Episodic Fiction: The link between memory and imagination

Written By Anna Sitsapesan

Memory is one of our most precious cognitive functions. It connects us with the actions and events of our pasts, and allows us to learn language, build relationships and retain life experiences that contribute to a unique sense of self. It is also notoriously unreliable. We forget where we’ve left our house keys, misplace the names and faces of people we really ought to know by now and can even create false memories consisting of events that did not occur. 

Our long term memory is multifaceted, but the components that make up our conscious recollections can be divided into semantic and episodic. Semantic is the memory of facts: for example, the knowledge that the Great Fire of London happened in 1666. The episodic side deals with events in time and space - what you would remember if you had lived through the Great Fire of London: the colour and noise of the flames, the smell of smoke, the path you took to escape, and when in your life it occurred in relation to everything else.

Episodic memory and imagination are conceptually intertwined. To imagine vividly, one usually has to have a previous encounter of what they’ve been asked to picture. Eating a chocolate bar might be easy to imagine for someone who has done so before, harder for someone who has only seen a chocolate bar and quite difficult for someone who has never heard of chocolate. Even if the imagined situation isn’t a single existing memory, it has still drawn upon countless experiences to be produced.

The connection between the two extends beyond the theoretical and has been described by scientific studies. A brain region called the medial temporal lobe, and in particular the hippocampus, has long been associated with episodic memory. As seen most famously in the case of Patient H.M., who received a bilateral temporal lobectomy to treat severe epilepsy, the result of hippocampal lesions (or as with H.M., total removal) is an inability to make new semantic or episodic memories (anterograde amnesia), as well as deficits in recalling old episodic memories from prior to the injury (episodic retrograde amnesia).^(1,2) Interestingly, these patients also have difficulty when asked to think about their future. Given that it hasn’t been experienced yet, this must involve a degree of imagination, not simply memory. In fact, in later studies, hippocampal lesion patients have been shown to struggle with envisioning anything vividly, be it the future, a memory or a completely novel experience existing outside of a defined time frame.⁽³⁾

The theory of scene construction seems to explain this.⁽⁴⁾ It is easy to think of the brain as a video recorder and when you press play on a memory, neurons fire in the correct order, and the event unfolds in your mind. This is not actually what takes place. Information is not consolidated like a reel of film, but rather in a form called a “schema”. These are collections of neurons within the neocortex that represent related stimuli: for example, the words ‘painting’, ‘gallery’ and ‘art’ could be part of a schema connected to the Louvre. During recall, the hippocampus takes that information and builds it into a memory in the form of a scene.⁽⁴⁾ This is scene construction, where the richness of re-experience is produced. However, the process is vulnerable to disruption during construction, and so could explain our ability to input false characteristics into existing memories.⁽⁴⁾ What is striking is that when we imagine, nearly the same process occurs; the hippocampus uses schema to construct a scene and we are able to visualise completely fictitious happenings.

Scene construction leaves many questions to be answered, and two that seem particularly important:

If this method of remembering leaves us open to interference, why have we developed it? And, how do we differentiate between a past experience and an imagined one?

As to the first question, there are several likely answers, one of which relates to efficiency and flexibility.⁽⁵⁾ Storing reams of exact memories, most of which are not necessary for survival, would be, in essence, a waste of space. Instead we have quick access to large amounts of data that can be adapted to meet the situation. Another reason that this system is beneficial is the ability to imagine. A constructive process of memory allows for the compilation of information to form a novel imagined scene. In particular the use of imagination in conjunction with memory could be important for planning and decision making. Deciding between two familiar routes to the same location should utilise memory of both, as well as imagination about what it will be like to travel them in the immediate future. This would explain why the hippocampus is shown to be connected to the prefrontal cortex which is responsible for executive function, and also why the hippocampus is active during decision making tasks.⁽⁶⁾

This leaves us with the second puzzle; the task of differentiating between consolidated episodic memory and imagination. Could every childhood memory simply be a fabrication? Most of us consciously distinguish our memories from things we’ve dreamt up, and generally we do this accurately. This means there is a process in the brain separating the two into distinct categories.

One can hypothesise about the role of semantic memory in episodic scene construction. Semantic memory formation, like episodic, is disrupted by medial temporal lobe lesions, despite pre-existing semantic memories being retained.^(1,2) Semantic memory may, therefore, be reliant on episodic memory for formation. Knowledge that the sky is blue stems from seeing it countless times, or in other words, multiple episodic memories. If new episodic memories can be consolidated as schema that then become part of our semantic memory, is recall of old episodic memories simply the reverse? The semantic knowledge of an event in time reimagined, not remembered, in the hippocampus, which fills in the gaps to produce the rich detail and vividness we associate with visualising a memory. This would explain why memories feel true; they are built on what our brain has predetermined as factual, perhaps due to passing a “reality threshold” while being experienced for the first time.⁽⁷⁾ Semantic knowledge, such as a suspect who we are told wears glasses, could therefore lead to a fabricated episodic memory where a witness remembers seeing a person in glasses, even if they never did. In that case, do we need to reconsider the lines drawn between episodic and semantic memory, and between recall and imagination? 

Until now, research has treated imagination, semantic and episodic memory as separate entities. The majority of studies have been designed to fit within these boundaries. If it is the case that episodic memory is a product of combination rather than a distinct neural circuit, should it be studied in isolation? Perhaps we could learn more about its defining functions and underlying neural processes by delving further into those that contribute to imagination and semantic memory. 

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References:

1. Squire LR. The legacy of patient H.M. for neuroscience. Neuron. 2009 Jan 15;61(1):6-9. doi: 10.1016/j.neuron.2008.12.023. PMID: 19146808; PMCID: PMC2649674
2. William Beecher Scoville and Brenda Milner. Loss of Recent Memory After Bilateral Hippocampal Lesions The Journal of Neuropsychiatry and Clinical Neurosciences Volume 12, Number 1 https://doi.org/10.1176/jnp.12.1.103-a 
3. Demis Hassabis, Dharshan Kumaran, Eleanor A. Maguire 

Using Imagination to Understand the Neural Basis of Episodic Memory

Journal of Neuroscience 26 December 2007, 27 (52) 14365-14374; DOI: 10.1523/JNEUROSCI.4549-07.2007

4. Daniel N. Barry, Eleanor A. Maguire,

Remote Memory and the Hippocampus: A Constructive Critique, Trends in Cognitive Sciences, Volume 23, Issue 2, 2019, Pages 128-142,

ISSN 1364-6613,

https://doi.org/10.1016/j.tics.2018.11.005. 

(https://www.sciencedirect.com/science/article/pii/S136466131830264X) 

5. Webb CE, Dennis NA. Memory for the usual: the influence of schemas on memory for non-schematic information in younger and older adults. Cogn Neuropsychol. 2020 Feb-Mar;37(1-2):58-74. doi: 10.1080/02643294.2019.1674798. Epub 2019 Oct 4. PMID: 31583953; PMCID: PMC8919503.
6. Enkavi, A.Z., Weber, B., Zweyer, I. et al. Evidence for hippocampal dependence of value-based decisions. Sci Rep 7, 17738 (2017). https://doi.org/10.1038/s41598-017-18015-4
7. Nadine Dijkstra, Thomas von Rein, Peter Kok, Stephen M. Fleming, A neural basis for distinguishing imagination from reality, Neuron, Volume 113, Issue 15, 2025,

Pages 2536-2542.e4,

ISSN 0896-6273, https://doi.org/10.1016/j.neuron.2025.05.015. 

(https://www.sciencedirect.com/science/article/pii/S0896627325003629) accessed 20/11/25