Cohorts 1 to 4 will consist of 8 participants. Within these cohorts, participants will be randomly assigned to double-blind treatment with an oral suspension of JNJ-54861911 3 mg, 10 mg, 30 mg, or 80 mg (n=6/cohort) or matching placebo (n=2/cohort). Cohorts 1 to 4 will be used for dose escalations and assessing the maximal tolerated dose using an oral suspension of JNJ-54861911. Cohort 5 will consist of 6 participants who will all receive open-label treatment with a single solid dose formulation of JNJ 54861911 25 mg. Cohort 5 will assess if the recently made available solid dose formulation (strength 25 mg) has similar pharmacokinetic properties and pharmacodynamic effects as the oral suspension at a dose level in the range that has been assessed earlier (Cohorts 1 to 4) and was found to be safe and well tolerated. All cohorts (Cohorts 1 to 5) will follow the same study assessments.