Author: IGIHE

{For most people having a good memory means being able to remember more information clearly for long periods of time. For neuroscientists too, the inability to remember was long believed to represent a failure of the brain’s mechanisms for storing and retrieving information.}

But according to a new review paper from Paul Frankland, a senior fellow in CIFAR’s Child & Brain Development program, and Blake Richards, an associate fellow in the Learning in Machines & Brains program, our brains are actively working to forget. In fact, the two University of Toronto researchers propose that the goal of memory is not to transmit the most accurate information over time, but to guide and optimize intelligent decision making by only holding on to valuable information.

“It’s important that the brain forgets irrelevant details and instead focuses on the stuff that’s going to help make decisions in the real world,” says Richards.

The review paper, published this week in the journal Neuron, looks at the literature on remembering, known as persistence, and the newer body of research on forgetting, or transience. The recent increase in research into the brain mechanisms that promote forgetting is revealing that forgetting is just as important a component of our memory system as remembering.

“We find plenty of evidence from recent research that there are mechanisms that promote memory loss, and that these are distinct from those involved in storing information,” says Frankland.

One of these mechanisms is the weakening or elimination of synaptic connections between neurons in which memories are encoded. Another mechanism, supported by evidence from Frankland’s own lab, is the generation of new neurons from stem cells. As new neurons integrate into the hippocampus, the new connections remodel hippocampal circuits and overwrite memories stored in those circuits, making them harder to access. This may explain why children, whose hippocampi are producing more new neurons, forget so much information.

It may seem counterintuitive that the brain would expend so much energy creating new neurons at the detriment of memory. Richards, whose research applies artificial intelligence (AI) theories to understanding the brain, looked to principles of learning from AI for answers. Using these principles, Frankland and Richards frame an argument that the interaction between remembering and forgetting in the human brain allows us to make more intelligent memory-based decisions.

It does so in two ways. First, forgetting allows us to adapt to new situations by letting go of outdated and potentially misleading information that can no longer help us maneuver changing environments.

“If you’re trying to navigate the world and your brain is constantly bringing up multiple conflicting memories, that makes it harder for you to make an informed decision,” says Richards.

The second way forgetting facilitates decision making is by allowing us to generalize past events to new ones. In artificial intelligence this principle is called regularization and it works by creating simple computer models that prioritize core information but eliminate specific details, allowing for wider application.

Memories in the brain work in a similar way. When we only remember the gist of an encounter as opposed to every detail, this controlled forgetting of insignificant details creates simple memories which are more effective at predicting new experiences.

Ultimately, these mechanisms are cued by the environment we are in. A constantly changing environment may require that we remember less. For example, a cashier who meets many new people every day will only remember the names of her customers for a short period of time, whereas a designer that meets with her clients regularly will retain that information longer.

“One of the things that distinguishes an environment where you’re going to want to remember stuff versus an environment where you want to forget stuff is this question of how consistent the environment is and how likely things are to come back into your life, ” says Richards.

Similarly, research shows that episodic memories of things that happen to us are forgotten more quickly than general knowledge that we access on a daily basis, supporting the old adage that if you don’t use it, you lose it. But in the context of making better memory-based decisions, you may be better off for it.

Source:Science Daily

{When you look at a picture of a mug, the neurons that store your memory of what a mug is begin firing. But it’s not a pinpoint process; a host of neurons that code for related ideas and items — bowl, coffee, spoon, plate, breakfast — are activated as well. How your brain narrows down this smorgasbord of related concepts to the one word you’re truly seeking is a complicated and poorly understood cognitive task. A new study led by San Diego State University neuroscientist Stephanie Ries, of the School of Speech, Language, and Hearing Sciences, delved into this question by measuring the brain’s cortical activity and found that wide, overlapping swaths of the brain work in parallel to retrieve the correct word from memory.}

Most adults can quickly and effortlessly recall as many as 100,000 regularly used words when prompted, but how the brain accomplishes this has long boggled scientists. How does the brain nearly always find the needle in the haystack? Previous work has revealed that the brain organizes ideas and words into semantically related clusters. When trying to recall a specific word, the brain activates its cluster, significantly reducing the size of the haystack.

To figure out what happens next in that process, Ries and colleagues asked for help from a population of people in a unique position to lend their brainpower to the problem: patients undergoing brain surgery to reduce their epileptic seizures. Before surgery, neurosurgeons monitor their brain activity to figure out which region of the brain is triggering the patients’ seizures, which requires the patients to wear a grid of dozens of electrodes placed directly on top of the cortex, the outermost folded layers of the brain.

While the patients were hooked up to this grid in a hospital and waiting for a seizure to occur, Ries asked if they’d be willing to participate in her research. Recording brain signals directly from the cortical surface affords neuroscientists like Ries an unparalleled look at exactly when and where neurons are communicating with one another during tasks.

“During that period, you have time to do cognitive research that’s impossible to do otherwise,” she said. “It’s an extraordinary window of opportunity.”

For the recent study, nine patients agreed to participate. In 15 minute-sessions, she and her team would show the patients an item on a computer screen — musical instruments, vehicles, houses — then ask them to name it as quickly as possible, all while tracking their brain activity.

They measured the separate neuronal processes involved with first activating the item’s conceptual cluster, then selecting the proper word. Surprisingly, they discovered the two processes actually happen at the same time and activate a much wider network of brain regions than previously suspected. As expected, two regions known to be involved in language processing lit up, the left inferior frontal gyrus and the posterior temporal cortex. But so did several other regions not traditionally linked to language, including the medial and middle frontal gyri, the researchers reported in the Proceedings of the National Academy of Sciences.

“This work shows the word retrieval process in the brain is not at all as localized as we previously thought,” Ries said. “It’s not a clear division of labor between brain regions. It’s a much more complex process.”

Learning exactly how the brain accomplishes these tasks could one day help speech-language pathologists devise strategies for treating disorders that prevent people from readily accessing their vocabulary.

“Word retrieval is usually effortless in most people, but it is routinely compromised in patients who suffer from anomia, or word retrieval difficulty,” Ries said. “Anomia is the most common complaint in patients with stroke-induced aphasia, but is also common in neurodegenerative diseases and normal aging. So it is critical to understand how this process works to understand how to help make it better.”

Source:Science Daily