Perirhinal Cortex is Involved in the Resolution of Learned Approach-Avoidance Conflict Associated with Discrete Objects

The rodent ventral and primate anterior hippocampus have been implicated in approach-avoidance (AA) conflict processing. It is unclear, however, whether this structure contributes to AA conflict detection and/or resolution, and if its involvement extends to conditions of AA conflict devoid of spatial/contextual information. To investigate this, neurologically healthy human participants first learned to approach or avoid single novel visual objects with the goal of maximizing earned points. Approaching led to point gain and loss for positive and negative objects, respectively, whereas avoidance had no impact on score. Pairs of these objects, each possessing nonconflicting (positive-positive/negative-negative) or conflicting (positive-negative) valences, were then presented during functional magnetic resonance imaging. Participants either made an AA decision to score points (Decision task), indicated whether the objects had identical or differing valences (Memory task), or followed a visual instruction to approach or avoid (Action task). Converging multivariate and univariate results revealed that within the medial temporal lobe, perirhinal cortex, rather than the anterior hippocampus, was predominantly associated with object-based AA conflict resolution. We suggest the anterior hippocampus may not contribute equally to all learned AA conflict scenarios and that stimulus information type may be a critical and overlooked determinant of the neural mechanisms underlying AA conflict behavior.

Examining the representational content of perirhinal cortex and posterior ventral visual pathway regions when maintenance of visual information is interrupted

The perirhinal cortex (PRC) is known to support recognition memory, working memory, and perception for objects. Often, information must be maintained in working memory in the face of ongoing visual perception, raising the question of how PRC and other regions supporting object representation deal with this conflict. Here, we used functional MRI to examine the representational content of human ventral visual pathway (VVP) regions, including perirhinal cortex (PRC), during a visual delayed match-to-sample task. Critically, interfering items from a different stimulus category to the target were presented to participants during the maintenance phase, creating conflict between the contents of working memory and ongoing perception. Using representational similarity analysis, we compared information content across study, interference and test phases to models that differed in the extent to which they predicted that information content would be maintained during the delay period and perturbed by interference. This revealed that lateral occipital and fusiform regions are best fit by models that reflect the stimulus content of the item currently being viewed, whereas PRC reflects the information content of the studied item, even when an interfering stimulus is presented during the delay. This division of labor within the VVP sheds light on the specialized nature of representations in VVP regions, including PRC. Our findings support a representational hierarchical understanding of medial temporal lobe function which posits that representations at the most anterior aspect of the VVP are more robust to ongoing perceptual activity.

Declines in representational quality and strategic retrieval processes contribute to age-related increases in false recognition

In a Yes/No object recognition memory test with similar lures, older adults typically exhibit elevated rates of false recognition. However, the contributions of impaired retrieval, relative to reduced availability of target details, are difficult to disentangle using such a test. The present investigation sought to decouple these factors by comparing performance on a Yes/No (YN) test to that on a Forced Choice (FC) test, which minimizes demands on strategic retrieval processes, enabling a more direct measure of the availability of object details. Older adults exhibited increased lure false recognition across test formats (Experiment 1), suggesting a decline in the availability of object details contributes to deficits in performance. Manipulating interference by varying the number of objects studied selectively enhanced performance in the FC test, resulting in matched performance across groups, whereas age differences in YN performance persisted (Experiment 2), indicating an additional contribution of impaired strategic retrieval. Consistent with differential sensitivity of test format to strategic retrieval and the quality of stimulus representations among older adults, variability in the quality of object representations, measured using a perceptual discrimination task, was selectively related to FC performance. In contrast, variability in memory control processes, as measured with tests of recall and executive function, was related to performance across test formats. These results suggest that both declines in the availability of object details and impaired retrieval of object details contribute to elevated rates of lure false recognition with age, and highlight the utility of test format for dissociating these factors in memory-impaired populations.