A comparison and evaluation of the predictions of relational and conjunctive accounts of hippocampal function

Abstract

Relational and conjunctive memory theory each postulate that the hippocampus participates in the formation of long-term memory representations comprised of associations between multiple elements. The goals of the current work were to clarify and contrast these theories by outlining the nature of the representations that are spared vs. impaired following hippocampal damage according to each theoretical perspective. Relational theory predicts that hippocampal lesions will impair performance on tasks that require the formation of new long-term representations in which distinct elements must be regarded in relation to all other elements. Representations that remain intact despite hippocampal damage include separate representations of distinct individual elements or multiple stimuli fused into a static "blend" such as several elements viewed from one vantage point. Additionally, the relational account predicts that rapid incidental online processing of the relations can be achieved through structures other than the hippocampus, but this information will not be stored. In contrast, conjunctive theory predicts that hippocampal damage will impair the rapid formation of unitary representations that contain features of elements and their relative relationships bound in an inflexible manner. Deficits in the rapid formation of these conjunctive representations result in impaired performance on tasks that require rapid incidental stimulus binding. However, intact formation of conjunctive representations can occur over multiple trials in the service of problem solving. Using these theoretical frameworks, recent findings from the human and nonhuman animal literature are reexamined in order to determine whether one theory better accounts for current findings. We discuss empirical studies that serve as "critical experiments" in addressing the relational vs. conjunctive debate, and find that the predictions of relational theory are supported by existing findings over those from the conjunctive account.

Schema-driven facilitation of new hierarchy learning in the transitive inference paradigm

“…3A), evidenced by the significant main effect of trial type in the ANOVA presented above (P , 0.001). This contrasts with a general trend in the literature for training trial performance to be numerically superior or comparable to test trial performance (e.g., Moses and Ryan 2006), as well as the pattern of findings observed in phase 1. Specifically, in phase 1, training and test trial performances (i.e., averaged across the phase) were comparable (mean training trial, 72.5% [SEM 2.0]; test trial, 70.6% [SEM 3.6]; no significant difference, P .…”

“…0.1). These results, therefore, are consistent with the operation of associative learning mechanisms during training trials (Moses and Ryan 2006;Zeithamova et al 2012).…”

“…In this study, we examine schema-based effects in the context of the transitive inference (TI) paradigm-an experimental scenario which provides a well-controlled setting in which to examine the influence of an associative schema (i.e., prior knowledge of the rank position of items in the hierarchy) on the learning of new information (i.e., relating to the rank position of novel items). To the best of our knowledge, however, the TI paradigm has not been employed with this purpose in mind, though it has been widely used across species to study the mechanisms that support inferential behavior and generalization, and in particular the specific contribution of the hippocampus (Bryant and Trabasso 1971; Chalmers 1977, 1992;Harris and McGonigle 1994;Rapp et al 1996;Dusek and Eichenbaum 1997;Delius and Siemann 1998;Greene et al 2001;Frank et al 2003Frank et al , 2005Heckers et al 2004;Titone et al 2004;Smith and Squire 2005;Moses and Ryan 2006;Moses et al 2010;Zeithamova et al 2012).In this three-phase study involving 30 participants, we used a version of the TI paradigm, which follows the lines of the original paradigm developed by Bryant and Trabasso (1971), and has been shown to ensure the development of robust transitivity performance across a group of participants, underpinned by relational knowledge of the hierarchy (see Materials and Methods) (Cohen and Eichenbaum 1993;Eichenbaum 2004;Smith and Squire 2005;. Our experimental design ( Fig.…”

Unconscious Relational Inference Recruits the Hippocampus

“…Our evidence supports recent accounts of medial temporal lobe functions that emphasize the computational capabilities of medial temporal structures and the nature of the information that is processed and stored in medial temporal regions (Eichenbaum et al, 1999(Eichenbaum et al, , 2007Ryan et al, 2000;Brown and Aggleton, 2001;Bussey and Saksida, 2005;Moses and Ryan, 2006;Mayes et al, 2007;Henke, 2010;Ranganath, 2010). These processing-based viewpoints advance our understanding because they reveal basic computational principles of medial temporal structures that come into effect in various cognitive situations.…”

“…These basic computational principles may help linking traditionally separate fields of research, such as long-and short-term memory (Ranganath, 2010); memory and perception (Bussey and Saksida, 2005); and memory, spatial navigation, future planning, and inference (Eichenbaum et al, 1999). More specifically, our evidence supports the relational memory theory that does not consider consciousness a necessary condition for hippocampal processing (Ryan et al, 2000;Moses and Ryan, 2006). According to the relational memory theory (Cohen and Eichenbaum, 1993), the hippocampus encodes a memory space in which the relationships between the various aspects of experienced events are associated in a flexible way that allows for inference and memory-based predictions.…”