Figure 3.

Effects of methylphenidate on SSRTT performance. Methylphenidate (threo-methyl α-phenyl-2-piperidineacetate, Sigma, UK) was administered (i.p.) 30 min before testing in sessions where the stop-signal position was set at 50% of the go response. Animals were given a single session with each dose of drug, based on a Latin square design, with at least 4 days of stable performance and baseline criteria between each treatment. All concentrations were calculated as free base and made up in physiological saline fresh on the day of use. Increasing doses of methylphenidate up to 1 mg/kg improved stopping behavior (a) and decreased SSRT (b), whereas higher doses were not as effective. There was little effect of methylphenidate on correct go trials, excepting a small decrease at 1 mg/kg (c), or on correct go reaction time (d), the number of trials initiated (e), the latency to initiate a trial (f) or reward collection latencies (g). Baseline data (BL—mean of the five sessions immediately preceding each drug treatment session) when the stop-signal presentation was concurrent with the start of the go response (ie, at 0%) are shown for illustrative purposes and were not included in the statistical analysis. Data are mean±SEM, n=13. **p<0.01 and *p<0.05 for pairwise differences related to dose of drug.