The striatum contains a number of different cell types which can be distinguished on the basis of morphological, cytological, and electrophysiological characteristics (Bennett and Wilson, 2000; Gerfen, 1988; Kawaguchi, 1993). Standard extracellular recording techniques are limited to using waveform shape or spike train statistics for cell type classification. While necessarily indirect, such approaches have been reported to match well with independently identified cell types (Mallet et al., 2005). We took a conservative approach in identifying putative parvalbumin-positive (PV+), aspiny FSIs by including only those cells which met both waveform shape criteria (Berke et al., 2004; Mallet et al., 2005; Sharott et al., 2009) and spike train criteria (Barnes et al., 2005; Schmitzer-Torbert and Redish, 2004b, 2008). Thus, only neurons that had less than 40% of total recording time in ISIs smaller than 2 s, and a post-spike suppression period of less than 0.1 ms (Schmitzer-Torbert and Redish, 2008), as well as a waveform peak width smaller than 0.15 ms, waveform valley width smaller than 0.35 ms, and a firing rate above 2 Hz (adapted from Berke et al., 2004) were
