Fig. 2.

Comparison of frequency distributions of all recorded midbrain units using multiple electrophysiological and pharmacological parameters. A: percentage of spikes occurring within bursts (%SWB) using a rate-independent burst definition (Kaneoke and Vitek 1996). B: half-action potential (AP) duration (inset, dotted line). C and D: dopamine (DA) D2-type receptor pharmacology showing the percentage of basal firing response to either quinpirole (Quin; C) or eticlopride (Etic; D) administration. E: average basal firing rate. F: coefficient of variation (CV) in the interspike interval (ISI) histogram. G and H: most parameters, including ISI skew (G) and basal firing rate (H), were log-transformed to determine whether additional patterns in the distribution would emerge. Log transformation of firing rate and, to a lesser extent, ISI skew revealed a bimodal distribution. Not all frequency distribution plots are shown due to space limitations.