Researchers discover brain activity that may mark memory formation

Each day that goes by, our brains store little pieces of information that make up memories. But how exactly does the brain create memories? Researchers from Johns Hopkins University in Baltimore, MD, believe they may be one step closer to finding the answer.

The research team, including senior author James Knierim of the Zanvyl Krieger Mind/Brain Institute at Johns Hopkins, recently published their findings in the journal Nature Neuroscience.

For their study, the team inserted small wires into the brains of rats to monitor their brain activity as they ran around a circular track. The researchers wanted to see when and where the rats' brain activity increased.

The team found that the rats stopped running approximately every 7 seconds and inspected their surroundings through a series of head movements - a behavior the researchers call "head scanning."

When looking at the rats' brain patterns at this point in time, the investigators found the head-scanning behavior triggered place cell activity - a process that helps the animals build a cognitive map of their environment.

As the rats continued to run around the track seconds later, the team noticed that their place cells were activated at the same area of track they paused at previously.

The researchers explain that this represents a "neural acknowledgement" that the moment they paused has been stored in the cognitive map of the hippocampus - a brain region that is responsible for processing episodic memories, such as memories of a holiday or a dinner date.

'Place fields' may mark point of memory formation

Explaining their findings in more detail, the research team says that the activation of place cells in the hippocampus allows humans and animals to know where they are in any given location.

Researchers say they may have pinpointed the beginning of memory formation in the brains of rats.

These cells are also "neural flags" that pinpoint experiences on a map. The researchers say this is similar to pinning a location of a restaurant on Google maps.

"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," explains Knierim.

"When you experience a new item in the environment, the hippocampus combines these inputs to create a new spatial marker of that experience."

Knierim refers to this spatial marker as a "place field." He says cells that were activated when rats were head scanning at a precise location took up a completely new location as soon as the animals passed the same area of the track. In other words, the cells adopted a new place field.

The researchers 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.

Although the research team says this study was conducted to better understand how our memories are formed and retrieved, they note that the findings could be used to improve understanding of brain trauma or hippocampal damage from Alzheimer's disease.

The research team states that:

"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.

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."

The team say that further research is warranted to investigate the formation and stability of place fields, as well as the newly activated place cells.

Earlier this year, clinical experts reported on a study suggesting that the brain updates memory to bring it in line with new experiences - a process the researchers say happens in the hippocampus.