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Moonlight

The Poplar Avenue at Moret, Cloudy Day, Morning via Alfred Sisley

Size: 59x73 cm Medium: oil on canvas

According to legend, Pythagoras invented a cup to prevent his students from drinking too greedily. If they overfilled the cup, it would immediately drain out all the fluid. The trick works thanks to a U-shaped tube in the center of the cup. As long as the liquid level is below the highest point in the U-tube, only the entrance side of the tube will be filled. As soon as the liquid level in the cup is higher, the weight of all that fluid forces liquid up and around the bend. This kicks off a siphoning effect that pulls all the fluid out. Coincidentally, this is the same way that toilet flushing works! Pulling the handle releases extra water into the bowl that raises the fluid level higher than the highest point in a U-bend. That establishes a siphon, which (provided nothing has clogged the pipe), empties the toilet bowl. (Video credit: Periodic Videos)

Spinal Stimulators Repurposed to Restore Touch in Lost Limb

Imagine tying your shoes or taking a sip of coffee or cracking an egg but without any feeling in your hand. That’s life for users of even the most advanced prosthetic arms.

Although it’s possible to simulate touch by stimulating the remaining nerves in the stump after an amputation, such a surgery is highly complex and individualized. But according to a new study from the University of Pittsburgh’s Rehab Neural Engineering Labs, spinal cord stimulators commonly used to relieve chronic pain could provide a straightforward and universal method for adding sensory feedback to a prosthetic arm.

For this study, published in eLife, four amputees received spinal stimulators, which, when turned on, create the illusion of sensations in the missing arm.

“What’s unique about this work is that we’re using devices that are already implanted in 50,000 people a year for pain — physicians in every major medical center across the country know how to do these surgical procedures — and we get similar results to highly specialized devices and procedures,” said study senior author Lee Fisher, Ph.D., assistant professor of physical medicine and rehabilitation, University of Pittsburgh School of Medicine. 

The strings of implanted spinal electrodes, which Fisher describes as about the size and shape of “fat spaghetti noodles,” run along the spinal cord, where they sit slightly to one side, atop the same nerve roots that would normally transmit sensations from the arm. Since it’s a spinal cord implant, even a person with a shoulder-level amputation can use this device 

Fisher’s team sent electrical pulses through different spots in the implanted electrodes, one at a time, while participants used a tablet to report what they were feeling and where.

All the participants experienced sensations somewhere on their missing arm or hand, and they indicated the extent of the area affected by drawing on a blank human form. Three participants reported feelings localized to a single finger or part of the palm.

“I was pretty surprised at how small the area of these sensations were that people were reporting,” Fisher said. “That’s important because we want to generate sensations only where the prosthetic limb is making contact with objects.”

When asked to describe not just where but how the stimulation felt, all four participants reported feeling natural sensations, such as touch and pressure, though these feelings often were mixed with decidedly artificial sensations, such as tingling, buzzing or prickling.

Although some degree of electrode migration is inevitable in the first few days after the leads are implanted, Fisher’s team found that the electrodes, and the sensations they generated, mostly stayed put across the month-long duration of the experiment. That’s important for the ultimate goal of creating a prosthetic arm that provides sensory feedback to the user. 

“Stability of these devices is really critical,” Fisher said. “If the electrodes are moving around, that’s going to change what a person feels when we stimulate.” 

The next big challenges are to design spinal stimulators that can be fully implanted rather than connecting to a stimulator outside the body and to demonstrate that the sensory feedback can help to improve the control of a prosthetic hand during functional tasks like tying shoes or holding an egg without accidentally crushing it. Shrinking the size of the contacts — the parts of the electrode where current comes out — is another priority. That might allow users to experience even more localized sensations. 

“Our goal here wasn’t to develop the final device that someone would use permanently,” Fisher said. “Mostly we wanted to demonstrate the possibility that something like this could work.”

To keep pain in check, count down

Diverse cognitive strategies affect our perception of pain. Studies by LMU neuroscientist Enrico Schulz and colleagues have linked the phenomenon to the coordinated activity of neural circuits located in different brain areas.

Is the heat still bearable, or should I take my hand off the hotplate? Before the brain can react appropriately to pain, it must evaluate and integrate sensory, cognitive and emotional factors that modulate the perception and processing of the sensation itself. This task requires the exchange of information between different regions of the brain. New studies have confirmed that there is a link between the subjective experience of pain and the relative levels of neural activity in functional structures in various sectors of the brain. However, these investigations have been carried out primarily in contexts in which the perception of pain was intensified either by emotional factors or by consciously focusing attention on the painful stimulus. Now, LMU neuroscientist Enrico Schulz, in collaboration with colleagues at the University of Oxford, has asked how cognitive strategies that affect one’s subjective perception of pain influence the patterns of neural activity in the brain.

In the study, 20 experimental subjects were exposed to a painful cold stimulus. They were asked to adopt one of three approaches to attenuating the pain: (a) counting down from 1000 in steps of 7, (b) thinking of something pleasant or beautiful, and (c) persuading themselves – by means of autosuggestion – that the stimulus was not really that bad. During the experimental sessions, the subjects were hooked up to a 7T magnetic resonance imaging (MRI) scanner to visualise the patterns of neural activity in the brain, which were later analysed in detail.

In order to assess the efficacy of the different coping strategies, participants were also asked to evaluate the subjective intensity of the pain on a scale of 0 to 100. The results revealed that the countdown strategy was the most effective of the three methods. “This task obviously requires such a high level of concentration that it distracts the subject’s attention significantly from the sensation of pain. In fact some of our subjects managed to reduce the perceived intensity of pain by 50%,” says Schulz. “One participant later reported that she had successfully adopted the strategy during the most painful phase of childbirth.”

In a previous paper published in the journal Cortex in 2019, the same team had already shown that all three strategies help to attenuate the perception of pain, and that each strategy evoked a different pattern of neural activity. In the new study, Schulz and his collaborators carried out a more detailed analysis of the MRI scans, for which they divided the brain into 360 regions. “Our aim was to determine which areas in the brain must work together in order to successfully reduce the perceived intensity of the pain,” Schulz explains. “Interestingly, no single region or network that is activated by all three strategies could be identified. Instead, under each experimental condition, neural circuits in different brain regions act in concert to varying extents.”

The attenuation of pain is clearly a highly complex process, which requires a cooperative response that involves many regions distributed throughout the brain. Analysis of the response to the countdown technique revealed close coordination between different parts of the insular cortex, among other patterns. The imaginal distraction method, i.e. calling something picturesque or otherwise pleasing to mind, works only when it evokes intensive flows of information between the frontal lobes. Since these structures are known to be important control centres in the brain, the authors believe that engagement of the imaginative faculty may require a greater degree of control, because the brain needs to search through more ‘compartments’ – to find the right memory traces, for instance. Comparatively speaking, counting backwards stepwise – even in such awkward steps – is likely to be a more highly constrained task. “To cope with pain, the brain makes use of a recipe that also works well in other contexts,” says Anne Stankewitz, a co-author of the new paper: “success depends on effective teamwork.” Her team now plans to test whether their latest results can be usefully applied to patients with chronic pain.

Actresses with passion in science

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