Scientists have discovered that by deactivating a major switch in the brain that is linked to learning and memory, memories become jumbled, like "hitting random notes on a keyboard," and lose their sense of association.
This is according to a study published in the journal PLOS One.
Researchers from the Medical College of Georgia at Georgia Regents University say they have "begun to crack the neural code" with their research, as it has allowed them to determine how thoughts and memories are created in real time.
Furthermore, they say their findings could help determine why humans can lose their memory during the aging process, which could lead to new treatments.
To reach their findings, the investigators conducted a mouse study in which they analyzed mice that were lacking a receptor called N-methyl-D-aspartate (NMDA) in the hippocampus - the region of the brain involved in memory forming, storing and organizing.
The NMDA receptor is responsible for memory function, learning and synaptic plasticity - the ability of synapses to strengthen or weaken over time.
Using a conditioning model showing how "repetition creates association," the investigators tested how the mice reacted to sounds that were linked to negative experiences. The mice were played a specific sound and were then given a mild foot shock 20 seconds later.
The investigators then compared the reactions of the mice with a functioning NMDA receptor to mice with a faulty NMDA receptor.
Memories dulled by lack of NMDA receptor
Mice with a functioning NMDA receptor were fast in realizing that the sound was an indicator of a foot shock - a normal response. However, mice with the faulty NMDA receptor struggled to make the connection.
Researchers have found that deactivating a receptor in the brain called NMDA causes memories to become jumbled.
The researchers explain that when the NMDA receptor is functioning, associations are made. But he says their findings show these associations are broken with a faulty NMDA receptor.
"You see a face and think of a name, you see your office, and you think you need to work; everything is associative," says Dr. Joe Tsien, neuroscientist at the Medical College of Georgia at Georgia Regents University. "But in mice lacking an NMDA receptor, you can tell the memory patterns are dull and dissociated."
To better understand the memory patterns associated with a functioning or faulty NMDA receptor, the researchers assigned musical notes that corresponded with the brain activity of the mice.
This revealed that normal mice had brain activity that played "dynamic rhythm," while mice with a faulty NMDA receptor had brain activity that played "random noise."
Dr. Tsien says that the mice with a faulty receptor form the initial patterns of association but do not remember them. He explains that "their tones are flat, the association is poor, while everything we register in the healthy brain is associative."
He says that through this research, they have begun to understand how thoughts and memories are made, adding:
"It has enabled us to understand for the first time how and whether the right keys are struck at the right time and in the right place and manner to make the beautiful sound of coherent memories and to compare what happens when a key element is missing."
Potential treatment for memory loss
Dr. Tsien says that if it is understood how and what the brain is remembering, this could lead to better treatment for disorders such as Alzheimer's disease and schizophrenia
"By knowing what these patterns look like and what they mean, you can use this signature to measure, for example, during aging, why we begin to lose memory and to identify and test drugs that are truly effective at aiding memory," he adds.
He says the next step for the research team is to determine how aging affects memory processes
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