Person:

Schacter, Daniel

Human cognition is increasingly characterized as an emergent property of interactions among distributed, functionally specialized brain networks. We recently demonstrated that the antagonistic “default” and “dorsal attention” networks—subserving internally and externally directed cognition, respectively—are modulated by a third “frontoparietal control” network that flexibly couples with either network depending on task domain. However, little is known about the intrinsic functional architecture underlying this relationship. We used graph theory to analyze network properties of intrinsic functional connectivity within and between these three large-scale networks. Task-based activation from three independent studies were used to identify reliable brain regions (“nodes”) of each network. We then examined pairwise connections (“edges”) between nodes, as defined by resting-state functional connectivity MRI. Importantly, we used a novel bootstrap resampling procedure to determine the reliability of graph edges. Furthermore, we examined both full and partial correlations. As predicted, there was a higher degree of integration within each network than between networks. Critically, whereas the default and dorsal attention networks shared little positive connectivity with one another, the frontoparietal control network showed a high degree of between-network interconnectivity with each of these networks. Furthermore, we identified nodes within the frontoparietal control network of three different types—default-aligned, dorsal attention-aligned, and dual-aligned—that we propose play dissociable roles in mediating internetwork communication. The results provide evidence consistent with the idea that the frontoparietal control network plays a pivotal gate-keeping role in goal-directed cognition, mediating the dynamic balance between default and dorsal attention networks.

When information is thematically related to previously studied information, gist-based processes contribute to false recognition. Using functional MRI, we examined the neural correlates of gist-based recognition as a function of increasing numbers of studied exemplars. Sixteen participants incidentally encoded small, medium, and large sets of pictures, and we compared the neural response at recognition using parametric modulation analyses. For hits, regions in middle occipital, middle temporal, and posterior parietal cortex linearly modulated their activity according to the number of related encoded items. For false alarms, visual, parietal, and hippocampal regions were modulated as a function of the encoded set size. The present results are consistent with prior work in that the neural regions supporting veridical memory also contribute to false memory for related information. The results also reveal that these regions respond to the degree of relatedness among similar items, and implicate perceptual and constructive processes in gist-based false memory.

Research examining the relation between explicit and implicit forms of memory has generated a great deal of evidence concerning the issue of multiple memory systems. This article focuses on an extensively studied implicit memory phenomenon, known as direct or repetition priming, and examines the hypothesis that priming effects on various tasks reflect the operation of a perceptual representation system (PRS)—a class of cortically based subsystems that operate at a presemantic level and support non conscious expressions of memory. Three PRS subsystems are examined: visual word form, structural description, and auditory word form. Pertinent cognitive, neuropsychological, and neurobiological evidence is reviewed, alternative classificatory schemes are discussed, and important conceptual and terminological issues are considered.

As part of the general trend toward interdisciplinary research in recent years, a growing number of investigators have come to consider both cognitive and neuroscientific perspectives when theorizing about memory. Although such cognitive neuroscience analyses are a relatively recent development, the approach has precedents in earlier scientific thinking about memory. In this article we present a historical review of three major issues in memory research---consolidation processes, the nature of memory representations, and multiple memory systems. We discuss the nature of the relation between cognitive and neuroscientific approaches to each of these issues with respect to the distinction between collateral, complementary, and convergent relations (Schacter, 1986). Although some early investigators offered analyses that linked psychological and physiological perspectives, there is little historical evidence of systematic or sustained interdisciplinary research. However, more recent work, especially with respect to hypotheses about memory systems, suggests progress toward establishing programmatic interdisciplinary research.

Recent neuroimaging work has demonstrated that the hippocampus is engaged when imagining the future, in some cases more than when remembering the past. It is possible that this hippocampal activation reflects recombining details into coherent scenarios and/or the encoding of these scenarios into memory for later use. However, inconsistent findings have emerged from recent studies of future simulation in patients with memory loss and hippocampal damage. Thus, it remains an open question as to whether the hippocampus is necessary for future simulation. In this review, we consider the findings from patient studies and the neuroimaging literature with respect to a new framework that highlights three component processes of simulation: accessing episodic details, recombining details, and encoding simulations. We attempt to reconcile these discrepancies between neuroimaging and patient studies by suggesting that different component processes of future simulation may be differentially affected by hippocampal damage.

Previous evidence has suggested a functional-anatomic dissociation between conscious and nonconscious processing during retrieval where early visual regions BA17/18 are associated with nonconscious processing and late visual regions BA19/37 are associated with conscious processing. However, evidence for this dissociation has only been observed using a limited number of experimental paradigms. In the present functional magnetic resonance imaging (fMRI) study, we tested the hypothesis that conscious processing during retrieval can occur in BA17/18 using memorial paradigms that recruited processing in these early visual regions. During the encoding phase of Experiment 1, abstract shapes with colored and oriented internal lines were presented to the left and right of fixation. During the retrieval phase, old shapes and new shapes were presented at fixation and participants classified each item as “old-left”, “old-right”, or “new”. The contrast of spatial memory-hits>spatial memory-misses (with accurate item memory) produced activity in BA17/18. During the encoding phase of Experiment 2, abstract shapes with colored and oriented internal lines were presented at fixation. During the retrieval phase, old shapes, changed shapes (with the same outline but different colored and oriented internal lines), and new shapes were presented at fixation and participants made an old-new classification during runs with a specific retrieval orientation or a non-specific retrieval orientation. Critically, the contrast of old-hits>old-misses during specific retrieval orientation produced activity in BA17/18. The results of the present experiments support the hypothesis that conscious processing during retrieval can occur in BA17/18.

People frequently imagine specific interpersonal experiences that might occur in their futures. The present study used a novel experimental paradigm to examine the influence of repeated simulation of future interpersonal experiences on subjective assessments of plausibility for positive, negative, and neutral events. The results demonstrate that repeated simulation increases estimates of plausibility for emotional, but not neutral, future interpersonal experiences. Additional correlational analyses reveal that increases in plausibility for emotional events are associated with concurrent increases in ease of simulation, event detail, and arousal. Implications for daily life and affective disorders such as depression and anxiety are noted.

When people revisit previous experiences, they often engage in episodic counterfactual thinking: mental simulations of alternative ways in which personal past events could have occurred. The present study employed a novel experimental paradigm to examine the influence of repeated simulation on the perceived plausibility of upward, downward, and neutral episodic counterfactual thoughts. Participants were asked to remember negative, positive, and neutral autobiographical memories. One week later, they self-generated upward, downward, and neutral counterfactual alternatives to those memories. The following day, they resimulated each of those counterfactuals either once or four times. The results indicate that repeated simulation of upward, downward, and neutral episodic counterfactual events decreases their perceived plausibility while increasing ratings of the ease, detail, and valence of the simulations. This finding suggests a difference between episodic counterfactual thoughts and other kinds of self-referential simulations. Possible implications of this finding for pathological and nonpathological anxiety are discussed.

One of the key goals of memory research is to develop a basic understanding of the nature and characteristics of memory processes and systems. Another important goal is to develop useful applications of basic research to everyday life. This editorial considers two lines of work that illustrate some of the prospects for applying memory research to everyday life: interpolated quizzing to enhance learning in educational settings, and specificity training to enhance memory and associated functions in individuals who have difficulties remembering details of their past experiences.

Imagining or simulating future events has been shown to activate the anterior right hippocampus (RHC) more than remembering past events does. One fundamental difference between simulation and memory is that imagining future scenarios requires a more extensive constructive process than remembering past experiences does. Indeed, studies in which this constructive element is reduced or eliminated by “pre-imagining” events in a prior session do not report differential RHC activity during simulation. In this fMRI study, we examined the effects of repeatedly simulating an event on neural activity. During scanning, participants imagined 60 future events; each event was simulated three times. Activation in the RHC showed a significant linear decrease across repetitions, as did other neural regions typically associated with simulation. Importantly, such decreases in activation could not be explained by non-specific linear time-dependent effects, with no reductions in activity evident for the control task across similar time intervals. Moreover, the anterior RHC exhibited significant functional connectivity with the whole-brain network during the first, but not second and third simulations of future events. There was also evidence of a linear increase in activity across repetitions in right ventral precuneus, right posterior cingulate and left anterior prefrontal cortex, which may reflect source recognition and retrieval of internally generated contextual details. Overall, our findings demonstrate that repeatedly imagining future events has a decremental effect on activation of the hippocampus and many other regions engaged by the initial construction of the simulation, possibly reflecting the decreasing novelty of simulations across repetitions, and therefore is an important consideration in the design of future studies examining simulation.