Using a mix of experimental studies and computational models, the researchers show that somatosensory feedback, or neural signals from specialized sensors throughout a cat’s body, help inform the spinal cord about the ongoing movement and coordinate the four limbs to keep cats from falling when they encounter obstacles. Research suggests that with those motion-related sensory signals the animal can walk even if the connection between the spinal cord and the brain is partially fractured.

Understanding the mechanisms of this type of balance control is particularly relevant to older people who often have balance issues and can injure themselves in falls. Eventually, the researchers hope this could bring new understanding to somatosensory feedback’s role in balance control. It could also lead to progress in spinal cord injury treatment because the research suggests activation of somatosensory neurons can improve spinal neural networks’ function below the site of spinal cord damage.

“We have been interested in the mechanisms that make it possible to reactivate injured networks in the spinal cord,” said School of Biological Sciences Professor Boris Prilutsky. “We know from previous studies that somatosensory feedback from moving legs helps activate spinal networks that control locomotion, enabling stable movement.”

Coordinated Cats

Although genetically modified mouse models have recently become dominant in neural control of locomotion research, the cat model offers an important advantage. When they move, mice remain crouched, meaning they are less likely to have balance problems even if somatosensory feedback fails. Humans and cats, on the other hand, cannot maintain balance or even move if they lose sensory information about limb motion. This suggests that larger species, like cats and humans, might have a different organization of spinal neural network controlling locomotion compared to rodents.

Georgia Tech partnered with researchers at the University of Sherbrooke in Canada and Drexel University in Philadelphia to better understand how signals from sensory neurons coordinate movements of the four legs. The Sherbrooke lab trained cats to walk on a treadmill at a pace consistent with human gait and then used electrodes to stimulate their sensory nerve.

The researchers focused on the sensory nerve that transmits touch sensation from the top of the foot to the spinal cord. By electrically stimulating this nerve, researchers mimicked hitting an obstacle and saw how the cats stumbled and corrected their movement in response. Stimulations were applied in four periods of the walking cycle: mid-stance, stance-to-swing transition, mid-swing, and swing-to-stance transition. From this, they learned that mid-swing and the stance-to-swing transition were the most significant periods because the stimulation increased activity in muscles that flex the knee and hip joints, joint flexion and toe height, step length, and step duration of the stimulated limb.

“In order to maintain balance, the animal must coordinate movement of the other three limbs, otherwise it would fall,” Prilutsky said. “We found that stimulation of this nerve during the swing phase increases the duration of the stance phase of the other limbs and improves stability.”

In effect, when the cat stumbles during the swing phase, the sensation triggers spinal reflexes that ensure the three other limbs stay on the ground and keep the cat upright and balanced, while the swing limb steps over the obstacle.

Computational Cats

With these Canadian lab experiments, the researchers at Georgia Tech and Drexel University are using observations to develop a computational model of the cat’s musculoskeletal and spinal neural control systems. The data gathered are used to compute somatosensory signals related to length, velocity, and produced force of muscles, as well as pressure on the skin in all limbs. This information forms motion sensations in the animal’s spinal cord and contributes to interlimb coordination by the spinal neuronal networks.

“To help treat any disease, we need to understand how the intact system works,” Prilutsky said. “That was one reason why this study was performed, so we could understand how the spinal networks coordinate limb movements and develop a realistic computational model of spinal control of locomotion. This will help us know better how the spinal cord controls locomotion.”

The study examined 850 galaxies at redshifts of z three through nine, or as they were roughly 11-13 billion years ago. Associate Professor Jeyhan Kartaltepe from Rochester Institute of Technology’s School of Physics and Astronomy said that JWST’s ability to see faint high redshift galaxies in sharper detail than Hubble allowed the team of researchers to resolve more features and see a wide mix of galaxies, including many with mature features such as disks and spheroidal components.

“There have been previous studies emphasizing that we see a lot of galaxies with disks at high redshift, which is true, but in this study we also see a lot of galaxies with other structures, such as spheroids and irregular shapes, as we do at lower redshifts,” said Kartaltepe, lead author on the paper and CEERS co-investigator. “This means that even at these high redshifts, galaxies were already fairly evolved and had a wide range of structures.”

The results of the study, which have been posted to ArXiv and accepted for publication in The Astrophysical Journal, demonstrate JWST’s advances in depth, resolution, and wavelength coverage compared to Hubble. Out of the 850 galaxies used in the study that were previously identified by Hubble, 488 were reclassified with different morphologies after being shown in more detail with JWST. Kartaltepe said scientists are just beginning to reap the benefits of JWST’s impressive capabilities and are excited by what forthcoming data will reveal.

“This tells us that we don’t yet know when the earliest galaxy structures formed,” said Kartaltepe. “We’re not yet seeing the very first galaxies with disks. We’ll have to examine a lot more galaxies at even higher redshifts to really quantify at what point in time features like disks were able to form.”

The study used an initial data set captured by CEERS when JWST first came online in June, but the survey has since captured a total of 60 observing hours, potentially providing thousands of high redshift galaxies to further explore. Kartaltepe said COSMOS-Web, the largest General Observer program selected for JWST’s first year, will provide an even larger sample through 255 hours of observing time with the telescope. COSMOS-Web began its observing campaign this month.

Several of Kartaltepe’s collaborators on the study were RIT students, including astrophysical sciences and technology Ph.D. students Caitlin Rose, Brittany Vanderhoof, and Isabella Cox; imaging science Ph.D. student James Liu; and undergraduate physics student Jayse Petersen.

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Materials provided by Rochester Institute of Technology. Original written by Luke Auburn. Note: Content may be edited for style and length.

The characteristic pulsations and brightness of RR Lyrae stars make them excellent “standard candles” for measuring galactic distances. These new observations allowed the researchers to trace the outer limits of the Milky Way’s halo.

“This study is redefining what constitutes the outer limits of our galaxy,” said Raja GuhaThakurta, professor and chair of astronomy and astrophysics at UC Santa Cruz. “Our galaxy and Andromeda are both so big, there’s hardly any space between the two galaxies.”

GuhaThakurta explained that the stellar halo component of our galaxy is much bigger than the disk, which is about 100,000 light years across. Our solar system resides in one of the spiral arms of the disk. In the middle of the disk is a central bulge, and surrounding it is the halo, which contains the oldest stars in the galaxy and extends for hundreds of thousands of light years in every direction.

“The halo is the hardest part to study because the outer limits are so far away,” GuhaThakurta said. “The stars are very sparse compared to the high stellar densities of the disk and the bulge, but the halo is dominated by dark matter and actually contains most of the mass of the galaxy.”

Yuting Feng, a doctoral student working with GuhaThakurta at UCSC, led the new study and is presenting their findings in two talks at the American Astronomical Society meeting in Seattle on January 9 and 11.

According to Feng, previous modeling studies had calculated that the stellar halo should extend out to around 300 kiloparsecs or 1 million light years from the galactic center. (Astronomers measure galactic distances in kiloparsecs; one kiloparsec is equal to 3,260 light years.) The 208 RR Lyrae stars detected by Feng and his colleagues ranged in distance from about 20 to 320 kiloparsecs.

“We were able to use these variable stars as reliable tracers to pin down the distances,” Feng said. “Our observations confirm the theoretical estimates of the size of the halo, so that’s an important result.”

The findings are based on data from the Next Generation Virgo Cluster Survey (NGVS), a program using the Canada-France-Hawaii Telescope (CFHT) to study a cluster of galaxies well beyond the Milky Way. The survey was not designed to detect RR Lyrae stars, so the researchers had to dig them out of the dataset. The Virgo Cluster is a large cluster of galaxies that includes the giant elliptical galaxy M87.

“To get a deep exposure of M87 and the galaxies around it, the telescope also captured the foreground stars in the same field, so the data we used are sort of a by-product of that survey,” Feng explained.

According to GuhaThakurta, the excellent quality of the NGVS data enabled the team to obtain the most reliable and precise characterization of RR Lyrae at these distances. RR Lyrae are old stars with very specific physical properties that cause them to expand and contract in a regularly repeating cycle.

“The way their brightness varies looks like an EKG — they’re like the heartbeats of the galaxy — so the brightness goes up quickly and comes down slowly, and the cycle repeats perfectly with this very characteristic shape,” GuhaThakurta said. “In addition, if you measure their average brightness, it is the same from star to star. This combination is fantastic for studying the structure of the galaxy.”

The sky is full of stars, some brighter than others, but a star may look bright because it is very luminous or because it is very close, and it can be hard to tell the difference. Astronomers can identify an RR Lyrae star from its characteristic pulsations, then use its observed brightness to calculate how far away it is. The procedures are not simple, however. More distant objects, such as quasars, can masquerade as RR Lyrae stars.

“Only astronomers know how painful it is to get reliable tracers of these distances,” Feng said. “This robust sample of distant RR Lyrae stars gives us a very powerful tool for studying the halo and testing our current models of the size and mass of our galaxy.”

This study is based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/IRFU, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii.