Associative structure of integrated temporal relationships.

According to the temporal-coding hypothesis (TCH; Savastano & Miller, Behavioural Processes 44:147-162, 1998), acquired associations include temporal information concerning the interval between the associated elements. Moreover, the TCH posits that subjects can integrate two independently acquired associations that share a common element (e.g., S2-S1 and S1-US), which results in the creation of a third association with its own temporal relationship (S2-US). Some evidence has suggested that such temporal integration occurs at the time of testing (Molet, Miguez, Cham, & Miller, Journal of Experimental Psychology: Animal Behavior Processes 38:369-380, 2012). Here we report two fear-conditioning experiments with rats conducted to identify the associative structure of the integrated temporal relationship. The goal was to distinguish between two possible associative structures that could exist following an initial test on which temporal integration occurs: (1) Conditioned responding to S2 on subsequent tests could be the result of recurring successive activation of two independently learned temporal maps that remain independently stored in memory (i.e., S2-S1 plus S1-US). (2) Temporal integration at the moment of initial testing could result in the formation of a direct S2-US (or S2-response) temporal map. Integration was found to occur at test and to produce a new association that was independent of associations with the common element (S1). However, the associative status of S1 appeared to modulate whether or not the new association with S2 was US-specific (S2-US) or directly activated a fear response (S2-response).