Where are my keys, or how does memory work

Do you forget if you closed the door to the apartment? Now you will find out why. Check how memory works.

You try at all costs to remember where you put the keys ... After all, it was at a certain time, you always do the same, why do you not remember? Why are you looking for keys?

Memory recovery has been the subject of countless animal studies and other human imaging work, but exactly how this process works - and how we make decisions based on memories - remains unclear.

In a new study published in the June 26 issue of Science magazine, a collaborative team of neuroscientists from Caltech and Cedars-Sinai Medical Center in Los Angeles identified different sets of individual neurons responsible for memory-based decision making.

- An important aspect of cognitive flexibility is our ability to selectively search for information in memory when we need it. For the first time neurons have been described in the human brain that signal memory-based decisions. In addition, our study shows how memories are selectively transferred to the frontal lobe and only when needed - says the author of the study.

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The study, which has an impact on the treatment of memory problems associated with Alzheimer's disease, epilepsy and schizophrenia, has been conducted in patients who have already undergone brain surgery. Volunteers looked at images on the screen and answered various questions about images, while researchers recorded the activity of individual neurons in their brains using implanted electrodes.

For example, the patient was shown a picture of a person he had never seen before and was asked: "Have you seen this face before?" or "Is this a face?" Both questions, respectively, help researchers distinguish memory-based decisions from non-memories-based decisions.

- We make decisions based on memories all the time - says lead author Juri Minxha - "Which restaurant should I choose tonight?" or "Where should I look for the keys now?" In this study, we asked simple 'yes' or 'no' questions to enable the volunteer to access his last memory or categorical knowledge.

Where is our memory?

Coding and memory searching occurs in the lower middle of the brain in a region called the medial temporal lobe, which includes the hippocampus. Decision-making processes involve an area in front of the brain called the medial frontal cortex.

- The ability to flexibly engage and use our memories to make decisions depends on the interaction between the frontal and temporal lobes, the first being the place of executive control, and the second the place to store such memories. Little was known before about how these two parts of the human brain interact - we find out.

In the study, scientists monitored individual neurons in both the temporal lobes and the frontal lobes of 13 people. The results revealed neurons encoding memories in the temporal lobe and "memory selection neurons" in the frontal lobe; these neurons do not store memories, but rather help to recover them.

- Both the medial temporal lobe and the medial frontal cortex become active when the decision requires the patient to remember something. The interaction between these two brain structures allows for the successful recovery of memory. So if we ask the patient if he has already seen the face, neurons in both regions will become active. But if we show them the same picture and ask, "Is that a face? ", Then the memory selection neurons are silent. Instead, we see a second clear population of neurons in the frontal lobe, which confirms the subject's current goal of image categorization.

The study also identified another set of 'contextual neurons' in the frontal lobe. These neurons encode information about the instructions given to the subject for a given task. For example, subjects were instructed to press a button or use eye movements to provide an answer to a question; contextual neurons signalled which of these two actions should be taken, regardless of the answer to the question.

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- Interestingly, we have found that the decision is represented by memory selection neurons in an abstract way so that the same neurons can signal this information in different contexts. This is probably responsible for the great flexibility we see in making decisions by people.

Communication between the temporal and frontal lobes has also been observed by analyzing theta waves, which are common in the temporal lobes. Researchers found that neurons in the frontal lobe selectively align their activity with theta waves in the temporal lobe only when subjects made a decision based on memory.

The researchers say they could even tell if the subject was to correctly identify the face simply by how strongly the memory selection neurons in the frontal lobes coordinated their activity with theta waves in the temporal lobe.

"In summary, our study reveals several key elements building the flexibility of human cognition," says Adolphs.