How Does Memory Work?

At the cellular level, it's a lot like faster networking

Newswise, May 25, 2016 — We tend to think our memory works like a filing cabinet. We experience an event, generate a memory and then file it away for later use. 

 However, according to medical research, the basic mechanisms behind memory are much more dynamic.

In fact, making memories is similar to plugging your laptop into an Ethernet cable—the strength of the network determines how the event is translated within your brain.

 Neurons (nerve cells in the brain) communicate through synaptic connections (structures that pass a signal from neuron-to-neuron) that “talk” to each other when certain neurotransmitters (chemicals that allow the transmission of these signals) are present. 

Think of a neurotransmitter as an email. If you’re busy and you receive one or two emails, you might ignore them.  

But, if you are bombarded with hundreds of emails from the same person, saying basically the same thing, all at the same time, you will likely begin to pay attention and start a conversation with the sender: Why on earth are you sending me all these emails?

 Similarly, neurons only open a line of communication with each other when they receive stimulation from several of the same neurotransmitters at once: Oh, my neighbor keeps hitting me with the same signal? I better talk to them! So, how exactly does this relate to memory? It’s the strength of these connections between neurons that determines how a memory is formed.

 “The persistent strengthening of these activated synapses (connections) between neurons is called long-term potentiation (LTP),” said William Griffith, Ph.D., a cellular neuroscientist and chair of the Department of Neuroscience and Experimental Therapeutics at the Texas A&M Health Science Center College of Medicine. “LTP is the most recognized cellular mechanism to explain memory because it can alter the strength between brain cell connections. If this strength is maintained, a memory can be formed.” 

LTP happens when nerve cells “fire” or talk to one another at an elevated rate without further increased stimulation from neurotransmitters. In a sense, it’s like building a relationship with the email sender.  

Once you’ve started a dialogue with the sender you’re in a better position to communicate more easily and maintain a strong rapport. Just like you might add the sender to your contact list, your brain has created a ‘strengthened synaptic contact.’ But, if you’re not talking, the relationship wanes. 

Likewise, your ability to recall and remember certain memories depends on maintaining the strength of this long-term connection between synaptic contacts. LTP acts as an Ethernet cable of sorts—allowing your brain to upload, download and process at a higher rate—which may explain why some memories are more vivid than others: the pathway on which you contact them performs at a faster pace. 

“The brain is a plastic organ,” Griffith explained. “This means it can easily reconfigure or modify itself. However, it’s also a muscle. You use it or you lose it. As the synapses and pathways between neurons are used, they gain the ability to become strengthened or permanently enhanced. This is the building block of how memory works.”

 In the same vein, losing this strong LTP— or heightened synaptic connections between neurons—could be the reason behind cognitive loss and impairment.

 “Because the brain is an organ, it will show wear and tear,” Griffith continued.

 “Many people believe this decrease in neurons ‘talking’ to one another is responsible for cognitive loss—because the pathways are not being used or strengthened. Just as muscles in the body atrophy when you don’t use them, the brain will deteriorate when it’s not stimulated.”

 Griffith said the argument about how memory is consolidated and retrieved is vast, and there are many aspects that still need to be studied about the phenomenon.

 “When you look at or smell something, it contributes to your memory of an event,” he said.

 “This can be mapped in many parts of the brain. Memory may also be involved in certain behaviors like addiction. Why does this happen? Is it because the pathways for addiction are strengthened, or because they’re repressed? We don’t know yet.”

 The science behind memory is a complex one, and will likely be studied for decades to come.

 “Many different pathways in the brain interact to set up complex circuits for different types of memories,” Griffith said. “There’s much debate and more research that needs to be done to fully comprehend how our brain generates, consolidates and retrieves memories.”

 About Texas A&M Health Science Center

Texas A&M Health Science Center is Transforming Health through innovative research, education and service in dentistry, medicine, nursing, pharmacy, public health and medical sciences. As an independent state agency and academic unit of Texas A&M University, the health science center serves the state through campuses in Bryan-College Station, Dallas, Temple, Houston, Round Rock, Kingsville, Corpus Christi and McAllen. Learn more at vitalrecord.tamhsc.edu or follow @TAMHSC on Twitter.

Grid Cells' Role in Human Imagination Revealed

Newswise, March 14, 2016 — Evidence of grid cell activity has been seen in healthy volunteers asked to imagine moving through an environment in new UCL (University College London) research funded by the Medical Research Council and Wellcome Trust.

The study, published in Current Biology, used fMRI scans to detect brain activity consistent with grid cell activity in the entorhinal cortex, an important 'hub' for navigation and memory.

The entorhinal cortex is one of the first areas affected by Alzheimer's disease, so the latest research could help to explain why people with Alzheimer's can have problems imagining as well as remembering things.

Grid cells are brain cells that act as an internal coordinate system, firing at a series of locations that form a hexagonal grid across our environment as we move around it.

The latest research provides the first evidence that these cells are also used when we imagine navigating, not only for tracking past or present environments.

"People with Alzheimer's disease can find it difficult to visualise and remember scenes, and our new findings may help to explain why," says senior author Professor Neil Burgess, Director of the UCL Institute of Cognitive Neuroscience.

"We previously developed a test called the Four Mountains Test, where participants have to hold in mind a mountainous landscape and then try to identify it from a line-up of four landscapes, one of which is the original shown at a different point of view.

“This test has recently been shown to correlate with the progression of Alzheimer's disease. So our latest research suggests that difficulties with the task may be related to a loss of grid cells in the entorhinal cortex."

The study suggests that grid cells are involved in a broader range of cognitive process than previously thought.

"It is particularly exciting to see the involvement of a specific type of neuron whilst people are simply imagining moving through an environment," explains lead author Dr Aidan Horner, who conducted the study at the UCL Institute of Cognitive Neuroscience and is now at the University of York.

"This suggests that grid cells may contribute to more than just spatial navigation and are involved more broadly in planning and imagining the future. It is particularly difficult to link work at the neuronal level with higher-order cognitive processes. It is therefore incredibly exciting to see evidence for grid cells in imagined navigation, bridging the gap between neurons and mental imagery."