Blame it on neurons if you can’t recall familiar names, sometimes

Most of us know that feeling of trying to retrieve a memory that does not come right away and neuroscientists have now identified different sets of individual neurons which help us retrieve memories when required, a hallmark of the human brain’s flexibility.

An essential aspect of cognitive flexibility is our ability to selectively search for information in memory when we need it. “This is the first time neurons have been described in the human brain that signal memory-based decisions.

In addition, our study shows how memories are transferred to the frontal lobe selectively and only when needed,” explained senior author Ueli Rutishauser, visiting associate in biology and bioengineering at California Institute of Technology (Caltech).

The volunteers viewed images on a screen and answered different types of questions about the images, while the researchers from Caltech and Cedars-Sinai Medical Center in Los Angeles recorded the activity of individual neurons in their brains using implanted electrodes.

For example, a subject might be shown a picture of somebody they had never seen before and asked, “Have you seen this face before?” or “Is this a face?”

“We make decisions based on retrieved memories all the time,” says lead author Juri Minxha, a postdoctoral scholar at Cedars Sinai.

The encoding and retrieval of memories occurs in the lower-middle portion of the brain in a region called the medial temporal lobe, which includes the hippocampus. Decision-making processes involve a region at the front of the brain called the medial frontal cortex. The ability to flexibly engage and utilize our memories to make decisions depends on interactions between the frontal and temporal lobes. The results revealed neurons that encode memories in the temporal lobe, and “memory choice neurons” in the frontal lobe; these neurons do not store memories but rather help retrieve them.

“So if we ask a patient if they have seen a face before, neurons in both regions become active. But if we show them the same image and ask, ‘Is this a face?’ then the memory choice neurons remain silent. Instead, we see a second distinct population of neurons in the frontal lobe, supporting the subject’s current goal of categorizing the image,” explained Minxha.