second-order stimulus (CS2), does not have any effect on CS1 (Debiec et al.). In the same study, the effect of activation (memory retrieval) on such an associative chain has been examined. Results demonstrated that protein synthesis inhibition after exposure to a single CS1 impairs responses to both CS1 and CS2, but protein synthesis inhibition after exposure to a single CS2, only disrupts CS2 and leaves CS1 freezing intact. Therefore, it is believed that when the first-order association is directly activated, it is placed into a labile state (as we would expect from reconsolidation research) which may affect dependent associations. However, when the first-order association is only indirectly activated (through the associative chain), it appears that there is not sufficient stimulation to kick off cellular processes which would place it in a labile state, so it remains fixed. References Learning