Memories are unreliable, at least for humans.

According to MIT scientist (and Nobel Prize winner) Susumu Tonegawa, as quoted in Scientific American, only humans have false memories.

“Humans are the most amazing, imaginative animals,” he said. “We are thinking. Lots of things are going on. Humans are recording what happens and passing it on.”

An imperfect memory, Tonegawa said, may be the price we pay for the imagination and creativity that makes us human.

The phenomenon of humans’ false memory is well-documented—in many court cases, defendants have been found guilty on testimony from witnesses and victims who were sure of their recollections, but DNA evidence later overturned the conviction.

But now, Tonegawa and his colleagues have succeeded in also creating false memories in mice, hoping to further understand where and how these fake memories are made in the human brain.

Memories are stored in networks of neurons that form memory traces for each experience we have. Scientists call these traces engrams, and can identify the cells that make up part of an engram for a specific memory and reactivate it with a technology called optogenetics.

Using optogenetics, Tonegawa’s research team started the experiment by putting mice in a chamber and recording their memories of that chamber. The chamber was harmless and pleasant enough that the mice felt comfortable exploring the space. The next day, the researchers moved the mice into a different chamber, stimulating the memory of the previous chamber. The scientists also lightly shocked the rodents’ feet.

On the third day, the mice were placed back into the first chamber. They now froze in fear, even though they had never been shocked there. A false memory had been incepted—the mice feared the memory of the first chamber because when the shock was given in the second, they were reliving the memory of being in the first.

The team discovered they could both implant false memories and that the neurological traces of these false memories are identical in nature to those of authentic memories. “Whether it’s a false or genuine memory, the brain’s neural mechanism underlying the recall of the memory is the same,” says Tonegawa.

The MIT team is now planning further studies of how memories can be distorted in the brain.

The study is published in the current edition of Science.

Image: Steve Ramirez and Xu Liu

In honor of Mother’s Day, today we’re featuring two recent science publications on mothering. Enjoy!

Last month a study in the Journal of Experimental Biology found that bees age faster when parenting. Those of us with our own brood at home might respond, “Well, duh!” My (well-covered) gray hair could tell you that.

But now we have proof. Norwegian scientist Daniel Münch wondered why winter bees were much longer lived than summer bees. In the summer, worker bees are mostly busy tending to the queen’s young and only live about two months total. In the winter, there are no young to tend to, and the bees can live up to seven months.

Münch and his colleagues performed the old switcheroo and transferred the winter bees’ hives indoors and brought the lab to more summery conditions. The queen started reproducing and the worker bees began their parenting. Sure enough, they witnessed a quicker decline.

In another experiment, when the scientists removed the young’uns, the worker bees showed no sign of aging. Get me a babysitter! Long-term!

Another recent study demonstrates that a mother’s arms are the best place for a young baby to be in terms of his or her chances of survival. Publishing in Current Biology, Kumi Kuroda and her colleagues determined that human babies and mouse pups alike automatically relax deeply when they are carried.

Whether held in a human mother’s arms or a mouse mom’s mouth, the research team found the infant calming response to maternal carrying is a coordinated set of nervous, motor and cardiac regulations. The scientists propose that it might be an evolutionarily conserved and essential component of mother-infant interaction.

Both mouse and human babies also stop moving when they are carried. And when baby mice are carried, their ultrasonic cries stop, too.

“This infant response reduces maternal burden of carrying and is beneficial for both the mother and the infant,” explains Kuroda, noting how stressful a crying baby can be on a parent.

Unfortunately, the study has no solution for when that calm and relaxed child starts crying again as soon as she is put back down. Further studies, please!

And to all of you moms out there, Happy Mother’s Day!

Image: Firmin Baes/Public Domain

Often we try and gather clues from extinction events to get hints about our future, but perhaps we’ve been missing the forest for the trees. Now, a team of researchers from Stanford and UC Berkeley are looking at past biodiversity loss for clues.

“If we only focus on extinction, we are not getting the whole story,” said Jessica Blois, PhD, lead author of a study published online in Nature yesterday.

Focusing on the last major warming event about 12,000 years ago, Blois and her Stanford colleague Elizabeth Hadly searched the Samwell Cave near Mt. Shasta for small mammal fossils. They also sampled the modern small mammal community by doing some live trapping in the area of the cave. (Jenny McGuire, a graduate student at the UC Berkeley, did the radiocarbon dating of the samples.)

They found big changes in the small mammal population. “In the Pleistocene, there were about as many gophers as there were voles as there were deer mice,” Hadly said. “But as you move into the warming event, there is a really rapid reduction in how evenly these animals are distributed.” As some species such as deer mice flourished, many other species declined.

Deer mice are considered a “weedy” species and, like the plants, don’t have a strong habitat preference—they are generalists that will move in wherever there is an opening. When they replace other small-mammal species, the effects ripple through the ecosystem.

“Small mammals are so common, we often take them for granted,” Blois said. “But they play important roles within ecosystems, in soil aeration and seed dispersal, for example, and as prey for larger animals.” And different small mammals play those roles differently. What’s more, “Even though all of the species survived, small mammal communities as a whole lost a substantial amount of diversity, which may make them less resilient to future change,” Blois said.

And according to Hadly, an extraordinarily rapid change is looming.

“The temperature change over the next hundred years is expected to be greater than the temperature that most of the mammals that are on the landscape have yet witnessed as a species,” she said.

Creative Commons image by r.i.c.h.

Two research articles published online yesterday in Nature publications follow mice research in two behavioral directions—one in father-child bonding and one on exhibiting pain—that may help humans in the future.

Neuroscientists in Calgary found that male mice that were allowed to nuzzle with their infant offspring were able to recognize those offspring as adults. According to Science Now, “That recognition correlates with new neuron growth in dad’s brain, the team reports online today in Nature Neuroscience. When Mak and Weiss injected a marker that tags newly formed neurons into the fathers just after their pups were born, they found up to 40% more new neurons in… mice that had nuzzled their pups.

“The results suggest that in mice, and perhaps in humans, young babies and dads bond biologically in ways that can last a lifetime.”

Other scientists in Canada studied facial expressions in mice, looking for signs of pain. They discovered that when subjected to moderate pain stimuli, mice showed discomfort through facial expressions in the same way humans do. (Watch Science in Action’s story about human facial expressions here.)

Their study, published online May 9 in the journal Nature Methods, also details the development of a Mouse Grimace Scale that could inform better treatments for humans and improve conditions for lab animals.

Continuing experiments in the lab will investigate whether the scale works equally well in other species, whether drugs given to mice after surgical procedures work well at their commonly prescribed doses, and whether mice can respond to the facial pain cues of other mice.

Creative Commons image by George Shuklin