In The News

Cells in the hippocampus store memories of acquaintances, a new study reports.

Mice have brain cells that are dedicated to storing memories of other mice, according to a new study from MIT neuroscientists. These cells, found in a region of the hippocampus known as the ventral CA1, store “social memories” that help shape the mice’s behavior toward each other.

The researchers also showed that they can suppress or stimulate these memories by using a technique known as optogenetics to manipulate the cells that carry these memory traces, or engrams.

“You can change the perception and the behavior of the test mouse by either inhibiting or activating the ventral CA1 cells,” says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and director of the RIKEN-MIT Center for Neural Circuit Genetics at the Picower Institute for Learning and Memory.

Tonegawa is the senior author of the study, which appears in the Sept. 29 online edition of Science. MIT postdoc Teruhiro Okuyama is the paper’s lead author.

Neuroscientists retrieve missing memories in mice with early Alzheimer’s symptoms.

In the early stages of Alzheimer’s disease, patients are often unable to remember recent experiences. However, a new study from MIT suggests that those memories are still stored in the brain — they just can’t be easily accessed.

The MIT neuroscientists report in Nature that mice in the early stages of Alzheimer’s can form new memories just as well as normal mice but cannot recall them a few days later.

Furthermore, the researchers were able to artificially stimulate those memories using a technique known as optogenetics, suggesting that those memories can still be retrieved with a little help. Although optogenetics cannot currently be used in humans, the findings raise the possibility of developing future treatments that might reverse some of the memory loss seen in early-stage Alzheimer’s, the researchers say.

Neuroscientists identify a brain circuit that is critical for forming episodic memories.

When you remember a particular experience, that memory has three critical elements — what, when, and where. MIT neuroscientists have now identified a brain circuit that processes the “when” and “where” components of memory.

This circuit, which connects the hippocampus and a region of the cortex known as entorhinal cortex, separates location and timing into two streams of information. The researchers also identified two populations of neurons in the entorhinal cortex that convey this information, dubbed “ocean cells” and “island cells.”

Previous models of memory had suggested that the hippocampus, a brain structure critical for memory formation, separates timing and context information. However, the new study shows that this information is split even before it reaches the hippocampus…

Artificially reactivating positive memories could offer an alternative to traditional antidepressants.

MIT neuroscientists have shown that they can cure the symptoms of depression in mice by artificially reactivating happy memories that were formed before the onset of depression.

The findings, described in the June 18 issue of Nature, offer a possible explanation for the success of psychotherapies in which depression patients are encouraged to recall pleasant experiences. They also suggest new ways to treat depression by manipulating the brain cells where memories are stored. The researchers believe this kind of targeted approach could have fewer side effects than most existing antidepressant drugs, which bathe the entire brain…

Scientists use optogenetics to reactivate memories that could not otherwise be retrieved.

Memories that have been “lost” as a result of amnesia can be recalled by activating brain cells with light.

In a paper published today in the journal Science, researchers at MIT reveal that they were able to reactivate memories that could not otherwise be retrieved, using a technology known as optogenetics.

The finding answers a fiercely debated question in neuroscience as to the nature of amnesia, according to Susumu Tonegawa, the Picower Professor in MIT’s Department of Biology and director of the RIKEN-MIT Center at the Picower Institute for Learning and Memory, who directed the research by lead authors Tomas Ryan, Dheeraj Roy, and Michelle Pignatelli…

MIT research sheds light on retrieving correct memories and how animals “think” when they self-correct their on-going behaviors.

Mice running mazes sometimes go left when they should go right. MIT’s Picower Institute for Learning and Memory researchers report in the April 24 online version of Cell that a certain pattern of brain waves pinpointed the precise moment the rodents chose the correct path to the reward–as well as when they noticed their errors. They also discovered that these brain waves appear in a delayed manner when animals changed their mind and self-corrected to correctly perform the task.

In humans and animals, rhythmic electrical oscillations produced by millions of neurons firing in sync are thought to play a role in memory formation and retrieval. For the first time, Picower Institute neuroscientists linked a specific synchronized oscillation pattern with its correlating behavior.

The work may lead to new therapies for patients suffering from Alzheimer’s disease and other memory impairments. What’s more, the results indicated that the trained mice in the study recognized and reversed their “oops” moments, raising tantalizing questions about the extent to which animals can analyze and control their own cognitive processes…

Study reveals how the brain links memories of events that occur one after the other.

Suppose you heard the sound of skidding tires, followed by a car crash. The next time you heard such a skid, you might cringe in fear, expecting a crash to follow — suggesting that somehow, your brain had linked those two memories so that a fairly innocuous sound provokes dread.

MIT neuroscientists have now discovered how two neural circuits in the brain work together to control the formation of such time-linked memories. This is a critical ability that helps the brain to determine when it needs to take action to defend against a potential threat, says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and senior author of a paper describing the findings in the Jan. 23 issue of Science.

“It’s important for us to be able to associate things that happen with some temporal gap,” says Tonegawa, who is a member of MIT’s Picower Institute for Learning and Memory. “For animals it is very useful to know what events they should associate, and what not to associate.”…

MIT neuroscientists map neural circuits involving the CA2 region of the hippocampus.

The hippocampus is the region of the brain that is responsible for episodic memory. For decades, neuroscientists have been mapping the hippocampus’s neural circuits to better understand how memories are stored, retrieved, and lost.

The trisynaptic circuit, discovered by the legendary anatomist Santiago Ramón y Cajal more than 100 years ago, has long been considered the anatomical substrate responsible for learning and memory. But the trisynaptic circuit involved only the entorhinal cortex and the dentate gyrus, CA1 region and CA3 region of the hippocampus; the tiny CA2 region of the hippocampus, located between CA1 and CA3, was not thought to play a critical role.

When a 2005 study using molecular cell markers revealed that the CA2 region might be wider than previously thought, neuroscientists began to wonder whether CA2 had a role in memory. To address this, scientists needed to know more about the CA2 region’s boundaries and its neural connections to CA1 and CA3. But traditional methodologies like dye injections and electrophysiological stimulation of axon bundles haven’t been up to the task…

Neuroscientists discover neurological hyperactivity that produces disordered thinking.

Schizophrenia patients usually suffer from a breakdown of organized thought, often accompanied by delusions or hallucinations. For the first time, MIT neuroscientists have observed the neural activity that appears to produce this disordered thinking.

The researchers found that mice lacking the brain protein calcineurin have hyperactive brain-wave oscillations in the hippocampus while resting, and are unable to mentally replay a route they have just run, as normal mice do.

Mutations in the gene for calcineurin have previously been found in some schizophrenia patients. Ten years ago, MIT researchers led by Susumu Tonegawa, the Picower Professor of Biology and Neuroscience, created mice lacking the gene for calcineurin in the forebrain; these mice displayed several behavioral symptoms of schizophrenia, including impaired short-term memory, attention deficits, and abnormal social behavior…