Goal-relevant information can be maintained in working memory over a brief delay interval to guide an upcoming decision. There is also evidence suggesting the existence of a complementary process: namely, the ability to suppress information that is no longer relevant to ongoing task goals. Moreover, this ability to suppress or inhibit irrelevant information appears to decline with age. In this study, we compared younger and older adults undergoing fMRI on a working memory task designed to address whether the modulation of neural representations of relevant and no-longer-relevant items during a delay interval is related to age and overall task performance. Following from the theoretical predictions of the inhibitory deficit hypothesis of aging, we hypothesized that older adults would show higher activation of no-longer-relevant items during a retention delay compared to young adults and that higher activation of these no-longer-relevant items would predict worse recognition memory accuracy for relevant items. Our results support this prediction and more generally demonstrate the importance of goal-driven modulation of neural activity in successful working memory maintenance. Furthermore, we showed that the largest age differences in the regulation of category-specific pattern activity during working memory maintenance were seen throughout the medial temporal lobe and prominently in the hippocampus, further establishing the importance of “long-term memory” retrieval mechanisms in the context of high-load working memory tasks that place large demands on attentional selection mechanisms.

According to the principle of reactivation, memory retrieval evokes patterns of brain activity that resemble those instantiated when an event was first experienced. Intuitively, one would expect neural reactivation to contribute to recollection (i.e., the vivid impression of reliving past events), but evidence of a direct relationship between the subjective quality of recollection and multiregional reactivation of item-specific neural patterns is lacking. The current study assessed this relationship using fMRI to measure brain activity as participants viewed and mentally replayed a set of short videos. We used multivoxel pattern analysis to train a classifier to identify individual videos based on brain activity evoked during perception and tested how accurately the classifier could distinguish among videos during mental replay. Classification accuracy correlated positively with memory vividness, indicating that the specificity of multivariate brain patterns observed during memory retrieval was related to the subjective quality of a memory. In addition, we identified a set of brain regions whose univariate activity during retrieval predicted both memory vividness and the strength of the classifier's prediction irrespective of the particular video that was retrieved. Our results establish distributed patterns of neural reactivation as a valid and objective marker of the quality of recollection.

How does the brain maintain to-be-remembered information in working memory (WM), particularly when the focus of attention is drawn to processing other information? Cognitive models of WM propose that when items are displaced from focal attention recall involves retrieval from long-term memory (LTM). In this fMRI study, we tried to clarify the role of LTM in performance on a WM task and the type of representation that is used to maintain an item in WM during rehearsal-filled versus distractor-filled delays. Participants made a deep or shallow levels-of-processing (LOP) decision about a single word at encoding and tried to recall the word after a delay filled with either rehearsal of the word or a distracting math task. Recalling one word after 10 sec of distraction demonstrated behavioral and neural indices of retrieval from LTM (i.e., LOP effects and medial-temporal lobe activity). In contrast, recall after rehearsal activated cortical areas that reflected reporting the word from focal attention. In addition, areas that showed an LOP effect at encoding (e.g., left ventrolateral VLPFC and the anterior temporal lobes [ATLs]) were reactivated at recall, especially when recall followed distraction. Moreover, activity in left VLPFC during encoding, left ATL during the delay, and left hippocampus during retrieval predicted recall success after distraction. Whereas shallow LOP and rehearsal-related areas supported active maintenance of one item in focal attention, the behavioral processes and neural substrates that support LTM supported recall of one item after it was displaced from focal attention.

When we have a rich and vivid memory for a past experience, it often feels like we are transported back in time to witness once again this event. Indeed, a perfect memory would exactly mimic the experiential quality of direct sensory perception. We used fMRI and multivoxel pattern analysis to map and quantify the similarity between patterns of activation evoked by direct perception of a diverse set of short video clips and the vivid remembering, with closed eyes, of these clips. We found that the patterns of distributed brain activation during vivid memory mimicked the patterns evoked during sensory perception. Using whole-brain patterns of activation evoked by perception of the videos, we were able to accurately classify brain patterns that were elicited when participants tried to vividly recall those same videos. A discriminant analysis of the activation patterns associated with each video revealed a high degree (explaining over 80% of the variance) of shared representational similarity between perception and memory. These results show that complex, multifeatured memory involves a partial reinstatement of the whole pattern of brain activity that is evoked during initial perception of the stimulus.

One of the classic categorical divisions in the history of memory research is that between short-term and long-term memory. Indeed, because memory for the immediate past (a few seconds) and memory for the relatively more remote past (several seconds and beyond) are assumed to rely on distinct neural systems, more often than not, memory research has focused either on short- (or “working memory”) or on long-term memory. Using an auditory–verbal continuous recognition paradigm designed for fMRI, we examined how the neural signatures of recognition memory change across an interval of time (from 2.5 to 30 sec) that spans this hypothetical division between short- and long-term memory. The results revealed that activity during successful auditory–verbal item recognition in inferior parietal cortex and the posterior superior temporal lobe was maximal for early lags, whereas, conversely, activity in the left inferior frontal gyrus increased as a function of lag. Taken together, the results reveal that as the interval between item repetitions increases, there is a shift in the distribution of memory-related activity that moves from posterior temporo-parietal cortex (lags 1–4) to inferior frontal regions (lags 5–10), indicating that as time advances, the burden of recognition memory is increasingly placed on top–down retrieval mechanisms that are mediated by structures in inferior frontal cortex.

The phonological loop system of Baddeley and colleagues' Working Memory model is a major accomplishment of the modern era of cognitive psychology. It was one of the first information processing models to make an explicit attempt to accommodate both traditional behavioral data and the results of neuropsychological case studies in an integrated theoretical framework. In the early and middle 1990s, the purview of the phonological loop was expanded to include the emerging field of functional brain imaging. The modular and componential structure of the phonological loop seemed to disclose a structure that might well be transcribed, intact, onto the convolutions of the brain. It was the phonological store component, however, with its simple and modular quality, that most appealed to the neuroimaging field as the psychological “box” that might most plausibly be located in the brain. Functional neuroimaging studies initially designated regions in the parietal cortex as constituting the “neural correlate” of the phonological store, whereas later studies pointed to regions in the posterior temporal cortex. In this review, however, we argue the phonological store as a theoretical construct does not precisely correspond to a single, functionally discrete, brain region. Rather, converging evidence from neurology, cognitive psychology, and functional neuroimaging argue for a reconceptualization of phonological short-term memory as emerging from the integrated action of the neural processes that underlie the perception and production of speech.