In a study of epilepsy patients, the National Institutes of Health found how a series of high-frequency brain waves can help us identify such differences between the past and the present.
“Our results suggest that any experience we store in memory can be used to set our expectations and predictions for the future,” said Dr. Kareem Zaghloul, principal researcher at the National Institute for Neurological Disorders and Stroke (NINDS) of the NIH. and lead author of the study published in Nature Communications.
“This study shows how the brain uses certain neural activity patterns to compare our expectations with the present. Ultimately, we hope that these results will help us better understand how the brain represents reality in healthy and disease-related conditions, ”added Zaghloul.
The study was conducted by Dr. Rafi Haque directed. Student at the Emory University School of Medicine in Atlanta, who did his dissertation with Dr. Zaghloul graduated. His primary research goal was to find out if a theory called predictive coding can be used to help our brains remember past experiences known as episodic memories.
“Predictive coding essentially says that the brain optimizes neural activity to process information. In other words, the theory predicts that the brain uses more neural activity to process new information than it does for things we are familiar with, ”said Dr. Haque.
“Years of research have shown that over time, we learn to expect what common sights like green grass look like or what everyday noises sound like certain birdsong. We wanted to know if the brain uses a similar process to manage our experiences, ”added Dr. Haque added.
To test this idea, the team worked with 14 patients with drug-resistant types of epilepsy whose brains had been surgically implanted with electrode grids as part of a study by the NIH Clinical Center to diagnose and treat their seizures.
The experiment began when patients were shown and asked to memorize a series of four natural scenes displayed on a computer screen. For example, one of the scenes was a brown bicycle leaning upright on a stand in front of a green bush.
A few seconds later, they were shown a new set of images and asked if they recognized the scene or noticed something else. Some images were the same as before, while others were slightly altered by adding or removing something like a red bird from the scene.
On average, patients successfully recognized 88 percent of the replay scenes, 68 percent of the scenes where something was missing, and 65 percent of the scenes where something was added. Either way, it took them about two and a half seconds to notice.
Another analysis of a subset of patients found that they successfully located 82 percent of the additions and 70 percent of the withdrawals. Oddly enough, her eyes often fixated on additions, but rarely on areas in the scene where something was removed.
“Overall, these results suggest that it only takes a moment to not only remember a new experience, but also to use memories of that experience to set future expectations,” said Dr. Zaghloul.
Meanwhile, electrical recordings revealed differences in brainwave activity between the times when patients successfully remembered replay scenes and the times when they discovered changes to a scene.
In both situations, the appearance of a scene on the computer screen triggered an increase in the strength of high-frequency waves of neural activity in the lateral occipital cortex, a visual processing center in the back of the brain. The rise flowed forward and arrived a few milliseconds later in a memory center called the medial temporal lobe.
In both situations, the patients’ brains seemed to reproduce the neural activity patterns observed when they first saw the scenes.
“These results support the idea that memories of visual experiences follow a certain path in the brain,” said Dr. Haque.
The difference, however, was that the increase in activity was greater when the patients saw a change in a scene.
In addition, during these moments a second, lower frequency wave appeared to rumble synchronously through the lateral occipital cortex and the medial temporal lobe.
“Our data support the idea that our expectations of visual experience are controlled by a feedback loop between the visual cortex and the medial temporal lobe,” said Dr. Zaghloul.
“High frequency waves of neural activity seem to give an error message when we see something that is not what we expected, while the low frequency waves may refresh our memories,” added Dr. Zaghloul added.
(This story was posted by a wire agency feed with no changes to the text.)
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