Taste, smell, vision, hearing, touch and… awareness of one’s body in space? Yes, humans have at least six senses, and a new study suggests that the last one, called proprioception, may have a genetic basis.
Proprioception refers to how your brain understands where your body is in space. When police ask a drunken person to touch their finger to the tip of their nose, they’re testing the sense of proprioception.
Previous research in mice has suggested that a gene called PIEZO2 may play a role in this sense, according to the study. The PIEZO2 gene tells cells to produce “mechanosensitive” proteins. Mechanosensation is the ability to sense force, for example, being able to feel when someone presses down on your skin. It also plays a role in proprioception, according to the study.
To understand the gene’s effect in humans, the researchers at the National Institutes of Health (NIH) identified two young patients who had very rare mutations in the gene, according to the study, published Wednesday (Sept. 21) in the New England Journal of Medicine. The patients also had joint problems and scoliosis, the researchers noted.
The patients were asked to perform several tests related to movement and balance, according to the study. In one test, for example, the researchers found that the patients had a great deal of difficultly walking when they were blindfolded.
In another test, the patients were asked to reach for an object in front of them, first with their eyes open and then while blindfolded. Compared with people who did not have the gene mutation, the patients had a much harder time reaching for the object when blindfolded, the researchers found.
Other tests showed that the blindfolded patients with the gene mutation had more trouble guessing the direction of movement of their arms and legs when being moved by the researchers. They also had more trouble feeling the vibrations from a buzzing tuning fork placed against their skin, compared with the control participants.
In a different experiment, one patient said that the feeling of someone gently brushing the skin of the forearm was prickly, as opposed to a pleasant sensation that’s normally reported.
The findings suggest that the patients who carry the mutations in the PIEZO2 gene are “touch-blind,” Alexander Chesler, a principal investigator at the National Center for Complementary and Integrative Health and the lead author of the study, said in a statement.
“The patient’s version of the gene PIEZO2 may not work, so their neurons cannot detect touch or limb movements,” Chesler said.
Other parts of the patients’ nervous systems, however, were working fine, according to the study. The patients could feel pain, itch and temperature normally, the researchers said. In addition, their brains and cognitive abilities were similar to those of the control subjects.
The researchers said that the PIEZO2 gene has been linked to genetic musculoskeletal disorders in previous studies. Indeed, the findings of the new study suggest that the gene may be required for normal skeletal growth and development, the researchers said. Another possible explanation is that the sense of touch and proprioception play a role inskeletal development, they wrote.
‘Super Sleepers’ May Actually Be Sleep Deprived
People who claim they can thrive on just a few hours of sleep may actually be more tired than they realize, a new study suggests.
For most people, getting less than the recommended 7 to 9 hours of sleep per night makes them feel groggy, exhausted and cranky. But for a very small number of people, sometimes called “super sleepers,” getting less than 7 hours of sleep does not seem to have any effect on how they say they feel. And there is some evidence suggesting that such people may be genetically wired to function on very little sleep.
However, the new results show that these people’s real-life functioning may actually be affected by the shortage of sleep even though they report feeling just fine, said study co-author Paula Williams, an associate professor of psychology at the University of Utah.
In the study, the researchers scanned the brains of 839 people while they were awake. The participants were divided into two groups: One group who reported sleeping between 7 and 12 hours per night in the past month, on average; the other group saying they slept 6 hours or less per night in the past month, on average. The researchers then divided the latter, short-sleeping group into people who said they felt too drowsy to function normally during the day because they got so little sleep, and those who said they felt fine despite getting very little sleep on a regular basis.
It turned out that many of the people who slept 6 hours or less per night showed brain patterns that are normally seen when a person is asleepand not when he or she is awake, according to the study, published Thursday (Sept. 15) in the journal Brain and Behavior. This finding may mean that some of those people, including those who denied being dysfunctional due to the small amounts of sleep they normally got, might have actually drifted off for a bit while they were having their brains scanned.
“People are notoriously poor at knowing whether they’ve fallen asleep for a minute or two,” study co-author Jeff Anderson, an associate professor of radiology at the University of Utah, said in a statement. The researchers said they think that the reason why those people may have possibly fallen asleep during the experiment is not only that they were tired, but also that they were bored — their attention was not being stimulated while they were having their brains scanned.
Previous research that looked at the personalities of super sleepers showed that they tend to constantly seek out stimulation, which may help them “override the need for sleep,” Williams said.
Such stimulation may be the reason why they do not perceive that they are actually drowsy, she added.
“But there is evidence that if you take away stimulation, they are still showing the signs of sleep deprivation,” even though they have the perception that they are not sleep deprived, she said. One real-life example of the consequence of being sleep deprived in conditions without adequate stimulation may be nodding off in the middle of a boring meeting, she said.
Sara G. Miller, Staff Writer