Browsing by Author "Cabeza, Roberto"

Preliminary evidence demonstrates that age-related differences in episodic memory performance become greater in tasks that have greater perceptual demands (e.g., task stimuli are visually degraded), but are attenuated in tasks that have greater semantic demands (e.g., task requires utilizing previous knowledge). This work suggests that age-related differences in how perceptual and semantic information are represented in the brain have an impact on episodic memory. Broadly, the goal of this thesis was to investigate this idea. To investigate this goal, while undergoing functional magnetic resonance imaging scanning, samples of younger and older adults studied and later retrieved their memories of pictures of either scenes (Study 1 and 2) or objects (Study 3). The first two studies found that, compared to younger adults, in older adults, (1) in occipitotemporal cortex, the quality of perceptual-related representations was attenuated, but, intriguingly, (2) in anterior temporal lobes and prefrontal cortex, the quality of semantic-related representations was similar and even enhanced; these effects were found to be related to episodic memory. Study 1 demonstrated this pattern in individual brain regions and Study 2 demonstrated that this pattern was also present in how information was distributed across the whole-brain network. In Study 3 it was found that these age-related differences in functional neural representations are the result of age-related visual signal loss and compensatory semantic-enhancing mechanisms. Taken together, the three studies highlight that age-related differences in neural representations have an impact on cognition and especially episodic memory.

Advanced age is associated with substantial changes in the brain. These changes can be attributed to many difference sources, such as detrimental effects of aging, brain’s compensatory responses to such negative effects, and cognitive or neural resources acquired over lifespan. As a result, under the same cognitive task, healthy older adults (OAs) often show recruitment of brain regions that are different from healthy young adults (YAs). These observations have been drawn from functional magnetic resonance imaging (fMRI) studies on aging and cognition, which have been largely based on univariate analysis that relates experimental conditions to activity level in individual brain region. While univariate analysis reveals the age differences in the recruitment of brain regions, much remains unknown regarding how these regions are playing their roles. Meanwhile, recent methodological advances in cognitive neuroscience have provided the opportunities to examine 1) functional communications across brain regions, and 2) information stored in the distributed neural representation in a region. In this dissertation, I described age-related differences in these two novel perspectives in a series of fMRI studies on episodic memory, a domain of cognition that is particularly affected by aging. In these studies, healthy YAs and OAs encoded and later retrieved images of scenes or objects inside the scanner. Analyses on functional brain network and neural representations were conducted on the neuroimaging data. These analyses revealed three main findings. First, neural representation and functional connectivity revealed reduced involvements of the core task regions in OAs. During encoding, early visual cortex (EVC) in OAs exhibited reduced representation of visual information. During retrieval, medial temporal lobe (MTL) in OAs exhibited reduced reconfiguration of functional connectivity associated with successful remembering. Second, enhanced recruitments of additional neural resources in OAs were also observed. During encoding, anterior temporal lobe (ATL) in OAs exhibited enhanced semantic representation. During retrieval, prefrontal cortex (PFC) in OAs showed enhanced functional connectivity and stronger reconfiguration of connectivity associated with successful remembering. Finally, we found that schematic knowledge affected functional communication in PFC and semantic representation in ATL differently in the two age groups, suggesting that schema-related strategies may be preferentially selected by OAs. Taken together, these studies depicted the detrimental effect of aging and brain’s adaptive changes in two novel perspectives: functional communication and information processing, which may contribute to a more comprehensive understanding of episodic memory function in aging populations.

Neuroimaging studies of episodic memory, or memory of events from our personal past, have predominantly focused their attention on medial temporal lobe (MTL). There is growing acknowledgement however, from the cognitive neuroscience of memory literature, that regions outside the MTL can support episodic memory processes. The medial prefrontal cortex is one such region garnering increasing interest from researchers. Using behavioral and functional magnetic resonance imaging measures, over two studies, this thesis provides evidence of a mnemonic role of the medial PFC. In the first study, participants were scanned while judging the extent to which they agreed or disagreed with the sociopolitical views of unfamiliar individuals. Behavioral tests of associative recognition revealed that participants remembered with high confidence viewpoints previously linked with judgments of strong agreement/disagreement. Neurally, the medial PFC mediated the interaction between high-confidence associative recognition memory and beliefs associated with strong agree/disagree judgments. In an effort to generalize this finding to well-established associative information, in the second study, we investigated associative recognition memory for real-world concepts. Object-scene pairs congruent or incongruent with a preexisting schema were presented to participants in a cued-recall paradigm. Behavioral tests of conceptual and perceptual recognition revealed memory enhancements arising from strong resonance between presented pairs and preexisting schemas. Neurally, the medial PFC tracked increases in visual recall of schema-congruent pairs whereas the MTL tracked increases in visual recall of schema-incongruent pairs. Additionally, ventral areas of the medial PFC tracked conceptual components of visual recall specifically for schema-congruent pairs. These findings are consistent with a recent theoretical proposal of medial PFC contributions to memory for schema-related content. Collectively, these studies provide evidence of a role for the medial PFC in associative recognition memory persisting for associative information deployed in our daily social interactions and for those associations formed over multiple learning episodes. Additionally, this set of findings advance our understanding of the cognitive contributions of the medial PFC beyond its canonical role in processes underlying social cognition.

The ability to re-experience the past is a defining feature of episodic memory. Yet we know that even the most detailed memories are distinct from the initial experiences to which they refer. This relationship between the initial encoding and subsequent retrieval of information is central to our understanding of memory and its capacity to connect us to the past. Past research has shown that neural signatures present during perception are reactivated during later memory, but the correspondence between this reactivation and various aspects of memory function remains unclear. This dissertation attempts to connect behavioral measures of memory to the reinstatement and modification of neural information that takes place when memories are retrieved. In the first two studies reported, functional magnetic resonance imaging (fMRI) is used to assess event-specific cortical patterns from encoding that are reinstated during retrieval (encoding-retrieval similarity, ERS). Increases in this fine-grained of reinstatement are found in occipitotemporal cortex (OTC) during detailed memory for scenes (Study 1), and in the medial temporal lobes (MTL) for the recovery of relational information (Study 2). In addition to reflecting encoding-related content, retrieval is also found to strengthen previously encoded information via hippocampally-mediated mechanisms in Study 3. Together, these studies demonstrate the detailed nature of information that is recovered across varying degrees of memory and show how retrieval can also alter stored representations, emphasizing the interactive nature of memory processes.

Humans make a variety of choices every day. Some of these choices are pretty mundane like whether to eat pancakes or oatmeal for breakfast. Others cost a little more, have a little bit of a longer impact, like which vacuum cleaner to buy on Amazon. And finally, there are choices that we don’t make very often—maybe even just once, that have enormous consequences in our lives like whether to choose Duke for graduate school. Deciding to choose one option over a set of alternatives involves imagining the future value that could be obtained by making those choices. Research on value-based decision making has recently begun to assess the impact of memory-related processes in making prospective decisions. Given that remembering the past and imagining the future rely on the same cognitive and neural mechanisms, researchers have investigated how imagining the future and remembering the past shift choice behavior. However, much of this research has focused on relatively abstract choices made in a laboratory setting rather than potentially more impactful long-term decisions that we make in everyday life. Overall, it is unclear to what extent memory-related systems impact a range of choices that humans make in everyday life from minor financial transactions to consequential life choices. Across three studies, I examine the role of the constructive memory process of imagination in decisions between shorter-term monetary rewards available at different temporal delays as well as longer-term consequential life choices like career decisions. Chapter 1 provides a general overview of past research on the role of constructive memory processes in making decisions. In chapter 2 (Study 1), after rehearsal of hypothetical imagined future events, younger adults and older adults made choices between larger-later and smaller-sooner monetary rewards. Some of the trials included a cue that invoked the imagined future event whereas other trials did not include a cue. Younger adults were more likely to choose larger, delayed monetary rewards on trials where the imagined future event was cued compared to trials without a cue. However, older adults did not show an effect of cued imagination. Across age groups, functional neuroimaging data revealed that trials with an imagination cue elicited greater engagement of regions that are part of the default mode network including the posterior cingulate cortex, angular gyrus, and medial prefrontal cortex. This network is commonly engaged during thinking about past memories as well as imagining the future in many studies that did not focus on decision making. Interestingly, this difference in neural activity did not vary across age groups even though the behavioral effect of the cue was limited to younger adults. In Chapter 3, I explore the effects of imagining previous successes and failures on choices between larger-later and smaller-sooner monetary rewards (Studies 2a & 2b). I find no conclusive evidence of differences in decisions based on whether people imagined successes or failures, even when comparing to a non-imagined, emotionally neutral control condition. Finally, in chapter 4, I extend this work into more complex career decision making. In a pilot study (Study 3), greater enjoyment of an imagined future career was associated with increased preference for that career option. Given the small and variable effects of imagining the future on decision making in Studies 1-3, two additional studies (Study 4a & 4b) evaluated the effects on decision making of an individual’s ability to vividly visualize, a different cognitive measure potentially relevant to thinking about and imagining the future. Using multivariate analyses, we found that vividness of visual imagery along with a set of individual difference measures related to future time perspective, self-efficacy, and well-being were associated with a set of variables crucial to career decision making. Together, these studies qualify our understanding of the role of imagination and visual imagery in decision making from choices between small rewards in the laboratory and consequential life choices. Overall various forms of imagination had relatively small and inconsistent effects on both laboratory-based and real-world decisions, whereas visual imagery had a moderate and consistent shared effect on real world decisions. The findings have broad implications for guiding prospective decisions in humans across the life span. For example, educational institutions currently have little to no focus on imagination and imagery in guiding developing students toward their future lives. There are critical opportunities in higher education to integrate imagination and imagery into living and learning communities to support students in their transitions to independent and rewarding careers.

Attention can take on many forms – it can be directed externally toward sensory information or internally toward self-generated information. It can be selective or sustained, and it can be goal-directed or spontaneous. A lot of research on attention-memory interactions has focused on selective, externally-directed attention, but we are constantly shifting between internally- and externally-directed attention and we can be distracted by both external and internal sources. There are also many instances in which we must maintain attention for long periods of time. To gain a more comprehensive understanding of the mechanisms by which attention and memory interact, more research is needed on the mnemonic consequences of the less investigated types of attention, such as internally-directed and sustained attention. In Chapters 2 and 3, I describe two electroencephalography (EEG) studies that investigated the neural mechanisms by which visual mental images that were generated during an internally-directed attention task are encoded into and retrieved from memory. Just as attention can be directed externally or internally, distraction can occur in various ways. For example, while listening to a lecture, our attention may be diverted toward the movement of the person seated next to us (an external distractor). Alternatively, attention can shift internally, towards random thoughts (an internal distractor). Both types of attention lapses will negatively affect encoding of the lecture, but may do so in different ways. In Chapter 4, I describe a simultaneous pupillometry-fMRI study that investigated the fluctuations of sustained attention with the presence of both external and internal distractors as well as the impact on subsequent memory. Finally, we must consider the role that cognitive control plays in modulating interactions between attention and memory. In Chapter 5, I describe a behavioral study that investigated the cognitive control processes triggered in response to an error and their impact on subsequent memory. Taken together, these 4 studies provide a more nuanced look at the mechanisms by which attention memory interact as we process information in different ways.