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When individuals select the recently studied (and familiar) item in a multiple-choice memory test, they direct a greater proportion of viewing time toward the to-be-selected item when their choice is correct than when their choice is incorrect. Thus, for both correct and incorrect choices, individuals indicate that the chosen item is old, but viewing time nevertheless distinguishes between old and new items. What kind of memory supports this preferential viewing effect? We recorded eye movements while participants made three-alternative, forced-choice recognition memory judgments for scenes. In experiment 1 ( n = 30), the magnitude of the preferential viewing effect was strongly correlated with measures of conscious, declarative memory: recognition accuracy as well as the difference in confidence ratings and in response times for correct and incorrect choices. In four analyses that minimized the contribution of declarative memory in order to detect a possible contribution from other processes, the preferential viewing effect was absent. In experiment 2, five memory-impaired patients with medial temporal lobe lesions exhibited a diminished preferential viewing effect. These patients also exhibited poor recognition accuracy and reduced differences in confidence ratings and response times for correct and incorrect choices. We propose that the preferential viewing effect is a phenomenon of conscious, declarative memory and is dependent on the medial temporal lobe. The findings support the link between medial temporal lobe function and declarative memory. When the effects of experience depend on the medial temporal lobe, the effects reflect conscious memory., Competing Interests: The authors declare no conflict of interest.

Declarative memory for rapidly learned, novel associations is thought to depend on structures in the medial temporal lobe (MTL), whereas associations learned more gradually can sometimes be supported by nondeclarative memory and by structures outside the MTL. A recent study suggested that even rapidly learned associations can be supported by structures outside the MTL when an incidental encoding procedure termed "fast mapping" (FM) is used. We tested six memory-impaired patients with bilateral damage to hippocampus and one patient with large bilateral lesions of the MTL. Participants saw photographs and names of animals, plants, and foods that were previously unfamiliar (e.g., mangosteen). Instead of asking participants to study name-object pairings for a later memory test (as with traditional memory instructions), participants answered questions that allowed them to infer which object corresponded to a particular name. In a second condition, participants learned name-object associations of unfamiliar items by using standard, explicit encoding instructions (e.g., remember the mangosteen). In FM and explicit encoding conditions, patients were impaired (and performed no better than a group that was given the same tests but had not previously studied the material). The same results were obtained in a second experiment that used the same procedures with modifications to allow for more robust learning and more reliable measures of performance. Thus, our results with the FM procedure and memory-impaired patients yielded the same deficits in learning and memory that have been obtained by using other more traditional paradigms.

The study of anterograde and retrograde amnesia (AA and RA) in the laboratory and the clinic has provided important information about the structure and organization of memory. The severity of AA is usually correlated with the severity of RA. Nevertheless, variations in the expression of AA and RA have been reported, which presumably reflect variation in the locus and extent of brain damage. The relationship between AA and RA has rarely been described quantitatively in groups of patients where detailed anatomical information is available. We have quantified the severity of AA and RA for factual information in 11 memory-impaired patients with bilateral medial temporal lobe lesions, including 5 for whom detailed post-mortem neurohistological information was available. The findings describe an orderly relationship between AA and RA, such that patients with more severe AA also had more extensive RA. In addition, RA was measurable only after AA reached a substantial level of severity. This relationship between AA and RA in patients with identified medial temporal lobe lesions appears to describe a general principle, which applies to a range of etiologies, including traumatic amnesia, where the locus and extent of brain damage is less well understood. Whenever patients deviate substantially from the relationship described here, one should be alert to the likelihood that significant damage has occurred outside or in addition to the structures in the medial temporal lobe., (© 2013 Published by Elsevier Ltd.)

Findings from functional MRI (fMRI) studies of recognition memory and the medial temporal lobe often suggest qualitative differences in the contribution of the hippocampus and perirhinal cortex. This interpretation is complicated by the fact that most of the methods intended to demonstrate qualitative differences also separate strong memories from weak memories. Thus, apparent qualitative differences might reflect quantitative differences in how measured activity in medial temporal lobe structures varies with memory strength. We tested the hypothesis that the relationship between activity at the time of study and subsequent memory strength is nonlinear in hippocampus and perirhinal cortex and also distinctly different in those two structures. We found that activity in the hippocampus was characterized by a positively accelerated function and that activity in the perirhinal cortex was associated with a statistically different, negatively accelerated function. Our results do not count against the possibility that these structures differ qualitatively in their contributions to memory. Rather, our findings show how an alternative interpretation based on quantitative differences can also account for a good deal of data, and they suggest that a demonstration of qualitative differences requires more stringent criteria than are achieved in most fMRI studies.

We measured brain activity using event-related fMRI as participants recalled answers to 160 questions about news events that had occurred during the past 30 years. Guided by earlier findings from patients with damage limited to the hippocampus who were given the same test material, we looked for regions that exhibited gradually decreasing activity as participants recalled memories from 1-12 years ago and a constant level of activity during recall of more remote memories. Regions in the medial temporal lobe exhibited a decrease in brain activity in relation to the age of the memory (hippocampus, temporopolar cortex, and amygdala). Regions in the frontal lobe, temporal lobe, and parietal lobe exhibited the opposite pattern. The findings for all of these regions were unrelated to the richness of the memories, to how well test questions were remembered later (encoding for subsequent memory), nor to how frequently semantic memories were accompanied by personal, episodic recollections. Last, activity in a different group of regions (perirhinal cortex, parahippocampal cortex, and inferior temporal gyrus) was associated with how well the test questions were subsequently remembered. The results support the idea that medial temporal lobe structures play a time-limited role in semantic memory.

We studied item and source memory with fMRI in healthy volunteers and carried out a parallel study in memory-impaired patients. In experiment 1, volunteers studied a list of words in the scanner and later took an item memory test and a source memory test. Brain activity in the hippocampal region, perirhinal cortex, and parahippocampal cortex was associated with words that would later be remembered (item memory). The activity in these regions that predicted subsequent success at item memory predicted subsequent source memory to a similar degree. In experiment 2, memory-impaired patients with damage thought to be limited to the hippocampal region were given an item memory test and a source memory test, as in experiment 1. The patients were similarly impaired on the item memory test and the source memory test. Together, the findings suggest that medial temporal lobe structures broadly support recognition memory function and that item memory and source memory similarly depend on these structures.