Tsinghua Guo Zengcai's team reveals the asymmetric interaction between the left and right hemispheres of short-term memory Cell Press Paper Express

life sciences

life science

On August 16, 2022, Tsinghua University School of Medicine, Tsinghua-Peking University Life Science Joint Center, Tsinghua-IDG/McGovern Institute for Brain Science Guo Zengcai's research group published a long article in Cell Reports titled "Left and right hemispheres are short.

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Questions and research significance

Although the overall structure of the left and right hemispheres of the brain is similar, one hemisphere can play a more important role in specific functions

The study focuses on short-term memory, which allows information to be temporarily maintained in the brain and plays an important role in complex cognitive processes such as reasoning, decision-making, understanding, problem solving and learning

Research result

The researchers trained mice to perform a short-term memory task (Fig 1A): the right whiskers of the mice were stimulated with different intensities with a rod.

Considering that in the above standard behavior, the training stimulates the mouse's right whiskers, and the right sensory information will first reach the left hemisphere.

Since only the right whiskers of the mice were stimulated in the above standard and reversed behaviors, did unilateral whisker stimulation lead to hemibrain dominance? To test this hypothesis, the researchers trained the behavior of simultaneous stimulation of bilateral whiskers, and observed a phenomenon similar to that of unilateral beard stimulation

Fig 1.

So, what is the neural mechanism for the existence of one hemisphere dominance? The researchers put forward two possible hypotheses: 1) the information encoding of the left and right hemispheres is asymmetric, and short-term memory is mainly encoded in the dominant hemisphere; 2) the interaction between the two hemispheres is asymmetric, The hemisphere on the dominant side has a greater influence on the non-dominant hemisphere (Fig 2)

Fig 2.
To explain the dominance of different hemispheres, this paper validates the encoding model and the interaction model
.

The researchers first analyzed the decision-coding ability of different neurons at the single-cell level, and found that both the left and right hemispheres contain similar proportions of decision-making neurons, and the distribution of their coding abilities is similar (Fig 3A)
.

In order to measure the ability of neurons to encode decisions in the left and right hemispheres at the population level, the researchers constructed a support vector machine to decode the decisions of mice, and found that the ability of neurons in the left and right hemisphere groups to encode decisions was similar (Fig.
3B)
.

Furthermore, by recording the activity of neurons in the left and right hemispheres at the same time, the researchers found that there is no situation where one hemisphere encodes a more accurate decision
.

These results all suggest that dominance is not due to the asymmetric encoding of decision information, thus negating the encoding model
.

Fig 3.
The ability of the left and right hemispheres to encode decision-making is similar
.

To test the interaction model, the researchers used optogenetics to inhibit the other hemisphere while recording from one hemisphere to study the contribution of inhibiting one hemisphere to the other
.

It was found that inhibition of the dominant hemisphere reduced the predictive ability of the other hemisphere to make decisions, while inhibition of the non-dominant hemisphere had less of an effect on the dominant hemisphere (Fig 4)
.

This result suggests that the dominant hemisphere determines the encoding of decisions by the non-dominant hemisphere, but not vice versa, establishing an interaction model
.

Fig 4.
The dominant hemisphere influences the non-dominant hemisphere more
.

The present study observed differences in the behavioral effects of inhibiting the frontal cortex between tasks, mice, and days
.

Such differences in behavioral experiments are often attributed to non-identical experimental conditions, insufficient sampling sites, or changes in the state of animals on different days
.

The researchers found that this difference came from changes in the strength of the interaction between the two hemispheres: if one hemisphere had a greater effect on the other hemisphere in an experiment, then inhibiting that hemisphere also had a greater effect on behavior (Fig.
5)
.

These results reveal that the interaction of the two hemispheres has important effects on behavior, and suggest that changes in behavior may be explained by effects on core brain regions
.

Fig 5.
Inhibition of one hemisphere has a behavioral effect proportional to its effect on the other hemisphere
.

Researcher Guo Zengcai from Tsinghua University School of Medicine and Tsinghua-IDG/McGovern Institute for Brain Science is the corresponding author of the paper
.

Dr.
Yin Xinxin (now working at Allen Institute for Neural Dynamics) from the School of Life Sciences of Tsinghua University is the first author of this paper; Dr.
Wang Yu (now a postdoctoral fellow at Tsinghua University) and current doctoral student Li Jiejue participated in the research of this topic
.

We would like to thank Dr.
Chang Zai from the Animal Center of Tsinghua University and other staff for their help in the breeding and strain identification of the mice
.

This research work was supported by the Innovation Group Project (32021002) and the General Project (32170998) of the Natural Science Foundation of China
.

Guo Zengcai's research group is also supported by the Tsinghua-Peking University Life Science Joint Center and the Tsinghua-IDG/McGovern Institute for Brain Science
.

Related paper information

The original paper was published in Cell Reports, a journal of CellPress Cell Press.