Increased social fear and decreased fear of objects in monkeys with neonatal amygdala lesions

The amygdala has been implicated in the mediation of emotional and species- specific social behavior (Kling et al., 1970; Kling and Brothers, 1992; Klu ver and Bucy, 1939; Rosvold et al., 1954). Humans with bilateral amygdala d amage are impaired in judging negative emotion in facial expressions and ma king accurate judgements of trustworthiness (Adolphs et al., 1998, 1994). A mygdala dysfunction has also been implicated in human disorders ranging fro m social anxiety (Birbaumer et al., 1998) to depression (Drevets, 2000) to autism (Bachevalier, 1994; Baron-Cohen et al., 2000; Bauman and Kemper, 199 3). We produced selective amygdala lesions in 2-week-old macaque monkeys wh o were returned to their mothers for rearing. At 6-8 months of age, the les ioned animals demonstrated less fear of novel objects such as rubber snakes than age-matched controls. However, they displayed substantially more fear behavior than controls during dyadic social interactions. These results su ggest that neonatal amygdala lesions dissociate a system that mediates soci al fear from one that mediates fear of inanimate objects. Furthermore, much of the age-appropriate repertoire of social behavior was present in amygda la-lesioned infants indicating that these lesions do not produce autistic-l ike behavior in monkeys. Finally, amygdala lesions early in development hav e different effects on social behavior than lesions produced in adulthood. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.