Tag Archives: memories

Opposing

Memories for opposing behaviors are stored in the same parts of the brain, study finds

The same brain region can both motivate us to undertake a learned behavior or suppress it altogether, a new study found. The results will help us better understand how our brain stores memories and how they’re called upon when needed.

Opposing

Image credits Gerd Altmann / Pixabay.

While there is a general consensus that different memories are stored in different areas of the brain, there has been a lot of debate if each area can hold contradicting memories — those that control opposing behavior. For example, are the behaviors for a red or green traffic light encoded in the same area of the brain?

Pushing both ways

Questions like this one may seem a bit like nit-picking, but they’re actually really important in understanding us and our minds. Memories make us who we are. They’re also what the brain relies on to decide when and whether to take an action. So scientists are obviously keen on understanding how they work.

A new study from The Scripps Research Institute comes to answer this question. It is the first to offer proof that the same brain region can both motivate and suppress the same learned behavior.

“We behave the way we do in a specific situation because we have learned an association — a memory — tying an environmental cue to a behavior,” said Nobuyoshi Suto, TSRI Assistant Professor of Molecular and Cellular Neuroscience and co-author of the study.

“This study provides causal evidence that one brain region can store different memories.”

Suto’s work focuses on the brain structures that control motivation. For the study, he and the team trained rats to press a lever to get a reward of sugar water. After they got this down (the rats caught on pretty fast) the researchers further trained the animals to recognize two colored lights: green if the reward was available when pressing the lever, red if they would receive none. The rats quickly started adjusting their behavior after training in response to the colors. They pressed the lever more often when the green light was on, and didn’t bother with it when the red one was shining.

Based on previous electrophysiology studies, the team suspected that the mice’s brains stored both sessions of training they received in a region of the brain called the infralimbic cortex.

“We’ve seen correlational evidence, where we see brain activity together with a behavior, and we connect the dots to say it must be this brain activity causing this behavior,” said Suto.

“But such correlational evidence alone cannot establish the causality — proof that the specific brain activity is directly controlling the specific behavior.”

A weapon against addiction

The scientists then started systematically switching off specific groups of brain cells, or ‘neural ensembles’. These ensembles react to ques signaling if the reward is available or not. With the neurons inactivated, the rats didn’t perform any of the behavior encoded in the memories of those ensembles.

This proves that distinct neural ensembles in the same region of the brain directly control reward-seeking behavior or its suppression. Suto called the findings a step towards understanding how different memories are stored in the brain. He says the findings could help battle addiction by discovering which neurons are activated to motivate or prevent drug relapse.

In the future, he’d like to look at what other brain regions these infralimbic cortex neurons may be communicating with. In addition, he also would like to determine the brain chemicals mediating the promotion or suppression of reward seeking.

The full paper “Distinct memory engrams in the infralimbic cortex of rats control opposing environmental actions on a learned behavior” has been published in the journal eLife.

Half of people ‘remember’ fake facts that never happened

A new study casts some doubt on something very personal: our memories.

Image credits: wesleynitsckie.

About one in two people are highly prone to ‘remembering’ events that never happened, researchers from the University of Warwick have found. Dr Kimberley Wade in the Department of Psychology proved that if people are told about a completely fictitious event from “their lives,” they start to imagine it, and about half of people are willing to accept it as reality.

She and her colleagues recruited 400 participants, asking them to “recall” several different types of false memories – such as taking a childhood hot air balloon ride, playing a prank on a teacher, or creating havoc at a family wedding. To some extent, more than 50% of them claimed they remember it – 30% of participants appeared to fully ‘remember’ the event while 23% showed signs that they accepted the suggested event to some degree.

The study brings into question some instances of witness testimony and forensic investigations, but also sheds some light on therapy practices. Wade comments:

“We know that many factors affect the creation of false beliefs and memories — such as asking a person to repeatedly imagine a fake event or to view photos to “jog” their memory. But we don’t fully understand how all these factors interact. Large-scale studies like our mega-analysis move us a little bit closer.

“The finding that a large portion of people are prone to developing false beliefs is important. We know from other research that distorted beliefs can influence people’s behaviours, intentions and attitudes.”

This could also be significant for groups of people, where memories are arguably even more susceptible to this kind of effect.


Journal Reference: Alan Scoboria, Kimberley A. Wade, D. Stephen Lindsay, Tanjeem Azad, Deryn Strange, James Ost, Ira E. Hyman. A mega-analysis of memory reports from eight peer-reviewed false memory implantation studies. Memory, 2016; 1 DOI: 10.1080/09658211.2016.1260747

Sea slugs can’t remember their dreams — and here’s why you can’t, either

Scientists identified a seemingly counterintuitive process in the brain that prevents stimuli from forming memories. This system also springs into action as you are waking up to prevent corruption of previous memories — which might explain why it’s so hard to remember what you dreamed about.

Image credits Karolina / Pexels.

Without any prior training or a handbook handy when you wake up, it’s incredibly hard (and frustrating) to try and remember what you dreamed about a few moments before. It’s like you’re grasping at a shape in the fog — you know something was there and you have a rough idea of what it was like but every time you reach out you’re met with a handful of nothing. But why is it so hard to remember?

It all comes down to how our brain forms memories. Some of the stimuli that bombards you each and every day are deemed important enough to be memorized, which our neurons do by forming connections between each other — known as “trace memories”. This, however, is only a temporary measure, since these initial connections (and so the memories they maintain) are pretty fragile. To turn them into long-term memories, the brain has to go through a process called consolidation.

This involves synthesizing proteins to strengthen trace memories. However, if new stimuli are recorded while this process takes place, they could disrupt the process or overwrite the memory trace. So you might run into all sorts of problems if your brain started consolidating willy-nilly in the middle of the day. Thankfully, it evolved to only do so at night while you’re sleeping. But just in case you wake up during consolidation, the brain has mechanisms in place to prevent you from interrupting the process.

Slugging it out for memory space

A new study by Prof. Abraham Susswein of the Mina and Everard Goodman Faculty of Life Sciences and The Leslie and Susan Gonda (Goldschmied) Multidisciplinary Brain Research Center at Bar-Ilan University has identified this mechanism. He and his colleagues studied the sea hare Aplysia who are surprisingly convenient subjects for neuroscientific studies — they have simple nervous systems made up of large neurons, and have also shown basic learning abilities.

They found that after training the slugs’ brains started producing low levels of consolidating proteins, levels which spiked when the sea slugs went to sleep. But by blocking the production of these proteins in sleeping slugs, they were able to prevent them from forming long-term memories — confirming that they too consolidate memories during sleep.

They also found that exposing the animals to stimuli as they were waking up didn’t trigger the formation of new memories — they tried training the animals after awakening them from sleep, but the slugs couldn’t learn. On awakening, their brain blocked any interaction between the stimuli and long-term memory. When treating the slugs with a drug that inhibits protein production prior to training, the slugs could generate long-term memories however.

Removing the protein block allows the formation of long-term memories of experience just after waking up — even experiences that are too brief to trigger memories in fully awake slugs.

“The major insight from this research is that there is an active process in the brain which inhibits the ability to learn new things and protects the consolidation of memories,” Susswein says.

The team also found that training sea slugs in social isolation seems to inhibit their learning abilities, and identified a similar process active in this state.

“Our next step following on from this work is to identify these memory blocking proteins and to fathom how they prevent the formation of new memories,” says Susswein,

“We may also find that the blocking process accounts for why we cannot remember our dreams when we wake up.”

One exciting possibility is that is these proteins can inhibit memory formation, they could potentially be used to block unwanted or traumatic memories such as those of PTSD patients.

The full paper “New learning while consolidating memory during sleep is actively blocked by a protein synthesis dependent process” has been published in the journal eLife.

 

Exerting self-control impairs your capacity to form memories

Our ability to inhibit impulsive behaviors, to exercise willpower, is considered a core feature of the brain’s executive functions. This, along with others such as reasoning, working memory and attention regulate our thoughts and guide our behavior, allowing us to adapt them to the changing demands of our environment. But the effort our brain puts into refraining from impulses is so great that it can actually diminish its ability to form memories of the experience.

Image via cbsnews

During the roaring 60’s, psychologist Walter Mischel performed something that we, today, call the Marshmallow Test. Several pre-schoolers were asked to sit at a table, one at a time, and a sweet treat was placed in front of them — a marshmallow, a biscuit or a pretzel. They were told that the researcher would leave the room, and they would remain alone for some time. If they could resist eating the sweet, the researcher would reward them with even more sugary goodies when he returned.

This was designed to test self-control and delayed gratification — the kids brains’ ability to resist the body’s natural instinct to eat when food is available for the promise of more, but at a later date. Biologically, it makes little sense — a missed meal could mean death, and there is no assurance that the researcher will uphold his promise. But self-control is an important part of human behavior in modern society — Mischel and his colleagues tracked some of the children as they grew up, and then claimed that those who managed to hold out for longer in the original experiment performed better at school, and went on to become more successful in life, than those who couldn’t resist the temptation to eat the treat before the researcher returned to the room.

The usual way neuroscientists test self-control — they call it response inhibition, because scientists like fancy names — is with a “Go/No-go” procedure, by showing participants a series of sensory cues — such as pictures — and asking them to respond to most of them by pressing a button. But a small part of the cues have something that differentiates them from the rest, and the participants are supposed to refrain from pressing the button when met with them. The number of times a participant incorrectly presses the button on these “no-go” trials is thus taken as a measure of their self-control.

During one such experiment earlier this year, Yu-Chin Chiu and Tobias Egner of Duke University in North Carolina started suspecting that response inhibition impairs memory encoding. They asked volunteers to perform a ‘Go/ no–go’ task, using photographs of faces as cues, and then tested their ability to recognize the faces used in the experiment. The participants’ memory of the faces they saw during the “no–go” trials was far worse than for the rest, and they hypothesized that response inhibition competes with memory encoding for common resources.

Chiu and Egner repeated the experiment using functional magnetic resonance imaging (fMRI). They recruited an additional 24 participants, asking them to perform a “Go/ No–go” task while having their brains scanned. Once again, they used photographs of faces as visual cues, and tested the participants’ ability to recognise them shortly afterwards. This confirmed their earlier findings — the participants’ memory was worse for the ‘no–go’ than for ‘Go’ faces. When faced with a cue and inhibiting a response, the scans revealed a flurry of overlapping activation patterns in brain regions withing the frontal and parietal lobes, areas previously tied to response inhibition.

More importantly, “no-go” trials caused a greater activation of these areas than “go” trials. One area in particular, the ventrolateral prefrontal cortex, showed a very strong link to participant’s ability to record memories — greater activation of neurons in this part of the brain reduced the participant’s ability to remember a face later on.  A significant reduction of activity in brain regions involved in visual processing and memory were also observed during ‘no–go’ trials compared to ‘go’ trials.

This strongly suggests a link between self-control and memory encoding — they operate using common brain structures and networks, and the “hardware” may be unable to keep up with the load. Chiu and Egner’s “inhibition-induced forgetting” hypothesis holds that neural resources are limited, and response inhibition saps them very quickly, allotting very little to the formation of memories.

We already know that paying close attention to something can make us oblivious to other things that would normally be glaringly obvious, and future research will likely reveal more about how attention, memory, and self-control are linked to each other, and to other components of the brain’s executive function system.

 

 

 

 

Photo: neuroanthropology.net -

Erasing traumatic memories using gene therapy

Photo: neuroanthropology.net -

Photo: neuroanthropology.net –

It’s estimated that some 8 million people in the United States suffer from post-traumatic stress disorder (PTSD), causing great angst, depression and poor social integration. There are numerous therapies and techniques designed to help patients recover and banish the specters that lurk in the deepest recesses of their minds, haunting them. A common psychotherapy is fighting fear with fear, by having the patient face his ordeal: basically, the patient is introduced in an environment where the trauma is re-lived. The basis is that as the patient relieves past traumatic events, this time in a controlled and safe environment, he may have a chance at overcoming it.

For many, the memories of their traumas, be them war scenes or child abuse, are so deeply entrenched that therapy fails. The older these memories are, the more difficult the therapy becomes. Now, MIT neuroscientists are  proposing a novel way of accessing and re-editing traumas by erasing the old memory to replace it with a fresh, safe one. Li-Huei Tsai, director of MIT’s Picower Institute for Learning and Memory, along with colleagues, studied the effects of a drug called a HDAC2 inhibitor on mice.

Previously, scientists demonstrated that when new memories are formed  the chromatin in neurons — DNA packaged with proteins — undergoes remodeling to facilitate the activation of certain genes required to create new memories. The MIT researchers wanted to see what happens in the case of the chromatin modifications that occur when previously acquired memories are extinguished. First, the researchers purposely induced a conditioned fear-response into  mice by placing them in a specific environment, where a mild electrical shock was applied. Then, the researchers attempted to recondition the mice by repeatedly placing them inside the environment, this time shock free.

[RELATED] Possibility of erasing unwanted memories emerges 

They found that during the first 24 hours of trauma,  extensive chromatin remodeling occurred during the reconditioning. For several hours after the mice were placed back in the feared chamber, there was a dramatic increase in histone acetylation of memory-related genes, caused by inactivation of the protein HDAC2. That histone acetylation makes genes more accessible, turning on the processes needed to form new memories or overwrite old ones.

Erasing bad memories

Mice which had memories older than 30 days, however, showed no change in histone acetylation. In other words, re-exposure to trauma can work effectively by changing the primary emotional response to it, as a result of erasing the previous memory, but there’s only a short window of opportunity available.

“If you do something within this window of time, then you have the possibility of modifying the memory or forming a new trace of memory that actually instructs the animal that this is not such a dangerous place,”   says Tsai. “However, the older the memory is, the harder it is to really change that memory.”

Based on these findings, the MIT scientists chose to experiment with a HDAC2 inhibitor, which can cause structural changes in the brain, essentially making it more plastic increasing the possibility that very strong new memories will override old, traumatic memories. Mice with trauma memories older than 30 days were treated with this inhibitor and subjected to the same re-conditioning technique. This time, their traumatic memories were extinguished just as easily as in the mice with 24-hour-old memories.

Moreover, the HDAC2 inhibitor treatment seems to turn on a group of genes, which in turn, eventually, activate other genes necessary for memory formation. In the hippocampus, the part of the brain where memory are stored, the number of neuron connections was found to be greater and stronger than usual.

“Our experiments really strongly argue that either the old memories are permanently being modified, or a new much more potent memory is formed that completely overwrites the old memory,” Tsai says.

“This could be a very promising way to bring older memories back, process them in the hippocampus, and then extinguish them with the correct paradigm,” says Jelena Radulovic, a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine who was not part of the research team.

There are already FDA approved drugs that contain HDAC2 inhibitors, used for cancer treatments. Tsai hopes that, considering this, a human clinical trial might commence soon to see how well an HDAC2 psychotherapy might fair. The results were reported in a paper published in the journal Cell.