C. Brock Kirwan

Visual Object Pattern Separation Deficits in Nondemented Older Adults.

Young and nondemented older adults were tested on a continuous recognition memory task requiring visual pattern separation. During the task, some objects were repeated across trials and some objects, referred to as lures, were presented that were similar to previously presented objects. The lures resulted in increased interference and an increased need for pattern separation. For each object, the participant was asked to indicate whether (1) this was the first time the object was seen (new), (2) the object was seen previously (old), or (3) the object was similar to a previous object (similar). Older adults were able to correctly identify objects as old or new as well as young adults; however, older adults were impaired when identifying lures as similar. Therefore, pattern separation may be less efficient in older adults resulting in poorer recognition memory performance when interference is increased.

A possible negative influence of depression on the ability to overcome memory interference.

Pattern separation is a mechanism for encoding memories, whereby distinct memory representations are created for very similar stimuli and events. It has been proposed that depression negatively impacts pattern separation abilities. However, a link between depression and performance in memory tasks requiring pattern separation is still unclear even though it is well established that depression is associated with reduced declarative memory performance and decreased hippocampal volume. Accordingly, we designed a study to investigate the relationship between pattern separation performance and the severity of depression symptoms in an otherwise healthy population. Participants completed a pattern separation memory test and a set of questionnaires to gauge their level of depression. We found a negative relationship between depression scores and pattern separation scores. These results provide support for the idea that depression is negatively related to pattern separation performance.

A demonstration that the hippocampus supports both recollection and familiarity

Recognition memory is thought to depend on two distinct processes: recollection and familiarity. There is debate as to whether damage to the hippocampus selectively impairs recollection or whether it impairs both recollection and familiarity. If hippocampal damage selectively impairs recollection but leaves familiarity intact, then patients with circumscribed hippocampal lesions should exhibit the full normal range of low-confidence and high-confidence familiarity-based recognition. High-confidence, familiarity-based decisions are ordinarily accompanied by successful recollection (when memory is intact). However, patients with hippocampal lesions, if recollection is impaired, should frequently experience high-confidence, familiarity-based recognition in the absence of recollection, and this circumstance (termed the “butcher-on-the-bus” phenomenon) should occur more often in patients than in healthy controls. We tested five patients with circumscribed hippocampal damage, asking them to recognize recently studied words as well as to remember the context in which the items were studied. Relative to controls, the patients exhibited no increased tendency to experience the butcher-on-the-bus phenomenon. The simplest explanation of the results is that hippocampal damage impairs familiarity as well as recollection. The same conclusion was suggested when two competing models of recognition memory were used to analyze the data.

Medial temporal lobe activity can distinguish between old and new stimuli independently of overt behavioral choice

We collected fMRI data and confidence ratings as participants performed a recognition memory task that intermixed recently studied words and new (non-studied) words. We first replicated a typical finding from such studies; namely, increasing activity in medial temporal lobe structures with increasing confidence in the old/new decision. Because there are greater proportions of old items at higher confidence levels, such activity could be related to the confidence ratings or to whether items are old or new. When activity associated with old and new items was analyzed separately, we found that activity in the hippocampus bilaterally, as well as in anterior parahippocampal gyrus, was associated with the actual old/new status of the items rather than to which items participants believed to be old. Accordingly, activity in the medial temporal lobe can be modulated by the old/new status of stimuli and does not always track the behavioral response.

Recognition memory and the hippocampus: A test of the hippocampal contribution to recollection and familiarity

It has been suggested that the hippocampus selectively supports recollection and that adjacent cortex in the medial temporal lobe can support familiarity. Alternatively, it has been suggested that the hippocampus supports both recollection and familiarity. We tested these suggestions by assessing the performance of patients with hippocampal lesions on recognition memory tests that differ in the extent to which recollection and familiarity contribute to the recognition decision. When targets and foils are highly similar, prior evidence suggests that, on a forced-choice test in which targets are presented together with highly similar, corresponding foils (the FC-C format), performance is supported primarily by familiarity. By contrast, when targets are presented together with foils that are similar to other targets (the FC-NC format) or when memory is tested in a yes/no (Y/N) format, performance is based much more strongly on recollection. Accordingly, a finding that hippocampal damage impaired both Y/N recognition and FC-NC recognition but spared FC-C recognition would suggest that the hippocampus selectively supports recollection. We administered Y/N, FC-C, and FC-NC tests to five memory-impaired patients with circumscribed hippocampal lesions and 14 controls. The patients were impaired on all three types of recognition test, and there was no indication that the patients were disproportionately benefited or disproportionately impaired on any test. This pattern of performance suggests that the hippocampus supports both recollection and familiarity.

Structural and functional correlates of behavioral pattern separation in the hippocampus and medial temporal lobe

Structures of the medial temporal lobe (MTL) are known to be involved in declarative memory processes. However, little is known about how age‐related changes in MTL structures, white matter integrity, and functional connectivity affect pattern separation processes in the MTL. In this study, we used magnetic resonance imaging (MRI) to measure the volumes of MTL regions of interest, including hippocampal subfields (dentate gyrus, CA3, CA1, and subiculum) in healthy older and younger adults. Additionally, we used diffusion tensor imaging to measure white matter integrity for both groups. Finally, we used functional MRI to acquire resting functional connectivity measures for both groups. We show that, along with age, the volume of left CA3/dentate gyrus predicts memory performance. Differences in fractional anisotropy and the strength of resting functional connections between the hippocampus and other cortical structures implicated in memory processing were not significant predictors of performance. As previous studies have only hinted, it seems that the size of left CA3/dentate gyrus contributes more to successful discrimination between similar mnemonic representations than other hippocampal sub‐fields, MTL structures, and other neuroimaging correlates. Accordingly, the implications of aging and atrophy on lure discrimination capacities are discussed.

When recognition memory is independent of hippocampal function

Significance Hippocampal damage has been thought to impair memory for all domains of material (sounds, objects, words, odors). We investigated face recognition memory in patients with hippocampal lesions or large medial temporal lobe lesions. Recognition of novel faces was unequivocally intact in hippocampal patients but only at a short retention interval. Recognition memory for words, buildings, famous faces, and inverted faces was impaired. For medial temporal lobe patients, memory was impaired in all conditions. Ordinarily, recognition memory judgments depend on an association between study items and the study context. We suggest that face memory is spared because face processing is specialized (and holistic), and that participants can make recognition judgments without making explicit reference to the study context. Hippocampal damage has been thought to result in broad memory impairment. Recent studies in humans, however, have raised the possibility that recognition memory for faces might be spared. In five experiments we investigated face recognition in patients with hippocampal lesions (H) or large medial temporal lobe (MTL) lesions, including patients where neurohistological information was available. Recognition of novel faces was unequivocally intact in H patients but only at a short retention interval. Recognition memory for words, buildings, inverted faces, and famous faces was impaired. For MTL patients, recognition memory was impaired for all materials and across all retention intervals. These results indicate that structures other than the hippocampus, perhaps the perirhinal cortex, can support face recognition memory in H patients under some conditions. The fact that the faces were novel when recognition memory was intact does not fully account for our findings. We propose that the role of the hippocampus in recognition memory is related to how recognition decisions are accomplished. In typical recognition tasks, participants proceed by forming an association between a study item and the study list, and the recognition decision is later made based on whether participants believe the item was on the study list. We suggest that face recognition is an exception to this principle and that, at short retention intervals, participants can make their recognition decisions without making explicit reference to the study list. Important features of faces that might make face recognition exceptional are that they are processed holistically and are difficult to verbally label.

Functional brain response to food images in successful adolescent weight losers compared with normal‐weight and overweight controls

Research conducted with adults suggests that successful weight losers demonstrate greater activation in brain regions associated with executive control in response to viewing high‐energy foods. No previous studies have examined these associations in adolescents. Functional neuroimaging was used to assess brain response to food images among groups of overweight (OW), normal‐weight (NW), and successful weight‐losing (SWL) adolescents.

What are the influences of orthogonally-manipulated valence and arousal on performance monitoring processes? The effects of affective state

Studies of the influence of affective state on the cognitive control process of performance monitoring are mixed and few studies have orthogonally manipulated affective valence and arousal. Performance monitoring can be measured using behaviors (e.g., response times and error rates) and components of the event-related potentials (ERPs), such as the error-related negativity (ERN), correct-related negativity (CRN), and post-error positivity (Pe). We used a pre/post design and standard mood induction paradigm in 121 healthy participants randomly assigned to orthogonal valence (positive or negative) and arousal (high or low) conditions (i.e., happy, calm, anxious, or sad mood states). Following mood induction, valence and arousal ratings differed between groups. Behavioral findings showed decreased accuracy in participants with high arousal and negative valence (i.e., anxious condition), but no additional response time (RT), post-error slowing, or accuracy effects. Amplitude of the CRN differentiated high and low valence, but was not related to arousal. Positive valence was associated with decreased CRN amplitude even when baseline affect and demographic variables were controlled. Valence and arousal did not significantly differentiate the amplitude of the ERN, although the ERN minus CRN difference was related to arousal but not valence ratings in multiple regression analyses. Affect-related differences were not shown for the Pe. Findings provide a context to understand how dimensional aspects of emotional valence and arousal influence performance-monitoring processes and suggest a need for further research on the functional role of the CRN and its relation to affective valence.

Recognition without awareness: An elusive phenomenon

Two recent studies described conditions under which recognition memory performance appeared to be driven by nondeclarative memory. Specifically, participants successfully discriminated old images from highly similar new images even when no conscious memory for the images could be retrieved. Paradoxically, recognition performance was better when images were studied with divided attention than when images were studied with full attention. Furthermore, recognition performance was better when decisions were rated as guesses than when decisions were associated with low or high confidence. In three experiments, we adopted the paradigm used in the earlier studies in an attempt to repeat this intriguing work. Our attempts were unsuccessful. In all experiments, recognition was better when images were studied with full attention than when images were studied with divided attention. Recognition was also better when participants indicated high or low confidence in their decision than when they indicated that their decision was a guess. Thus, our results conformed to what typically has been reported in studies of recognition memory, and we were unable to demonstrate recognition without awareness. We encourage others to explore this paradigm, and to try to identify conditions under which the phenomenon might be demonstrated.