From the Ties That Bind file: Neckties may be more than just uncomfortable. A study summarized in American Family Physician reports that men wearing ties had lower scores on a test of mental agility than those more comfortably dressed. The Cornell University researchers who did the study think reduced blood flow to the brain accounts for a decline in "rapidity of visual response" . . . Egg consumption is down. In 1976, Americans used to eat 276 eggs a year per capita, but that is expected to dip to 246 this year. At its peak, in 1945, a typical American ate 400 a year, said the U.S. Department of Agriculture. The department said concern about cholesterol and changing tastes account for the drop. For most people, however, high-fat foods such as meat and fried chicken pose at least as great a heart risk as the cholesterol in egg yolks, experts believe . . . British scientists have produced the world's first test-tube chickens. The birds were fertilized in a lab and incubated in hollowed-out eggshells topped with plastic wrap, the science journal Nature reported last week. The technique may one day allow breeding of chickens that are healthier and hardier than those bred today, helping in the fight against world hunger, said the scientists at the Edinburgh Research Station . . .