First recognition of self in the mirror is spurred by touch

Most babies begin recognizing themselves in mirrors when they are about a year and half old. This kind of self-recognition is an important developmental milestone, and now scientists at The University of Texas at Austin have discovered a key driver for it: experiences of touch.

Their new study found babies who were prompted to touch their own faces developed self-recognition earlier than those who did not.

The research was published this month in the journal Current Biology.

"This suggests that babies pulling on their toes or tapping their fingers are not just playing," said Jeffrey Lockman, a professor of human development and family sciences at UT and senior author on the paper.

"They are developing self-awareness through self-directed activity. I think this work demonstrates a possible mechanism by which self-recognition can develop based on active experience that human babies naturally generate."

Researchers began by placing small vibrating discs on the foreheads and cheeks of toddlers when they were around 14 months old, before the usual age at which self-recognition occurs.

In response to the vibration, the children would reach up and touch the disc.

Next, researchers turned the children to face a mirror and watched as they reached up to touch the discs.

Researchers then had the children perform the standard mirror-mark test for self-recognition in which a small mark of paint or makeup was placed on each child's face.

If the child looked in the mirror and touched the mark on their own face or said words like their name or "me," they demonstrated self-recognition.

Researchers also observed a control group of children who were exposed to the laboratory experience with mirrors but not the vibrating discs.

Both groups were comparable at the beginning of the study and observed monthly until they recognized themselves or reached 21 months.

The children who touched their face more frequently recognized themselves in the mirror about two months earlier, on average, than when children typically first begin to recognize themselves in a mirror.

The study challenges a longstanding assumption that self-recognition in early childhood is somehow hardwired.

For a long time, scientists believed early recognition in the mirror was a built-in function of human brains and those of our closest primate relatives, versus linked to sensory or motor experiences.

The researchers said the findings may have implications for interventions for children with motor development delays.

"Interventions for infants who have issues related to motor skills are typically focused on reaching for objects in the external world and manipulating them," Lockman said.

"These findings suggest that reaching to the body may be equally important and that exploring the body is the gateway to self-knowledge."

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Plants can distinguish when touch starts and stops, study suggests

Even without nerves, plants can sense when something touches them and when it lets go, a Washington State University-led study has found.

In a set of experiments, individual plant cells responded to the touch of a very fine glass rod by sending slow waves of calcium signals to other plant cells, and when that pressure was released, they sent much more rapid waves. While scientists have known that plants can respond to touch, this study shows that plant cells send different signals when touch is initiated and ended.

"It is quite surprising how finely sensitive plants cells are -- that they can discriminate when something is touching them. They sense the pressure, and when it is released, they sense the drop in pressure," said Michael Knoblauch, WSU biological sciences professor and senior author of the study in the journal Nature Plants. "It's surprising that plants can do this in a very different way than animals, without nerve cells and at a really fine level."

Knoblauch and his colleagues conducted a set of 84 experiments on 12 plants using thale cress and tobacco plants that had been specially bred to include calcium sensors, a relatively new technology. After placing pieces of these plants under a microscope, they applied a slight touch to individual plant cells with a micro-cantilever, essentially a tiny glass rod about the size of a human hair. They saw many complex responses depending on the force and duration of the touch, but the difference between the touch and its removal was clear.

Within 30 seconds of the applied touch to a cell, the researchers saw slow waves of calcium ions, called cytosolic calcium, travelling from that cell through the adjacent plant cells, lasting about three to five minutes. Removal of the touch showed an almost instant set of more rapid waves that dissipated within a minute.

The authors believe these waves are likely due to the change in pressure inside the cell. Unlike animal cells with permeable membranes, plant cells also have strong cellular walls that cannot be easily breached, so just a light touch will temporarily increase pressure in a plant cell.

The researchers tested the pressure theory mechanically by inserting a tiny glass capillary pressure probe into a plant cell. Increasing and decreasing pressure inside the cell resulted in similar calcium waves elicited by the start and stop of a touch.

"Humans and animals sense touch through sensory cells. The mechanism in plants appears to be via this increase or decrease of the internal cell pressure," said Knoblauch. "And it doesn't matter which cell it is. We humans may need nerve cells, but in plants, any cell on the surface can do this."

Previous research has shown that when a pest like a caterpillar bites a plant leaf, it can initiate the plant's defensive responses such as the release of chemicals that make leaves less tasty or even toxic to the pest. An earlier study also revealed that brushing a plant triggers calcium waves that activate different genes.

The current study was able to differentiate the calcium waves between touch and letting go, but how exactly the plant's genes respond to those signals remains to be seen. With new technologies like the calcium sensors used in this study, scientists can start to untangle that mystery, Knoblauch said.

"In future studies, we have to trigger the signal in a different way than has been done before to know what signal, if touch or letting go, triggers downstream events," he said.

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Pair of studies uncover surprising new roles for spinal cord and brainstem in touch

The sense of touch is essential to almost everything we do, from routine tasks at home to navigating unfamiliar terrains that may conceal dangers. Scientists have long been interested in understanding exactly how the touch information we obtain with our hands and other parts of the body makes its way to the brain to create the sensations we feel.

Yet, key aspects of touch -- including how the spinal cord and brainstem are involved in receiving, processing, and transmitting signals -- have remained poorly understood.

Now, a pair of papers by scientists at Harvard Medical School reveal critical new insights into how the spinal cord and brainstem contribute to the sense of touch.

Specifically, the research shows that the spinal cord and the brainstem, previously thought to be mere relay centers for touch information, are actively involved in processing touch signals as they travel to higher-order brain regions.

One study, published Nov. 4 in Cell, shows that specialized neurons in the spinal cord form a complex network that processes light touch -- think the brush of a hand or a peck on the cheek -- and sends this information to the brainstem.

In another study, published Nov. 23 in Nature, researchers established that direct and indirect touch pathways work together, converging in the brainstem to shape how touch is processed.

"These studies focus the spotlight on the spinal cord and the brainstem as sites where touch information is integrated and processed to convey different types of touch. We hadn't fully appreciated before how these areas contribute to the brain's representation of vibration, pressure, and other features of tactile stimuli," said David Ginty, the Edward R. and Anne G. Lefler Professor of Neurobiology in the Blavatnik Institute at HMS and the senior author on both papers.

Although the studies were conducted in mice, mechanisms for touch are largely conserved across species, including humans, which means the basics of touch processing could be useful for scientists studying human conditions such as neuropathic pain characterized by touch dysfunction.

"This detailed understanding of tactile sensation -- that is, feeling the world through contact with the skin -- may have profound implications for understanding how disease, disorder, and injury can affect our ability to interact with the environment around us," said James Gnadt, program director at the National Institute of Neurological Disorders and Stroke (NINDS), which provided part of the funding for the studies.

Overlooked and underappreciated

The historical view of touch is that sensory neurons in the skin encounter a touch stimulus such as pressure or vibration and send this information in the form of electrical impulses that travel directly from the skin to the brainstem. There, other neurons relay touch information to the brain's primary somatosensory cortex -- the highest level of the touch hierarchy -- where it is processed into sensation.

However, Ginty and his team wondered if and how the spinal cord and brainstem are involved in processing touch information. These areas occupy the lowest level of the touch hierarchy, and combine to form a more indirect touch pathway into the brain.

"People in the field thought that the diversity and richness of touch came just from sensory neurons in the skin, but that thinking bypasses the spinal cord and brainstem," said Josef Turecek, a postdoctoral fellow in the Ginty lab and the first author on the Nature paper.

Many neuroscientists are not familiar with spinal cord neurons, called postsynaptic dorsal column (PSDC) neurons, that project from the spinal cord into the brainstem -- and textbooks tend to leave PSDC neurons out of diagrams depicting the details of touch, Turecek explained.

For Ginty, the way that the spinal cord and brainstem have been overlooked in touch brings to mind early research on the visual system. Initially, scientists studying vision thought that all processing occurred in the visual cortex of the brain. However, it turned out that the retina, which receives visual information long before it reaches the cortex, is heavily involved in processing this information.

"Analogous to research on the visual system, these two papers address how touch information coming from the skin is processed in the spinal cord and brainstem before it moves up the touch hierarchy to more complex brain regions," Ginty said.

Connecting the dots

In the Cell paper, the researchers used a technique they developed to simultaneously record the activity of many different neurons in the spinal cord as mice experienced various types of touch. They discovered that over 90 percent of neurons in the dorsal horn -- the sensory processing area of the spinal cord -- responded to light touch.

"This was surprising because classically it was thought that dorsal horn neurons in the superficial layers of the spinal cord respond mostly to temperature and painful stimuli. We hadn't appreciated how light-touch information is distributed in the spinal cord," said Anda Chirila, a research fellow in the Ginty lab and the co-lead author on the paper with graduate student Genelle Rankin.

Moreover, these responses to light touch varied considerably across genetically different populations of neurons in the dorsal horn, which were found to form a highly interconnected and complex neural network. This variation in responses, in turn, gave rise to a diversity of touch information carried from the dorsal horn to the brainstem by PSDC neurons. In fact, when the researchers silenced various dorsal horn neurons, they saw a reduction in the diversity of light-touch information conveyed by PSDC neurons.

"We think this information on how touch is encoded in the spinal cord, which is the first site in the touch hierarchy, is important for understanding fundamental aspects of touch processing," Chirila said.

In their other study, published in Nature, scientists focused on the next step in the touch hierarchy: the brainstem. They explored the relationship between the direct pathway from sensory neurons in the skin to the brainstem and the indirect pathway that sends touch information through the spinal cord, as described in the Cell paper.

"Brainstem neurons get both direct and indirect input, and we were really curious about what aspects of touch each pathway brings to the brainstem," Turecek said.

To parse this question, the researchers alternately silenced each pathway and recorded the response of neurons in mouse brainstems. The experiments showed that the direct pathway is important for communicating high-frequency vibration, while the indirect pathway is needed to encode the intensity of pressure on the skin.

"The idea is that these two pathways converge in the brainstem with neurons that can encode both vibration and intensity, so you can shape responses of those neurons based on how much direct and indirect input you have," Turecek explained. In other words, if brainstem neurons have more direct than indirect input, they communicate more vibration than intensity, and vice versa.

Additionally, the team discovered that both pathways can convey touch information from the same small area of skin, with information on intensity detouring through the spinal cord before joining information on vibration that travels directly to the brainstem. In this way, the direct and indirect pathways work together, enabling the brainstem to form a spatial representation of different types of touch stimuli from the same area.

Finally on the map

Up until now, "most people have viewed the brainstem as a relay station for touch, and they haven't even had the spinal cord on the map at all," Ginty said. For him, the new studies "demonstrate that there's a tremendous amount of information processing occurring in the spinal cord and brainstem -- and this processing is critical for how the brain represents the tactile world."

Such processing, he added, likely contributes to the complexity and diversity of the touch information that the brainstem sends to the somatosensory cortex.

Next, Ginty and team plan to repeat the experiments in mice that are awake and behaving, to test the findings under more natural conditions. They also want to expand the experiments to include more types of real-world touch stimuli, such as texture and movement.

The researchers are also interested in how information from the brain -- for example, about an animal's level of stress, hunger, or exhaustion -- affects how touch information is processed in the spinal cord and brainstem. Given that touch mechanisms appear to be conserved across species, such information may be especially relevant for human conditions such as autism spectrum disorders or neuropathic pain, in which neural dysfunction causes hypersensitivity to light touch.

"With these studies we've laid the fundamental building blocks for how these circuits work and what their importance is," Rankin said. "Now we have the tools to dissect these circuits to understand how they're functioning normally, and what's changing when something goes wrong."

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Enhanced touch screens could help you 'feel' objects

The next time you buy a new couch, you may not ever have to leave your old one to get a feel for the texture of the new material.

Dr. Cynthia Hipwell, Oscar S. Wyatt Jr. '45 Chair II Professor in the J. Mike Walker '66 Department of Mechanical Engineering at Texas A&M University, is leading a team working to better define how the finger interacts with a device with the hope of aiding in the further development of technology that goes beyond sensing and reacting to your touch.

The team's research was recently published and featured on the cover of the journal Advanced Materials.

The ultimate goal of furthering this human-machine interface is to give touch devices the ability to provide users with a richer touch-based experience by equipping the technology with the ability to mimic the feeling of physical objects. Hipwell shared examples of potential implementations ranging from a more immersive virtual reality platform to tactile display interfaces like those in a motor vehicle dashboard and a virtual shopping experience that would let the user feel the texture of materials before purchasing them.

"This could allow you to actually feel textures, buttons, slides and knobs on the screen," Hipwell said. "It can be used for interactive touch screen-based displays, but one holy grail would certainly be being able to bring touch into shopping so that you could feel the texture of fabrics and other products while you're shopping online."

Hipwell explained that at its essence, the "touch" in current touch screen technology is more for the screen's benefit than the user. With the emergence and refinement of increasingly sophisticated haptic technology, that relationship between user and device can grow to be more reciprocal.

She added that the addition of touch as a sensory input would ultimately enrich virtual environments and lighten the burden of communication currently carried by audio and visuals.

"When we look at virtual experiences, they're primarily audio and visual right now and we can get audio and visual overload," Hipwell said. "Being able to bring touch into the human-machine interface can bring a lot more capability, much more realism, and it can reduce that overload. Haptic effects can be used to draw your attention to make something easier to find or easier to do using a lower cognitive load."

Hipwell and her team are approaching the research by looking at the multiphysics -- the coupled processes or systems involving multiple physical fields occurring at the same time -- of the interface between the user's finger and the device. This interface is incredibly complex and changes with different users and environmental conditions.

"We're looking at electro-wetting effects (the forces that result from an applied electric field), electrostatic effects, changes in properties of the finger, the material properties and surface geometry of the device, the contact mechanics, the fluid motion, charge transport -- really, everything that's going on in the interface to understand how the device can be designed to be more reliable and higher performing," Hipwell said. "Ultimately, our goal is to create predictive models than enable a designer to create devices with maximum haptic effect and minimum sensitivity to user and environmental variation."

As research into and development of the technology continues to progress, Hipwell said she predicts consumers will begin to see early elements implemented into common devices over the next few years, with some early products already in development.

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A common ancestor for cells involved in hearing and touch

The sensory cells in the inner ear and the touch receptors in the skin actually have a lot in common, according to a new study from the USC Stem Cell laboratory of Neil Segil published in the Proceedings of the National Academy of Sciences (PNAS).

"There are striking similarities in the development of two types of specialized sensory cells: the so-called 'hair cells' that receive sound vibrations in the inner ear, and the Merkel cells that sense light touch at the surface of the skin," said Segil, who is a Professor in the Department of Stem Cell Biology and Regenerative Medicine, and the USC Tina and Rick Caruso Department of Otolaryngology -- Head and Neck Surgery. "Ultimately, these developmental similarities are a legacy of shared evolutionary history. This demonstrates how the story of evolutionary developmental biology, or 'evo devo,' also extends to what we call the 'epigenetic level' -- or how genes are regulated."

In the study, PhD student Haoze (Vincent) Yu, postdoctoral scholar Litao Tao, and their colleagues identified a shared mechanism involved in gene regulation or epigenetics, that enables stem cells and progenitor cells to differentiate into more specialized hair cells and Merkel cells.

In order to begin the process of differentiation, the right parts of a stem cell's DNA need to be taken out of storage. Each human cell can store around six feet of DNA in its nucleus, because this DNA is wound around tiny "spools" made up of proteins called histones. These spools of DNA and histone protein are further packed together to form what are known are nucleosomes, which are stacked to create chromatin, which is the material that makes up the chromosomes.

When DNA is wound tightly into this storage configuration, the chromatin is closed and inaccessible to the protein ATOH1. This protein is a "master regulator" that can activate a network of differentiation genes in the DNA within the chromatin -- but not without first gaining access.

To this end, ATOH1 stimulates the production of a second protein known as POU4F3, an aptly named "pioneer factor" with the ability to venture into new frontiers by binding to closed and inaccessible chromatin. After POU4F3 blazes a trail by binding to the closed chromatin, ATOH1 is able to move forward with engaging and activating the network of genes that drives differentiation into hair cells and Merkel cells.

Strikingly, there is significant overlap in the specific regions of chromatin that POU4F3 makes accessible to ATOH1 in hair cells and Merkel cells.

"It's remarkable that these two cell types, which are both involved in sensing mechanical stimuli but derive from distinct parts of the embryo, both rely on the same ATOH1/POU4F3 mechanism in order to differentiate," said Segil. "Our study suggests that this mechanism is extremely ancient, and emerged before hair cells and Merkel cells diverged from a common evolutionary ancestor -- an 'ur-mechanoreceptor' cell type."

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Technology that restores the sense of touch in nerves damaged as a result of injury

Tel Aviv University's new and groundbreaking technology inspires hope among people who have lost their sense of touch in the nerves of a limb following amputation or injury. The technology involves a tiny sensor that is implanted in the nerve of the injured limb, for example in the finger, and is connected directly to a healthy nerve. Each time the limb touches an object, the sensor is activated and conducts an electric current to the functioning nerve, which recreates the feeling of touch. The researchers emphasize that this is a tested and safe technology that is suited to the human body and could be implanted anywhere inside of it once clinical trials will be done.

The technology was developed under the leadership of a team of experts from Tel Aviv University: Dr. Ben M. Maoz, Iftach Shlomy, Shay Divald, and Dr. Yael Leichtmann-Bardoogo from the Department of Biomedical Engineering, Fleischman Faculty of Engineering, in collaboration with Keshet Tadmor from the Sagol School of Neuroscience and Dr. Amir Arami from the Sackler School of Medicine and the Microsurgery Unit in the Department of Hand Surgery at Sheba Medical Center. The study was published in the journal ACS Nano.

The researchers say that this unique project began with a meeting between the two Tel Aviv University colleagues -- biomedical engineer Dr. Maoz and surgeon Dr. Arami. "We were talking about the challenges we face in our work," says Dr. Maoz, "and Dr. Arami shared with me the difficulty he experiences in treating people who have lost tactile sensation in one organ or another as a result of injury. It should be understood that this loss of sensation can result from a very wide range of injuries, from minor wounds -- like someone chopping a salad and accidentally cutting himself with the knife -- to very serious injuries. Even if the wound can be healed and the injured nerve can be sutured, in many cases the sense of touch remains damaged. We decided to tackle this challenge together, and find a solution that will restore tactile sensation to those who have lost it."

In recent years, the field of neural prostheses has made promising developments to improve the lives of those who have lost sensation in their limbs by implanting sensors in place of the damaged nerves. But the existing technology has a number of significant drawbacks, such as complex manufacturing and use, as well as the need for an external power source, such as a battery. Now, the researchers at Tel Aviv University have used state-of-the-art technology called a triboelectric nanogenerator (TENG) to engineer and test on animal models a tiny sensor that restores tactile sensation via an electric current that comes directly from a healthy nerve and doesn't require a complex implantation process or charging.

The researchers developed a sensor that can be implanted on a damaged nerve under the tip of the finger; the sensor connects to another nerve that functions properly and restores some of the tactile sensation to the finger. This unique development does not require an external power source such as electricity or batteries. The researchers explain that the sensor actually works on frictional force: whenever the device senses friction, it charges itself.

The device consists of two tiny plates less than half a centimeter by half a centimeter in size. When these plates come into contact with each other, they release an electric charge that is transmitted to the undamaged nerve. When the injured finger touches something, the touch releases tension corresponding to the pressure applied to the device -- weak tension for a weak touch and strong tension for a strong touch -- just like in a normal sense of touch.

The researchers explain that the device can be implanted anywhere in the body where tactile sensation needs to be restored, and that it actually bypasses the damaged sensory organs. Moreover, the device is made from biocompatible material that is safe for use in the human body, it does not require maintenance, the implantation is simple, and the device itself is not externally visible.

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Fingerprints' moisture-regulating mechanism strengthens human touch

 

Fingerprint ridges close-up.

Human fingerprints have a self-regulating moisture mechanism that not only helps us to avoid dropping our smartphone, but could help scientists to develop better prosthetic limbs, robotic equipment and virtual reality environments, a new study reveals.

Primates -- including humans, monkeys and apes -- have evolved epidermal ridges on their hands and feet with a higher density of sweat glands than elsewhere on their bodies. This allows precise regulation of skin moisture to give greater levels of grip when manipulating objects.

Fingerprints help to increase friction when in contact with smooth surfaces, boost grip on rough surfaces and enhance tactile sensitivity. Their moisture-regulating mechanism ensures the best possible hydration of the skin's keratin layer to maximise friction.

Researchers at the University of Birmingham worked with partners at research institutions in South Korea, including Seoul National University and Yonsei University -- publishing their findings today in Proceedings of the National Academy of Sciences (PNAS).

Co-author Mike Adams, Professor in Product Engineering and Manufacturing, at the University of Birmingham commented: "Primates have evolved epidermal ridges on their hands and feet. During contact with solid objects, fingerprint ridges are important for grip and precision manipulation. They regulate moisture levels from external sources or the sweat pores so that friction is maximised and we avoid 'catastrophic' slip and keep hold of that smartphone."

"Understanding the influence of finger pad friction will help us to develop more realistic tactile sensors -- for example, applications in robotics and prosthetics and haptic feedback systems for touch screens and virtual reality environments."

Ultrasonic lubrication is commonly used in touch screen displays that provide sensory 'haptic' feedback, but its effectiveness is reduced when a user has dry compared with moist finger pads. Moreover, being able to distinguish between fine-textured surfaces, such as textiles, by touch relies on the induced lateral vibrations but the absence of sliding friction inhibits our ability to identify what we are actually touching.

Fingerprints are unique to primates and koalas -- appearing to have the dual function of enhancing evaporation of excess moisture whist providing a reservoir of moisture at their bases that enables grip to be maximised.

The researchers have discovered that, when finger pads are in contact with impermeable surfaces, the sweat from pores in the ridges makes the skin softer and thus dramatically increases friction. However, the resulting increase in the compliance of the ridges causes the sweat pores eventually to become blocked and hence prevents excessive moisture that would reduce our ability to grip objects.

Using hi-tech laser-based imaging technology, the scientists found that moisture regulation could be explained by the combination of this sweat pore blocking and the accelerated evaporation of excessive moisture from external wetting as a result of the specific cross-sectional shape of the epidermal furrows when in contact with an object.

These two functions result in maintaining the optimum amount of moisture in the fingerprint ridges that maximises friction whether the finger pad is initially wet or dry.

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Breaking the skill limit, pianists attain more delicate touch

 In JST Strategic Basic Research Programs, Drs. Masato Hirano and Shinichi Furuya, Sony Computer Science Laboratories, Inc., discovered a training method to further improve the delicate touch of pianists.

Experts such as pianists, athletes and surgeons acquire advanced skills through tremendous amounts of practice. It is difficult to further improve upon these skills, and the methods for exceeding these limits have not been clarified.

The research group developed a system that freely controls the weight of piano keys using a haptic device, which enables to control the strength and direction of the force. This same group has also invented active haptic training (AHT) that enhances tactile force sense during exercise by presenting the tasks of discriminating the difference in piano key weights and the correctness of answers. Three experiments were conducted using AHT in 64 pianists and 25 ordinary persons who had received no professional music training. The results showed that enhancing the somatosensory function of fingertips with AHT could improve the accuracy of keystrokes, breaking through the ceiling effect of over-trained skills. Such skill improvement was not observed through usual repetitive practice, or in ordinary persons with no piano experience.

This study demonstrated that, in order to exceed the limits in the exercise skills of experts, it was important to optimize the method rather than increase the amount of training. This finding is expected to be useful for elucidating principles of the nervous system that define the limits in exercise skills, new training theories to exceed the limits of experts' expertise, and functional flexibility (plasticity) of the expert's brain, as well as in the development of rehabilitation methods for neurological disorders in which finger functions were impaired due to excessive training.

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Touch and taste? It's all in the tentacles

 

Suction cups on octopus tentacles

Octopuses have captured the human imagination for centuries, inspiring sagas of sea monsters from Scandinavian kraken legends to TV's "Voyage to the Bottom of the Sea" and, most recently, Netflix's less-threatening "My Octopus Teacher." With their eight suction-cup covered tentacles, their very appearance is unique, and their ability to use those appendages to touch and taste while foraging further sets them apart.

In fact, scientists have wondered for decades how those arms, or more specifically the suction cups on them, do their work, prompting a number of experiments into the biomechanics. But very few have studied what is happening on a molecular level. In a new report, Harvard researchers got a glimpse into how the nervous system in the octopus' arms (which operate largely independently from its centralized brain) manage this feat.

The work published Thursday in Cell.

The scientists identified a novel family of sensors in the first layer of cells inside the suction cups that have adapted to react and detect molecules that don't dissolve well in water. The research suggests these sensors, called chemotactile receptors, use these molecules to help the animal figure out what it's touching and whether that object is prey.

"We think because the molecules do not solubilize well, they could, for instance, be found on the surface of octopuses' prey and [whatever the animals touch]," said Nicholas Bellono, an assistant professor of molecular and cellular biology and the study's senior author. "So, when the octopus touches a rock versus a crab, now its arm knows, 'OK, I'm touching a crab [because] I know there's not only touch but there's also this sort of taste.'"

In addition, scientists found diversity in what the receptors responded to and the signals they then transmitted to the cell and nervous systems.

"We think that this is important because it could facilitate complexity in what the octopus senses and also how it can process a range of signals using its semi-autonomous arm nervous system to produce complex behaviors," Bellono said.

The scientists believe this research can help uncover similar receptor systems in other cephalopods, the invertebrate family that also includes squids and cuttlefish. The hope is to determine how these systems work on a molecular level and answer some relatively unexplored questions about how these creatures' capabilities evolved to suit their environment.

"Not much is known about marine chemotactile behavior and with this receptor family as a model system, we can now study which signals are important for the animal and how they can be encoded," said Lena van Giesen, a postdoctoral fellow in the Bellono Lab and lead author of the paper. "These insights into protein evolution and signal coding go far beyond just cephalopods."

Along with Giesen, other co-authors from the lab include Peter B. Kilian, an animal technician, and Corey A.H. Allard, a postdoctoral fellow.

"The strategies they have evolved in order to solve problems in their environment are unique to them and that inspires a great deal of interest from both scientists and non-scientists alike," Kilian said. "People are drawn to octopuses and other cephalopods because they are wildly different from most other animals."

The team set out to uncover how the receptors are able to sense chemicals and detect signals in what they touch, like a tentacle around a snail, to help them make choices.

Octopus arms are distinct and complex. About two-thirds of an octopus's neurons are located in their arms. Because the arms operate partially independently from the brain, if one is severed it can still reach for, identify, and grasp items.

The team started by identifying which cells in the suckers actually do the detecting. After isolating and cloning the touch and chemical receptors, they inserted them in frog eggs and in human cell lines to study their function in isolation. Nothing like these receptors exists in frog or human cells, so the cells act essentially like closed vessels for the study of these receptors.

The researchers then exposed those cells to molecules such as extracts from octopus prey and others items to which these receptors are known to react. Some test subjects were water-soluble, like salts, sugars, amino acids; others do not dissolve well and are not typically considered of interest by aquatic animals. Surprisingly, only the poorly soluble molecules activated the receptors.

Researchers then went back to the octopuses in their lab to see whether they too responded to those molecules by putting those same extracts on the floors of their tanks. They found the only odorants the octopuses receptors responded to were a non-dissolving class of naturally occurring chemicals known as terpenoid molecules.

"[The octopus] was highly responsive to only the part of the floor that had the molecule infused," Bellono said. This led the researchers to believe that the receptors they identified pick up on these types of molecules and help the octopus distinguish what it's touching. "With the semi-autonomous nervous system, it can quickly make this decision: 'Do I contract and grab this crab or keep searching?'"

While the study provides a molecular explanation for this aquatic touch-taste sensation in octopuses through their chemotactile receptors, the researchers suggest further study is needed, given that a great number of unknown natural compounds could also stimulate these receptors to mediate complex behaviors.

"We're now trying to look at other natural molecules that these animals might detect," Bellono said.

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