Three social-preference measures in PKU monkeys.

Of twenty-four one-year-old rhesus, half were brain damaged from excessive phenylalanine (PKU) administered either pre- or post-natally. When compared on three measures of affiliation--(a) a simultaneous forced-choice proximity circus test, (b) a sequential free-operant Butler-box test, and (c) a social group in a playroom--the duration measure of the circus gave the best differentiation between stimulus animals, the Butler box the poorest. Both types of PKU monkeys were found to strongly prefer familiar PKU monkeys, and controls to refer unfamiliar followed by familiar controls. This extends preference research to induced brain damage and confirms behavioural abnormality in PKU macaques, an abnormality detectable by both humans and other monkeys.