Scientists talked about the mechanism of temporary storage of information in the brain
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- Scientists talked about the mechanism of temporary storage of information in the brain
American scientists have found out how the neural network in the brain of a fruit fly quickly switches between tracking the current direction and temporarily saving it. The smell of food triggers the interaction of two groups of cells, thanks to which the insect continues to move along the chosen course even after the smell disappears. How the neural "gates" are arranged, why memory needs both stability and flexibility, and what experiments on flies can tell about the work of the brain — in the Izvestia material.
Why does the brain need a memory for a few seconds
The confirmation code is only needed until it is entered in the required field. You have to hold the beginning of a sentence to understand its end. The direction of movement may need to be maintained when the landmark disappears for a short time. In all these cases, the information remains available for the current task.
This function is performed by the working memory. The US National Institute of Mental Health (NIMH) defines it as actively retaining and flexibly updating information related to a goal or task. It has a limited capacity and must withstand interference.
Short—term and working memory are similar, but not completely identical concepts. The first is related to the temporary storage of information, the second is related to its retention and use in current activities. In the new study, the researchers studied a specific navigation task: how the fly's brain maintains the direction necessary to continue moving.
Why was memory studied on fruit flies?
There are tens of billions of neurons in the human brain, while the fruit fly has less than 200,000. However, these nervous systems have common principles of organization and transmission of signals between cells. This makes the fruit fly a convenient model for studying individual brain mechanisms.
An additional advantage is a detailed map of the connections in the brain of an adult fly. It is called a connectome and shows which neurons are connected to each other. Such a map helps to find chains that are potentially involved in certain behaviors.
But an anatomical diagram is not enough. The connection between two cells does not mean that they constantly interact in the same way. Their work may vary depending on external signals and the condition of the animal.
Therefore, the researchers compared the structure of the neural network with the activity of cells and the behavior of flies. They were interested in how a particular chain moves from the perception of current information to its preservation.
How the smell triggered movement
In the experiment, the flies were given the smell of apple cider vinegar. The insects started moving in the direction of the smell and continued moving for several more seconds after it disappeared. This behavior made it possible to track how the brain holds a navigation target with a short-term loss of an external signal. The smell is no longer coming in, but the chosen direction still persists and affects movement.
To monitor brain activity, an installation was used in which a fly could walk on a small ball supported by a stream of air. Its rotation made it possible to track the insect's movements. The odour supply and the direction of the air flow were also monitored in the installation.
The scientists studied the activity of nerve cells, recorded their electrical signals, and used computer simulations. The combination of these methods helped to test which interactions could explain the observed behavior.
"Our study shows how a neural circuit forms short—term memory in response to a smell, allowing the fly to remember the direction and move towards its source," said Katherine Nagel, senior author of the study and associate professor of neuroscience at the Grossman School of Medicine at New York University.
Which neurons held the direction
The study focused on two groups of neurons, PFG and hΔK. During the directional movement, they showed similar stable patterns of activity, which indicated teamwork.
These cells form a feedback network: signals can pass between groups of neurons and maintain activity within the circuit. This organization allows information to persist for some time after the external stimulus disappears.
Such chains are called attractor networks. An attractor is a stable state that the system reaches. In this case, we are talking about a stable distribution of neuron activity associated with the chosen direction.
What does the experiment show and what does it not prove
The results provide a concrete example of how a feedback network can maintain a temporary signal and quickly switch between states. The computer model reproduced the key features of the activity of the studied neurons, and the observations of the cells were consistent with the proposed mechanism.
However, the study focuses on a specific circuit in the drosophila brain and a specific behavior — navigation triggered by smell. It does not establish that all types of short-term memory work according to the same scheme.
The temporary retention of a fly's direction also cannot be directly equated to memorizing a numeric code or understanding a sentence by a human. These tasks relate to different conditions and nervous systems. They are united by a more general question: how to keep up-to-date information without losing the ability to update it quickly.
The authors are interested in the possibility of a similar principle in other neural networks. But for such a conclusion, it is necessary to examine their structure and operation separately. The current result primarily clarifies the mechanism in the studied chain.
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