Linking the Past to the Future Through Memory
Our past, present, and future are intimately linked by our memories. Scientists know now that the same brain processes we use to remember the past, also help us plan for the future and imagine different possible scenarios. Recent research even suggests that in depressed people, impaired memory not only makes it difficult for remember past events but also to imagine different outcomes – making their situation feel even more dire.
Donna Rose Addis of The University of Auckland will discuss that work – and the larger body of work linking memories of our past to how we see our future – at the upcoming CNS conference in San Francisco. A recipient of this year's Young Investigator Award, Addis gave CNS a preview of her talk, including the factors that shape how we view our past and futures, such as new work that highlights the role of individual differences in creativity.
Memory is not just for remembering. It is becoming increasingly apparent that memory has an important role to play in other functions that directly impact our psychological well-being.
CNS: Please explain the link between episodic memory and future planning.
Addis: Recent research has shown that episodic memory – our memory for past personal experiences – does more than simply allow us to remember our pasts. It also appears to be intimately linked to our ability to imagine our futures. So, for instance, although I have never given a talk at the CNS conference, I can create a vivid imagination of what this experience might be like, drawing on my previous experiences of giving talks, my memories of being at this conference venue in previous years, and recalling the people I often see at this conference, and so forth. Thus, it seems that our episodic memory provides for us the "fodder", the details of people we know and places we have been, that we can use to construct a novel scenario in our imagination.
Two lines of research provide strong evidence that this is indeed the case. First, when imagining future events, the brain network that is active is strikingly similar to the network that is activated by remembering our past. This similarity suggests that when imagining, we draw on many of the same processes required when we remember (such as, for instance, mental imagery) as well as recalling details from memory to aid in the imagination process.
Second, studies on individuals with some degree of memory loss (from healthy older adults to people with Alzheimer's disease and amnesia) have revealed that when access to episodic memory details is compromised, there is a corresponding loss of details in the future events they imagine. However, other patient studies have shown that having access to memory details is not enough – we have to be able to combine these in a meaningful way that results in a coherent future scenario.
CNS: How did you become interested in studying human memory?
Addis: Many of my colleagues have said they study memory because they've never had a good memory. My experience is completely the opposite – I have always had a really good memory especially for episodic detail. When writing exams I could see my pages of handwritten notes in my mind's eye, and when recounting past events, vivid multi-sensory detail comes back. The way our minds can allow us to re-experience moments from the past – mental time travel – is an amazing ability.
And as an undergraduate majoring in History and Psychology, I was naturally fascinated by the stories of everyday people, their lives and their memories, and how our memories make us who we are. So for my first ever research project (for my master's degree) was an intersection of all these interests: I examined how autobiographical memory loss in Alzheimer's disease affects one's sense of self. In the 15 years since, I have had the pleasure of being able to contribute to our understanding about how memory works, and the privilege, from the memories generously shared by my participants, to learn much about what it was like to grow up in an earlier time and experience different historical events.
CNS: What have you been most surprised to learn about human memory?
Addis: One of the most surprising discoveries to emerge during my short time in the field is the increasing understanding that the hippocampus – the brain structure quintessentially associated with memory for over 50 years – does more than just memory. It is now clear that, beyond memory, the hippocampus also plays a role in perceiving our visual worlds, processing language, holding information in mind, navigating around environments, creativity, and as my research has shown, imagining the future. One of the essential functions of the hippocampus may be the ability to integrate or "bind" different elements. So when we need to integrate information together – whether different features of a perceived object, disparate elements into a creative idea, two landmarks across town, or episodic memory details into an imagined scenario – the hippocampus makes an important contribution to making these links.
CNS: How do you test episodic memory and future simulation abilities in the lab?
Addis: Because I am interested in autobiographical memory and imagination, I have aimed to keep my studies as naturalistic as possible while still retaining sufficient experimental control. Many of my studies have incorporated two important design elements: (1) using personally-tailored stimuli (based on a participant's own memories) to elicit memories and simulations; and (2) collecting ratings about the participant's subjective inner experience.
A typical experiment involves two sessions. In the first session, participants recall episodic memories from their past, identifying a person, place and object featuring in each memory. Often we need over 100 memories for a given experiment, so this session can take up to 4 hours! Approximately a week later, they come back to the lab or to the MRI scanner. During this session, we present participants with cues to trigger the retrieval of memories or the imagination of future events. After remembering or imagining as much detail as possible, participants make a series of ratings regarding their subjective experience.
In fMRI studies, this design enables us to compare and contrast brain activity during memory retrieval and future simulation and how this changes according to subjective experience. In behavioral studies, participants describe their memories and imaginings aloud; we then score in very fine detail the different kinds of content comprising their descriptions.
These basic methods have enabled me to investigate many fascinating questions, including: Do the subjective qualities of memories and imaginations influence hippocampal activity? What is the specific role of the hippocampus in future simulation? Do all kinds of future simulation result in similar patterns of brain activity? What makes some simulations memorable and other forgettable? How do particular disorders or damage affect the content of memories and simulations? And what changes to brain activity and connectivity are evident in individuals with impaired memory and imagination?
CNS: What are you most excited to share about your work at the CNS meeting?
Addis: I am most excited to be presenting some of our latest findings at CNS. This includes some recent work exploring changes in the ability to imagine the future in depression.
While it is well established that depressed individuals have difficulty remembering episodic memories, there is comparatively little research exploring impairments in future simulation. Our results show that while both memory and imagination are impaired, the ability to simulate future events appears to be particularly affected – which may contribute to sense of hopelessness that is so characteristic of depression. Moreover, while research on episodic memory impairments in depression has focused primarily on psychological factors (such as avoidance and rumination), our fMRI results indicate that brain changes also play a role. Specifically, we found that the activation of the hippocampus during memory and imagination was significantly reduced in depression, and its connectivity with other brain regions was altered. These observations dovetail with other findings that repeated episodes of depression can damage the hippocampus.
CNS: What factors are most important in shaping our episodic memory and then, in turn, our future simulations?
Addis: Factors that can influence the vividness and accessibility of autobiographical episodic memories include the memory's emotional tone and personal significance, how remote the event is from the present, whether the memory is experienced from a first or third person perspective, and how often the memory is rehearsed. Moreover, episodic memory is a constructive process; although memories may seem like verbatim recordings of the past, they are actually reconstructed from constituent details every time we retrieve them. Although the constructive nature of episodic memory does make it vulnerable to distortions, such as incorporating an incorrect detail into a memory, we have argued that the advantage of this constructive system is that episodic details are easily extracted for use in future simulations.
Similar to memory, factors such as temporal distance, emotionality and perspective also influence the future simulations. For instance, distant future events tend to lack rich episodic detail and be more abstract and general in nature. Moreover, the familiarity of the episodic details comprising an imagined event can influence the vividness of a future simulation and, as we have found, whether that simulation will be encoded into memory.
We have also found that individual differences in creativity are associated with the vividness of future simulations. Interestingly, however, we found that this association was unique to future events; creativity was not associated with the vividness of memories or other forms of simulation (e.g., imagining past events).
CNS: What do you most want people to understand about your work?
Addis: Memory is not just for remembering. It is becoming increasingly apparent that memory has an important role to play in other functions that directly impact our psychological well-being. Memory contributes to our ability to imagine future events, which in turn aids our future planning abilities; by allowing us to mentally try out different strategies and work through potential outcomes, simulation can increase coping and decrease worry about upcoming events.
Moreover, memory is critical for our sense of who we are – in the past, present and the future. Memory does not only hold important knowledge about our lives and our personal attributes and traits; through mental time travel, episodic memory can also directly transport us into past, to the person that lived through our previous experiences, and into the future, to the person we are yet to become.
-Lisa M.P. Munoz
Addis will give her award lecture on Sunday, March 29, 2015, 1:30 –2:30 pm, in the Grand Ballroom A in the Hyatt Regency San Francisco.
By lmunoz Filed Under: Uncategorized
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