BPN14770 is a selective, phosphodiesterase 4D (PDE4D) negative allosteric modulator (PDE4D-NAM) being developed for the treatment of Alzheimer's disease (AD). PDE4D in brain modulates a key biochemical pathway that regulates changes in gene expression important for learning and memory. The process of forming long term memories results from biochemical and structural changes in the connections between neurons which allow the storage of information within a neural circuit. By improving the ability of the brain to form and consolidate long term memories, BPN14770 may improve synaptic function in AD patients and thereby brain resilience to the disease. BPN14770 has completed the first human Phase 1 clinical trial assessing safety, tolerability and pharmacokinetics after a single oral dose. The compound was rapidly absorbed into the blood, showed linear dose proportionality of exposure, was well tolerated, and provided evidence of central target engagement. The BPN14770 Clinical Study Objectives are the following: 1. To evaluate the safety and tolerability profile of multiple oral ascending dose levels of BPN14770 in healthy young and elderly subjects. 2. To characterize the plasma PK profile of BPN14770 following oral administration in healthy young and elderly subjects. 3. To provide assessment of the cognitive effect of BPN14770 in healthy elderly subjects. The study will enroll up to 84 subjects. Cognitive assessments will include measures of longer forms of visual and verbal memory with 24 hr delayed recall which we hypothesize will be the signature of the activation of the PKA-CREB pathway for synapse formation and stabilization. Compared to the assessment of immediate forms of memory, there have been few attempts to assess the effects of investigational drugs on longer forms of memory.