Remembering the Past

A big focus of our research at the Memory Lab is to discover how we are able to remember the past in rich detail. The hippocampus is crucial to this process: more vividly detailed memories are associated with higher levels of hippocampal activity and hippocampal damage results in reduced episodic detail.

The hippocampus doesn't work in isolation, and is part of a whole-brain network supporting AM retrieval. We've have found that distinct parts of this network are associated with different types of memory (e.g., specific vs. general AMs) and different "routes" to memory (e.g., (e.g., generative vs. direct retrieval). Currently, we are exploring the contributions of other parts of this network to AM retrieval, such as the cerebellum.
In left temporal lobe epilepsy, connections by-pass of the damaged hippocampus during AM retrieval (Addis et al., 2007, Brain)

In left temporal lobe epilepsy, connections by-pass of the damaged hippocampus during AM retrieval (Addis et al., 2007, Brain)

Activation when remembering past events and imagining future events (Addis et al 2007, Neuropsychologia)

Activation when remembering past events and imagining future events (Addis et al 2007, Neuropsychologia)

Imagining the Future

In 2007, we reported that imagining the future engaged the same neural network as remembering the past. This finding was one of three studies on imagination published that year that propelled future events into the field of memory research. Since then, we have found that behavioural and neural changes in past events are also evident for imagined events in healthy older adults; we have also reported similar parallel changes in Alzheimer's disease.

More recently we have found that in depression, imagining the future appears to be more affected than remembering the past. This finding, along with increased hippocampal activity, suggest that future simulation is a more intensive process than remembering - perhaps reflecting the fact that future events are novel constructions that require encoding. More recently, we have begun to explore other factors that contribute to imagination, including the familiarity of details from episodic memory and creativity, as well as the ways in which imagination can affect memory accuracy.

Memory and Identity

Using methods from neuropsychology and social psychology, we have examined the impact of AM loss on identity in Alzheimer's disease. This study revealed that loss of early memories (late childhood/early adulthood) had the most significant effects on the strength and quality of identity, even when controlling for general cognitive decline. These results prompted us to consider how episodic and semantic aspects of AM contribute to the content and continuity of identity, and we proposed a distinction between narrative and phenomenological forms of self-continuity. More recently, we have developed a novel framework that maps two dimensions of self (subjective/objective and present/temporally-extended) onto semantic and episodic aspects to AM.
Novel framework mapping aspects of the self to aspects of AM (proposed by Prebble et al., 2013, Psychological Bulletin)

Novel framework mapping aspects of the self to aspects of AM (proposed by Prebble et al., 2013, Psychological Bulletin)

Modulation of inferior frontal activity in response to encoding demands is significantly reduced in older adults
(Addis et al., 2014, NeuroImage)

Modulation of inferior frontal activity in response to encoding demands is significantly reduced in older adults

(Addis et al., 2014, NeuroImage)

Neurocognitive Aging

A strand that is woven through all of our research topics is how the brain and cognition changes in healthy aging and age-related brain disorders. As described above, we have explored changes in future simulation in healthy aging, Alzheimer's disease and semantic dementia. With respect to memory, we have examined age-related changes in brain activity when encoding verbal information, emotional images and emotional scenes.

We have also found ways in which memory reductions can be mitigated. With collaborators at Macquarie University, we found that older adults retrieve more episodic detail about their past experiences when they remember with their spouse as compared to when they remember alone.

In a current work on aging, we are examining whether differences in brain variability underpin changes in cognition. We are also using fMRI to understand why the ability to recognize some emotions (e.g., fear) is reduced in older age while other emotions (e.g., disgust) is relatively preserved.