Action...Cut! Sitting in the Director's Chair of Our Brain
Our brains “edit” the raw live feed of our daily lives into meaningful memories.
Posted Nov 08, 2018
Think for a moment about what you did yesterday. Or last Saturday. Or Christmas Day two years ago. On any one of those days, you did or experienced literally millions of assorted things—lifted your hand toward a light switch, heard an acorn fall onto the sidewalk, took a sip from your coffee cup, and yet, as you recall the day, you don’t remember it as an undifferentiated flood of isolated actions and sensory stimuli, but rather as events or scenes composed of such fragmentary bits of information. The memory of lifting your hand to the light switch was part of a scene that might be titled “Walking in the front door after a hard day of work.” The sound of an acorn hitting the driveway was a brief moment from a scene called “Raking the leaves for the first time this fall.” Taking a sip from your coffee cup belongs to a happy scene that you might call “Christmas morning: relaxing while the kids play with their toys.”
While the recollection of such scenes from our autobiographical past appears perfectly natural to us, a little reflection on the way we actually experience our lives on a moment-to-moment basis should give us pause to wonder why we remember it in such an orderly way and not as an unbroken stream of assorted actions and sensations, which is how “reality” actually comes at us. It is almost as if there is a movie director in our brain yelling “action” and “cut” at opportune moments in order to divide that unbroken memory stream into units that we later remember as autobiographical experiences, or “scenes,” to continue the movie analogy. A recent study at the University of Cambridge suggests that this analogy is actually a pretty accurate description of how our brain forms episodic memories (i.e. memories of the events, or “episodes” from our lives).
Cognitive neuroscientists examined the data from two brain-imaging studies in which people watched movies (Forrest Gump and Alfred Hitchcock’s Bang! You’re Dead) while undergoing a functional MRI. Prior to the fMRI study, a group of independent observers had watched the two films and identified what they perceived to be boundaries between scenes by pressing a button to indicate the point at which “one event (meaningful unit) ended and another began.” The researchers aligned the subjectively reported scene boundaries with the fMRI data to look for correlations between the placement of those boundaries and changes in brain activity in the participants viewing the films while in the scanner. Paying particular attention to activity in the hippocampus, a part of the brain which plays an integral role in memory formation and retrieval, the researchers found that the “correspondence between the hippocampal events and event boundaries was highly significant.” Among both groups of participants, the event boundaries identified by independent observers reliably predicted an increase in hippocampal activity, suggesting that the hippocampus played a key role in breaking the movies down into discrete, meaningful scenes.
Recognizing the sensitivity of the hippocampus to time and space, the researchers added predictors to account for temporal and spatial changes across event boundaries, and the correlation between hippocampal activity and event boundaries was still significant. Many event boundaries were identified in scenes involving no changes in space or time, such as the scene early in Forrest Gump where Forrest sits silently on the park bench. Even though time and location remain constant throughout the scene, the moment at which Forrest first speaks was identified as an event boundary, indicating a more subtle delineation of scenes than could be accounted for by simple changes in time and space.
The correspondence of hippocampal activity to the subjective perception of where movie scenes begin and end suggests that our brain divides the stream of images and sounds that make up a movie into meaningful units that allow us to make sense of the movie as a whole. And while a movie is, admittedly, not real life, the experience of watching a movie—especially for the first time, is not unlike the flood of sensory information that comprises our moment-to-moment experience of real life. The Cambridge study suggests the possibility that the hippocampus plays a similar editorial role in the way we perceive and—just as importantly--remember our experiences. In the same way that a movie director’s editorial vision makes the difference between a meaningful movie and two hours of raw security camera footage, the boundary-setting function of our hippocampus allows us to remember our past as a lifetime of meaningful events rather than an unbroken chain of fleeting sensory impressions. Sitting in the metaphorical director’s chair of the brain, our hippocampus transforms the minutes that we live through into the moments we remember.
Ben-Yakov, Aya, and R. Henson. The hippocampal film-editor: sensitivity and specificity to event boundaries in continuous experience. Journal of Neuroscience. Published online October 8, 2018. doi:10.1523/JNEUROSCI.0524-18.2018.
Parimoo, Shireen. “The Hippocampus Represents Event Boundaries During Film-Viewing.” BrainPost, 16 Oct. 2018, www.brainpost.co/weekly-brainpost/2018/10/16/the-hippocampus-represents-event-boundaries-during-film-viewing.
Sanders, Laura. “How Your Brain Is like a Film Editor.” Science News, 1 Nov. 2018, www.sciencenews.org/article/how-your-brain-film-editor.