Why We Remember: Revealing the Hidden Power of Memory

Where is My Mind?

• By one estimate, the average American is exposed to 34GB (or 11.8hr) of information a day
• Hermann Ebbinghaus “On Memory: A contribution to Experimental Psychology (1885) - tried to memorize trigrams, established the idea of a forgetting curve over time.
• In essence, neurons function like a democracy with alliances or “cell assemblies”.
• Somewhere is the brain’s speech centers a large coalition of neurons cases votes for “bath”, a smaller coalition votes for “path”, and an even smaller minority votes for other candidates. Within less than half a second, the vote is tallied, and ultimately the baby picks up that it is time for a bath. The connections between the neutaons that supported bath are strengthened, and connections with neurons that voted for the wrong sound are weakened. As those neurons settle into coalitions that differentiate between the sound the baby is hearing, they are becoming less sensitive to sound differences that don’t exist in that language. It’s as if the neurons are choosing between a small number of candidates based on a few key issues.
• The connections in your brain are constantly being reshaped with the goal of improving your perception, movement, and thinking as you gain more and more experiences. Moreover, as you go past simple perception (what we see, hear, touch, taste, and smell) and move into higher-order functions (eg judgement, evaluation, and problem-solving), the brain is remarkably plastic, and the neural elections are highly contested.
• Interference - there is an intense competition between the coalition that has the memory you’re looking for and coalitions representing other memories you don’t need at that moment.
• The memories that are the most distinctive are the easiest to remember because they stand out relative to everything else.
• Attention - is our brain’s way of prioritizing what we are seeing, hearing, and thinking about.
• Intention - guide’s your attention to lock on to something specific.
• The prefrontal cortex:
  • I the “central executive” of the brain. Several regions all over the brain have relatively specialized functions, and the job of the prefrontal cortex is to serve as a central executive, coordinating activity across these networks in the service of the mutual aim.
  • Helps us learn with attention
  • Takes up about a third of the real estate in the human brain
  • Frontal lobotomy - removal of the prefrontal cortex - but rather than treating any underlying mental illness, it leaves patients in a zombielike state, apathetic, docile, and devoid of motivation.
  • The more numbers people had to keep in mind, the more activity was apparent in the prefrontal cortex - it plays a part in temporarily holding information.
  • People without a functioning prefrontal cortex could do fine when they were given clear instructions and no distractions, but they struggled when they had to spontaneously use memory strategies or follow through on a task when irrelevant things competed for their attention.
  • Is intensively activated when a person had to use intention to stay on task, focus on distinctive information, resist distractions, or initiate some kind of mnemonic strategy.
  • ADHD is associated with atypical activity in the prefrontal cortex.
  • As we get older, we can still learn, but we have more trouble focusing on the details we want to take in and we often end up learning things that might be irrelevant.
  • Certain part of the prefrontal cortex are thinned out, on average, in people who do heavy media multitasking.
• Use intention to guide our attention so we can remember what matters. Balance the needs of the experiencing self and the remembering self.

Travelers of Time and Space

• We often think about memory as a record of what happened, but the human brain has the remarkable capability to link up the “what” with the where, when, and how. This explains why the experience of remembering is so often accompanied by an ephemeral sense of pastness that’s almost impossible to put into words. It’s also why, if we are in the right place at the right time, lost memories seem to find us.
• That sense of being in a particular time and place is called context, and it is critical for our day-to-day memory experiences. A great deal of everyday forgetting happens not because our memories have disappeared but because we can’t find our way back to them. In the right context, however, memories that have seemed long gone can suddenly resurface back to the forefront of our recall.
• Endel Tulving, in 1972, coined the term “episodic memory” to differentiate from “semantic memory”. To remember an event (episodic memory), we need to mentally return to a specific place and time; but to have knowledge (semantic memory), we need to be able to use what we previously learned across a range of contexts.
• For Tulving remembering puts us in a state of consciousness in which we feel as if we were transported to the past. A key characteristic of human consciousness is that we are “capable of mental time travel, roaming at will over what has happened as readily as over what might happen, independently of the physical laws that govern the universe.”
• You can confidently pull up facts about Paris (semantic memory) and vividly reexperience a trip to Paris (episodic memory), yet the two experiences are totally different.
• AIs have problems with “catastrophic forgetting”, where they learn a rule and then an exception to the rule makes them then throw away everything they had learnt around that rule to date. But we have episodic memory, which is not designed to capture the common elements of all our experiences; it stores and indexes every event differently, so you don’t get mixed up when you learn the exception to the rule.
• The neocortex works like a traditional neural network, enabling us to pick up facts, while the hippocampus is responsible for the brain’s amazing ability to rapidly create new memories for events.
• Brenda Milner, in 1957, published a paper about Patient H.M., Henry Molaison who had his seizures treated by removing about 5cm of tissue from the left and right hippocampus. Milner’s paper definitively linked the formation of new memories to the hippocampus.
• Ranganath suggested that the pattern of light and dark pixels identified by fMRI might be a unique configuration acting as a pointer to a particular memory like a QR code. When thinking about two separate episodic memories about the same person, the neocortex seemed to store the general facts about who and what were in the event, while in the hippocampus, the memory codes for the two related events looked totally different.
• The cell assemblies that allow us to remember particular parts of an event are in separate areas of the brain that normally do not talk to one another. The only thing they have in common is that they were active around the same time. The hippocampus, however, has connections to many of these areas, and its job is to store links to the different cell assemblies that come to life at a given moment. If you revisit the place, then the hippocampus would help reactivate all those cell assemblies, enabling you to reexperience seeing your friend. The hippocampus enables us to “index” memories for different events according to when and where they happened, not according to what happened. Because it organizes memories according to the context, recalling something from one event makes it easier to retrieve other events that happened around the same time or place, painting a fuller picture.
• Pulling up a memory of the recent past helps to ground you in the here and now. According to one prominent theory, episodic memory emerged in evolution from the more basic ability to learn where we are in the world.
• Sea lions without a functioning hippocampus grow disoriented. Lost, and unable to recall their foraging sites, they become malnourished and ultimately stranded onshore.
• The hippocampus is one of the first areas of the brain ravaged by Alzheimer’s, and this is probably why patients in the early stages frequently get lost and lost track of the passage of time. You see the look of fear on a face when a patient becomes unmoored from their sense of when and where they are in the world, like treading water in the open ocean.
• All the external factors from our environment, along with the motivations, thoughts, and feelings that characterize our internal world, come together to form the unique context that envelops our experience at any given time. When we access a particular episodic memory, we can pull up a bit of that past mental state, too.
• Two events that occurred close together in time are going to have more contextual elements in common than events that occurred further apart in time.
• Place, smells, tastes, and music are all powerful cues for episodic memories.
• Our emotions also contribute to context, which means that our feelings in the present affect what we can recall from the past. When we get angry, it’s easy to pull up all those memories that give us more reasons to be annoyed, and it’s harder to access the memories that don’t.
• The essential trick performed by the hippocampus is that it takes in information about the things in which we are interested, and it ties it up with information about the context, all the other stuff that’s going on in the background. We experience zillions of repetitive events, but the context makes each unique, and we can use context as a lifeline to find our way back to those things we seem to always lose.
• The further back in time you try to go, the harder it is for your brain to pull up a past context, and in some cases you won’t be able to do it. Science backs infantile amnesia where you can’t have episode memories before the age of two because the hippocampus is still developing and the entire neocortex is being massively reorganized.
• Event boundaries. We naturally update our sense of context when we experience a shift in our perception of the world around us, and those points mark the boundary between one event and another. People are better at remembering information that occurred at an event boundary then they are at remembering information from the middle of the event, and this is because the hippocampus waits to store a memory for an event until right after an event boundary - so we only encode the memory once we have a full understanding of the event.
  • Event boundaries happen all the time and don’t necessarily require a change in location. Anything that alters your sense of the current context - a shift in the topic of conversation, a change in your immediate goals, or the onset of something surprising - can lead you to put up an event boundary.
• During the Covid epidemic, confined to home and with few event boundaries to provide meaningful structure to their lives, millions of people all over the world felt as if they were living in the twilight zone, floating aimlessly through time and space.
• Nostalgia - on average, people find it easier to recall positive experiences than negative ones, and this positivity bias increases as we get older, which might explain older adults’ penchant for nostalgia.
  • The reminiscence bump - when we look back at the past, we tend to focus on a specific period of our lives, between the ages of ten and thirty - something about listing to a song or watching a movie from those formative years can give us a sense of meaning, connecting us to an idealized sense of who we are.
  • The cost of nostalgia is that it can leave us feeling disconnected from our lives in the present, giving us a sense that things aren’t as they were in the “good old days”.
• Rumination - is the evil twin of nostalgia, and a prime example of how not to use episodic memory.