Single-Blind, Randomised, Placebo-Controlled First Time in Human Study to Evaluate Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of Single Oral Escalating Doses of GSK1018921 in Healthy Volunteers and to assess the effect of a single dose of GSK1018921 on quantitative EEG and Mismatch Negativity in a separate cohort of healthy smoker volunteers