By now, everyone must be familiar with the inside out organization of the cephalopod eye relative to ours: they have photoreceptors that face towards the light, while we have photoreceptors that are facing away from the light. There are other important differences, though, some of which came out in a recent Nature podcast with Adam Rutherford (which you can listen to here), which was prompted by a recent publication on the structure of squid rhodopsin.
I’m busy preparing my lecture for genetics this morning, in which I’m going to be talking about some chromosomal disorders … and I noticed that this summary of Fragile-X syndrome that was on the old site hadn’t made it over here yet. A lot of the science stuff here actually gets used in my lectures, so they represent a kind of scattered online notes, so I figured I’d better put this one where I can find it.
I haven’t even finished grading the last of the developmental biology papers, and already my brain is swiveling towards the genetics literature, as I get in the right frame of mind to teach our core genetics course in the spring. And, lo, here is a new paper in PNAS that addresses details of a topic I bring up every time.
There are a surprising number of heritable diseases that share a couple of common traits: they are neurodegenerative, causing progressive loss of neural control, and they also exhibit a phenomenon called genetic anticipation—they tend to get worse, with earlier onset and more severe affects with each generation. Some of these diseases may be rather obscure, for instance
Haw-River Syndrome (AKA Dentatorubral-pallidoluysian atrophy),
Friedreich Ataxia,
Machado-Joseph Disease, or
X-linked Spinal and Bulbar Atrophy Disease (AKA Kennedy Disease), but others you’ve probably heard of, like
Myotonic dystrophy and
Huntington Disease. These are dreadful diseases that are variable in their pattern of appearance, and have terrible symptoms, like loss of motor control, chorea, seizures, dementia, and eventually, death.
Jay Hosler has a new book out, Optical Allusions(amzn/b&n/abe/pwll). If you’re familiar with his other books, Clan Apis(amzn/b&n/abe/pwll) and The Sandwalk Adventures(amzn/b&n/abe/pwll), you know what to expect: a comic book that takes its science seriously. Hosler has a fabulous knack for building serious content into a light and humorous medium, just the kind of approach we need to get wider distribution of science into the culture.
This one has a strange premise. Wrinkles the Wonder Brain is an animated, naked brain working for the Graeae Sisters, and he loses the one eye they share between them — so he has to go on a quest to recover it. I know, it sounds like a stretch, but it works in a weird sort of way, and once you start rolling with it, you’ll find it works. Using that scenario to frame a series of encounters, Wrinkles meets Charles Darwin and learns how evolution could produce something as complex as an eye; talks about the sub-optimal design of retinal circuitry with a cow superhero; discovers sexual dimorphism with a crew of stalk-eyed pirates; learns about development of the eye from cavefish and a cyclops; chats with Mr Sun about the physics of radiation; there are even zombie G proteins and were-opsins in a lesson about shape changing. This stuff is seriously weird, and kids ought to eat it up.
It isn’t all comic art, either. Each chapter is interleaved with a text section discussing the details — you can read the whole thing through, skipping the text (like I did…), and then go back and get more depth and directions for future reading in the science. This is a truly seditious strategy. Suck ’em in with the entertainment value, and then hand ’em enough substance that they might just start thinking like scientists.
It’s all good stuff, too. A colleague and I have been considering offering an interdisciplinary honors course in physics and biology with the theme of the eye, specifically for non-science majors, and this book has me thinking it might make for a good text. It’ll grab the English and art majors, and provide a gateway for some serious discussions that will satisfy us science geeks. I recommend it for you, too — if you have kids, you should grab all of Hosler’s books. Even if you don’t have kids, you’ll learn a lot.
Jay Hosler also explains the intent of the project, and you can read an excerpt.
Many of you have already seen the gorgeous video below: it’s a spectacularly beautiful animation of the activity in a cell.
I like it, and it’s a useful illustration, but … there’s something fundamental that it gets completely wrong. So today I’m not going to praise it, I’m going to criticize it. It’s a substantial criticism, too, one that means I wouldn’t show this video in my classes without spending more time explaining the error than it takes to show it.
A friend of mine, who’s name won’t be mentioned, blacked out in class the other day. Since then, he’s been on a seizure drug. The drug is giving a very weird side effect. It must be affecting his auditory cortex, because he is hearing all audio roughly a half-octave lower than what it really is. In fact, he’s using a sound editing program to raise his entire music library up the ~half-octave to compensate. The name of the drug is Tegretol. In the midst of headaches over finals, I’ll see if I can find any interesting papers on it.
On the one hand, this is a strange tale of mutant, bisexual, necrophiliac flies, and you’ve got to love it for the titillating nature of the experiments. But on the other, much more interesting hand, it’s a story about drilling down deeply into the causes of a complex behavior, and tracing it to a single gene product — and it also reveals much about the way the chemicals sloshing about in the brain can modulate responses to stimuli. Work by Grosjean and others on a simple Drosophila mutant, genderblind, which causes flies to be indiscriminate about gender in their courtship, opens up a window into how sexual responses are shaped and specified.
Think about human sexual responses. Some of us, when we see an attractive woman, are at least mildly aroused; others are have their sexual interest picqued when they see an attractive man; still others might feel sexual urges when they see a shoe, or a plush animal, or a pot of baked beans. No matter what the stimulus, these are all biological responses, with something in the environment matching some trigger in our brains and initiating a cascade of neural, neurochemical, and hormonal activity that leads to sexual behaviors. The question we want to address is what every step in the biology is doing; unfortunately, human behaviors are both too complex and not amenable to ethical experimentation, so we turn instead to simpler organisms that allow us to find simpler causes and carry out thorough experiments to probe the behavior.
Wow, it’s been a little while since I last blogged. I’ve been busy trying to stain the eyes of my zebra fish, but still with little luck. My goal is to dye the retinas and their resulting optic nerves and neural pathways of developing zebrafish. After staining the retinas and optic nerve, I was going to keep a group under constant intense lighting conditions, another group under a regular 12 hour dark and 12 hour light cycle, while raising yet another group in complete darkness for 6 days after fertilization. I would then test their visual processing skills by rotating a stimulus around their tank and seeing whether or not members of each group followed the stimulus. However, I haven’t been able to do even one run through as I can’t get my fish to live long enough or stain them early enough.
I’ve been using self made micro spotters to inject dye into the retinas of these developing fish, but there are a lot of problems that I’m still running into. One of the largest is that I can’t seem to get the retinas stained until the fish are at least 2 or 3 days old (post fertilization). By this time a lot of early development in the retina as well as neural construction of pathways to the optic tectum and lateral geniculate (some of the primary visual sensory areas of the fish brain) have already occurred. To make matters worse, the fish often times don’t survive past four or five days after staining. This might be due to poor maintenance (whoops), but they should survive if I simply feed them and change their water every other day. I really think that I might be poking through the retina and damaging other tissues when I stain with my micro spotters. I know there are many fancy pants scientists reading this right now who could do the experiment in their sleep, but I guess I’m still just figuring out what doing science is really all about (which is why I love this class).
~Bright Lights
Two big specialty science carnivals are up today: Circus of the Spineless #27
and
Encephalon #37. Take your pick, invertebrates or nervous systems…or read them both.
Some observations on working with zebrafish:
Their vision isn’t as reliable as I thought. They would try like there’s no tomorrow to swim through the Plexiglas wall when there’s a hold only a few inches over. If I want to continue my experiments without having an aneurysm, I’ll have to make a few changes.
1 – The walls will have to be marked up opaque so that the fish don’t keep trying to swim through them.
2 – Since they have trouble navigating the single chamber, I’ll have to use plastic sheets to funnel them toward the door.
3 – I have a new set of tests to run. Is it the food that draws the fish into the food chamber, or is it the pheromones of the “social reward” of other fish that is repulsing the fish away. Once I get back to school after Thanksgiving, looks like I’ve got my work cut out for me.
For this week’s in-class “NeuroSlam” I spoke about a paper on mirror-touch synesthesia– a condition in which an individual reports feeling an actual tactile sensation in response to seeing someone else touched. For example, this synesthete would feel as if someone touched their arm if they saw someone touching another’s arm. Inspired by an fMRI of a mirror-touch synesthete that showed hyperactivity of mirror-touch network neurons (mirror neurons we all have in the somatosensory cortex, premotor cortex, and parts of the temporal lobe that fire in response to touch and viewing touch), researchers Micheal J Banissy and Jamie Ward wanted to study empathy in mirror-touch synesthetes as empathy is believed to be related to mirror neurons.
In addition to providing evidence for mirror-touch synesthetes experiencing a synesthesia very similar to actual touch, Banissy and Ward measured empathy in these individuals using a psychological test. They reported that synesthetes scored much higher in the “emotional reactivity” subset of the empathy quotient but not in “cognitive empathy” or “social skills.” This supports the theory that mirror neurons do play a role in empathy as well as the idea that empathy is a complex neurological process that can’t be be wholly described in one neural network.
Banissy, M.J., Ward, J. Mirror-touch synesthesia is linked with empathy. Nature Neuroscience 10, 815 – 816 (2007)
Published online: 17 June 2007 | doi:10.1038/nn1926
