Memories are made of this
Dr Muireann Irish’s research explores episodic and autobiographical memory in frontotemporal dementia. She has developed a new line of research investigating how damage to the memory system in neurodegenerative conditions affects the ability to imagine possible future events.
Much in the same way as the quality of a photograph begins to fade with time, such is the fate of the memories from our past. While some experiences remain remarkably durable and fresh in our minds, many of our memories begin to lose their vibrancy, emotional quality, and vividness. When we recall these older memories, they no longer capture the original thoughts, feelings, and details of the original experience.
How damage to the brain in dementia affects the ability to remember
The brain regions that allow us to relive events from the past remain a source of debate in the scientific literature. Most studies have used functional neuroimaging studies in healthy young individuals to try to uncover the brain structures that are essential to remember the past, however, we work from the other end of spectrum to understand how damage to the brain in dementia affects the ability to remember.
In a study recently published in the journal PLoS One, my colleagues and I tested the ability of people with Alzheimer’s disease and frontotemporal dementia to recall personal events that occurred recently (within the last year) versus much further back into the past (up to 40 years ago). We specifically wanted to explore the brain regions that are important for recent versus older memory retrieval to understand how brain lays down, or consolidates, memories.
We used a structured interview technique in which participants were asked to describe significant events from their recent and distant past. To ensure that participants recalled as much detail as possible, we provided targeted questions regarding the event, time, place, sensory, and emotional details of the event. We then conducted neuroimaging analyses of brain scans to investigate which regions of the brain support the ability to remember recent versus older memories.
Older memories were associated with the temporal cortices, regions that are specialised for the processing of general knowledge. This finding suggests that with the passage of time older memories become more fact-like and lose many of their original sensory and perceptual qualities.
In contrast, recent memories were associated with a structure deep in the midline of the brain (the posterior cingulate cortex), which supports self-referential processing, and the generation of visual imagery. This finding suggests that recent memories differ from remote memories in terms of their visual quality and feelings of self-relevance.
One region that was implicated across all time periods, however, was the hippocampus, a structure that has long been known to be important for memory. Our findings reveal that the hippocampus is essential for retrieving any type of memory, irrespective of whether the event has been recently experienced, or must be dug out from much further back in the past.
Why is memory for the past so important?
Memory represents an incredibly complex process, and one that we tend to take for granted. It is only when someone close to us begins to experience memory loss that we can truly appreciate the importance of this function. Without our memories, we lose our sense of self and identity. Even more distressing, is the fact that reminiscing allows us to connect socially with others, by sharing experiences and reliving past times. Finally, the ability to remember our past, allows us to envisage the future, a process that is essential for a positive outlook and a sense of emotional wellbeing.
For people with dementia, as memories begin to fade, it becomes increasingly important to find meaningful ways to connect with these individuals. Encouraging the reminiscence of memories that remain intact, is one way to foster a sense of worth in the dementia sufferer and to encourage social interaction. A number of studies incorporating music and art therapy have proved promising in enhancing the recollection of past events in dementia individuals.
Memory represents the treasure chest containing all of our precious experiences from the past. It is important therefore, not only to appreciate the complexity of memory, but also what it must be like to lose the trophies from our past, and ultimately a fundamental part of the self.