Remembrance of things past

I'm going to begin today's post with a bit of shameless self-promotion.  The wonderful site The Skeptic is sponsoring a contest to select (amongst other things) the best skeptical blog of 2012, and if you have read and enjoyed Skeptophilia, I'd like to toss aside my usual charming modesty and ask for your vote.  It takes only a moment -- click on the site link I posted above, and go down to the heading "Best Blog of 2012," and put in my website address (skeptophilia.blogspot.com).  I'd appreciate it immensely!

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I've been interested in memory as long as I can remember.  Part of the reason is that my own personal brain seems to be made up of a rather peculiar assemblage of things I can remember with apparent ease and things that I don't seem to be able to remember at all.  I recall music with no effort whatsoever; I once put a nifty little Serbian dance tune into long-term storage for over twenty years after hearing it twice (and not practicing it or writing it down in the interim).  Names, likewise, stick with me; I know more scientific names of obscure species than is useful or even reasonable, and it's not from engaging in any sort of surreptitious memorization of taxonomic lists late at night when no one's looking.  That sort of stuff simply sticks.

On the other hand, numbers.  I know people who can remember what their phone number was in houses they haven't lived in for thirty years.  I'm lucky when I can remember what my phone number is now.  In this day of passwords, PINs, and so on, there are a variety of number/letter combinations I'm expected to remember, and the maximum amount of these I seem to be able to recall is: one.  For all of the passwords where this is possible, I use the same one.  If anyone ever discovers it, I'm royally screwed.  Fortunately, it's pretty obscure, so I don't think it's likely (meaning you shouldn't waste your time trying to figure it out).

It does, however, point up something odd about memory, which is how compartmentalized it is.  People can be exceptionally good at certain types of memory, and rather bad at others.  A few things, however, seem common to all sorts of memory; repetition improves retention, memory consolidation increases after sleep, and we all get worse at it (all types) as we age.

This last one is the subject of a recent bit of research published in Nature (available here), by Zhenzhong Cui, Ruiben Feng, Stephanie Jacobs, Yanhong Duan, Huimin Wang, Xiaohua Cao, and Joe Z. Tsien, as a collaborative project between Georgia Health Sciences University and East China Normal University.  The experiments involved using transgenic mice that overproduced a neurotransmitter receptor called NR2A, and found that they were significantly poorer than normal at forming new long-term memories than ordinary mice were.  The reason, the researchers speculate, is that this receptor is involved in weakening the synaptic firing patterns from old memories.

Put another way, it seems like one of the reasons we become more forgetful as we age is that we aren't as good at getting rid of things we already have stored in there.  In an interview with The New York Times, study lead author Joe Z. Tsien compares our brains when young to a blank page, and older brains to a page from a newspaper.  "The difference is not how dark the pen is," he said, "but that the newspaper already has writing on it."

"What our study suggests," Tsien added, "is that it’s not just the strengthening of connections, but the weakening of the other sets of connections that creates a holistic pattern of synaptic connectivity that is important for long-term memory formation."

In other words, our brains really do fill up and (in some sense) run out of space.

It's a funny thought, isn't it?  One of the reasons I can't remember where I left my keys is because my brain still is determined to hang onto the name of my 7th grade English teacher (Mrs. Trowbridge).

I find this a fascinating result, partly because it contradicts my long-held belief (admittedly based on no evidence whatsoever) that no one ever gets close to the actual memory storage capacity of the brain.  Also, it brings up the questionably prudent possibility of developing technology to selectively erase memories, à la Eternal Sunshine of the Spotless Mind.  Not, in this case, to eliminate traumatic or unpleasant memories, as it was for Jim Carrey's character -- but to free up hard drive space.

In any case, this is only the beginning.  A dear friend of mine, the brilliant (now retired) Cornell human genetics professor Dr. Rita Calvo, once made the prediction that "if the 20th century was the century of the gene, the 21st will be the century of the brain."  We are, she said, right now with respect to our understanding of the brain approximately where we were in 1913 with respect to our understanding of genetics -- we know a little bit of the "what" and the "how much," but almost nothing about the "how" and the "why."

If so, we should be looking forward to some amazing advances over the next few years, and I'm sure I'll have to do a lot of reading to keep up with the research even well enough to teach competently my Introductory Neurology class.  It's exciting, however, to think that we may finally be elucidating the inner workings of our most intricate organ, and finding out how it does one of the most mysterious things of all -- storing, and retrieving, information.

Oh, and one more thing; did you vote for my blog?  I hope you hadn't forgotten.

Amodal nudity

I am endlessly interested in human perception.  The way our sensory systems, and the sensory-integrative parts of the brain, work is one of the most fascinating parts of biology -- and one of the least understood.  And it only gets more interesting when you combine it with that topic that everyone thinks about and pretends that they don't: sex.

I started considering the connection between sex and perception because of an article on the James Randi Educational Foundation's website called "The Lurking Pornographer: Why Your Brain Turns Bubbles into Nude Bodies."  In it, we find photos that lead to the rather startling conclusion that when a swimsuit-clad individual has the swimsuit covered up by strategically placed blank space, our brain makes the executive decision that the person in the photograph is naked.

Don't believe me?  Take a look:

And lest you think it's just because men are sex-obsessed, it works for photographs of guys, too:

 

The author of the article, Kyle Hill, explains this effect as the "lurking pornographer" in the brain; that the brain is always "looking for the body parts we are trying to cover up" as an outcome of the pressure to reproduce.  I wonder, though, if it might be simpler than that; my guess is that this is just a form of amodal completion, where the brain tries to fill in the gaps in incomplete images in the way that requires the least assumptions.  A simple example is the Kanisza triangle:

That you have a white triangle overlaid on top of a triangular outline and three black circles is a simpler explanation than having three V-shaped bits and three black Pac-Man shapes all laid out just so as to appear to make two triangles.  But amodal completion, like any inference based on incomplete information, can also get it wrong.  Consider the horse(s) and cat(s) in the following drawing:

Two horses (in the left-hand drawing) and two cats (in the right-hand one) are merged into one by the brain "forcing" a wrong interpretation -- amodally completing the two animals into a single, extra-long horse and cat because of trying to fill in the missing pieces in the simplest possible way.

Likewise, when we have no other information about a person -- all we see is skin -- inferring a swimsuit seems like a jump.  The easier solution is that they're running around naked.  And of course, the fact that this stimulates our brains in a different way makes us stick with that solution once we've arrived at it.

It's like our neural network is hardwired with a perceptual form of Ockham's Razor, especially when the simpler solution is one that's kind of fun to look at.

Still, there's no doubt that most of our brains are obsessed with sex.  The three chemicals that mediate the majority of the sexual response -- dopamine, oxytocin, and endorphin -- are a mighty powerful cocktail, and none of them have much to do with thinking.  Interestingly, dopamine is the same neurotransmitter that is involved in addiction -- which may explain why the "sex drive" is called a "drive."

Oh, and about all of the claims that men think about sex twice as much as women do; there may be something to it.  According to recent research by Dr. Ananya Mandal, the preoptic nucleus of the hypothalamus, which is one area of the brain involved in sexual response and mating behavior, is 2.2 times larger in men than in women.  Size apparently matters -- in that respect, at least.

Anyhow, I thought all of this was pretty cool.  It's always interesting to find out why we do what we do.  It's why I found Desmond Morris' classic book The Naked Ape so fascinating when I first ran into it, at age 17 -- I'd never before considered human behavior from the standpoint of looking at humanity as if we were just another animal species.  And far from being demeaning, that perceptual shift leaves me feeling interconnected to the rest of the natural world in a far more intricate way.  We have reasons for doing what we do, just like every other living thing on Earth -- including the birds and the bees.