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The Neuroscience of Forming New Memories

Scientists have identified how new memories are encoded by individual neurons.

Vladgrain/Shutterstock
Source: Vladgrain/Shutterstock

In a breakthrough discovery, an international team of neuroscientists has identified how individual neurons in the brain fire differently when a new memory is formed. This is the first time neuroscientists have identified how memories are formed and new learning takes place by individual neurons. 

The July 2015 study, “Rapid Encoding of New Memories by Individual Neurons in the Human Brain,” was published in the journal Neuron. This study pinpoints how neurons change their firing properties at the exact moment that someone forms a new memory and reveals the single-neuron underpinnings of human memory formation.

The new study is a collaboration between Dr. Matias Ison and Professor Rodrigo Quian Quiroga at the University of Leicester and Itzhak Fried, M.D., Ph.D., from UCLA Medical Center who is a neurosurgeon and senior co-author of the study.

More specifically, the reseachers discovered that individual neurons in a brain region called the medial temporal lobe (MTL) play a key role in our ability to instantly form new memories about life events and experiences.

The MTL includes a system of related brain structures that are essential for declarative, or "explicit" memories, which are the conscious memories we have of facts and events. The MTL system consists of the hippocampal region as well as the adjacent perirhinal, entorhinal, and parahippocampal cortices.

For this study, the researchers recorded the activity of more than 600 individual neurons using electrodes implanted in the medial temporal lobe of 14 epileptic patients with severe epilepsy. The neuroscientists were able to track and record individual neurons in the MTL throughout the learning process and formation of new memories.

How Might the “Jennifer Aniston Neuron” Revolutionize Brain Science?

In a Hollywood related twist, members of the team previously identified what they coined the "Jennifer Aniston neuron" which represented how the firing of a single neuron linked with an image was related to memory formation. In the recent study, the team was able to prove their hypotheses by demonstrating how new memories are formed using other images of celebrities paired with iconic landmarks. 

Courtesy of University of Leicester
Seeing Clint Eastwood and the Leaning Tower of Pisa together instantly encodes a new memory. 
Source: Courtesy of University of Leicester

In the first phase of the experiment, test subjects viewed pictures of people, such as family members and famous actors or athletes. They also saw separate free-standing images of famous landmarks, such as the Eiffel Tower or the White House. Then they saw a composite image containing a previously viewed person with one of the landmarks in the same photo. The pairing of a person with a landmark was designed to mimic the experience of meeting an individual in a particular place.

The neuroscientists discovered that the same neuron that fires for one image (i.e. Jennifer Aniston) would also fire instantly for another image (i.e. Eiffel Tower) if the study participant had been shown an image of Jennifer Aniston standing in front of the Eiffel Tower. The same would happen if test subjects saw a picture of Clint Eastwood standing in front of the Leaning Tower of Pisa, etc. 

The reseachers were surprised that these changes in neuronal firing occurred at the exact moment of learning and that memories could become hardwired after a single viewing of a photo. These results reveal previously hidden clues about how clusters of neurons work individually to encode related concepts and form new memories.

Leigh Prather/Shutterstock
Source: Leigh Prather/Shutterstock

In a press release, Rodrigo Quian Quiroga, head of the Centre for Systems Neuroscience at the University of Leicester explains, "The remarkable result was that the neurons changed their firing properties at the exact moment the subjects formed the new memories—the neuron initially firing to Jennifer Aniston started firing to the Eiffel Tower at the time the subject started remembering this association." 

"The astonishing fact was that these changes were dramatic, occurring at the exact moment of learning, even after one trial," Ison added. "The emergence of associations between concepts after a single trial, linked to rapid neural activity changes, turned out to be ideal for the creation of new episodic memories."

Conclusion: Understanding Memory Formation Has Broad Implications

The study suggests that the experience of learning can be traced back to changes in individual neurons in the brain. The researchers were able to demonstrate that a single neuron encodes the memory of the person as well as the place if both are shown together. This forms a new memory of a person and place linked together. 

Having a better understanding of how new memories are formed creates exciting new possibilities for neuroscience. The researchers are optimistic that someday these findings might improve the lives of neurological patients with dementia or memory impairment, such as in Alzheimer's disease, traumatic brain injury, or epilepsy.

Ison concluded, "A better understanding of how assemblies of neurons represent learning and memory might lead to novel ideas about our memory capacities and how these might deteriorate in patients suffering from certain neurological disorders."

In future studies, the researchers will examine why some seemingly related concepts are consolidated into long-term memories while others are forgotten. They'll also investigate whether it's possible to retrieve specific memories or learned associations by stimulating specific neurons. Stay tuned!

To watch Rodrigo Quian Quiroga describe his research, please watch this video: 

If you'd like to read more on this topic, check out my Psychology Today blog posts:

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