Ranganath, who is the Director of the Memory and Plasticity Programme, Department of Psychology and Neuroscience at the University of California at Davis, and Director of the university’s Dynamic Memory Lab, a world-leading research laboratory, writes in his new book, Why We Remember: The Science of Memory and How it Shapes Us (Faber), how memory shapes our lives and identities, influences our choices and can even be used to navigate our futures. He speaks of memory updating—the strengthening, weakening or modifying of memories—as being at the heart of psychotherapy, which is fundamentally about changing connections we made in the past in the face of new information. “If we can harness remembering to reframe the way we look at the past, we can update our painful memories so that we experience them in a more tolerable way, possibly leading us to growth.”

Charan Ranganath

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There can be risks when we dig for memories, he points out, although these are significantly different from the reframing of emotional memories that give rise to negative feelings, like anxiety and stress. “Because it can be challenging to differentiate between memory and imagination, people can sometimes reconstruct events inaccurately, and when the event is recalled over and over again, that memory could get corrupted. For example, there are a number of cases when police officers repeatedly asked a witness to remember what they saw, and when the officers provided their own information about the suspect, this information became incorporated into the witness’s memory. We see similar outcomes in situations where a psychotherapist is actively pushing a patient to look for traumatic memories that they are not currently reporting. If the therapist encourages the patient to imagine things that could have happened, they can eventually generate memories for abuse experiences that are distorted or even false.”

Ranganath, who has been recognised with numerous awards, including a Guggenheim Fellowship and the Leverhulme Professorship at the University of Cambridge, has spent over 25 years studying the intricate mechanisms of memory. “I’ve managed to stay interested in this subject after all these years because just when I become complacent about ‘figuring it out’, I am faced with findings that challenge my core assumptions. If you’re doing science right, you should be wrong occasionally, and those are opportunities for ‘aha’ moments. For instance, I used to think of the brain as a collection of specialised areas, but then, I ran across studies that got me to think about how networks of brain areas might interact with one another. Over the course of my career, I’ve found that progress usually comes not in the form of answers, but rather in the form of better questions,” he shares.

Ranganath writes about several scientific breakthroughs in his book, from experiments that suggested a parallel between imagination and memory to Estonian-born psychology professor Endel Tulving’s differentiation of episodic memory (allows us to recall events from the past) from semantic memory (enables us to recall facts or knowledge about the world, regardless of when and where that information was learned). But the one that he considers among the most significant was the ability to read out patterns of brain activity to identify how different brain areas store memories. “When you look at functional MRI experiments, you can see that in any brain area, there are subtle differences in the pattern of activity when people are recalling different kinds of information. I used to think this was just random error or ‘noise.’ But after talking with other researchers, I began to ask whether the patterns of activity might be more like a QR code, providing an index to the content of a memory. For instance, I might have one pattern of brain activity when recalling something involving my brother Ravi, and a different one when recalling something about my dog Blondie.” 

He also writes compellingly about how research into the Default Mode Network (DMN), a set of neocortical areas which are turned on by default whenever we disengage from the outside world, has potential importance for our understanding of Alzheimer’s and other neurodegenerative diseases. The protein amyloid accumulates in the DMN in about 20 per cent of older adults long before symptoms show up and the only way to develop useful treatments for Alzheimer’s are to administer drugs to people who are at risk at this preclinical stage.

While pointing out that he is not an expert on Alzheimer’s pathology per se, Ranganath notes the widespread recognition of the fact that neurodegenerative disease can start years before symptoms are obviously apparent, and as many as one in five people over the age of 70 might meet criteria for preclinical Alzheimer’s Disease (AD). “Fortunately, not everyone in the preclinical stage converts to full-blown AD, but the risk is much higher. In the book, I point out that if you wait to administer treatment for AD until someone is in its early stages, the battle is already lost. Because the brain pathology is so significant by that point that you can’t retrieve the neurons you’ve lost.”