Bartlett and others have consistently pointed out that memory is constructive. Bartlett argued that memory is influenced by a person’s prior knowledge, beliefs, and expectations and that one uses these factors to fill in gaps in his or her memory to create a coherent story or narrative. For example, in one of his famous studies, Bartlett asked participants to read a Native American folk tale and then recall it from memory several times over a period of weeks or months. He found out that as time went on, the participants’ recall of the story became distorted; they adapted to fit pre-existing knowledge and cultural expectations. In particular, participants tended to omit or distort details that did not fit their existing cultural schema. Also, the famous experiment, “War of the Ghost” showed that memory is not just a factual recording of what has occurred, but that we make “effort after meaning”. Memory is shaped by an individual’s prior experience, current beliefs, and future expectations, and we draw upon these schemas to complete a narrative. Rather than a literal recall of the past, memory builds on these prior beliefs and experiences to reconstruct the experience. Tulving is another influential scholar who pointed to the constructed nature of episodic memory. According to Tulving, when we recall past events, we do not just retrieve stored information about the event, but rather actively fill in gaps with our own knowledge, expectations, and assumptions. Bartlett and Tulving’s work of the 1960s and 70s has been extremely influential, and many scholars studying memory have built on their framework to examine the various ways in which memory is constructed.
While the fact that our memory is constructive is widely accepted in the literature, many have debated the cause behind it. The Constructive Episodic Simulation Hypothesis is one such attempt at providing an answer. It is a hypothesis about the “origins” of episodic memory, an attempt to explain why memory is constructed as such. According to the hypothesis, our memory is structured in a constructive fashion to be utilized in the future. While many conceive of memory to be primarily a storage of the past, the hypothesis claims that memory plays a critical future-oriented function. As Schacter and Addis put it, “an important function of a constructive episodic memory is to allow individuals to simulate or imagine future episodes, happenings and scenarios”. Memory is essentially future-oriented, and this direction requires memory to be constructive.
What this means is that the brain flexibly extracts and recombines elements of previous experience for future simulation. This happens through the challenging two-step process of binding and separating noted above. As explained earlier, the brain coordinates multiple neural networks, combines specific elements to form a coherent episode, and keeps the units separate for use in future mental tasks. Since the future is not a literal replay of the past, flexibly using memories from previous experiences is necessary for future simulation. In other words, this whole process allows us to simulate, imagine, or ‘pre-experience’ events that have never occurred in the exact form in which we imagine them.
Scholars have described this constructive process through the concept of ‘gist.’ Gist, or semantic clustering, is a method used by the brain to effectively manage all memory fragments. In fact, memory is not scattered in a completely random fashion, but rather in the form of organized clusters that consist of similar blocks of ‘gist’ or meaning. The brain flexibly extracts elements from each ‘gist’ cluster and recombines them to simulate a future. To remember the episode, our brain needs to integrate fragments from different gist groups that each represent the people we interacted with, the place the party was held, the food we ate, and the emotions we experienced. On the other hand, to simulate or ‘pre-experience’ the next year’s birthday party, we use the same gist groups but different kernels from the group. Say the party was held in a swimming pool last year. Then, we can probably imagine our next year’s birthday party taking place in a public park or at home, somewhere other than the swimming pool visited the previous year.
The Constructive Episodic Simulation Hypothesis has been supported by a growing body of research, which has found that many of the same brain regions that are active during episodic memory retrieval are also active during future thinking and imagination. In other words, the same cognitive processes that are involved in remembering past events are also used to imagine and simulate future events.
This common region is often referred to as the Default Network. The particular brain region, default network, consists of the medial temporal lobe including the hippocampus, frontal lobe, posterior cingulate, retrosplenial cortex, and lateral parietal. Functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET) have observed overlap in the brain activity of default network regions when remembering past events and imagining future events. The default network is the very region that carries out the challenging two-step process of binding and separating.
