A new look at light

You might know that your retina senses light primarily through its rods and cones which are sensory cells specialized in converting photons into electrical signals.


Pisa at Sunset (I took this picture)


What you might not know is that there is a third light-sensitive cell in the mammalian eye. These cells are retinal ganglion cells (RGCs), but not all RGCs are directly sensitive to light.

But what you really probably don't know is that these RGCs sense light using the same protein that allows a toad's (Xenopus Laevis) skin to sense light (melanopsin). 


"It's true, I tell ya!"

These cells (the non-rod, non-cone light sensors) react to light directly, but they aren't exactly good at it. Their sensitivity is lower than the rods and cones, and they don't seem to transmit shape or color information.  So what is their purpose? Why have a secondary set of cells that sense light in a poor and unfocused way when you already have highly specialized rods and cones? 

To make it even more confusing, the rods and cones actually connect to these cells, adding their light-sensing information to theirs. 

weird, right? In a recent review paper, Pickard and Sollars (2012) explain that these cells likely play a role in controlling the sleep-wake cycle (circadian rhythm). Rats and mice with strongly degenerated rods and cones still set their circadian clock by the light cycle they are exposed to.  These cells send strong projections to the hypothalamus which controls everything sleep-wake cycle.


In addition, these cells or at least the melanopsin gene, may play a role in Seasonal Affective Disorder (SAD) by modulating the light-dependent cycles of the suprachiasmatic nucleus (a part of the hypothalamus).



SAD (source)

Their vague ability to sense 'brightness' makes these cells nicely suited to regulating the body's response to daily and seasonal changes in light. But whether these cells need to be light-sensitive to perform these functions or whether their sensitivity to light is just an evolutionary remnant is unclear. 



© TheCellularScale



 Pickard GE, & Sollars PJ (2012). Intrinsically photosensitive retinal ganglion cells. Reviews of physiology, biochemistry and pharmacology, 162, 59-90 PMID: 22160822



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Let me answer your questions: Part 1

One of the most entertaining things about writing this blog, is seeing the search terms that people have used to find it. Some of them leave me completely befuddled ("Giraffe eating man"), and some are amusing combinations of words that happened to be in a particular post. But my favorite ones take the form of questions.

(by Nanecakes)

I am pretty sure that most of the questions people have used to find my blog are not answered in my blog, and I hate the thought of disappointing people. So I thought I would take some time and answer a few of my favorites.

(All of these are actual 'search terms' that showed up on my blogger stats, I am not making these up.)



1. "Do neurons make you smart?"


This is a surprisingly interesting question. My answer is probably. All the evidence points to us needing neurons to think.  When neurons get damaged in certain parts of the brain, things start going badly in the 'smart' department. If you had no neurons, you probably couldn't think. 
There are two caveats that make this question interesting. 

1. Sometimes things that do not have neurons act 'smart' (see my post about the almost-neurons of the Venus Fly trap)

2. If neurons make you smart, they also make you stupid. You need neurons to perform a 'stupid' action just as much as you need neurons to perform a 'smart' action. An example here is when I am trying to drive somewhere I don't often go, I might accidentally find myself on my way to work.  I might think "how stupid of me, I wasn't even thinking" And it would be true.  The stupid action of turning the wrong way is because my striatal neurons have encoded the drive to work really strongly. 



2. "Does Shrek wear pants?"

This question directed someone to my post "How animals, Shrek, and Yoda stimulate your neurons."

And yes, in fact, Shrek does wear pants, though I had to google that term myself to find out. The issue here is that Shrek's pants are a dark olive color, close in hue to his skin tone, making it hard to tell and remember that he is wearing pants under that short tunic thing. 

UPDATE: 8/6/12 I have been informed by an astute reader that Shrek does not in fact wear 'pants' but rather 'tights'.  I suppose this is a more accurate description of his attire, so I formally apologize for spreading Shrek-related misinformation.

3. "Why is it better to play female Mass Effect?"


This is sort of answered by "4 reasons all women should play Mass Effect" But the question is specifically referring to playing the game as a woman rather than as a man.

A lot of people play Mass Effect as a woman because they think the voice-acting is better. (I agree with this)

I imagine most women play Mass Effect as a woman for the same reason most men play Mass Effect as a man. It's more fun to be a character when you can relate yourself to the character. I think it would be great if everyone played Mass Effect as a woman in a perspective taking experiment.

And I think Commander Shepard makes an excellent role model for young girls aspiring to one day save the galaxy.

FemShep Barbie (pure genius from Introverted Wife)

(FemShep Barbie would be such great friends with my Computational Neuroscientist Barbie!)


Readers, I hope you have found this post informative. I plan to continue answering these important questions for you in the future. 

© TheCellularScale

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The effect of familiar male voices on neurons

male zebra finch trying to impress female (Max-Planck)

Zebra finches are a popular model for language learning because unlike most research animals which may have instinctual vocalizations, zebra finches (the male ones at least) learn their signature song from experience.

The importance of social experience in male song learning is clear, but what about the effect of social experience on the female response to the male voice?

Menardy et al., 2012 (figure 2C)

Menardy et al., (2012) have recently analyzed the neural response in females to the male distance calls (not songs).  They tested the  response in anesthetized birds, but also in awake, alert birds. To do so, they used a nifty little recording device that they mounted on the back of the females.


They tested the response of the neurons in the caudomedial nidopallium (NCM) to the calls of the female's mate (4 months spent together), a non-mate familiar male (3 days spent together), and an unfamiliar male (complete stranger).

In general, the neurons in the female NCM responded more strongly to the calls of the males that they knew than to the stranger's call. 

Menardy et al., 2012 (figure 5A)

So why is this and what does it mean? The authors point out that this change in neural response could be a result of extensive social interactions (the female bird spent some quality time with the mate and the familiar male), or it could be a result of having heard the call before. 

In other words, Is the NCM encoding a recognition signal ('ah, that's Nick's voice') or a familiarity signal ('I've heard this sound before')?

It is likely that some form of neuroplasticity is taking place during the male-female interactions, but the mechanisms and the meaning behind it are not clear yet. Some interesting experiments might be to test the effect of traditional 'learning disruptors' (such as protein synthesis inhibitors) on this neural preference for familiarity. 

© TheCellularScale


Menardy F, Touiki K, Dutrieux G, Bozon B, Vignal C, Mathevon N, & Del Negro C (2012). Social experience affects neuronal responses to male calls in adult female zebra finches. The European journal of neuroscience, 35 (8), 1322-36 PMID: 22512260

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Chlamydia Symptoms (Signs) in Men and Women!

Image credit to shutterstock


The “STDs” or “Sexually transmitted diseases” are on the rise -- according to a CDC report. And did you know that Chlamydia is the most commonly reported -- it is the no one of STDs. Anyone (either men or women) can get it. The Chlamydia symptoms either in men or women typically don’t develop quickly, even in many cases the disease may cause no signs. If the signs

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Lichen Sclerosus Treatment in Women and Men (FAQs)

Image credit to shutterstock


What is lichen sclorosus? What are current treatments for this disease, and when you should call /see a doctor? It is a kind of uncommon long-term problem of skin. The areas of skin that affected by this disease are more likely to be patchy, and thinner & more white than normal. It can occur on the skin of any part of the body, but in many cases it usually affects

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Treatment for Aspergers Symptoms in Children!

Image credit to shutterstock


The right strategies and treatment is important to promote a child with aspergers into well-adjusted adults -- though the core symptoms of this developmental problem are not easy to be cured! One of major goals of the treatment for aspergers symptoms in children is intended to improve the patient’s abilities when interacting with others, so thus trouble associated

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Aspergers in Adults, Teens, and Children -- More Symptoms!

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The most major symptom of aspergers (either in children, teen, and adults) is a significant problem with social situations -- though there are also other possible symptoms and signs that can appear! The symptoms (most of them) also can persist through the teen years. The social skills in teens with apergers may be able to successful improve, but in many cases

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