Seeing the world smaller after a stroke

  In December 2017, a 66-year-old Dutch man suffered a stroke, resulting in hypoxia in the right back of his brain. After rescue, he was out of danger. But something strange happened: everything he saw was much smaller than normal. For example, at a clothing store, he picked up an oversized T-shirt, thinking it was the medium he usually wears; he thought his wife must have washed the curtains in hot water because they looked like they had shrunk .
  To find out what was going on, a Dutch neuroscientist devised a series of tests for him. For privacy, the patient is referred to as DN.
  In one test, DN needed to visually estimate the size of 10 different cubes on the table. Consistent with his experience, each cube he estimated was about 30 percent smaller than it actually was.
  This perceptual distortion may be related to the problematic left visual field in DN. For example, when he looks at two cubes next to each other, he always thinks that the one on the left is smaller than the one on the right, even if they are actually the same size or the one on the left is slightly larger than the one on the right. Computer tests also showed that he also had difficulty recognizing the shape, position and movement of objects in his left visual field. This is not surprising, since information from the left visual field is normally processed by the right hemisphere, which is the site of DN stroke damage.

  An alligator lay motionless on a flat muck on the seafloor, grinning at the camera. It is two meters long and its skin is covered with dark green scales.
  In fact, this is the carcass of an alligator, which had been placed in a wire cage a day earlier and sank to the seabed at a depth of 2 kilometers in the Gulf of Mexico. There, a submersible and cameras were waiting for it. Under the control of the crew on board, a robotic arm reached into the cage and retrieved the body and placed it on the seabed.
  The next day, scientists on board watched a horrific scene on camera: Despite its tough skin, the alligator had been eaten by a swarm of carrion-eating giant king worms — which looked like ratwomen. (As the saying goes, tide bugs), each of them is the size of a football.
  Through this experiment, scientists learned about the ecology of the deep sea. The eating of alligator carcasses shows how ecosystems in deep-sea habitats are built on carcasses of animals that sink from the surface to the bottom of the ocean.
food sources for deep sea animals

  The depths of the ocean have long been considered a no-go zone for life, but more than a century ago, the assertion that the deep sea was lifeless was dismissed by naturalists. The vast ocean that covers nearly 71 percent of the Earth’s surface is actually the largest habitat for life on Earth. To this day, scientists are still trying to discover the limits of life on Earth by discovering bizarre new species and even entirely new ecosystems in the depths of the ocean. For example, in 2014, scientists discovered a species of snail fish in the Mariana Trench in the western Pacific Ocean that lives 8 kilometers underwater, breaking the deepest diving record for known fish; there is a hydrothermal vent in the Gulf of California, towering carbonic acid Around the salt chimney is a breeding ground for red-headed tube worms. These tube worms can live up to two or three hundred years and are one of the longest-lived animals on earth…
  So, what do these deep-sea animals feed on? At a depth of 200 meters, the only sunlight that can penetrate is dim blue light, but it is not enough to promote photosynthesis, so at this depth, no plants can survive. At a depth of more than 1,000 meters underwater, there is no light at all. This means that in the vast deep water area, there are no plants to provide animals with food, so what do the animals in the deep sea eat? Scientists speculate that they live only on organic matter—primarily dead plankton—that sink from the water’s surface. Because these food scraps drift slowly to the bottom of the sea like snow flakes, biologists gave them a poetic name – “sea snow”.
  However, not all sea snow can fall to the bottom of the sea, and many are eaten by other animals in the process of sinking: shrimps use the combs on their legs to sift the water, and use the sifted sea snow as a meal; swimming snails Will secrete mucus to salvage sea snow; vampire squid will wave long filaments to collect falling sea snow, and then roll it up and swallow it… Even at its peak, only 2% of the food produced on the water reaches the surface. 2 kilometers deep underwater. In this way, food sources for deep-sea animals are even more scarce. So what do they do for a living? Experiments by scientists throwing dead alligators into the deep sea show that they can only survive on food as large as crocodiles that reach the depths of the ocean.
  This is indeed the case, with nearly 1 million American alligators living in the southern United States. Storms can sweep dead alligator carcasses offshore. Elsewhere, there are large populations of saltwater crocodiles, caimans and other large reptiles living on the shoreline, whose dead bodies may also end up sinking to the bottom of the ocean.
gluttonous dinner under the sea

  In addition to alligator carcasses, sinking whale carcasses can also form food-rich “oases” on the seafloor that can last for decades. The first is that swimming scavengers, such as the moray-eel-shaped hagfish and the burr-covered polychaete worms, strip the soft tissue from the whale carcass and feast on it. And “opportunists” like crabs and snails flock around whale carcasses, feeding on the scraps left by scavengers. At the same time, anaerobic bacteria begin to break down its bones. These microbes, mixed with the sediment on the seafloor, coat whale bones in thick, colorful mats that attract shrimp, crabs and sea snails to feed.

Vampire squid rely on a filament to collect ‘sea snow’

  Especially in this experiment where the scientists sank the alligator’s body to a depth of 2 kilometers, the scientists did make a big discovery. After 50 days, they salvaged the crocodile wreck and found among the crocodiles what was commonly found on dead whale bones – a fluffy red worm. This is a bone-eating worm, sometimes called a zombie worm. Bone-eating worms look more like plants than animals, and they have roots and pink flower-like gills. Instead of a mouth and stomach, they absorb and digest collagen from dead fish bones through their roots with the help of symbiotic microbes in their bodies.
  The worms were first discovered in dead whale bones in 2002, and dozens of such worms have since been found in various submerged animal bones. But the two found in the alligators this time around were previously unknown species.

Bone-eating worms look more like plants than worms
Another food source on the ocean floor

  Reptile carcasses aren’t the only food source for deep-sea life. In addition to dropping an alligator, the team also sank large chunks of wood in the Gulf of Mexico. It is worth noting that on the seabed of the deep ocean, some animals seem to eat rotting wood.
  Perhaps this is not surprising, since rivers on land often carry large numbers of uprooted trees into the sea. After the trees are soaked, they eventually sink to the bottom of the sea. This is also a valuable resource for the seabed where food is scarce.
  The team kept the logs on the seafloor for 12 to 18 months before salvaging them and analyzing which animals made homes on them. Studies have shown that there are more than 60 species of animals on the logs. Among them is a species of wood-eating clams, which use the sharp edges of their shells to burrow into the wood, creating burrows that other animals, including sea cucumbers, lobsters and starfish, can inhabit.
  In this study, marine ecologists mainly wanted to confirm an ecological conjecture. The conjecture, proposed in the 1960s, says that the smaller and more isolated an island is, the fewer species will live on it. This conjecture is generally established on islands. Now ecologists want to see if that holds true in “oases” formed by sinking wood in the deep ocean.
  Studies of alligator carcasses and logs that have sunk to the bottom have shown that many deep-sea creatures depend on land animals and plants for their survival. Therefore, the land and the seabed, although seemingly distant, are closely related.

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