Friday, December 14, 2007

My eyes... my eyes... my eye color fascination

I admit, I am totally fascinated by eye color. I think it is pretty neat that the differing colors ultimately depend on the amount of melanin (pigment of skin and hair too) in the iris of the eye. Recall that the iris is the round structure in the front of your eye that forms and adjusts the opening called the pupil. Since melanin pigment ranges from black to brown, you might predict that eye (actually iris) colors should simply be shades of brown or light brown or even yellow... basically variations of brown. Yet, look around and you see eyes of blue, grey, green, and all shades of brown. Students are often surprised that there is no blue pigment in the iris or green pigment... just varying amounts of brown melanin. So how do we get all the amazing shades and colors of the iris? I was curious too...

Iris collage: digital images taken in BIO 25, Fall 2006/2007

Using Google, I came across the following wikipedia-ish website with a very nice description of the structural determinants of eye color... you should check it out.

According to this website, the overall determinants of eye color are the combination in the amount of melanin in the iris and the scattering of light (light bouncing back from an object) from the iris' structural, connective tissue layer (i.e., the stromal layer) made with lots of collagen. An iris with high amounts of melanin absorbs more light and appears as brown and there is very little scattering/reflection from the collagen layers of the iris so it appears smooth or velvety (see image above). Now, what about blue and green... in these cases there is less melanin pigment to absorb light and thus the light hits the collagen layer and is scattered/reflected as blue or grey-ish. With green/hazel eyes, there are moderate amounts of melanin which abrorbs some light and this would appear yellow or light brown but there is also some blue color from the remaining light hitting the collagen layers... yellow + blue =? Green. The greater amount of scattered/reflected light from the stromal layer in green or blue eyes gives the iris the weblike or stringy appearance as compared to the smooth brown eyes. But besides the differences in melanin, structurally the brown eyes would seemingly have the same stringy, weblike structure but you don't see it since the light is absorbed and not scattered. Get it? Freckles on the iris seem to be clusters of melanocytes with melanin pigment... oh yeah, the pupil is black since it is a hole and like a doorway into an unlit room, it looks dark or black. Shine enough light into the pupil and you get a reflection back from the retina that appears? Red due to blood vessels.... red eye in your pictures.

Monday, December 3, 2007

Young chimps better college students in memory test... do'h!

Ouch, this one hurts... if you are a college student, not really. A recent study of memory in chimps compared responses on a series of memory tests between the chimps and college students. The BBC headline reads "Chimps beat humans in memory test." After reading the story at BBC news, I decided to look at the original research article published in the scientific journal Current Biology and my personal opinion is that the results are far from saying that chimps memorize better than humans... and of course there is no implication that chimps are smarter than college students. But that type of headline is certain to catch your attention when reading google news. Anyway... the chimps did in fact respond faster in memory tasks (was accuracy in the task sacrificed for speed?) and the single best chimp did beat out the average performance of the students. Keep in mind these tasks were testing short term memory only. Longterm memory was not examined and as anatomy / physiology students you can appreciate that we test your longterm retention on exams :)

But this research is very cool and it certainly suggests that chimps have tremendous ability in terms of short memory tasks, possibly better than many human subjects. They also suggest young chimps have a so called "photographic" memory. In fact, the best performing chimp (of the three tested) was able out perform the combined averages of 9 college students. So, yes, one chimp did beat the college students in this specific memory test. Sign him up for anatomy and physiology? Maybe not... if you watch the video you will see that the memory task is very specific to being able to memorize a complex visual field of numbers and then immediately trying to identify their correct position. Also, looking at the actual published figures suggests to me that humans took longer to respond but had better accuracy. So the chimps might go faster since they may not be as preoccupied with being correct... as the big brain cousins of the chimp, we are usually worried about doing things the right way. There is also interesting discussion about the decline in photographic memory capabilities as humans and chimps age. Cool stuff... you should read the BBC article and even the actual study since it is very short. Check out these videos of the chimps in action!

Saturday, December 1, 2007

An old story but.... the Real Rain Man and Savantism

In 2005, Scientific American published a story on Kim Peek, the real life inspiration for the character Raymond Babbitt played by Dustin Hoffman in Rain Man. Peek has what is known as savantism (savant syndrome) in that he has extraordinary mental / memory skills and yet has severe mental disabilities.

Credit: Scientific American

Peek's brain has numerous congenital abnormalities including macroencephaly (i.e., he has a very large brain) and an undersized cerebellum. Most notably, his brain lacks all major connections between the left and right cerebral hemispheres... for the anatomy students that is the corpus callosum and the anterior / posterior commissures. Interestingly, Peek has not been diagnosed with autism although many savants have autism or autistic characteristics.

Savant syndrome describes a person having a severe developmental or mental handicap with extraordinary mental abilities not found in most people. This means a lower than average general intelligence (IQ) but very high narrow intelligence in one or more fields. Savant syndrome skills involve striking feats of memory and arithmetic calculation and sometimes include unusual abilities in art or music. Savant syndrome is sometimes abbreviated as "savantism", and individuals with the syndrome are often nicknamed savants. Credit: Wikipedia
Savants are fascinating given the inconsistency between being mentally handicapped while still possessing nearly incomprehensible mental capabilities. The mental skills of savants raise interesting questions: Does their congenital brain damage stimulate compensatory development in some other area of the brain, or does it simply allow otherwise latent abilities to emerge? Below is an example of Peek's memory capabilities... anybody who reads Tom Clancy novels knows that they are dense with info and long... making this all the more impressive:

"He can, indeed, pull a fact from his mental library as fast as a search engine can mine the Internet. He read Tom Clancy’s The Hunt for Red October in one hour and 25 minutes. Four months later, when asked, he gave the name of the Russian radio operator in the book, referring to the page describing the character and quoting several passages verbatim. Kim began memorizing books at the age of 18 months, as they were read to him. He has learned 9,000 books by heart so far. He reads a page in eight to 10 seconds and places the memorized book upside down on the shelf to signify that it is now on his mental hard drive." Credit: Scientific American
To learn more about Savant Syndrome visit the Wisconsin Medical Society website. Watch video of Kim Peek... the Real Rain Man.