The purpose of the study is to measure the uptake, distribution, and clearance of 11C-MK-3168 by Positron Emission Tomography (PET) scan and to model the tissue specific kinetics of 11C-MK-3168 with the appropriate input function in human brain in Part A; to measure blocking of retention of 11C-MK-3168 at the estimated time to maximum plasma concentration after dosing (tmax) following each single oral doses of JNJ-42165279 and model the exposure/enzyme interaction of JNJ-42165279 in Part B; to measure the saturation of enzyme inhibition in the brain at steady state plasma concentrations of JNJ-42165279 (on Day 8) after 7 once-daily doses of JNJ-42165279 by conducting PET studies with 11C-MK-3168 at trough plasma concentrations on Day 2 in Part C.

This is an open-label (both [participants and investigator] know what treatment participants will receive) study. This study consists of 3 consecutive parts: A, B, and C. Each part will consist of a screening phase (between 21 to 2 days prior to the study medication), a treatment phase (Part A: 1 day; Part B: 8 days; Part C: 8 days), and the end-of-study/ follow-up visit (within 5 to 7 days after last PET scan). In the treatment phase of the Part A, participants will undergo a baseline PET/computed tomography scan (after administration of 11C-MK-3168 on Day 1); In Part B, participants will undergo a baseline PET scan, followed by 2 post-treatment PET scans after 2 single doses of JNJ-42165279 on Days 1 and 8; in Part C, participants will undergo a baseline PET scan, followed by 2 post-treatment PET scans after 24 hours postdose of JNJ-42165279 on Days 1 and 7. Safety will be evaluated by the assessment of adverse events, vital signs, 12-lead electrocardiogram, clinical laboratory testing, physical examination (including weight and tympanic temperature [temperature measure in an ear]), and neurological examination. The total duration of study participation for a participant will be approximately 4 weeks for Part A and approximately 5 weeks for Parts B and C.

Inclusion Criteria:

• Body mass index (BMI) between 18 and 30 kg/m2 inclusive (BMI = weight/height2)
• Non-smoker (not smoked for 3 months prior to screening)
• Agree to use one of the protocol mentioned barrier methods of birth control

Exclusion Criteria:

• Exposed to 1 millisievert or more of ionizing radiation in the year before the start of this study
• Clinically significant abnormal laboratory values and abnormal physical and neurological examination at screening
• Any clinically significant Magnetic Resonance Imaging (MRI) abnormalities at screening, as determined by a neuroradiologist, which are relevant for the study
• Allen test (test to assess the arterial blood flow to the hand) indicating abnormal blood supply to the hand
• Has implanted or embedded metal objects, or fragments in the head or body that would present a risk during the MRI scanning procedure