Neurons in Action

Researchers image the electrical impulses of the C. elegans and zebrafish nervous systems.

By | May 19, 2014

C. elegansWIKIMEDIA, NATIONAL HUMAN GENOME RESEARCH INSTITUTEResearchers from the United States and Vienna have simultaneously imaged the activity of all 302 neurons of C. elegans, revealing how quickly nervous impulses traverse the worm. The team then used the technique, which involves engineering neurons to light up when firing, to image the brains of transparent zebrafish larvae. While scientists have long mapped the neuronal connections of various organisms—the entire connectome of C. elegans was first published in 1986, for example—the new results, published yesterday (May 18) in Nature Methods, represent the first time that the activity of an organism’s entire nervous system has been viewed in real time.

“The connectome and activity are entirely complementary,” Misha Ahrens, a neurobiologist at the Howard Hughes Medical Institute's Janelia Farm Research Campus in Ashburn, Virginia, told Nature News. “You’re not going to understand the nervous system by observing one or the other.”

“What’s very impressive about it is that it is such an elegantly simple implementation,” Aravinthan Samuel, a professor of physics at Harvard University who was not part of the research team, said in a press release. “I could imagine many labs adopting this.”

To achieve this imaging success, neuroscientist Alipasha Vaziri of the University of Vienna and his colleagues turned to light-field deconvolution microscopy, which yields 3–D images based on images from a set of tiny lenses. With up to 50 images per second, the researchers captured real-time neural activity of the brain, ventral cord, and tail as each worm performed natural behaviors such as crawling. Turning to zebrafish larvae, the researchers were able to visualize the activity of about 5,000 neurons in the brain as the fish responded to chemical odors.

“Looking at the activity of just one neuron in the brain doesn’t tell you how that information is being computed; for that, you need to know what upstream neurons are doing. And to understand what the activity of a given neuron means, you have to be able to see what downstream neurons are doing,” coauthor Ed Boyden, an associate professor of biological engineering and brain and cognitive sciences at MIT, said the release. “In short, if you want to understand how information is being integrated from sensation all the way to action, you have to see the entire brain.”

The challenge now, Boyden added, is to improve the imaging speed and resolution to be able to observer larger swaths of neurons in complex organisms. In the long run, the researchers hope that they might even be able to visualize activity across individual neurons, tracking activity in the neuronal bodies, dendrites, and axons. (For more on other recent advances in neuroimaging, see “Brains in Action.”)

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Avatar of: James V. Kohl

James V. Kohl

Posts: 481

May 20, 2014

From another information source: "The patterns of synaptic connections perfectly mirror the fundamental differences in the feeding behaviours of P. pacificus and C. elegans", Ralf Sommer concludes.  That suggests the patterns are nutrient-dependent and pheromone-controlled via the ability of food odors and pheromones to induce and control the de novo Creation of olfactory receptor genes.

The patterns do not appear to be the result of mutations and natural selection that some theorists still claim are responsible for the evolution of biodiversity. Those theorists seem to be incapable of recognizing the most obvious pattern of all -- the one that links ecological variation to ecological adaptations in species from microbes to man via conserved molecular mechanisms.

Indeed, it would not make sense in the light of biology if Mosaic Copy Number Variation in Human Neurons was not directly linked to "...patterns of synaptic connections [that] perfectly mirror the fundamental differences in the feeding behaviours of P. pacificus and C. elegans" via a "straightforward hypothesis... that neurons with different genomes will have distinct molecular phenotypes because of altered transcriptional or epigenetic landscapes." That straightforward hypothesis can be compared to any null hypothesis that attempts to incorporate mutations and natural selection for anything except food.

In the light of physics, chemistry, and molecular biology, the comparison I have in mind suggests that -- in the null hypothesis -- natural selection for something else results in the increasing organismal complexity manifested in the morphological and behavioral phenotypes of individuals and species. However, I don't think that any experimental evidence supports the null hypothesis.

"...gradual mutation followed by selection has not, as a matter of fact, been demonstrated to be necessarily a cause of speciation." -- Denis Noble 

Is Denis Noble suggesting that nothing about mutation-initiated natural selection and evolution makes sense in the light of biology? Perhaps not, but I am suggesting that the link from ecological variation to ecological adaptations in species from microbes to man is fully supported by experimental evidence -- and that mutation-initiated natural selection is not.

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