Bats bolster brain hypothesis, maybe technology, too

Amid a neuroscience debate about how people and animals focus on distinct objects within cluttered scenes, some of the newest and best evidence comes from the way bats “see” with their ears, according to a new paper in the Journal of Experimental Biology. In fact, the perception process in question could improve sonar and radar technology.

Bats demonstrate remarkable skill in tracking targets such as bugs through the trees in the dark of night. James Simmons, professor of neuroscience at Brown University, the review paper’s author, has long sought to explain how they do that.

It turns out that experiments in Simmons’ lab point to the “temporal binding hypothesis” as an explanation. The hypothesis proposes that people and animals focus on objects versus the background when a set of neurons in the brain attuned to features of an object all respond in synchrony, as if shouting in unison, “Yes, look at that!” When the neurons do not respond together to an object, the hypothesis predicts, an object is relegated to the perceptual background.

Because bats have an especially acute need to track prey through crowded scenes, albeit with echolocation rather than vision, they have evolved to become an ideal testbed for the hypothesis.

“Sometimes the most critical questions about systems in biology that relate to humans are best approached by using an animal species whose lifestyle requires that the system in question be exaggerated in some functional sense so its qualities are more obvious,” said Simmons, who plans to discuss the research at the 2014 Cold Spring Harbor Asia Conference the week of September 15 in Suzhou, China.

A focus of frequencies

Here’s how he’s determined over the years that temporal binding works in a bat. As the bat flies it emits two spectra of sound frequencies — one high and one low — into a wide cone of space ahead of it. Within the spectra are harmonic pairs of high and low frequencies, for example 33 kilohertz and 66 kilohertz. These harmonic pairs reflect off of objects and back to the bat’s ears, triggering a response from neurons in its brain. Objects that reflect these harmonic pairs in perfect synchrony are the ones that stand out clearly for the bat.

Of course it’s more complicated than just that. Many things could reflect the same frequency pairs back at the same time. The real question is how a target object would stand out. The answer, Simmons writes, comes from the physics of the echolocation sound waves and how bat brains have evolved to process their signal. Those factors conspire to ensure that whatever the bat keeps front-and-center in its echolocation cone will stand out from surrounding interference.

The higher frequency sounds in the bat’s spectrum weaken in transit through the air more than lower frequency sounds. The bat also sends out the lower frequencies to a wider span of angles than the high frequencies. So for any given harmonic pair, the farther away or more peripheral a reflecting object is, the weaker the higher frequency reflection in the harmonic pair will be. In the brain, Simmons writes, the bat converts this difference in signal strength into a delay in time (about 15 microseconds per decibel) so that harmonic pairs with wide differences in signal strength end up being perceived as way out of synchrony in time. The temporal binding hypothesis predicts that the distant or peripheral objects with these out-of-synch signals will be perceived as the background while front-and-center objects that reflect back both harmonics with equal strength will rise above their desynchronized competitors.

With support from sources including the U.S. Navy, Simmons’s research group has experimentally verified this. In key experiments (some dating back 40 years) they have sat big brown bats at the base of a Y-shaped platform with a pair of objects – one a target with a food reward and the other a distractor – on the tines of the Y. When the objects are at different distances, the bat can tell them apart and accurately crawl to the target. When the objects are equidistant, the bat becomes confused. Crucially, when the experimenters artificially weaken the high-pitched harmonic from the distracting object, even when it remains equidistant, the bat’s acumen to find the target is restored.

In further experiments in 2010 and 2011, Simmons’ team showed that if they shifted the distractor object’s weakened high-frequency signal by the right amount of time (15 microseconds per decibel) they could restore the distractor’s ability to interfere with the target object by restoring the synchrony of the distractor’s harmonics. In other words, they used the specific predictions of the hypothesis and their understanding of how it works in bats to jam the bat’s echolocation ability.

If targeting and jamming sound like words associated with radar and sonar, that’s no coincidence. Simmons works with the U.S. Navy on applications of bat echolocation to navigation technology. He recently began a new research grant from the Office of Naval Research that involves bat sonar work in collaboration with researcher Jason Gaudette at the Naval Undersea Warfare Center in Newport, R.I.

Simmons said he believes the evidence he has gathered about the neuroscience of bats not only supports the temporal binding hypothesis, but also can inspire new technology.

“This is a better way to design a radar or sonar system if you need it to perform well in real-time for a small vehicle in complicated tasks,” he said.

Bats are amazing. In darkest night they easily navigate and find food using a system of biosonar that exceeds anything humans have devised. Perhaps the best characterized bat is the mustached bat, studied extensively by Nobuo Suga (I actually interviewed with him when I was searching for a postdoctoral position many years ago). Suga’s experiments include a real “bat mobile” whereby he would study bat biosonar in the absence of potentially confounding wing flaps, and a pendulum-like “bat swing” that allowed him to carry out important studies of the Doppler shift compensation response. Using these methods along with careful electrophysiological recordings, he revealed a complex auditory cortical network with remarkable specializations that reflected the bat’s unique environmental niche.  See the full comic here.

Looking to Animals for Ultrasound Technology

Sonar and ultrasound, which use sound as a navigational device and to paint accurate pictures of an environment, are the basis of countless technologies, including medical ultrasound machines and submarine navigation systems. But when it comes to more accurate sonar and ultrasound, animals’ “biosonar” capabilities still have the human race beat.

But not for long. In a new project that studies bats, dolphins and mole rats, Prof. Nathan Intrator of Tel Aviv Univ.’s Blavatnik School of Computer Science, in collaboration with Brown Univ.’s Prof. Jim Simmons, is working to identify what gives biosonar the edge over human-made technologies. Using a unique method for measuring how the animals interpret the returning signals, Intrator has determined that the key to these animals’ success is superior, real-time data processing. “Animal ‘echolocations’ are done in fractions of milliseconds, at a resolution so high that a dolphin can see a tennis ball from approximately 260 feet away,” he says, noting that the animals are able to process several pieces of information simultaneously.

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Zooming in for a safe flight

Bats do not use sight to navigate when flying. Instead, they emit ultrasound pulses and measure the echoes reflected from their surroundings. They have an extremely flexible internal navigation system that enables them to do this. A new study published in Nature Communications shows that when a bat flies close to an object, the number of active neurons in the part of a bat’s brain responsible for processing acoustic information about spatial positioning increases. This information helps these masters of flight to react rapidly and avoid obstacles.

As nocturnal animals, bats are perfectly adapted to a life without light. They emit echolocation sounds and use the delay between the reflected echoes to measure distance to obstacles or prey. In their brains, they have a spatial map representing different echo delays. A study carried out by researchers at Technische Universität München (TUM) has shown for the first time that this map dynamically adapts to external factors.

Closer objects appear larger

When a bat flies in too close to an object, the number of activated neurons in its brain increases. As a result, the object appears disproportionately larger on the bat’s brain map than objects at a safe distance, as if it were magnified. “The map is similar to the navigation systems used in cars in that it shows bats the terrain in which they are moving,” explains study director Dr. Uwe Firzlaff at the TUM Chair of Zoology. “The major difference, however, is that the bats’ inbuilt system warns them of an impending collision by enhancing neuronal signals for objects that are in close proximity.”

Bats constantly adapt their flight maneuvers to their surroundings to avoid collisions with buildings, trees or other animals. The ability to determine lateral distance to other objects also plays a key role here. Which is why bats process more spatial information than just echo delays. “Bats evaluate their own motion and map it against the lateral distance to objects,” elaborates the researcher.

Brain processes complex spatial information

In addition to the echo reflection time, bats process the reflection angle of echoes. They also compare the sound volume of their calls with those of the reflected sound waves and measure the wave spectrum of the echo. “Our research has led us to conclude that bats display much more spatial information on their acoustic maps than just echo reflection.”

The results show that the nerve cells interpret the bats’ rapid responses to external stimuli by enlarging the active area in the brain to display important information. “We may have just uncovered one of the fundamental mechanisms that enables vertebrates to adapt flexibly to continuously changing environments,” concludes Firzlaff.

L'uomo pipistrello esiste...e non è Batman!

La natura ha dotato alcuni animali, come i pipistrelli, i delfini ed altri Odontoceti, in condizioni di scarsa visibilità, della capacità di misurare lo spazio circostante e ciò che in esso è contenuto. Questo fenomeno, noto come tecnica di ecolocalizzazione o biosonar, utilizza lo stesso …

Made a new account. The name “echolocate” was available, and since I’ve got a bat theme going (thatdarnbat, battea) I decided hey why not? I checked to see if Biosonar was available, and luck would have it that this little guy was in the pound! It was too perfect, I had to snatch him up. u3u
Maybe he’ll be my mutant Korbat, whenever I get my hands on a potion ahah.

Also I guess I made a Bori because Neopets wouldn’t let me proceed without making a dang pet. I have too many already, stop it Neopets.