This study is a phase 1, double-blind, placebo-controlled crossover study of SAGE-718 using a ketamine challenge, to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamic response using magnetic resonance imaging in healthy subjects

Inclusion Criteria:

1. Subject is willing and able to provide 2 forms of identification; at least 1 must have a photo.
2. Subject has a body weight ≥50 kg and body mass index ≥18.0 and ≤30.0 kg/m2 at screening.
3. Subject is healthy with no history or evidence of clinically relevant medical disorders as determined by the Investigator.

Exclusion Criteria:

1. Subject has a history or presence of any psychiatric disease or condition including suicidal ideation or behavior, has answered YES to any question on the C-SSRS at screening or admission, or is currently at risk of suicide in the opinion of the Investigator
2. Subject has a history or presence of a neurologic disease or condition, including but not limited to epilepsy, closed head trauma with clinically significant sequelae, or a prior seizure.
3. Subject has a family history of epilepsy.
4. Subject has evidence of any metal in the body that may be contraindicated for receiving an MRI. This includes, but is not limited to: cardiac pacemaker, surgical implants, previous accident resulting in metal or shrapnel lodged internally, tattoos inked with metallic dyes, or a history of metal work without using protective eyewear.
5. Subject has claustrophobia or a history of claustrophobia.
6. Subject is unable or unwilling to remove piercings and/or jewelry that contain metal.

Data sharing will be consistent with the results submission policy of ClinicalTrials.gov.