Associative processes in differentially reared rhesus monkeys (Macaca mulatta): blocking.

Nine isolate and 6 socially reared adult rhesus monkeys were examined in a standard blocking procedure. A tone was paired with a startle stimulus (US) during Phase 1. A tone-light compound CS was paired with a US during Phase 2. In Phase 3, the light was presented alone to test for blocking. Results showed that learning about the light was blocked in social controls, but not in isolates. These data suggest isolates processed information atypically, in that they developed an association to a redundant cue. A second group of isolates (n = 3) underwent the identical procedures. However, conditioned reactions to the tone were extinguished before testing. Test responding was significantly reduced in this group, that is, blocking was obtained. These data suggest the within-compound association developed during Phase 2 mediated the isolate blocking deficit. Together, these findings imply long-term intellectual consequences of early social impoverishment. Such deficits may be mediated by alterations in central dopamine systems.