 Single-blind, single-centre, fixed-order study to evaluate the PD effects of a single oral dose and multiple oral doses of ESL BIA 2-093 in healthy volunteers. A single dose of oral ESL 900 mg was followed by consecutive 7-day periods of: Placebo, ESL 800 mg, and ESL 1200 mg each given QD. The single dose was chosen to assess the ESL acute response relationship with respect to cognitive and motor skill performance, and the multiple doses were chosen to further characterize the ESL dose response relationship with respect to cognitive and motor skill performance. 