Neurons in the Brain Tune into Different Frequencies for Different Spatial Memory Tasks

Your brain transmits information about your current location and memories of past locations over the same neural pathways using different frequencies of a rhythmic electrical activity called gamma waves, report neuroscientists at The University of Texas at Austin.

The research, published in the journal Neuron on April 17, may provide insight into the cognitive and memory disruptions seen in diseases such as schizophrenia and Alzheimer’s, in which gamma waves are disturbed.

Previous research has shown that the same brain region is activated whether we’re storing memories of a new place or recalling past places we’ve been.

“Many of us leave our cars in a parking garage on a daily basis. Every morning, we create a memory of where we parked our car, which we retrieve in the evening when we pick it up,” said Laura Colgin, assistant professor of neuroscience and member of the Center for Learning and Memory in The University of Texas at Austin’s College of Natural Sciences. “How then do our brains distinguish between current location and the memory of a location? Our new findings suggest a mechanism for distinguishing these different representations.”

Memory involving location is stored in an area of the brain called the hippocampus. The neurons in the hippocampus that store spatial memories (such as the location where you parked your car) are called place cells. The same set of place cells are activated both when a new memory of a location is stored and, later, when the memory of that location is recalled or retrieved.

When the hippocampus forms a new spatial memory, it receives sensory information about your current location from a brain region called the entorhinal cortex. When the hippocampus recalls a past location, it retrieves the stored spatial memory from a subregion of the hippocampus called CA3.

The entorhinal cortex and CA3 transmit these different types of information using different frequencies of gamma waves. The entorhinal cortex uses fast gamma waves, which have a frequency of about 80 Hz (about the same frequency as a bass E note played on a piano). In contrast, CA3 sends its signals on slow gamma waves, which have a frequency of about 40 Hz.

Colgin and her colleagues hypothesized that fast gamma waves promote encoding of recent experiences, while slow gamma waves support memory retrieval.

They tested these hypotheses by recording gamma waves in the hippocampus, together with electrical signals from place cells, in rats navigating through a simple environment. They found that place cells represented the rat’s current location when cells were active on fast gamma waves. When cells were active on slow gamma waves, place cells represented locations in the direction that the rat was heading.

“These findings suggest that fast gamma waves promote current memory encoding, such as the memory of where we just parked,” said Colgin. “However, when we need to remember where we are going, like when finding our parked car later in the day, the hippocampus tunes into slow gamma waves.”

Because gamma waves are seen in many areas of the brain besides the hippocampus, Colgin’s findings may generalize beyond spatial memory. The ability for neurons to tune into different frequencies of gamma waves provides a way for the brain to traffic different types of information across the same neuronal circuits.

Colgin said one of the next steps in her team’s research will be to apply technologies that induce different types of gamma waves in rats performing memory tasks. She imagines that they will be able to improve new memory encoding by inducing fast gamma waves. Conversely, she expects that inducing slow gamma waves will be detrimental to the encoding of new memories. Those slow gamma waves should trigger old memories, which would interfere with new learning.

Why your nose can be a pathfinder

When I was a child I used to sit in my grandfather’s workshop, playing with wood shavings. Freshly shaven wood has a distinct smell of childhood happiness, and whenever I get a whiff of that scent my brain immediately conjures up images of my grandfather at his working bench, the heat from the fireplace and the dog next to it.

Researchers at the Kavli Institute for Systems Neuroscience have recently discovered the process behind this phenomenon. The brain, it turns out, connects smells to memories through an associative process where neural networks are linked through synchronised brain waves of 20-40 Hz.

– We all know that smell is connected to memories, Kei Igarashi, lead author, explains.– We know that neurons in different brain regions need to oscillate in synchrony for these regions to speak effectively to each other. Still, the relationship between interregional coupling and formation of memory traces has remained poorly understood. So we designed a task to investigate how odour-place representation evolved in the entorhinal and hippocampal region, to figure out whether learning depends on coupling of oscillatory networks.

Smell guides the way in maze
The researchers designed a maze for rats, where a rat would see a hole to poke its nose into. When poking into the hole, the rat was presented with one of two alternative smells. One smell told the rat that food would be found in the left food cup behind the rat. The other smell told it that there was food in the right cup. The rat would soon learn which smell would lead to a reward where. After three weeks of training, the rats chose correctly on more than 85% of the trials. In order to see what happened inside the brain during acquisition, 16–20 electrode pairs were inserted in the hippocampus and in different areas of the entorhinal cortex.

After the associations between smell and place were well established, the researchers could see a pattern of brain wave activity (the electrical signal from a large number of neurons) during retrieval.

Coherent brain activity evolves with learning
– Immediately after the rat is exposed to the smell there is a burst in activity of 20–40 Hz waves in a specific connection between an area in the entorhinal cortex, lateral entorhinal cortex (LEC), and an area in the hippocampus, distal CA1 (dCA1), while a similar strong response was not observed in other connections, Igarashi explains.

This coherence of 20–40 Hz activity in the LEC and dCA1 evolved in parallel with learning, with little coherence between these areas before training started. By the time the learning period was over, cells were phase locked to the oscillation and a large portion of the cells responded specifically to one or the other of the smell-odour pairs.

Long distance communication in brain mediated by waves
– This is not the first time we observe that the brain uses synchronised wave activity to establish network connections, Edvard Moser, director of the Kavli Institute for Systems Neuroscience says. – Both during encoding and retrieval of declarative memories there is an interaction between these areas mediated through gamma and theta oscillations. However, this is the first study to relate the development of a specific band of oscillations to memory performance in the hippocampus. Together, the evidence is now piling up and pointing in the direction of cortical oscillations as a general mechanism for mediating interactions among functionally specialised neurons in distributed brain circuits.

So, there you have it – the signals from your nose translate and connect to memories in an orchestrated symphony of signals in your head. Each of these memories connects to a location, pinpointed on your inner map. So when you feel a wave of reminiscence triggered by a fragrance, think about how waves created this connection in the first place.

Neuroscientists Find Brain Activity May Mark the Beginning of Memories

By tracking brain activity when an animal stops to look around its environment, neuroscientists at Johns Hopkins University believe they can mark the birth of a memory.

Using lab rats on a circular track, James Knierim, professor of neuroscience in the Zanvyl Krieger Mind/Brain Institute at Johns Hopkins, and a team of brain scientists, noticed that the rats frequently paused to inspect their environment with head movements as they ran. The scientists found that this behavior activated a place cell in their brain, which helps the animal construct a cognitive map, a pattern of activity in the brain that reflects the animal’s internal representation of its environment.

In a paper recently published in the journal Nature Neuroscience, the researchers state that when the rodents passed that same area of the track seconds later, place cells fired again, a neural acknowledgement that the moment has imprinted itself in the brain’s cognitive map in the hippocampus.

The hippocampus is the brain’s warehouse for long- and short-term processing of episodic memories, such as memories of a specific experience like a trip to Maine or a recent dinner. What no one knew was what happens in the hippocampus the moment an experience imprints itself as a memory.

“This is like seeing the brain form memory traces in real time,” said Knierim, senior author of the research. “Seeing for the first time the brain creating a spatial firing field tied to a specific behavioral experience suggests that the map can be updated rapidly and robustly to lay down a memory of that experience.”

A place cell is a type of neuron within the hippocampus that becomes active when an animal or human enters a particular place in its environment. The activation of the cells help create a spatial framework much like a map, that allows humans and animals to know where they are in any given location. Place cells can also act like neural flags that “mark” an experience on the map, like a pin that you drop on Google maps to mark the location of a restaurant.

“We believe that the spatial coordinates of the map are delivered to the hippocampus by one brain pathway, and the information about the things that populate the map, like the restaurant, are delivered by a separate pathway,” said Knierim. “When you experience a new item in the environment, the hippocampus combines these inputs to create a new spatial marker of that experience.”

In the experiments, researchers placed tiny wires in the brains of the rats to monitor when and where brain activity increased as they moved along the track in search of chocolate rewards. About every seven seconds, the rats stopped moving forward and turned their heads to the perimeter of the room as they investigated the different landmarks, a behavior called “head-scanning.”

“We found that many cells that were previously silent would suddenly start firing during a specific head-scanning event,” said Knierim. “On the very next lap around the track, many of these cells had a brand new place field at that exact same location and this place field remained usually for the rest of the laps. We believe that this new place field marks the site of the head scan and allows the brain to form a memory of what it was that the rat experienced during the head scan.”

Knierim said the formation and stability of place fields and the newly-activated place cells requires further study. The research is primarily intended to understand how memories are formed and retrieved under normal circumstances, but it could be applicable to learning more about people with brain trauma or hippocampal damage due to aging or Alzheimer’s.

“There are strong indications that humans and rats share the same spatial mapping functions of the hippocampus, and that these maps are intimately related to how we organize and store our memories of prior life events,” said Knierim. “Since the hippocampus and surrounding brain areas are the first parts of the brain affected in Alzheimer’s, we think that these studies may lend some insight into the severe memory loss that characterizes the early stages of this disease.”

(Image: Shutterstock)

Study says we’re over the hill at 24

It’s a hard pill to swallow, but if you’re over 24 years of age you’ve already reached your peak in terms of your cognitive motor performance, according to a new Simon Fraser University study.

SFU’s Joe Thompson, a psychology doctoral student, associate professor Mark Blair, Thompson’s thesis supervisor, and Andrew Henrey, a statistics and actuarial science doctoral student, deliver the news in a just-published PLOS ONE Journal paper.

In one of the first social science experiments to rest on big data, the trio investigates when we start to experience an age-related decline in our cognitive motor skills and how we compensate for that.

The researchers analyzed the digital performance records of 3,305 StarCraft 2 players, aged 16 to 44. StarCraft 2 is a ruthless competitive intergalactic computer war game that players often undertake to win serious money.

Their performance records, which can be readily replayed, constitute big data because they represent thousands of hours worth of strategic real-time cognitive-based moves performed at varied skill levels.

Using complex statistical modeling, the researchers distilled meaning from this colossal compilation of information about how players responded to their opponents and more importantly, how long they took to react.

“After around 24 years of age, players show slowing in a measure of cognitive speed that is known to be important for performance,” explains Thompson, the lead author of the study, which is his thesis. “This cognitive performance decline is present even at higher levels of skill.”

But there’s a silver lining in this earlier-than-expected slippery slope into old age. “Our research tells a new story about human development,” says Thompson.

“Older players, though slower, seem to compensate by employing simpler strategies and using the game’s interface more efficiently than younger players, enabling them to retain their skill, despite cognitive motor-speed loss.”

For example, older players more readily use short cut and sophisticated command keys to compensate for declining speed in executing real time decisions.

 The findings, says Thompson, suggest “that our cognitive-motor capacities are not stable across our adulthood, but are constantly in flux, and that our day-to-day performance is a result of the constant interplay between change and adaptation.”

Thompson says this study doesn’t inform us about how our increasingly distracting computerized world may ultimately affect our use of adaptive behaviours to compensate for declining cognitive motor skills.

But he does say our increasingly digitized world is providing a growing wealth of big data that will be a goldmine for future social science studies such as this one.

Sleep-dependent memory consolidation and accelerated forgetting

Accelerated long-term forgetting (ALF) is a form of memory impairment in which learning and initial retention of information appear normal but subsequent forgetting is excessively rapid. ALF is most commonly associated with epilepsy and, in particular, a form of late-onset epilepsy called transient epileptic amnesia (TEA). ALF provides a novel opportunity to investigate post-encoding memory processes, such as consolidation. Sleep is implicated in the consolidation of memory in healthy people and a deficit in sleep-dependent memory consolidation has been proposed as an explanation for ALF. If this proposal were correct, then sleep would not benefit memory retention in people with ALF as much as in healthy people, and ALF might only be apparent when the retention interval contains sleep. To test this theory, we compared performance on a sleep-sensitive memory task over a night of sleep and a day of wakefulness. We found, contrary to the hypothesis, that sleep benefits memory retention in TEA patients with ALF and that this benefit is no smaller in magnitude than that seen in healthy controls. Indeed, the patients performed significantly more poorly than the controls only in the wake condition and not the sleep condition. Patients were matched to controls on learning rate, initial retention, and the effect of time of day on cognitive performance. These results indicate that ALF is not caused by a disruption of sleep-dependent memory consolidation. Instead, ALF may be due to an encoding abnormality that goes undetected on behavioural assessments of learning, or by a deficit in memory consolidation processes that are not sleep-dependent.

Full Article

(Image: Courtney Icenhour)

Kids’ earliest memories might be earlier than they think

The very earliest childhood memories might begin even earlier than anyone realized – including the rememberer, his or her parents and memory researchers.

Four- to 13-year-olds in upstate New York and Newfoundland, Canada, probed their memories when researchers asked: “You know, some kids can remember things that happened to them when they were very little. What is the first thing you can remember? How old were you at that time?” The researchers then returned a year or two later to ask again about earliest memories – and at what age the children were when the events occurred.

“The age estimates of earliest childhood memories are not as accurate as what has been generally assumed,” report Qi Wang of Cornell University and Carole Peterson of Memorial University of Newfoundland in the March 2014 online issue of Developmental Psychology. “Using children’s own age estimates as the reference, we found that memory dating shifted to later ages as time elapsed.”

Childhood amnesia refers to our inability to remember events from our first years of life. Until now, cognitive psychologists estimated the so-called childhood amnesia offset at 3.5 years – the average age of our very earliest memory, the authors noted in their report, “Your Earliest Memory May Be Earlier Than You Think: Prospective Studies of Children’s Dating of Earliest Childhood Memories.”

But the children who originally answered, for example, “I think I was 3 years old when my dog fell through the ice,” postdated that same earliest memory by as much as nine months when asked – in follow-up interviews a year or two years later – to recall again. In other words, as time went by, children thought the same memory event occurred at an older age than they had thought previously. And that finding prompts Wang and Peterson to question the 3.5-year offset for childhood amnesia.

“This can happen to adults’ earliest childhood memories, too,” says Wang, professor of human development and director of the Social Cognition Development Laboratory in Cornell’s College of Human Ecology. “We all remember some events from our childhood. When we try to reconstruct the time of these events, we may postdate them to be more recent than they actually were, as if we are looking at the events through a telescope. Although none of us can recall events on the day of our birth – childhood amnesia may end somewhat earlier than the generally accepted 3.5 years.”

Parents might help because they have more clues (e.g., where they lived, what their children looked like at the time of events) to put their children’s experiences along a timeline. When asked, for example, “How old was Evan when Poochie fell through the ice?” they erred less than Evan had. Still, they are not free from errors in their time estimates.

The only way to settle that, Wang and Peterson mused, would be to look for documented evidence – a parent’s diary, for instance, or a newspaper account of Poochie’s memorable rescue.

New Studies Show Promise for Brain Training in Improving Fluid Intelligence

Whether computerized games designed by psychologists and neuroscientists can literally make people smarter has been hotly debated by scientists, with a small but outspoken cadre of skeptics demanding stronger proof. Now two new studies have found the kind of real-world benefits from the brain-training games that skeptics have been calling for.

The first, published today in the Proceedings of the National Academy of Sciences, found that less than six hours of brain games played over the course of 10 weeks enabled poor first-graders who attend school irregularly due to family problems to catch up with their regularly-attending peers in math and language grades.

The second, presented over the weekend at the Cognitive Neuroscience Society meeting in Boston, combined the results of 13 previous studies of computerized brain-training in young adults to conclude that training significantly enhances fluid intelligence—the fundamental human ability to detect patterns, reason, and learn.  That is, practicing the games literally makes people smarter.  

Together with other recent studies demonstrating real-world benefits of brain training in healthy older adults, preschoolers, and school children with ADHD, the new papers appear to provide fresh ammunition to psychologists and neuroscientists whose research has been under attack by a handful of skeptics who insist that the training is a waste of time.

Read more