Chapter 3 explains how memory works more through reconstruction than perfect retrieval. When recalling an event, we piece together incomplete fragments, filling in gaps based on our expectations, beliefs and prior knowledge. This process is prone to errors and distortions without us realizing it.

Comparisons of John Dean's Watergate testimony to tape recordings and of Dan Simons' 9/11 memories to what actually happened show how faulty even vivid, confidently-held memories can be. Memory researcher Frederic Bartlett proposed memories change over time to fit a more coherent narrative aligned with our understanding.

Section: 1, Chapter: 3

Author: Leonard Mlodinow

Chapter 6 traces the long history of memory training and how its role in Western civilization has changed over time. In the ancient world, before cheap writing materials were available, enormous value was placed on committing knowledge to memory. Orators like Cicero would memorize hours-long speeches, poets would recite epic stories passed down for generations, and scholars would memorize entire books.

Well into the Middle Ages memory skills were considered a core part of education and high culture. But with Gutenberg's invention of the printing press, books became more widespread, and the value placed on memorization gradually declined. By the 19th century, rote learning in schools was increasingly criticized as stifling to creativity.

The Romantics valued inspiration and emotion over meticulous learning. As books became cheaper, the great traditions of memory training faded into obscurity. Only in our own time, with the pioneering work of a few iconoclasts, have the ancient techniques been systematically revived.

Section: 1, Chapter: 6

Author: Joshua Foer

That frustrating feeling of blanking on a word or name you're sure you know is called a "tip of the tongue" (TOT) experience. It occurs when there's only partial activation between the concept you're searching for and it's name/label.

• It happens to all ages but increases after age 40 due to slower neural processing. TOT becomes more noticeable and worrisome to older adults.
• Proper names are the most common targets of TOT because, unless meaningful to you, they lack semantic associations in the brain (the "Baker/baker paradox")
• Cues like seeing/hearing the first letter or number of syllables sometimes slip through during TOT. An "ugly sister" - a similar-ish but wrong word - may also come to mind

Section: 2, Chapter: 8

Author: Lisa Genova

How memories are made:

• Memories are formed through lasting physical changes in the brain in response to experiences. The process involves four steps:

1. Encoding - translating sensory information into neurological language,
2. Consolidation - linking related neural activity into a connected pattern,
3. Storage - maintaining the neural pattern over time through structural changes,
4. Retrieval - reactivating the stored neural pattern to recall the memory.

• The hippocampus is essential for consolidating new consciously retrievable memories by binding together disparate neural activity.

Section: 1, Chapter: 1

Author: Lisa Genova

Chapter 3 covers working memory - the temporary, limited memory store for the present moment.

• Working memory only holds what you're paying attention to right now, for about 15-30 seconds. It's constantly updated as events unfold moment to moment.
• Visual working memory is like a "mental scratchpad" and auditory working memory is like a brief "mental soundtrack" or "echo".
• Working memory has a small capacity, able to hold only about 7 ± 2 "chunks" of information at a time. Chunking information into meaningful units can expand how much you can fit in working memory.
• Important information can be plucked from working memory and consolidated into long-term memory via the hippocampus if it captures your attention. The rest is quickly forgotten as working memory updates.

Section: 1, Chapter: 3

Author: Lisa Genova

Chapter 11 explores how forgetting isn't always a passive, uncontrolled process - we can actively choose to forget things we don't want to retain, though it's not always easy. Unwanted thoughts and memories can be intentionally suppressed by redirecting attention whenever they come to mind, depriving them of the rehearsal needed to solidify long-term storage.

In many everyday situations, some strategic forgetting is beneficial. Truly traumatic, intrusive memories are much harder to shake, but working with a therapist to reframe them into less devastating terms during reconsolidation may lessen their sting. Memory and forgetting have a yin-yang relationship - both are essential for a healthy, well-functioning mind.

Section: 2, Chapter: 11

Author: Lisa Genova

Chapter 15 details the complex effects of stress on memory formation and retrieval.

• Acute stress causes release of hormones epinephrine and cortisol, which signal the amygdala to activate the hippocampus to consolidate the stressful event as a memory. This prioritizes storage of important, survival-relevant information.
• An optimal amount of acute stress improves attention and memory formation. Too little stress and consolidation isn't boosted.
• Chronic stress leads to prolonged cortisol release, impairing the hippocampus and its ability to form new memories. It can even cause hippocampal neurons to wither and die.
• Techniques like meditation, exercise, yoga and reframing negative thoughts can reduce perceived stress and protect the brain from its memory-harming effects.

Section: 3, Chapter: 15

Author: Lisa Genova

Both when remembering the past and imagining the future, the human brain tends to "fill in" missing details that weren't originally stored, in order to construct a coherent scene or narrative.

• In memory, we don't store every detail of a past event. When we later retrieve that memory, the brain fills in plausible details to flesh it out, but these details may be inaccurate.
• When imagining a future event, the brain constructs a scene with many assumed details that may not match the actual details that will exist in that future moment.

In both cases, we aren't aware in the moment that our brain is "making up" details that feel real to us. We tend to trust that the details in our remembered and imagined scenes are accurate.

Section: 2, Chapter: 2

Author: Daniel Gilbert

Episodic memories, though often vividly recalled, are highly prone to distortion and inaccuracy. Episodic memories are incomplete from the start because we only encode select details.

During consolidation, memories are frequently edited with elaborations, reinterpretations and flat-out fabrications filled in unconsciously. Memories change a bit each time we recall them based on our current mood, knowledge and beliefs. The altered version overwrites the original in a process called reconsolidation.

In studies, people have been easily manipulated to recall detailed memories of getting lost in a mall, spilling punch on a bride, and seeing footage of 9/11 planes crashing that doesn't actually exist

Section: 2, Chapter: 7

Author: Lisa Genova

the 19th century, mnemonic techniques enjoyed a brief popular resurgence not as learning tools, but as performance. Traveling "professors" of memory would put on stage shows demonstrating seemingly superhuman memorization and calculation abilities.

One of the most famous, Alphonse Loisette (real name Marcus Dwight Larrowe), charged exorbitant sums for his memory training courses and was as celebrated as he was controversial. Even Mark Twain fell under his tutelage for a time, though he would later come to regret his association with the huckster.

Figures like Loisette represented a "vulgarization" of the classical art of memory, turning it into little more than a vaudeville act. But while serious interest in mnemonics waned, these performers unintentionally kept the ancient techniques alive until their academic and practical value could be rediscovered in the late 20th century.

Section: 1, Chapter: 6

Author: Joshua Foer

The difference between memory for facts and events vs. memory for skills:

• Declarative memories are consciously recalled facts (semantic memory) and personal experiences (episodic memory). They feel effortful to retrieve and are easy to forget.
• Non-declarative "muscle memories" are unconscious memories for how to perform learned motor skills (typing, bike-riding, playing an instrument, etc). They are automatic and durable, but take a lot of repetition to acquire.
• Muscle memories rely on the basal ganglia and cerebellum to consolidate, not the hippocampus, so they were spared in famous amnesic patient HM who could form new skill memories but no new declarative memories after his hippocampus was removed.
• Both types of long-term memory formation require attention and practice, but muscle memory mastery takes much more repetition than factual or event memory.

Section: 1, Chapter: 4

Author: Lisa Genova

Just as we mispredict our future feelings, we also misremember our past feelings. Our memories of past emotional reactions are skewed by our current perspectives.

• When recalling a restaurant where we got food poisoning, we remember the overall experience as worse than it actually was in the moment.
• When reminiscing about an old relationship, we mentally exaggerate either the good or the bad aspects, painting a simpler picture than the nuanced reality.
• When describing past hardships to others, we play up the intensity for dramatic effect or to garner sympathy.

We don't do this on purpose - the distortions arise naturally in memory. We recall events through the lens of hindsight and our current goals. Just as imagination fails to capture the nuances of the future, memory fails to accurately reflect the nuances of the past.

Section: 6, Chapter: 10

Author: Daniel Gilbert

Chapter 10 dives into the unavoidable fading of memories over time, a phenomenon first scientifically studied by Hermann Ebbinghaus in the 1800s. His famous "forgetting curve" shows that memory loss happens rapidly at first, then tapers off, with about 25% of the original material retained in the long run if there's no further review.

This forgetting occurs because the neural connections housing the memory physically decay if not reactivated. However, some residual trace remains - relearning forgotten material goes faster than the first time, a "savings" effect.

To combat time's memory-eroding effects, repeated retrieval of the memory is key, preferably spaced out over time vs. crammed. Overlearning, continuing to study even after you can accurately recall it, also helps cement long-term retention.

Section: 2, Chapter: 10

Author: Lisa Genova

Small, close-knit groups can develop a kind of shared memory system called transactive memory. Over time, members unconsciously divvy up and specialize in remembering different types of information based on their unique skills:

• Bob becomes the go-to for tech help and fixes everyone's computer issues
• Alice is the expert on company history and institutional knowledge
• Charlie knows all about their clients' businesses and needs

The group's memory becomes a division of cognitive labor, not just a sum of individual minds. They can collectively store and process far more knowledge than any one person.

This works through intimate social bonds, not org charts. Transactive memory is why small, tight-knit teams are often more efficient than large bureaucratic divisions.

Section: 1, Chapter: 5

Author: Malcolm Gladwell

In the climax of his year-long memory quest, Foer competes in the USA Memory Championship in New York City. Up against experienced mental athletes, Foer is a clear underdog, but his training pays off in a stunning upset. In the first event, memorizing the names of 99 strangers' faces, Foer comes in third, beating out dozens of more experienced competitors. But it's his performance in the next event, "speed cards," where he really shines.

Using the mnemonic "person-action-object" system, he was able to memorize the order of a shuffled deck of cards in just over a minute and a half - a new US record. As the day goes on, Foer continues to hold his own against the field, advancing to the final round against former champion Ram Kolli. In the ultimate showdown, a trial to see who can memorize the most from a double deck of cards, Foer emerges victorious. The former journalist had become the new US memory champion, proving just how far dedication and smart training techniques can take you.

Section: 1, Chapter: 11

Author: Joshua Foer

Is it really possible to have a "photographic memory" like the famous savant S, automatically recording everything you see and hear in perfect detail? Foer argues the answer, with one notable exception, is no. The one credible case of photographic memory comes from "Elizabeth," a Harvard student studied in the 1970s who could fuse two images in her mind into a mental composite. He concludes that true photographic memory is at best exceedingly rare, and possibly nothing more than an urban legend.

If savants aren't relying on innate photographic memory, how do they perform such remarkable mental feats? Brain scans of savants like the famous Kim Peek (the inspiration for Rain Man) show unusual patterns of damage, especially to the left hemisphere, along with hyper-connectivity in other areas. This suggests savants' abilities may emerge from unique constraints that force their brains to operate differently, not inborn superiority. Foer argues this is also how memory techniques seem to work - by consciously constraining our minds to encode information in more memorable ways, while screening out distractions and irrelevant stimuli. The lesson is that incredible memory isn't just for savants.

Section: 1, Chapter: 10

Author: Joshua Foer