Transient global amnesia (TGA) is a clinical syndrome characterized by the abrupt onset of a massive episodic memory deficit that spares other cognitive functions. If the anterograde dimension is known to be impaired in TGA, researchers have yet to investigate prospective memory (PM)—which involves remembering to perform an intended action at some point in the future—in this syndrome. Furthermore, as executive functions are thought to be spared in this syndrome, TGA provides an opportunity to examine the impact of a massive “pure” memory impairment on PM. We assessed 38 patients with a newly designed protocol that distinguished between the prospective (remembering to do something at the appropriate time) and retrospective (remembering what has to be done) components of PM. Moreover, we investigated episodic memory with an anterograde memory task and assessed executive functions, anxiety and mood, as well as their links with PM. We demonstrated that PM is impaired during TGA, with a greater deficit for the retrospective component than for the prospective component. Furthermore, we highlighted a strong link between these two components. Anterograde episodic memory impairments were correlated with retrospective component deficits in TGA patients, although we were able to confirm that executive functions are globally spared. We discuss this pattern of results within the theoretical framework of PM, putting forward new arguments in favor of the idea that PM deficits can occur mainly because of a massive anterograde memory deficit. The clinical consequences of PM impairment in TGA are examined.

During memory encoding, increased hippocampal activity—thought to reflect the binding of different types of information into unique episodes—has been shown to correlate with subsequent recollection of those episodes. Repetition priming—thought to induce more efficient perceptual processing of stimuli—is normally associated with decreased neocortical activity and is often assumed to reduce encoding into episodic memory. Here, we used fMRI to compare activity to primed and unprimed auditory words in the presence of distracting sounds as a function of whether participants subsequently recollected the word–sound associations or only had a feeling of familiarity with the word in a subsequent surprise recognition task. At the behavioral level, priming increased the incidence of subsequent recollection. At the neuronal level, priming reduced activity in the superior temporal gyrus (STG) but also reversed the traditional increase in encoding-related hippocampal activity associated with subsequent recollection relative to subsequent familiarity. To explain this interaction pattern, further analyses using dynamic causal modeling showed an increase in connectivity from left STG to left hippocampus specific to words that were later recollected. These findings show that successful episodic encoding is not determined solely by local hippocampal activity and emphasize instead the importance of increased functional neocortical–hippocampal coupling. Such coupling might be a better predictor of subsequent recollection than the direction of local hippocampal changes per se. We propose that one consequence of priming is to “free up” attentional resources from processing an item in a noisy context, thereby allowing greater attention to encoding of that context.

This study set out to establish the relationship between changes in episodic memory retrieval in normal aging on the one hand and gray matter volume and 18 FDG uptake on the other. Structural MRI, resting-state 18 FDG-PET, and an episodic memory task manipulating the depth of encoding and the retention interval were administered to 46 healthy subjects divided into three groups according to their age (young, middle-aged, and elderly adults). Memory decline was found not to be linear in the course of normal aging: Whatever the retention interval, the retrieval of shallowly encoded words was impaired in both the middle-aged and the elderly, whereas the retrieval of deeply encoded words only declined in the elderly. In middle-aged and elderly subjects, the reduced performance in the shallow encoding condition was mainly related to posterior mediotemporal volume and metabolism. By contrast, the impaired retrieval of deeply encoded words in the elderly group was mainly related to frontal and parietal regions, suggesting the adoption of inefficient strategic processes.

The present work was aimed at characterizing picture priming effects from two complementary behavioral and functional neuroimaging (positron emission tomography, PET) studies. In two experiments, we used the same line drawings of common living/nonliving objects in a tachistoscopic identification task to contrast two forms of priming. In the within-format priming condition (picture-picture), subjects were instructed to perform a perceptual encoding task in the study phase, whereas in the cross-format priming condition (word-picture), they were instructed to perform a semantic encoding task. In Experiment 1, we showed significant priming effects in both priming conditions. However, the magnitude of priming effects in the same-format/perceptual encoding condition was higher than that in the different-format/semantic encoding condition, while the recognition performance did not differ between the two conditions. This finding supports the existence of two forms of priming that may be subserved by different systems. Consistent with these behavioral findings, the PET data for Experiment 2 revealed distinct priming-related patterns of regional cerebral blood flow (rCBF) decreases for the two priming conditions when primed items were compared to unprimed items. The same-format priming condition involved reductions in cerebral activity particularly in the right extrastriate cortex and left cerebellum, while the different-format priming condition was associated with rCBF decreases in the left inferior temporo-occipital cortex, left frontal regions, and the right cerebellum. These results suggest that the extrastriate cortex may subserve general aspects of perceptual priming, independent of the kind of stimuli, and that the right part of this cortex could underlie the same-format-specific system for pictures. These data also support the idea that the cross-format/semantic encoding priming for pictures represents a form of lexico-semantic priming subserved by a semantic neural network extending from left temporo-occipital cortex to left frontal regions. These results reinforce the distinction between perceptual and conceptual priming for pictures, indicating that different cerebral processes and systems are implicated in these two forms of picture priming.