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▎Edited by WuXi AppTec Content Team When you try to remember a set of mobile phone numbers, you need to complete two types of information at the same time: 11 numbers (ie events) and their sequences
.
At this point, you are completing a sequence memory
.
Sequence memory is a fundamental cognitive function of the brain, but how the brain stores sequence memory remains a mystery
.
In a new study published in "Science", Tang Shiming's group from Peking University School of Life Sciences and Wang Liping's group from the Center for Excellence in Brain Science and Intelligent Technology (Institute of Neuroscience), Chinese Academy of Sciences, Shanghai Brain Science and Brain-like Research Center Researcher Min Bin collaborated to uncover the coding mechanism of neurons storing sequence memory in rhesus monkeys
.
There have been different conjectures about how sequence memory is encoded
.
The advent of in vivo two-photon calcium imaging allows researchers to monitor the flow of calcium ions in neurons in real time, track neuronal action potentials, and reveal from the activity patterns of specific neurons, how the brain stores sequences memory
.
Image credit: 123RF In the latest study, the research team used in vivo two-photon calcium imaging to record the activity of thousands of neurons in the lateral prefrontal cortex of macaque monkeys, the area responsible for working memory
.
They first trained the macaques to perform a sequence memory task: At the beginning of the experiment, the macaques stared at the center of the screen, and three different light spots (all located on the vertices of a regular hexagon) flashed rapidly in sequence on the screen
.
What the macaques have to do is memorize the position and sequence of the three light spots, and after a few seconds, report the results in sequence through the movement of their eyes
.
The intervening seconds is the stage in which the monkey brain stores sequence memory, and neuronal activity during this period reflects the way the memory is stored
.
▲The neural coding mechanism of brain sequence memory: A, Macaque remembers the sequence of light point positions; BD, Two-photon imaging monitors the activity of neurons in the prefrontal cortex group (Image source: Reference [1]) According to the existing theory, the research team conjectures, Macaque monkeys also form a "screen" in their brains
.
The events that the macaques see, that is, the positions of the dots, are stored on this "screen"
.
But the question is, the macaque saw 3 points in sequence, so how does its brain store the positions and sequences of these 3 points at the same time? The calcium imaging results show that the information for each event is stored in a two-dimensional subspace, a corresponding "screen"
.
In each subspace, the positions of the points correspond to the hexagonal structures seen by the macaques
.
These subspaces are nearly orthogonal to each other
.
That is to say, the macaques participating in this experiment have seen 3 events successively, so in the sequence memory stage, there are also 3 "screens" on its lateral prefrontal cortex corresponding to the events one by one
.
They do not interfere with each other and store the information of 3 events in sequence
.
Decoding analysis using machine learning revealed that these "screens" are common to different types of spatial sequences
.
Interestingly, the research team also noticed that the "screen" corresponding to the earliest event was larger, and as the sequence increased, the "screen" gradually became smaller and the probability of error was higher
.
A possible explanation is that the information in the lower order is allocated fewer resources, resulting in a smaller "screen" and a lower degree of discrimination
.
We also have an intuitive feeling about this: when we memorize a series of information, the later information is more prone to errors
.
▲Neural group encoding and decoding in sequence memory (Image source: Reference [1]) Thus, this study reveals the simple encoding rules for brain neuron groups to store sequence memory, and also for how neural networks perform symbolic representation.
Puzzles offer new ideas
.
This finding will play an important role in future neuroscience and artificial intelligence research
.
Xie Yang, a postdoctoral fellow in the Wang Liping Research Group of the Center for Excellence in Brain Science and Intelligent Technology Innovation, Chinese Academy of Sciences, and Hu Peixuan, a research assistant, are the co-first authors of the paper.
Researcher Tang Shiming, researcher Min Bin of the Shanghai Center for Brain Science and Brain-like Research, and Wang Liping of the Center for Excellence in Brain Science and Intelligent Technology Innovation of the Chinese Academy of Sciences are the co-corresponding authors
.
This research project was funded by the National Natural Science Foundation of China and the Peking University-Tsinghua Joint Center for Life Sciences
.
References: [1] Yang Xie et al, Geometry of sequence working memory in macaque prefrontal cortex, Science (2022).
DOI: 10.
1126/science.
abm0204 [2] Science published the results of the Center of Excellence for Brain Intelligence, Chinese Academy of Sciences, revealing sequence working memory Geometric Structure Represented in the Brain of Macaque Monkeys.
Retrieved Feb 10th, 2022 from http:// Shiming Tang’s group published a paper in collaboration with Science Revealing the encoding mechanism of brain sequence memory.
Retrieved Feb 10th, 2022 from https://mgv.
pku.
edu.
cn/kxyj/kxjz/359887.
htm
.
At this point, you are completing a sequence memory
.
Sequence memory is a fundamental cognitive function of the brain, but how the brain stores sequence memory remains a mystery
.
In a new study published in "Science", Tang Shiming's group from Peking University School of Life Sciences and Wang Liping's group from the Center for Excellence in Brain Science and Intelligent Technology (Institute of Neuroscience), Chinese Academy of Sciences, Shanghai Brain Science and Brain-like Research Center Researcher Min Bin collaborated to uncover the coding mechanism of neurons storing sequence memory in rhesus monkeys
.
There have been different conjectures about how sequence memory is encoded
.
The advent of in vivo two-photon calcium imaging allows researchers to monitor the flow of calcium ions in neurons in real time, track neuronal action potentials, and reveal from the activity patterns of specific neurons, how the brain stores sequences memory
.
Image credit: 123RF In the latest study, the research team used in vivo two-photon calcium imaging to record the activity of thousands of neurons in the lateral prefrontal cortex of macaque monkeys, the area responsible for working memory
.
They first trained the macaques to perform a sequence memory task: At the beginning of the experiment, the macaques stared at the center of the screen, and three different light spots (all located on the vertices of a regular hexagon) flashed rapidly in sequence on the screen
.
What the macaques have to do is memorize the position and sequence of the three light spots, and after a few seconds, report the results in sequence through the movement of their eyes
.
The intervening seconds is the stage in which the monkey brain stores sequence memory, and neuronal activity during this period reflects the way the memory is stored
.
▲The neural coding mechanism of brain sequence memory: A, Macaque remembers the sequence of light point positions; BD, Two-photon imaging monitors the activity of neurons in the prefrontal cortex group (Image source: Reference [1]) According to the existing theory, the research team conjectures, Macaque monkeys also form a "screen" in their brains
.
The events that the macaques see, that is, the positions of the dots, are stored on this "screen"
.
But the question is, the macaque saw 3 points in sequence, so how does its brain store the positions and sequences of these 3 points at the same time? The calcium imaging results show that the information for each event is stored in a two-dimensional subspace, a corresponding "screen"
.
In each subspace, the positions of the points correspond to the hexagonal structures seen by the macaques
.
These subspaces are nearly orthogonal to each other
.
That is to say, the macaques participating in this experiment have seen 3 events successively, so in the sequence memory stage, there are also 3 "screens" on its lateral prefrontal cortex corresponding to the events one by one
.
They do not interfere with each other and store the information of 3 events in sequence
.
Decoding analysis using machine learning revealed that these "screens" are common to different types of spatial sequences
.
Interestingly, the research team also noticed that the "screen" corresponding to the earliest event was larger, and as the sequence increased, the "screen" gradually became smaller and the probability of error was higher
.
A possible explanation is that the information in the lower order is allocated fewer resources, resulting in a smaller "screen" and a lower degree of discrimination
.
We also have an intuitive feeling about this: when we memorize a series of information, the later information is more prone to errors
.
▲Neural group encoding and decoding in sequence memory (Image source: Reference [1]) Thus, this study reveals the simple encoding rules for brain neuron groups to store sequence memory, and also for how neural networks perform symbolic representation.
Puzzles offer new ideas
.
This finding will play an important role in future neuroscience and artificial intelligence research
.
Xie Yang, a postdoctoral fellow in the Wang Liping Research Group of the Center for Excellence in Brain Science and Intelligent Technology Innovation, Chinese Academy of Sciences, and Hu Peixuan, a research assistant, are the co-first authors of the paper.
Researcher Tang Shiming, researcher Min Bin of the Shanghai Center for Brain Science and Brain-like Research, and Wang Liping of the Center for Excellence in Brain Science and Intelligent Technology Innovation of the Chinese Academy of Sciences are the co-corresponding authors
.
This research project was funded by the National Natural Science Foundation of China and the Peking University-Tsinghua Joint Center for Life Sciences
.
References: [1] Yang Xie et al, Geometry of sequence working memory in macaque prefrontal cortex, Science (2022).
DOI: 10.
1126/science.
abm0204 [2] Science published the results of the Center of Excellence for Brain Intelligence, Chinese Academy of Sciences, revealing sequence working memory Geometric Structure Represented in the Brain of Macaque Monkeys.
Retrieved Feb 10th, 2022 from http:// Shiming Tang’s group published a paper in collaboration with Science Revealing the encoding mechanism of brain sequence memory.
Retrieved Feb 10th, 2022 from https://mgv.
pku.
edu.
cn/kxyj/kxjz/359887.
htm
