for spike sorting. Single units were defined as those 1) having a consistent waveform shape, 2) being a separable cluster in PCA space, and 3) having a consistent refractory period of at least 2 ms in interspike interval histograms. As in our past work, putative cortical interneurons were excluded at initial spike-sorting because they were difficult to definitively identify (Narayanan and Laubach 2009 (link); Emmons et al. 2017 (link)). Putative DMS medium spiny neurons (MSNs) were further separated from striatal interneurons based on waveform peak-to-trough ratio and the half-peak width (Fig. 1C; Berke, 2011 (link)). All neuronal analyses focused on putative pyramidal neurons and MSNs. Counts of recorded neurons are in Table 1, note that the same electrodes are recorded from across days.