Hologram Method Used to Study Neurons
Neuron in 3-D: Scientists can create three-dimensional images of neurons using a technique known as holographic microscopy.
Credit: Lyncée Tec
The approach could ultimately be used to rapidly screen new drugs designed to protect brain cells
MIT Technology Review, September 14, 2011 — Scientists in Switzerland have developed a novel way to monitor a neuron’s electrical activity by bathing it in laser light. The technique, called holographic microscopy, doesn’t require the invasive electrodes or dyes typically used to measure cell activity. Researchers say the approach could be used to rapidly screen new drugs designed to protect brain cells.
Holographic microscopy shines laser light on an object and computationally reconstructs the object’s form based on how the light waves are deformed. The technology is most commonly used to study materials—to search for flaws on the surfaces of lenses or microchips, for example. But scientists have recently begun to use it on living cells.
Because cells are transparent, changes to the light that passes through the cell—known as the refractive index—can be used to calculate both the cell’s shape and its contents. The cell’s contents are directly related to its electrical activity: when a neuron becomes electrically active, channels in the neuron’s membrane open, allowing both water and ions to rush into the cell.
“The change in water content changes the refractive index, so we are able to monitor current without electrodes,” says Pierre Magistretti, director of the Brain Mind Institute at the Ecole Polytechnique Fédérale de Lausanne, in Switzerland. Magistretti led the research. By using both conventional electrode recording and the holographic technique to monitor neurons grown in petri dishes, Magistretti and collaborators confirmed that holographic microscopy could accurately track electrical activity in the cell. The research was published this month in Journal of Neuroscience.
While electrode-based recording can monitor only a handful of neurons at a time, holographic microscopy could be used to monitor many more neurons simultaneously. In addition, the microscopes used in the technique can capture up to 500 images per second, generating movies of the cell’s electrical activity.
Magistretti says that beyond basic research, this approach could be used to quickly search for compounds with particular neural properties. During stroke, for example, neurons deprived of oxygen and glucose eventually die. The researchers showed that they can detect this type of cell death with holographic microscopy much more quickly than with other methods. For drug screens, they could re-create this stressful environment in a petri dish and then use holographic microscopy to look for compounds that prevent cell death.
Use of the technology is currently limited to a single layer of neurons grown in culture. The researchers now hope to use it to monitor simple neural circuits—connected neurons growing in a dish—as well as other cell types. The ultimate goal is to use it to monitor more complex configurations, such as slices of brain tissue, which better reflect the behavior of the intact brain. “If they can adapt the method to neurons connected in slices, it will be much more useful,” says Floyd Bloom, a neuroscientist at Scripps Research Institute. Bloom is optimistic: “I don’t think anyone could have predicted that they would have got as far as they did.”
A Step toward Holographic Videoconferencing
Video hologram: This display can refresh the image every two seconds.
Credit: gargaszphotos.com/University of Arizona
A full-color holographic display system refreshes every two seconds, fast enough to send live 3-D images
MIT Technology Review, by Katherine Bourzac — Researchers have made a major step toward a holographic videoconferencing system that would let people communicate with one another almost as if they were in the same room. They have developed a full-color, 3-D display that refreshes every two seconds, and they’ve used it to send live images of a researcher in California to collaborators in Arizona. In the coming years, the researchers hope to develop a system that refreshes at standard video rates and can compete with other 3-D displays.
“Holography makes for the best 3-D displays because it’s closest to how we see our surroundings,” says Nasser Peyghambarian, chair of photonics and lasers at the University of Arizona. A hologram is a display that uses an optical effect called diffraction to produce the light that would have come from an object in the image if the physical object were in front of the viewer. Holographic images appear to project out into the space in front of the display. By walking around a holographic image, it’s possible to see objects in it from different angles.
Holograms don’t require glasses to view, and unlike other glasses-free 3-D systems, multiple people can use them simultaneously without having to stand in a particular place. But the development of holographic displays has lagged behind that of other 3-D systems because of the difficulty in creating holographic materials that can be rapidly rewritten to refresh the image.
The first video holographic display was made at MIT’s Media Lab in 1989. The volume of the hologram was just 25 cubic millimeters, smaller than a thimble. Since then, researchers have been trying to develop practical holographic systems but have come up against limitations in scaling these displays up to larger sizes. A big challenge has been the attempt to eliminate expensive optical components without sacrificing the refresh rate.
A few companies sell 3-D displays for medical and design applications, but many of these systems don’t produce true holograms, and they tend to be expensive, not least because they’re produced in small amounts. “Some need lasers, some need powerful computers to operate, or many displays stacked together,” says Jennifer Colegrove, director of display technologies at industry research firm DisplaySearch. She notes that in 2010, such “volumetric” displays will generate $5 million in revenue, a small sliver of the $1 billion 3-D display market. Despite their expense, she says, “these displays are still primitive,” and lack a combination of image quality, speed, and display size.
In collaboration with Nitto Denko Technical, the California-based research arm of a Japanese company, Peyghambarian has been working to improve the sophistication and refresh rate of holographic displays. The new displays refresh significantly faster than previous systems and are the first to be combined with a real-time camera system to show live images rather than ones recorded in advance. The new displays are based on a composite materials system developed by Nitto Denko Technical. In 2008, the groups produced a four-inch-by-four-inch red holographic display that could be rewritten every four minutes. By improving the materials used to make the display and the optical system used to encode the images, they have now demonstrated a full-color holographic display that refreshes every two seconds. This work is described today in the journal Nature.
The key to the technology is a light-responsive polymer composite layered on a 12-inch-by-12-inch substrate and sandwiched between transparent electrodes. The composite is arranged in regions called “hogels” that are the holographic equivalent of pixels. Writing data to the hogels is complex, and many different compounds in the composite play a role. When a hogel is illuminated by an interference pattern produced by two green laser beams, a compound called a sensitizer absorbs light, and positive and negative charges in the sensitizer are separated. A polymer in the composite that’s much more conductive to positive charges than negative ones pulls the positive charges away.
This charge separation generates an electrical field that in turn changes the orientation of red, green, and blue dye molecules in the composite. This change in orientation changes the way these molecules scatter light. It’s this scattering that generates a 3-D effect. When the hogel is illuminated with light from an LED, it will scatter the light to make up one visual point in the hologram.
Writing the data to the holographic display used to take several minutes. Part of the way the Nikko Denko researchers sped up the process was to decrease the viscosity of the dye materials so that they can change position more rapidly. The movement of the dye molecules inside the composite is analogous to the movement of liquid crystals in a conventional display, says Joseph Perry, professor of chemistry at Georgia Tech. A path to further increasing the speed of the display might be to make these materials more like liquid crystals, which can switch not just at video rates but faster than the human eye is capable of detecting.
Another boost in speed came from using a faster laser to write the data. For this to work, the researchers also had to pair the laser with polymers in the display that could respond to these faster pulses, separating charges to generate the electric fields with less delay time. In another advance over previous work, the company has developed a full set of dye molecules for red, green, and blue.
To demonstrate the relative speed of the system, the group used it as a “telepresence” system similar to the holographic communications used in sci-fi movies like Star Wars—but much choppier. Multiple cameras recorded images of an employee at Nitto Denko; these images were processed to create the data to write each hogel, and sent to the group in Arizona, where the holographic display showed a 3-D projection of their California collaborator. “Now what we can display is like a slow movie,” says Peyghambarian. To make a holographic video system, they’ll need to increase the display’s refresh speed to at least 30 frames per second.
The university and Nitto Denko groups are working with Michael Bove at MIT on improving the fidelity of the images. “What they’re reporting works beautifully, without a lot of computation,” Bove says. In hopes of making the imagery clearer, Bove has developed a system to render holographic video very rapidly on an ordinary computer graphics chip.
The New York Times, GoogleNews.com, September 14, 2011, WASHINGTON (AP) — Major elements of the patent system overhaul legislation:
—Switches the basic standard of patent approval from a “first-to-invent” to “first-inventor-to file.”
—Gives the Patent and Trade Office more authority to set fees and keep the fees it collects so that it has enough money to reduce the backlog in processing patent applications.
—Seeks to improve patent quality by allowing third parties a chance to submit information on pending applications and establishing a review process to challenge faulty patents.
—Provides more certainty to patent owners by reducing administrative challenges.
—Encourages manufacturing by expanding prior user rights for manufacturers using a process before a patent is granted.
—Creates a way to weed out invalid but existing patents on methods of conducting business.
—Creates a supplemental examination system where applicants, particularly small inventors and startups that may lack filing expertise, can return to the patent office with additional material to clarify issues with their applications.
The south side of the James Madison Building in Alexandria, Virginia. It is one of the five buildings that forms the headquarters of the United States Patent and Trademark Office. All the top PTO officials have offices in this building.
Photo Credit: by Coolcaesar
Relief representing the Patent Office at the
Herbert C. Hoover Building