If Our Brains Are So Active During Infancy, Why Don’t We Remember Anything From That Time?

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If our brains are so active and developing during infancy, why don’t we remember anything from that time?

Fabian van den Berg:

Ah, infantile amnesia as it’s better known. Weird, isn’t it? It’s a pretty universal phenomenon where people tend to have no memories before the age of four-ish and very few memories of the ages five to seven. What you say in the question is true, our brains are indeed very actively developing in that time, but they are still developing after five years as well.

The specifics aren’t known just yet. It’s tricky because memory itself is very complicated and there are swaths of unknowns that make it difficult to say for certain why we forget these early memories. This will be mostly about consensus and what can be supported with experiments.

(Image based on data from Rubin & Schulkind, 1997 [1] )

I’ll skip the whole introduction to memory bit and state that we focus on the episodic/autobiographical memories only—events that happened to us in a certain place at a certain time. And we have two forgetting phases, the early one until about four years old, and a later one from about five to seven years old, where we have very few memories.

The first notion to go is that this is “just normal forgetting,” where it’s just difficult to remember something from that long ago. This has been tested and it was found that forgetting happens quite predictably, and that the early years show less memories than they should if it was just regular old forgetting.

This leaves us with infantile amnesia, where there are probably two large camps of explanations: One says that children simply lack the ability to remember and that we don’t have these memories because the ability to make them doesn’t develop until later. This is the late emergence of autobiographical memory category.

The second big camp is the disappearance of early memory category, which says that the memories are still there, but cannot be accessed. This is also where the language aspect plays a part, where language changes the way memories are encoded, making the more visual memories incompatible with the adult system.

Both of them are sort of right and sort of wrong; the reality likely lies somewhere in between. Children do have memories, we know they do, so it’s not like they cannot form new memories. It’s also not likely that the memories are still there, just inaccessible.

Children do remember differently. When adults recall, there is a who, what, where, when, why, and how. Kids can remember all of these too, but not as well as adults can. Some memories might only contain a who and when (M1), some might have a how,
where, and when (M3), but very few, if any, memories have all the elements. These elements are also not as tightly connected and elaborated.

Kids need to learn this; they need to learn what is important [and] how to build a narrative. Try talking to a child about their day: It will be very scripted [and] filled with meaningless details. They tell you about waking up, eating breakfast, going to school, coming home from school, etc. Almost instinctively an adult will start guiding the story, asking things like, “Who was there?" or "What did we do?”

It also helps quite a bit to be aware of your own self, something that doesn’t develop until about 18 months (give or take a few). Making an autobiographical memory is a bit easier if you can center it around yourself.

(Image from Bauer (2015) based on the Complementary Process Account [2] )

This method of forming memories makes for weak memories, random spots of memories that are barely linked and sort of incomplete (lacking all the elements). Language acquisition can’t account for all that. Ever met a three-year old? They can talk your ears off! So they definitely have language. Children make weak memories, but that doesn’t completely tell you why those memories disappear, but I’ll get there.

The brain is still growing, very plastic, and things are going on that would amaze you. Large structures in the brain are still specifying and changing, the memory systems are part of that change. There’s a lot of biology involved and I’ll spare you all the science-y sounding brain structures. The best way to see a memory is as a skeleton of elements, stored in a sort of web.

When you remember something, one of the elements is activated (which can be by seeing something, smelling something, or any kind of stimulus), which travels through the web activating all the other elements. Once they are all activated, the memory can be built, the blanks are filled in, and we “remember."

This is all well and good in adults, but as you can imagine this requires an intact web. The weak childhood memories barely hung together as they were, and time is not generous to them. Biological changes can break the weak memories apart, leaving only small isolated elements that can no longer form a memory. New neurons are formed in the hippocampus, squeezing in between existing memories, breaking the pattern. New strategies, new knowledge, new skills—they all interfere with what and how we remember things. And all of that is happening very fast in the first years of our lives.

We forget because inefficient memories are created by inefficient cognitive systems, trying to be stored by inefficient structures. Early memories are weak, but strong enough to survive some time. This is why children can still remember. Ask a four-year-old about something important that happened last year and chances are they will have a memory of it. Eventually the memories will decay over the long term, much faster than normal forgetting, resulting in infantile amnesia when the brain matures.

It’s not that children cannot make memories, and it’s not that the memories are inaccessible. It’s a little bit of both, where the brain grows and changes the way it stores and retrieves memories, and where old memories decay faster due to biological changes.

All that plasticity, all that development, is part of why you forget. Which makes you wonder what might happen if we reactivate neurogenesis and allow the brain to be that plastic in adults, huh? Might heal brain damage, with permanent amnesia as a side-effect ... who knows!

Footnotes

[1] Rubin, D. C., & Schulkind, M. D. (1997). Distribution of important and word-cued autobiographical memories in 20-, 35-, and 70-year-old adults. Psychol Aging.

[2] Bauer, P. J. (2015). A complementary processes account of the development of childhood amnesia and a personal past. Psychological review, 122(2), 204.

This post originally appeared on Quora. Click here to view.

What Would Happen If a Plane Flew Too High?

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Tom Farrier:

People have done this, and they have died doing it. For example, in October 2004, the crew of Pinnacle Airlines 3701 [PDF]  was taking their aircraft from one airport to another without passengers—a so-called "repositioning" flight.

They were supposed to fly at 33,000 feet, but instead requested and climbed to 41,000 feet, which was the maximum altitude at which the aircraft was supposed to be able to be flown. Both engines failed, the crew couldn't get them restarted, and the aircraft crashed and was destroyed.

The National Transportation Safety Board determined that the probable causes of this accident were: (1) the pilots’ unprofessional behavior, deviation from standard operating procedures, and poor airmanship, which resulted in an in-flight emergency from which they were unable to recover, in part because of the pilots’ inadequate training; (2) the pilots’ failure to prepare for an emergency landing in a timely manner, including communicating with air traffic controllers immediately after the emergency about the loss of both engines and the availability of landing sites; and (3) the pilots’ improper management of the double engine failure checklist, which allowed the engine cores to stop rotating and resulted in the core lock engine condition.

Contributing to this accident were: (1) the core lock engine condition, which prevented at least one engine from being restarted, and (2) the airplane flight manuals that did not communicate to pilots the importance of maintaining a minimum airspeed to keep the engine cores rotating.

Accidents also happen when the "density altitude"—a combination of the temperature and atmospheric pressure at a given location—is too high. At high altitude on a hot day, some types of aircraft simply can't climb. They might get off the ground after attempting a takeoff, but then they can't gain altitude and they crash because they run out of room in front of them or because they try to turn back to the airport and stall the aircraft in doing so. An example of this scenario is described in WPR12LA283.

There's a helicopter version of this problem as well. Helicopter crews calculate the "power available" at a given pressure altitude and temperature, and then compare that to the "power required" under those same conditions. The latter are different for hovering "in ground effect" (IGE, with the benefit of a level surface against which their rotor system can push) and "out of ground effect" (OGE, where the rotor system supports the full weight of the aircraft).

It's kind of unnerving to take off from, say, a helipad on top of a building and go from hovering in ground effect and moving forward to suddenly find yourself in an OGE situation, not having enough power to keep hovering as you slide out over the edge of the roof. This is why helicopter pilots always will establish a positive rate of climb from such environments as quickly as possible—when you get moving forward at around 15 to 20 knots, the movement of air through the rotor system provides some extra ("translational") lift.

It also feels ugly to drop below that translational lift airspeed too high above the surface and abruptly be in a power deficit situation—maybe you have IGE power, but you don't have OGE power. In such cases, you may not have enough power to cushion your landing as you don't so much fly as plummet. (Any Monty Python fans?)

Finally, for some insight into the pure aerodynamics at play when airplanes fly too high, I'd recommend reading the responses to "What happens to aircraft that depart controlled flight at the coffin corner?"

This post originally appeared on Quora. Click here to view.

Why Are Some Men's Beards a Different Color Than Their Hair?

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Throughout civilization, beards have acted as a silent communicator. For some, it's a symbol of virility and power. For others, being hirsute is mandated by religion, marital status, or both. (Amish single men are clean-shaven; husbands are not.) Seeing an unkempt, scraggly beard could be an indication of a person's economic status or their lack of vanity. One man, Hans Langseth, sprouted a 17-foot-long chin warmer for the unique identity it afforded him. (He kept it neatly rolled over a corn cob when he wasn't busy showing it off.)

Langseth's whiskers, which wound up in the Smithsonian, present a curious timeline of his life. The furthest end of the beard was a vibrant brown, grown out when he was younger. The ends closer to his face—and to the end of his life in 1927—were yellowed.

While age can certainly influence hair and beard color, it doesn't explain why a younger man can sport a decidedly different beard tone than what's on the rest of his head. Other follicular forces are at work.

By default, scalp hair is white. It gets its color from melanin, turning it everything from jet black to dirty blonde. Pheomelanin infuses hair with red and yellow pigmentation; eumelanin influences brown and black. Like shades of paint, the two can mix within the same hair shaft. (Melanin production decreases as we age, which is why hairs start to appear gray.) But not all follicles get the same dose in the same combination. While you might sport a light brown top, your beard could be predominantly dark brown, or sport patches of lighter hairs in spots. Eyebrow hair will probably appear darker because those follicles tend to produce more eumelanin.

If you're wondering why these two-toned heads often have a red beard but not red hair, there's an answer for that, too. While all hair color is genetic, one gene in particular, MC1R, is responsible for a red hue. If you inherit a mutated version of the gene from both parents, you're likely to have red hair from head to toe. (Hopefully not too much toe hair.) But if you inherit MC1R from just one parent, it might only affect a portion of your follicles. If that swatch of color annoys you for whatever reason? There’s always beard dye.

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