Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School (14 page)

The end result of their association is the creation of long-term memories. How they work to provide stable memories is not well understood, even after three decades of research. We do know something about the characteristics of their communication:

1) Sensory information comes into the hippocampus from the cortex, and memories form in the cortex by way of the reverse connections.

2) Their electrical marriage starts out being amazingly chatty. Long after the initial stimulus has exited, the hippocampus and the relevant cortical neurons are still yapping about it. Even when I went to bed that night, the hippocampus was busy feeding signals about Austerlitz back to the cortex, replaying the memory over and over again while I slept. This offline processing provides an almost absurdly powerful reason to advocate for regular sleep. The importance of sleep to learning is described in detail in Chapter 7.

3) While these regions are actively engaged, any memory they mediate is labile and subject to amendment. But it doesn’t stay that way.

4) After an elapsed period of time, the hippocampus will let go of the cortex, effectively terminating the relationship. This will leave only the cortex holding the memory of the event. But there’s an important caveat. The hippocampus will file for cellular divorce only if the cortical memory has first become fully consolidated–only if the memory has changed from transient and amendable to durable and fixed. The process is at the heart of system consolidation, and it involves a complex reorganization of the brain regions supporting a particular memory trace.

So how long does it take for a piece of information, once recruited for long-term storage, to become completely stable? Another way of asking the question is: How long does it take before the hippocampus lets go of its cortical relationship? Hours? Days? Months? The answer surprises nearly everybody who hears it for the first time. The answer is: It can take
years
.

memories on the move

Remember H.M., the fellow whose hippocampus was surgically removed, and along with it the ability to encode new information? H.M. could meet you twice in two hours, with absolutely no recollection of the first meeting. This inability to encode information for long-term storage is called anterograde amnesia. Turns out this famous patient also had retrograde amnesia, a loss of memory of the past. You could ask H.M. about an event that occurred three years before his surgery. No memory. Seven years before his surgery. No memory. If that’s all you knew about H.M, you might conclude that his hippocampal loss created a complete memory meltdown. But that’s where you’d be wrong. If you asked H.M. about the distant past, say early childhood, he would display a perfectly normal recollection, just as you and I might. He can remember his family, where he lived, details of various events, and so on. This is a conversation with a researcher who studied him for many years:

Researcher:
Can you remember any particular event that was special—like a holiday, Christmas, birthday, Easter?
(Now remember, this is a fellow who cannot ever remember meeting this researcher before this interview, though the researcher has worked with him for decades.)

H.M.:
There I have an argument with myself about Christmas time.
Researcher:
What about Christmas?

H.M.:
Well, ’cause my daddy was from the South, and he didn’t celebrate down there like they do up here—in the North. Like they don’t have the trees or anything like that. And uh, but he came North even though he was born down Louisiana. And I know the name of the town he was born in.

If H.M can recall certain details about his distant past, there must be a point where memory loss began. Where was it? Close analysis revealed that his memory doesn’t start to sputter until you get to about the 11th year before his surgery. If you were to graph his memory, you would start out with a very high score and then, 11 years before his surgery, drop it to near zero, where it would remain forever.

What does that mean? If the hippocampus were involved in all memory abilities, its complete removal should destroy all memory abilities—wipe the memory clean. But it doesn’t. The hippocampus is relevant to memory formation for more than a decade after the event was recruited for long-term storage. After that, the memory somehow makes it to another region, one not affected by H.M.’s brain losses, and as a result, H.M. can retrieve it. H.M., and patients like him, tell us the hippocampus holds on to a newly formed memory trace for years. Not days. Not months.
Years
. Even a decade or more. System consolidation, that process of transforming a labile memory into a durable one, can take years to complete. During that time, the memory is not stable.

There are, of course, many questions to ask about this process. Where does the memory go during those intervening years? Joseph LeDoux has coined the term “nomadic memory” to illustrate memory’s lengthy sojourn through the brain’s neural wilderness. But that does not answer the question. Currently nobody knows where it goes, or even
if
it goes. Another question: Why does the hippocampus eventually throw in the towel with its cortical relationships, after spending years nurturing them?

Where is the final resting place of the memory once it has fully consolidated? At least in response to that last question, the answer is a bit clearer. The final resting place for the memory is a region that will be very familiar to movie buffs, especially if you like films such as
The Wizard of Oz, The Time Machine,
and the original
Planet of the Apes
.

Planet of the Apes
was released in 1968, the same year of the Soviet invasion, and appropriately dealt with apocalyptic themes. The main character, a spaceman played by Charleton Heston, had crash-landed onto a planet ruled by apes. Having escaped a gang of malevolent simians at the end of the movie, the last frames show Heston walking along a beach. Suddenly, he sees something off camera of such significance that it makes him drop to his knees. He screams. “You finally did it. God damn you all to hell!” and pounds his fists into the surf, sobbing.

As the camera pulls back from Heston, you see the outline of a vaguely familiar sculpture. Eventually the Statue of Liberty is revealed, half buried in the sand, and then it hits you why Heston is screaming. After this long cinematic journey, he wasn’t adventuring on foreign soil. Heston never left Earth. His ending place was the same as his starting place, and the only difference was the timeline. His ship had “crashed” at a point in the far future, a post-apocalyptic Earth now ruled by apes. The first time I encountered data concerning the final resting place of a fully consolidated memory, I immediately thought of this movie.

You recall that the hippocampus is wired to receive information from the cortex as well as return information to it. Declarative memories appear to be terminally stored in the same cortical systems involved in the initial processing of the stimulus. In other words, the final resting place is also the region that served as the initial starting place. The only separation is time, not location. These data have a great deal to say not only about storage but also about recall. Retrieval for a fully mature memory trace 10 years later may simply be an attempt to reconstruct the initial moments of learning, when the memory was only a few milliseconds old! So, the current model looks something like this:

1) Long-term memories occur from accumulations of synaptic changes in the cortex as a result of multiple reinstatements of the memory.

2) These reinstatements are directed by the hippocampus, perhaps for years.

3) Eventually the memory becomes independent of the medial temporal lobe, and this newer, more stable memory trace is permanently stored in the cortex.

4) Retrieval mechanisms may reconstruct the original pattern of neurons initially recruited during the first moments of learning.

forgetting

Solomon Shereshevskii, a Russian journalist born in 1886, seemed to have a virtually unlimited memory capacity, both for storage and for retrieval. Scientists would give him a list of things to memorize, usually combinations of numbers and letters, and then test his recall. As long as he was allowed 3 or 4 seconds to “visualize” (his words) each item, he could repeat the lists back perfectly, even if the lists had more than 70 elements. He could also repeat the list backward.

In one experiment, a researcher exposed Shereshevskii to a complex formula of letters and numbers containing about 30 items. After a single retrieval test (which Shereshevskii accomplished flawlessly), the researcher put the list in a box,
and waited 15 years
. The scientist then took out the list, found Shereshevskii, and asked him to repeat the formula. Without hesitation, he reproduced the list on the spot, again without error. Shereshevskii’s memory of everything he encountered was so clear, so detailed, so
unending
, he lost the ability to organize it into meaningful patterns. Like living in a permanent snowstorm, he saw much of his life as blinding flakes of unrelated sensory information, He couldn’t see the “big picture,” meaning he couldn’t focus on commonalities between related experiences and discover larger, repeating patterns. Poems, carrying their typical heavy load of metaphor and simile, were incomprehensible to him. In fact, he probably could not make sense of the sentence you just read. Shereshevskii couldn’t forget, and it affected the way he functioned.

The last step in declarative processing is forgetting. The reason forgetting plays a vital role in our ability to function is deceptively simple. Forgetting allows us to prioritize events. Those events that are irrelevant to our survival will take up wasteful cognitive space if we assign them the same priority as events critical to our survival. So we don’t. We insult them by making them less stable. We
forget
them.

There appear to be many types of forgetting, categories cleverly enumerated by Dan Schacter, the father of research on the phenomenon, in his book
The Seven Sins of Memory
. Tip-of-the-tongue issues, absent-mindedness, blocking habits, misattribution, biases, suggestibility—the list reads like a cognitive Chamber of Horrors for students and business professionals alike. Regardless of the type of forgetting, they all have one thing in common. They allow us to drop pieces of information in favor of others. In so doing, forgetting helped us to conquer the Earth.

ideas

How can we use all of this information to conquer the classroom? The boardroom? Exploring the timing of information re-exposure is one obvious arena where researchers and practitioners might do productive work together. For example, we have no idea what this means for marketing. How often must you repeat the message before people buy a product? What determines whether they still remember it six months later, or a year later?

Minutes and hours

The day of a typical high-school student is segmented into five or six 50-minute periods, consisting of unrepeated (and unrelenting) streams of information. Using as a framework the timing requirements suggested by working memory, how would you change this five-period fire hose? What you’d come up with might be the strangest classroom experience in the world. Here’s my fantasy:

In the school of the future, lessons are divided into 25-minute modules, cyclically repeated throughout the day. Subject A is taught for 25 minutes, constituting the first exposure. Ninety minutes later, the 25-minute content of Subject A is repeated, and then a third time.
All
classes are segmented and interleaved in such a fashion. Because these repetition schedules slow down the amount of information capable of being addressed per unit of time, the school year is extended into the summer.

Days and weeks

We know from Robert Wagner that multiple reinstatements provide demonstrable benefit over periods of days and even weeks.

In the future school, every third or fourth day would be reserved for reviewing the facts delivered in the previous 72 to 96 hours. During these “review holidays,” previous information would be presented in compressed fashion. Students would have a chance to inspect the notes they took during the initial exposures, comparing them with what the teacher was saying in the review. This would result in a greater elaboration of the information, and it would help the teachers deliver accurate information. A formalized exercise in error-checking soon would become a regular and positive part of both the teacher and student learning experiences.

It is quite possible that such models would eradicate the need for homework. At its best, homework served only to force the student to repeat content. If that repetition were supplied during the course of the day, there might be little need for further re-exposure. This isn’t because homework isn’t important as a concept. In the future school, it may simply be unnecessary.

Could models like these actually work? Deliberately spaced repetitions have not been tested rigorously in the real world, so there are lots of questions. Do you really need three separate repetitions per subject per day to accrue a positive outcome? Do all subjects need such repetition? Might such interleaved vigor
hurt
learning, with constant repetitions beginning to interfere with one another as the day wore on? Do you really need review holidays, and if so, do you need them every three to four days? We don’t know.