In one of those end-of-the-year "Top 10" lists that are so popular,
New Scientist compiled a list of its
top 10 brain articles. As I scanned through the list, I spotted one that I knew had a crayfish connection: "
Does the brain feature built-in noise?"
When you type "crayfish" into
Google Scholar, the first two hits, with over 600 citations each, both relate to noise, and they concern one experiment. The first contains a review of the second, so the second paper, by Douglass and collegues (1993), is the primary article.
The paper is about stochastic resonance in crayfish.
Yup.
That one's going to take some explaining.
Imagine you're on the ground, trying to pick apples off an apple tree on a completely calm, windless day. You can only reach (or jump!) so far, and the apples on the branch remain
just out of reach.
Now imagine the same scenario, but instead with a little gust wind blowing. Now the branches, instead of staying still, start to sway in the breeze. And just once in a while, that extra push from the breeze puts an apple close enough that you can grab it. That random movement of gusty wind actually helped accomplish something. That's much like stochastic resonance.
Of course, there will be limits to this. If the wind gets too severe, the branches of the apple tree will be flailing around so much that grabbing an apple will get harder and harder, not easier.
The
New Scientist article put it like this:
Noise is usually a nuisance, as anyone who lives under a flight path or has tried to listen to a distant AM radio station can testify. But to engineers it can be a godsend, and now its benefits are cropping up in biology, too. More than a decade of research suggests that under some circumstances, a small injection of noise can sharpen up the way in which an organism senses its environment. For example, crayfish are better at detecting the subtle fin movements of predatory fish when the water is turbulent rather than still.
The experimenters recorded from sensory hairs (sometimes called tactile afferents) on the tailfan of crayfish. These small hairs are very sensitive to water movement, and feed into various systems, including the escape response system. In the escape system (and no doubt neurons), no
one sensory cell has a big enough signal to reach the threshold for the next cell in the chain to fire. Thus, a little random noise in the environment actually makes the sensory hairs more likely to fire the target neurons, because the noise pushes the system a little closer to threshold overall. And the authors performed experiments showing that this actually occurs with real neurons in real animals. That's what the graph shows: the best signal (Y axis) is here there's a little noise, not at the lowest noise level (X axis).
It's not at all intuitive, yet it's probably very common in biological and non-biological systems. And that combination is arguably why this is one of the most cited crayfish papers in biology.
ReferencesDouglass JK, Wilkens L, Pantazelou E, & Moss F. 1993. Noise enhancement of information transfer in crayfish mechanoreceptors by stochastic resonance.
Nature 365(6444): 337-340.
http://dx.doi.org/10.1038/365337a0
If your Christmas cards are not sufficiently crustacean inspired, click here for a PDF of a Christmas card you can print out and mail to your friends or attach to their presents.
Fabritius-Vilpoux K, Bisch-Knaden S & Harzsch S. Engrailed-like immunoreactivity in the embryonic ventral nerve cord of the Marbled Crayfish (Marmorkrebs). Invertebrate Neuroscience 8(4): 177-197.
A paper making a quite surprising claim snuck out back in August. Yue and colleagues, collecting Procambarus clarkii in China, claim to have found genetically identical individuals. They found 15 individuals that are genetically identical to at least one other individual in their sample of 120. This provides evidence of cloning in this very commonly used lab species. This is highly surprising if true, since there have been no shortage of labs working on P. clarkii over the years.
Yue GH, Wang GL, Zhu BQ, Wang CM, Zhu ZY, Lo LC. 2008. Discovery of four natural clones in a crayfish species Procambarus clarkii. International Journal of Biological Sciences 4(5):279-282. http://www.biolsci.org/v04p0279.htm
In one of those end-of-the-year "Top 10" lists that are so popular, New Scientist compiled a list of its top 10 brain articles. As I scanned through the list, I spotted one that I knew had a crayfish connection: "Does the brain feature built-in noise?"
The experimenters recorded from sensory hairs (sometimes called tactile afferents) on the tailfan of crayfish. These small hairs are very sensitive to water movement, and feed into various systems, including the escape response system. In the escape system (and no doubt neurons), no one sensory cell has a big enough signal to reach the threshold for the next cell in the chain to fire. Thus, a little random noise in the environment actually makes the sensory hairs more likely to fire the target neurons, because the noise pushes the system a little closer to threshold overall. And the authors performed experiments showing that this actually occurs with real neurons in real animals. That's what the graph shows: the best signal (Y axis) is here there's a little noise, not at the lowest noise level (X axis).
Although this blog is focused on science, I do occasionally get questions about Marmorkrebs as pets, which is great. I am planning on doing a little frequently asked questions list on pet care, but here's a couple of thoughts for those keeping Marmorkrebs as pets.
This week, Science published an article about zebrafish development. The article, however, does not do justice to the joyous, glorious movies that it is about. Single frames don't do -- you really have to see these things in motion. 
