This study is investigator-and-subject blind, sponsor open, randomized, placebo-controlled, parallel study in healthy subjects to evaluate central (CSF) and peripheral (plasma) pharmacodynamics effects (Abeta) over 36 hours post single doses of PF-06648671. Two cohorts will be run in sequential. the first cohort is to evaluate the Abeta effect at top dose of 300 mg PF-06648671 and second cohort is to evaluate the Abeta effect at top dose (if more subjects are required) and/or 1-2 lower doses