Can being well hydrated improve one’s mood? Sharpen mental machinations? The researchers behind the new Pryme Vessyl cup ($99) think so. “Mood balance, cognitive performance, attention, focus—all are dramatically impacted by your hydration,” says Hanson Lenyoun, MD, a Harvard University graduate and Columbia-trained physician who helped develop the 16-ounce glass-lined cup, which logs how much fluid a person imbibes throughout the day. The cup syncs up with a smartphone app that collects details abou…