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Why We Remember: Revealing the Hidden Power of Memory

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Where is My Mind? - The Neocortex

  • 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 - The Hippocampus

  • 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.

Reduce, Reuse, Recycle - Schemas and the Default Mode Network (DMN)

  • We can keep up to only 3-4 pieces of information in mind at once, but there is a huge loophole: there is no set definition for what constitutes one piece of information. Chunking allows us to compress massive amounts of data into a manageable amount of information that is easily accessible.
  • Like memory athletes, chess grand masters use a combination of skill, training, and experience - aka expertise - to chunk at lightning speed. Expertise changes the way we mobilize the prefrontal cortex. Experts develop particular ways to extract the most useful information about what they are trying to remember, allowing them to bypass the limitations of memory by leveraging their expertise.
  • Expertise isn't just about seeing patterns, it's about the way we find them. As we gain expertise in any topic, we can exploit what we have learned to focus on the most important bits of new information that we need.
  • The human brain is not a memorization machine; it's a thinking machine.
  • A schema is a kind of mental framework that allows our minds to process, organize, and interpret a great deal of information with minimal effort. A schema is like a blueprint for a space or an event. Event schemas provide the structure that allows us to rapidly form memories for a complex event. They are like scripts for ordering coffee, meeting a colleague, going to the cinema, etc.
  • In some way or another, every expert exploits the power of schemas to organize what they need to remember into a framework they can access later.
  • The Default Mode Network (DMN) is a set of neocortical areas that consume the most energy in the brain, yet activity in these areas seems to go down when people are focusing their attention on some arbitrary task. Brain activity in the hippocampus is tightly linked with what is going on in the DMN. It seems that cell assemblies in the DMN store the schemas we use to understand the world, dissecting the events we experience into pieces so that we can use them in new ways to construct new memories. The hippocampus could, in turn, put the pieces together to store a specific episodic memory.
  • In an experiment about watching and recounting the plots of movies:
    • The DMN was providing the raw materials needed to understand and remember each movie, but it was not storing context-specific episodic memories. Instead of storing a unique memory code for each movie, the DMN was breaking up each movie into components that were repeatedly reused to understand or remember other movies that shared the same components. Memory codes in one part of the DMN could tell us whether the subject was watching or remembering a movie that took place in a supermarket or a café, whereas memory codes in a different part of the DMN could tell us whether A or B was the star in the movie.
    • In contrast to the DMN, the hippocampus, which supports episodic memory by putting together information from all over the brain - did have a separate memory code for each movie. And unlike the DMN, the hippocampus only seemed to store a memory for the beginning and end of each movie (ie, the event boundaries).
    • Thanks to the DMN, I can reuse my supermarket schema every time I shop for groceries, and I can reuse my A schema every time I see A. And thanks to the hippocampus, I can also form different memories for every specific occasion that I run into A at the supermarket.
  • Forming an episodic memory is a bit like building with LEGOs, breaking down models and using the independent components again and again in different contexts.
  • It's now clear that amyloid - a protein implicated in the development of Alzheimer's disease - accumulates in the DMN in about 20% of older adults long before any symptoms are apparent.
  • A chess grand master has a library of chess game schemas, each containing templates for entire sequences of moves you typically see in a game. Those schemas allow them to remember sequences of moves in past games, to understand what is happening in a game in real time, and to predict likely moves that an opponent could make in the future. By exploiting that expert knowledge, a seemingly complex configuration of pieces can easily be understood as one step in a series of moves that might wipe out a number of pieces and lead to a checkmate.
  • Schemas allow us to see through an event, capturing the deeper structures of how everything is connected. In doing so, we can compress memories of hundreds, even thousands, of experiences into a format that enables us to make inferences and predictions about events we haven't yet experienced. Schemas allow us to use knowledge about what has happened to get a head start on what will happen.

Just My Imagination

  • Shereshevsky - the capacity of his memory had no distinct limits.
  • He may have had synesthesia - every stimulus, regardless of which sense it came through, triggered every other sense. He could taste words, see music and smell colors.
  • The connection between the worlds he created in his mind and the world he lived in was so visceral that he could elevate his hear rate by simply imagining he was running for a train. He could raise the temperature of one hand and lower the other by picturing one hand on a stove and the other resting on a block of ice.
  • The brain activity changes that occur when people imagine these kinds of scenarios are remarkably similar to those that occur when people recall events that they actually experienced.
  • "Remembering is not the re-excitation of innumerable fixed, lifeless and fragmentary traces. It is an imaginative reconstruction." We do not simply replay a past event, but use a small amount of context and retrieved information as a starting point to imagine how the past could have been. We put together a story on the fly, based on our personal and cultural experiences, and tack on those retrieved details to flesh out the story. Bartlett's insight is key to understanding why the brain's machinery for imagination and for memory aren't completely independent - they are both based on pulling up knowledge about what can happen, though not necessarily what did happen.
  • The hippocampus might get us back to some of the cell assemblies that were active during some moments in a conversation, but we still need to use schemas in the default network to make sense of what we are pulling up. this reconstruction is prone to error, however, because schemas capture what typically happens, not what did happen.
  • Our minds are constantly churning with what-ifs. We conjure up scenarios for what could happen in the future, and we wonder what our present would be like if past events had turned out differently. All the scenarios we imagine leave us with memories of events we have never experienced, and our memories don't come with labels certifying them as imagined or real.
  • So we need reality monitoring. The more sensory details that come to mind when you remember an event, the more likely it is that it really happened, because on average what we imagine is not as detailed as what we have experienced.
  • We can counteract the fallibility of memory by considering not only the quality of the details that seem to put us back in a specific place and time but also the likelihood that those details could have been constructed to create an alternative reality. As with all critical thinking, it helps to remain skeptical until presented with further evidence.
  • Monitoring the details of our memories engages the most evolutionarily advanced areas of the human prefrontal cortex.
  • Confabulation: Some people who have extensive damage to the prefrontal cortex can confidently recall things that never happened. We all are guilty of minor confabulations. When we're tired or stressed out, or when our attention is divided by multitasking, reality monitoring goes out the window. As we get older, prefrontal function gets words, and we find it harder to tell the difference between imagination and experience.
  • In 1928, Bartlett speculated that creative works are constructed by essentially doing the opposite of reality monitoring - that is, by pulling up fragments of memories and then assembling those bits and pieces into a cohesive product of imagination.
  • The hippocampus and the DMN might function at the crossroads between memory and imagination by allowing us to extract the ingredients from past experiences and recombine them into new creations.
  • AI art is not about generating something new, it's about taking elements from preexisting human art and recombining them (based on human direction and curation).
  • We now know that it is in that space where memory meets imagination that we interpret reality and create our greatest treasures.

More Than a Feeling - the Amygdala

  • Our emotions, as well as the actions and choices they influence, are shaped by basic survival circuits in the brain that motivate us to avoid threats, find sustenance, and reproduce. When these circuits go into overdrive, we tend to experience intense emotions, such as elation, lust, panic, anxiety, or disgust. These are experiences we remember most vividly, because they provide valuable information that we can use in the future to stay safe, thrive, and reproduce.
  • Neuromodulators promote plasticity, enabling long-lasting changes in the connections between neurons in the cell assemblies that are activated when we learn something new.
  • Noradrenaline (AKA norepinephrine) is released all over the brain in response to threats. Emotional arousal changes what we will remember, rather than simply how much. If you get mugged your attention will be on the weapon pointed at you rather than the mugger's shoes. It's easy to forget more mundane experiences, but hard to let go of a traumatic memory: our brains are designed to hold on to the events that revved us up, ostensibly because remembering those events has survival value.
  • When we recall a time our survival circuits were called into action, the hippocampus works with the amygdala. As the hippocampus forms memories that capture the context at that moment, the amygdala is connecting those memories with the survival circuits that generate the raw sensations. Later on, when remembering, the amygdala brings us back to the heat of the moment, making us feel as if we are vividly reexperiencing the event.
  • We feel anxious when we think something bad might happen, but we cannot predict or control whether it will happen.
  • Cortisol spikes when you are stressed out to improve your ability to retain memories for what happened right before or after the stressful event. Like noradrenaline, stress hormones seem to promote plasticity, initiating the cascade of changes that consolidate connections within the cell assemblies representing the memory for a stressful event.
  • Stress tips the chemical balance in the brain, downregulating the executive functions mediated by the prefrontal cortex and enhancing the sensitivity of the amygdala.
  • In the healthy brain, if the hippocampus does its job, then memories for traumatic events should be associated with a specific context. Hippocampal dysfunction in experimentally stressed lab animals, and in humans with PTSD may cause traumatic memories to become overgeneralized.
  • Dopamine is central to helping us form lasting memories for rewarding experiences. Like other neuromodulators, dopamine promotes plasticity, and its release tends to be concentrated in several brain areas that are important for helping us learn how to get rewards:
    • Dopamine in the amygdala helps us learn about cues that signal an upcoming reward.
    • In the hippocampus, it helps us learn about the contexts where we are likely to get rewards.
    • in the nucleus accumbens, it helpus us learn what we need to do to get the reward.
  • Over all, dopamine associates cues, contexts, and actions that lead to rewards and sets expectations that shape our experience when we get them.
  • We are wired to learn only when the outcomes don't match up with our expectations.
  • Sudden drops in dopamine activity drain motivation, while an increase in dopamine activity can be energizing.
  • We often feel intensely motivated to seek out a reward even when we know it won't necessarily be pleasurable - cheating on a diet, smoking a cigarette when we have quit - this is the result of dopamine driving us.
  • In gambling studies, when people unexpectedly won a bet, we saw a large neural response, but when they expected to win and did, we saw only a small neural response. if a person had a large neural response after seeing the outcome of the bet, they would be more likely to make the same bet next. The people who favored risky bets showed more activity in reward-learning circuits when they won than people who tended to play it safe. And unlike risk-averse subjects, risk-takers still got a bump of activity in the reward circuit even when they lost a risky bet. At least some people might have a reward-learning circuit that leads them to persist in making risky decisions even after bad outcomes.
  • Cocaine, meth, heroin, opioids, and alcohol all activate the dopamine system, and can lead to powerful addictions.

All Around Me Are Familiar Faces

  • We tend to be more interested in exploring things that are new to us, than in things we have seen before.
  • Electrical signals in the perirhinal cortex can artificially produce a sense of intense familiarity or novelty. This suggests that it might be responsible for that sense of familiarity we naturally experience when we visit a place or see a person we have seen before.
  • The more activity in the perirhinal cortex when our volunteers read a word in the MRI scanner, the more familiar that word would seem when they saw it again on the surprise test. And, unlike with the hippocampus, activity in the perirhinal cortex was not related to people's ability to recollect the context of words that they had studied. Memories are not just strong of weak; rather the human brain has two different kinds of memory:
    • Episodic memory, which is supported by the hippocampus
    • Familiarity, which is supported by the perirhinal cortex.
  • Cell assemblies all over the brain are in constant flux, reorganizing and optimizing so that the neural elections that determine our perceptions, thoughts, and actions will come to swift and decisive conclusions. When those tweaks happen in sensory areas, they help us read, see, and experience the world more efficiently. Those little tweaks also happen in higher-level areas of the brains, such as the perirhinal cortex, that integrate information from our different senses to help build semantic memories.
  • All this neural plasticity seems to happen without our awareness, but the outcome can be sensed. the more familiar we become with something, the more our cell assemblies become fine-tune to recognize that thing later on. So, if we pay attention to how much mental effort we put in to read a word or recognize a face, we can get a sense of how much experience we have with it.
  • When you initially think about a concept, such as a rambutan, activity spikes in the perirhinal cortex. It's as if this area of the brain is trying to match the word to a template you haven't yet created. In the aftermath of that encounter, the neural coalitions in this area get reorganized. The next time you think about rambutans, there's less activity because the election is resolved faster. The tweaking that happens after repeatedly seeing that word improves the brain's efficiency, reducing brain activity in the perirhinal cortex and making it easier to access the concept of rambutans.
  • We often (mis)use familiarity as a heuristic, or mental shortcut, to guide decisions. Moreover, we can be blissfully unaware of these influences and instead reinforce our sense of free will by constructing stories that assign meaning to our choices and actions.
  • Experience doesn't just change what you see, it changes what you look for. People tend to pay attention to the features that best distinguish faces of people from their own race, at the expense of features that help us recognize faces from other races.
  • Like every other aspect of memory, familiarity has both a good and a bad side. It can be a useful by-product of how the brain is constantly becoming more efficient in its perceptions, but its slippery nature means that the fluency that results from mere exposure to something can operate under the radar of awareness, influencing our choices, judgments, and behavior. When we go on autopilot, familiarity can constrain our options and leave us with a smaller world.

Turn and Face the Strange

  • Memory's most important feature - orienting us to the future.
  • Our memories of the past - "the old" - enable us to allocate critical resources to what is new and what has changed.
  • Prediction errors initiate a cycle in the brain in which memory orients us to the unexpected, stimulating curiosity and motivating us to explore and resolve the gaps between our predictions and what we face in the present.
  • Our eyes move about 4 times a second.
  • When entering a space, we have:
    • General knowledge (semantic memory) of what is supposed to be in a particular place.
    • Familiarity - our eyes don't linger on things that are familiar, because we don't need to work as hard to process information about familiar objects, faces, or places.
  • A major evolutionary function of the hippocampus is to tall us about places that are new or different, so we can explore and learn about these aread.
  • Seeing something new or out of place should trigger a signal from the hippocampus stimulating us to explore out surroundings.
  • Activity in the hippocampus increased when the subjects looked at pictures of new places.
  • The brain's response to what is new is tightly coupled to our ability to remember what we have previously encountered, and that a loss of this novelty response may be an early indicator of risk for Alzheimer's disease.
  • The hippocampus is critical for attuning our attention to changes in our environment.
  • We might rely on these hippocampal memories to guide what to expect in the here and now. If something isn't in the right place, your spider-sense goes off, and your brain sends a signal to your eyes to scan that area so you can figure out what happened.
  • Seeing the place was enough to trigger retrieval of a memory from the hippocampus.
  • The hippocampus is one of the most evolutionary ancient structures in the brain.
  • The orienting response, is an orchestration of changes in the brain and the body in response to something new or surprising. Our pupils enlarge, increasing sensitivity to light. Blood is pumped to the brain and constricted in the rest of the body, and the brain gets a brief shot of neuromodulators, such as dopamine, noradrenaline, and acetylcholine. There's also a coordinated changes in neural activity throughout a network of brain areas, including the hippocampus and the prefrontal cortex.
  • The orienting response is probably one of the most reliable indicators of a functioning hippocampus.
  • The hippocampus is like a "What is it?" detector, alerting the brain to something unexpected. It preferentially forms memories for the oddball images.
  • Activity in the accumbens spiked about half a second after they saw the oddball image and the findings suggested that surprising or unexpected events can be sufficient to trigger activity in this system even when we do not get an external reward.
  • Curiosity is triggered when we discover a discrepancy between what we know and what we'd like to know, a nebulous space "the information gap". Loewenstein proposed that curiosity is about the motivation to seek information, rather than the satisfaction of getting our questions answered. This drive is evolutionarily adaptive because it helps us maintain a balance between exploration (of the new) and exploitation (of the existing).
  • By tapping into the reward circuitry, curiosity can enhance memory. This circuitry isn't about rewards, per se; it's about mobilizing us to learn and pursue anything we perceive to have value. And after food, water, and other basic needs are met, this means information.
  • People have tendencies, conscious, or unconscious, about whether to respond to the unknown with curiosity or anxiety.

Press Play and Record

  • The catalyst for memory updating is the very act of remembering.
  • Every time we recall an experience is one link in a neural chain subject to edits and updates, so that, over time, our memories can drift further and further from that initial event.
  • We are especially vulnerable to misinformation at the moment of remembering.
  • When we revisit a memory over and over, subtle alterations can creep in with each repetition. It's a bit like making a copy of a copy of a copy; the neural connections that hold together a memory are tweaked, and these changes can enlarge some aspects of the experience, while causing us to lose some of the details that keep the memory in focus. Like the fuzzy letters on my college band flyers, events from the distant past can seem more remote and blurry every time we call upon them, and noise becomes more prominent, corrupting the memory a bit more each time it's recalled.
  • They made a painstakingly detailed computer model of hippocampus!
  • Implanted memories, such as being lost in a mall are not entirely false; rather they are most likely imaginative constructions that incorporate information from schemas and details from real experiences.
  • Memory is malleable, but it isn't mush.
  • The sequence of steps in consolidation seems to happen whenever we retrieve a memory.
  • We already know that memories can be strengthened, weakened, or modified from the moment they are pulled up. This kind of memory updating is at the heart of psychotherapy, which is fundamentally about changing connections that we made in the past in the face of new information. The goal isn't to erase someone's memories of what happened but to adaptively update memories and change one's relationship with the past by approaching it from a different perspective.

Some Pain, More Gain

  • Error-driven learning is how we learn to make skilled movements by observing the difference between what we intend to do and what we actually do.
  • The benefits of testing do not come from making mistakes per se, but rather from challenging yourself to pull up what you have learned. To understand why, let's go back to our cell assemblies analogy. When you test yourself, your brain will try to generate the right answer, but the result isn't quite perfect.
  • Stress testing your memory like this exposes the weaknesses in the cell assemblies so that the memory can be updated, strengthening the useful connections and pruning the one that are gettin in the way. Rather than relearning the same thing over and over, it's much more efficient to tune up the right neural connections and fix just those parts that we are struggling with. Memory updating is the key, because the most efficient way for our brains to save space and learn quickly is to focus on what we didn't already know.
  • Memory is not a collection of isolated islands; it's an ecosystem of interacting cell assemblies.
  • Retrieval-induced forgetting - When recalling one memory can make it harder to pull up related memories.
  • Retrieval-induced facilitation - When people were tested on one of the facts in an article, the benefits of that test spilled over to related facts.
  • The shared episodic memory means that an alliance is built between the cell assemblies that back the different components of the lasagna dinner, and when we recall the lasagna, error-driven learning tightens up the alliance, pulling up other connected elements from the same event.
  • The spacing effect - if you keep returning to the same information periodically, the hippocampus can continually update those memories until they have no discernible context, making it easier to access them in any place at any time.
  • During sleep, the brain goes back and forth between at least five different states. Slow-wave sleep (SWS) and rapid eye movement (REM sleep work hand-in-hand to transform our recent experiences into knowledge that we can use:
    • SWS is the deepest sleep stage - there is a fully orchestrated interaction between the hippocampus and the neocortex during SWS. Large, slowly traveling electrical waves cycle across the neocortex, with smaller waves of activity called spindles riding atop the crest. Meanwhile in the hippocampus, little bursts of activity called ripples bubble up, and during each ripple, individual neurons in the hippocampus that were active during the daytime come back to life, firing off in little sequences. Ripples, in turn, trigger bursts of activity in the default mode network (DMN), which helps us use schemas to learn about new events, and in the prefrontal cortex, which helps us intelligently use schemas to form memories for events and reconstruct them later on.
    • REM is when dreams occur, and the dynamics of neocortical activity during REM might explain the vivid, lifelike experiences and bizarre logic that accompany our dreaming life. During REM sleep, the brain is generating its on sensory input and tries to make sense of it in the form of dreams, constructing an alternate reality all while you are in bed.
  • Sleep may create an environment where cell assemblies active during different events play well together, rather than competing. When information from one event was reactivated in the model, the neocortex used this information to initiate a chain reaction of free associations. Information from different events was reconciled through error-driven learning, bringing out what was common across different events. The model suggest that when memories are reactivated during a test, error-driven learning helps to strengthen those specific memories, but when memories are reactivated during sleep, error-driven learning helps the brain to use threads of disparate experiences to weave a tapestry of knowledge.
  • Sleep helps us integrate what we have recently learned across different events so we can use that information more efficiently. Memories for events sometimes become less context-dependent after sleep, and we are sometimes better at seeing big-picture relationships between small pieces of information that we had previously learned, and we are better able to use this information to solve problems.
  • Sleep can allow us to convert memory into wisdom.
  • The hippocampus helps us pull up specific patterns of brain activity that take us back to a particular place and time, whereas the neocortex stores the semantic knowledge that enables us to understand what happens in an event and make predictions and inferences in new situations. During SWS, the hippocampus can ignite cell assemblies that captured important experiences from the previous day (episodic memory), and then during REM, the neocortex can play around with this information, free-associating to discover possible connections between different events we've experienced.
  • After a challenging bout of work, it can help to get a good night's sleep, take a nap, or at least take a little time to rest. During these down states, our brains can use error-driven learning to piece together elements from different experiences, potentially allowing us to see things from a different perspective, giving us leverage to tackle problems that previously seemed insurmountable.
  • Targeted memory reactivation (inception) - the sleeping brain is highly receptive to the outside world.

When We Remember Together

  • The very act of sharing our past experiences can significantly change what we remember and the meaning we derive from it.
  • We construct our sense of identity in part, through memories shared with our family and friends, as well as the memories shared across members from the same culture or nation. And our identities are built on ground that is constantly shifting, as we collaborate with one another to continually reconstruct and update our individual and collective memories.
  • Children whose mothers asked open-ended questions and elaborated on their children's answers tend to remember more of their life experiences and put them together in a more coherent narrative than those whose mothers ask their children to recall specific information. These kinds of interactions can significantly impact a child's self-concept. Children who are encourage to have a voice develop more ownership over their sense of self because they are allowed to be authors of their personal narratives. Conversely, disallowing certain stories to be told or negating or disputing a child's perspective can undermine their sense of the experience and be detrimental to the development of the self.
  • The process by which storytelling can change our view of the past can be seen as an extension of the principles that govern individual memory. When we remember, our reconstructions of the past are dominated by the beliefs and perspective we adopt in the moment, in this case while we share those memories with others. We tailor narratives for our audience, who can reinterpret our memories and reflect them back to us from a different perspective. As we interact with the audience to reconstruct our past experiences, memories can be updated in the process, allowing us to see our personal past from a different view.
  • When people hear part of a story that can be stitched into a narrative with other story elements heard several minutes before, hippocampal activity increases and the memory code in the hippocampus is transformed.
  • Collaborative inhibition - Surprisingly, those working in a group had worse memory performance.
  • Collaborative facilitation - tends to happen when people have shared expertise that enables them to work as a team. The key to successful collaborative memory seems to lie in having some common ground, along with an appreciation for each other's distinctive contributions.
  • What makes people susceptible to fake news? We have a bias to believe and therefore remember information that is consistent with our preexisting beliefs. Fake news is easier to digest if it comes in a flavor we already like. Consistent with research on social contagion, belief in fake news is also increased when the information is emotionally arousing, when it includes photoes as well as text, and when it comes from a source we know and trust.
  • "Push-polls" designed not to collect opinions, but to spread misinformation. They seem to work by letting misinformation burrow into our memory
  • Seeking out a fact check after consuming fake news can enable us to update our memories and thereby curtail the effects of misinformation.
  • As we go about our lives, connections between neurons are constantly formed and modified, resulting in cell assemblies that help us sense, interact with, and understand the world around us. These intricately connected neural networks give us the ability to weave together the threads of the past so that we may envision how the future will unfold.
  • Semantic memory, in particular, remains robust into old age.
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