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Understanding the Nature of Memory
The concept of memory has enthralled many a poet, musician, and soap opera writers alike. Our research explores the nature of memory—what memories consist of, how they are made, where they are stored, and how they are retrieved. Further, by investigating memory impairments in cases of amnesia, as well as in other disorders, we glean insight into the composition and organization of memory that would otherwise occur in a neurologically healthy brain. Our research has shown that one type of memory—relational memory—may be conceived as a series of linkages across time, across space, and/or across distinct items. Together, these relations are the building blocks of our memories for events in our lives, and form the basis of our knowledge. Relational memories are flexible: new links can be added, others may fade away. The links may be accessible under different scenarios from which they had originally been learned, and they may even be used without any conscious awareness for them. We have shown how this type of memory is dependent on the hippocampus and related structures within the medial temporal lobe of the brain. We continue to investigate how the features of relational memory may either be independent or interact with one another: for instance, do we need to remember time in order to remember space? If we remember a spatial relation, does that automatically give rise to the relations in memory surrounding time? By understanding the nuances in how memories are built, and how they may be expressed, our research reveals the myriad ways in which memory permeates our every thought and action.

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The Reciprocal Relationship between Seeing and Remembering

It is fairly intuitive that we remember what we have seen. Less obvious is the idea that how we explore the visual world with our eyes can reveal specifics about what we remember, and can even determine if we recall a memory correctly in the first place. Using eyetracking, neuroimaging, and computational modelling methods, our research explores the intersection between active vision and memory. We have shown that there are numerous polysynaptic structural connections between regions of the oculomotor system that guide viewing and the regions of the medial temporal lobe, including the hippocampus, that are important for memory. The oculomotor and memory systems can communicate with one another quite rapidly, allowing visual information to quickly become part of memory, and allowing memory to influence where the eyes look, in a cyclical and ongoing fashion. Scanpaths—the particular sequences of eye movements—are embedded into our memories, and they can be subsequently reinstated to help retrieve memories. The manner by which we explore the world changes both with age and with disorders that affect the medial temporal lobe, such as mild cognitive impairment, Alzheimer’s disease, and amnesia. Our research continues to explore how these changes to viewing behaviour create changes in the fidelity of memories. Moreover, we are investigating how compromise to the medial temporal lobe may result in an inability to leverage eye movement patterns to accurately recall memories. Thus, whether the eyes are a window into the soul may remain a philosophical debate; our research shows that the eyes are, at the very least, a window into memory.

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Detecting and Remediating Memory Impairments

Many adults experience difficulties with memory as they age. Specifically, older adults often have difficulties with relational memory—the ability to bind, or form arbitrary relations among items. For example, remembering where you left your keys, or remembering the name of the person you just met, are each examples of relational memory. These memory impairments mimic those that are seen in amnesic cases, who have damage to regions of the medial temporal lobe in the brain, suggesting that aging is associated with a gradual decline in these regions. Our research uses a multi-modal approach (i.e., examining cognition and behavior in conjunction with assessing neural structure and function) to detect these impairments in memory as early as possible, with the goal of creating screening tools that will help older adults understand their brain health. Our work is also focused on developing cognitive strategies that may allow older adults, and even some amnesic cases, to either remediate, or circumvent, their memory impairments. We have shown that appealing to prior knowledge can help form new relational memories, and that such a strategy is most effective for older adults prior to the onset of mild cognitive impairment, or Alzheimer’s disease. Similarly, we have developed a strategy—unitization—that allows relations to be recast as a single unit in memory, thereby circumventing damaged brain systems. Unitization is the only long-lasting strategy that has been shown to support memory in older adults as well as in some cases of amnesia. Our research continues to investigate who may benefit from these cognitive strategies based on their current cognitive and brain profiles, and to develop these strategies for use in everyday situations.