Watching somebody relieve an itch with a delightful old scratch can have you dragging your nails over your skin as quick as you can say, “Aaaaah … that’s the spot.”
Contagious scratching doesn’t just affect humans. Similar reactions are seen in mice when they see their rodent friends digging in. A new study of mice scratching revealed something very unusual about this social phenomenon.
The brain’s visual processing hardware is not involved in the physiological process of being inspired after seeing the action performed by another.
This means that if one rodent scratched its itch, other rodents will do the same, even though they don’t have pictures of their scratching behavior.
This might sound like a superpower but it is possible to respond to visual stimuli even if the visual cortex that processes them is damaged.
The phenomenon is called “blindsight”, or unconscious sight. Recent researchThis suggests that it is based upon a subcortical path, which transmits information from the eyes to other parts and bypasses the visual cortex entirely.
It’s basically a neural shortcut that allows blind people to navigate a hallway without being able to see.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture” allowfullscreen>
Similar pathways might alert mice to blind itching. Researchers disabling the visual cortex in mice in a lab experiment resulted in the animals scratching themselves even though they were able to see if another mouse was doing the same.
Recordings of the activity in mice brain cells indicate that the ‘itching contagion’ begins with specialized light sensitive cells in the retina called intrinsically photographic retinal ganglion cell (ipRGC).
These less-known retinal cell connections connect directly to the brain region responsible in triggering a neurological scratching sequence, also known as The suprachiasmatic nucleus (SCN). Subcortical pathways are located deep in the brain. They allow light to set the circadian rhythm without needing to be visual interpreted as an image.
Scientists have done some amazing things in the past. SpeculativeAlthough it has not been determined, it is possible that ipRGCs may play a role in blindsight.
Although ipRGCs may be helpful in vision, they are not capable of rendering a scene. Yet, new research on mice shows otherwise.
When ipRGCs were stopped sending signals to mice models, contagious scratching behavior was not observed in the animals, even though researchers maintained their visual system intact.
“This contagious itch – which is a reflex response in mice, just as grooming is – must be somehow important for survival,” ConclusionZhou-Feng Chen, neurobiologist from Washington University in St Louis.
Contagious itch can occur in humans as well. However, mice are able to manage it by a pathway that isn’t known to be responsible. This could indicate that imitative scratching may be an ancient protective behavior.
Chen says it’s like a frog taking on an insect. Frogs lackMammals have the same neurological wiring that interprets vision, but their eyes still transmit information about light via retinal Ganglion cells.
These ganglion cells, which are sensitive to movement because of the speed at which a frog can catch its prey, are especially sensitive. A frog’s sticky tongues seem able to tell where to go when a fly buzzes near it.
It seems that mice have a similar reflex. They sense the scratching of their companions without having to go through the trouble of acquiring the neurology needed to convert it into a visual impression.
Although it is not clear why contagious scratching may work in mice, mindless response to threats on cue could give social animal a competitive advantage.
The researchers also suggest that contagious behavior like this might be primitive form of emotional transmission. The new ipRGC pathway discovered in mice may be connected to the thalamus (the brain’s seat for sensory information relaying) which was also implicated in recent research. Processing emotional stimuli.
Stress is, in essence, a feeling of emotional tension. Itching can be nothing but stressful.
The stress hormone cortisol was elevated in mice’s blood after they were shown videos of scratching mice. This suggests that itch contagion is more than a form motor mimicry. It conveys information about an animal’s distress.
“Contagious itching in humans may look different than what we have seen in mice.” Says Chen.
“It’s probable that the human response to contagious itch requires the visual cortex. However, contagious itching may not be an evolutionary trait in humans. To understand why certain behaviors are important for survival, you need to look back at animals like these mice.
Aside from ipRCGs, other researchers have pointed to mirror neurons – brain cells that are active when we imitate actions or negative affect – having a role in the contagiousness of human scratching.
Future studies will compare other mammals to gain a better understanding of these pathways as well as their evolutionary history.
“This type of contagious behavior can be found in all animals.” Says Chen.
The study was published by Cell Reports.
