A tiny ladderlike beam of silicon converts light into vibrations and vice versa with extremely high efficiency, physicists report. That may seem like an esoteric result, but the finding could open the way to new physics and someday serve as a key element in optical microcircuits akin to the electronic microcircuits in computer chips.

Although the effect is ordinarily very small, light exerts forces on the things it strikes or flows through. In recent years, physicists have exploited those forces to set micrometer-sized objects aquiver. For example, 4 years ago, a team led by Kerry Vahala of the California Institute of Technology (Caltech) in Pasadena showed that light leaking out the side of a nearby optical fiber could make a tiny disk of glass vibrate. And 2 years ago, Daniel Gauthier of Duke University in Durham, North Carolina, and colleagues showed that light traveling down a fiber could make the fiber itself shake. In fact, they stored a pulse of light as a vibration and released it nanoseconds later.

Now, Oskar Painter, Matt Eichenfield, and colleagues at Caltech have taken these efforts a big step forward. Along with Vahala, the applied physicists have designed a gadget that increases the strength of the interaction of light and vibrations by orders of magnitude, potentially opening the way to optical microchips in which low-frequency vibrations or microwaves control high-frequency optical signals or vice versa. The device combines two different but related fields: photonics and phononics.

For more than a decade, physicists have been developing so-called photonic crystals. These are samples of glass or other light-transmitting materials filled with regular patterns of holes, which alter the way light waves can travel–in much the same way that the array of atoms in a crystal affects the way electrons can move through it. In such photonic crystals, light of certain wavelengths cannot propagate, as the waves overlap and interfere to cancel themselves out. However, light of such a wavelength can be trapped within the crystal if the spacing of the holes is changed in one spot to allow it to exist there. Sound also consists of waves, so similar holey structures can be used to make phononic crystals that affect sounds in much the same way.

Eichenfield, Painter, and colleagues fashioned a hybrid photonic/phononic crystal out of a tiny bridge of silicon less than a micrometer wide and about 20 micrometers long. They etched rectangular holes into the beam to make a ladderlike structure, with several of the holes in the middle slightly closer together to trap light and vibrations of the same wavelengths but vastly different frequencies. The researchers then fed light into the beam with an optical fiber and measured the light reemerging from it. At predictable wavelengths, the amount of light coming back out dipped, showing that some of the light was getting trapped in the beam.

The researchers also looked at the total range of frequencies of the light coming out and found that some of it had been transferred to microwave frequencies–the exact frequencies of trapped vibrations, the team reports online this week in Nature. That shift proved that the light was making the beam vibrate and that the jiggling was then affecting the light and converting some of it to microwaves. In fact, each photon pushes on the beam with 10 times the force of gravity, Painter estimates.

“It’s an incredibly exciting piece of work,” says Duke’s Gauthier. That’s because the conversion of light to vibration is so much stronger than it has been in previous experiments. “People tend to use meters of optical fiber and milliwatts of laser power, whereas they have used a micrometer-sized device and microwatts of power.” The device could have numerous applications, says physicist John Page of the University of Manitoba in Winnipeg, Canada. Specifically, the advance could pave the way to using vibrations or microwaves to control optical signals and to fashion switches, filters, or mixers in optical circuits on microchips.”

Over-expressing a gene that lets brain cells communicate just a fraction of a second longer makes a smarter rat, report researchers from the Medical College of Georgia and East China Normal University.

Dubbed Hobbie-J after a smart rat that stars in a Chinese cartoon book, the transgenic rat was able to remember novel objects, such as a toy she played with, three times longer than the average Long Evans female rat, which is considered the smartest rat strain. Hobbie-J was much better at more complex tasks as well, such as remembering which path she last traveled to find a chocolate treat.

The report comes about a decade after the scientists first reported in the journal Nature that they had developed “Doogie,” a smart mouse that over-expresses the NR2B gene in the hippocampus, a learning and memory center affected in diseases such as Alzheimer’s. Memory improvements they found in the new genetically modified Long Evans rat were very similar to Doogie’s. Subsequent testing has shown that Doogie maintained superior memory as he aged.

“This adds to the notion that NR2B is a universal switch for memory formation,” says Dr. Joe Z. Tsien, co-director of the MCG Brain & Behavior Discovery Institute and co-corresponding author on the paper published Oct. 19 in PLoS One. Dr. Xiaohua Cao at East China Normal University also is a co-corresponding author.

The finding also further validates NR2B as a drug target for improving memory in healthy individuals as well as those struggling with Alzheimer’s or mild dementia, the scientists says.

NR2B is a subunit of NMBA receptors, which are like small pores on brain cells that let in electrically-charged ions that increase the activity and communication of neurons. Dr. Tsien refers to NR2B as the “juvenile” form of the receptor because its levels decline after puberty and the adult counterpart, NR2A, becomes more prevalent.

While the juvenile form keeps communication between brain cells open maybe just a hundred milliseconds longer, that’s enough to significantly enhance learning and memory and why young people tend to do both better, says Dr. Tsien, the Georgia Research Alliance Eminent Scholar in Cognitive and Systems Neurobiology. This trap door configuration that determines not just how much but how fast information flows is unique to NMBA receptors.

Scientists found that Hobbie-J consistently outperformed the normal Long Evans rat even in more complex situations that require association, such as working their way through a water maze after most of the designated directional cues and the landing point were removed. “It’s like taking Michael Jordan and making him a super Michael Jordan,” Deheng Wang, MCG graduate student and the paper’s first author, says of the large black and white rats already recognized for their superior intellect.

But even a super rat has its limits. For example with one test, the rats had to learn to alternate between right and left paths to get a chocolate reward. Both did well when they only had to wait a minute to repeat the task, after three minutes only Hobbie-J could remember and after five minutes, they both forgot. “We can never turn it into a mathematician. They are rats, after all,” Dr. Tsien says, noting that when it comes to truly complex thinking and memory, the size of the brain really does matter.

That’s one of the reasons scientists pursue this type of research: to see if increased production of NR2B in more complex creatures, such as dogs and perhaps eventually humans, gets the same results. He also is beginning studies to explore whether magnesium – a mineral found in nuts, legumes and green vegetables such as spinach – can more naturally replicate the results researchers have obtained through genetic manipulation. Magnesium ion blocks entry to the NMDA receptor so more magnesium forces the brain cell to increase expression levels of the more efficient NR2B to compensate. This is similar to how statin drugs help reduce cholesterol levels in the blood by inhibiting its synthesis in the liver.

Scientists created Hobbie-J and Doogie by making them over-express CaMKII, an abundant protein that works as a promoter and signaling molecule for the NMDA receptor, something that likely could not be replicated in humans. In October 2008, they reported in Neuron that they could also safely and selectively erase old and new memories alike in mice by over-expressing CaMKII while the memory was being recalled

“We want to make sure this is a real phenomenon,” Dr. Tsien says of the apparent connection between higher levels of NR2B and better memory. “You should never assume that discovery you made in a cell line or a mouse can be translated to other species or systems unless you do the experiments.” He adds that the failure of new drugs and other disappointments result from the lack of sufficient scientific evidence.

The transgenic rat has other practical value as well. There is substantial scientific and behavior data already available on rats and because rats are larger, it’s easier to do memory tests and record signals from their brain. For example they are strong enough to press levers to get a food reward and their size and comfort level with water means they won’t just float aimlessly in a water maze as “fluffy” mice tend to do.