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Working memory relies on reciprocal interactions across the brain – Neuroscience News

Summary: The researchers demonstrate how visual working memory is maintained across interconnected brain regions in mice.

source: Sainsbury’s Welcome Center

How does the brain remember a phone number before calling? Working memory is an essential component of cognition, as it allows the brain to remember information temporarily and use it to direct future behaviour.

While several previous studies have revealed the involvement of many brain regions, it is still unclear how these multiple regions interact to represent and maintain working memory.

In a new study published today in temper natureNeuroscientists at UCL’s Sainsbury Wellcome have investigated the reciprocal interactions between two brain regions that account for visual working memory in mice.

The team found that connectivity between these two working memory sites, the parietal cortex and the premotor cortex, was jointly dependent on momentary time scales.

There are many different types of working memory, and for the past 40 years, scientists have tried to figure out how they are represented in the brain.

said Dr. Ivan Voitov, a research fellow in the Mrsic-Flogel Laboratory and first author on the paper.

To overcome this challenge, SWC researchers have compared a task that relies on working memory to a simpler task that does not rely on working memory. In the working memory task, rats were given a sensory stimulus followed by a delay and then had to match the next stimulus with the stimulus they saw before the delay.

This means that during the delay period, the mice needed a representation in their working memory of the first stimulus to succeed in the task and receive a reward. In contrast, in the task independent of working memory, the decision made by rats regarding the secondary stimulus was unrelated to the first stimulus.

By comparing these two tasks, the researchers were able to note a portion of the neural activity that was based on working memory rather than normal activity that was only related to the task environment.

They found that most of the neural activity was unrelated to working memory, and instead representations of working memory were included within “high-dimensional” activity patterns, meaning that only small fluctuations around the average firing of individual cells were carrying together working memory information.

To understand how these representations are preserved in the brain, neuroscientists used a technique called optogenetics to selectively silence parts of the brain during the delay period and observed disruption of what the mice were remembering.

Interestingly, they found that silencing working memory representations in either the parietal or frontal motor cortical areas resulted in similar deficits in the rats’ ability to remember the previous stimulus, implying that these representations were instantaneously dependent on each other during the delay.

To test this hypothesis, the researchers disabled one region while recording activity communicated to it by the other region. When the parietal cortex was disrupted, the activity delivered by the cortex to the parietal cortex was largely unchanged in terms of mean activity.

They found that most of the neural activity was unrelated to working memory, and instead representations of working memory were included within “high-dimensional” activity patterns, meaning that only small fluctuations around the average firing of individual cells were carrying together working memory information. The image is in the public domain

However, representation of working memory activity was specifically disabled. This was also true in the reverse experiment, when they disrupted the motor cortex and they looked at the parietal cortex and also noted a working memory-specific disturbance of cortical and cortical communication.

“By recording and processing from long-term circuits in the cerebral cortex, we have discovered that working memory resides in co-dependent patterns of activity in interconnected cortical areas, thus preserving working memory through instant reciprocal communication,” said Professor Tom Mersic-Flugel. D., director of the Sainsbury Wellcome Center and co-author of the paper.

The researchers’ next step is to look for patterns of activity common to these regions. They also plan to study more complex working memory tasks that modulate the specific information that is stored in working memory as well as its strength.

For this purpose, neuroscientists will use interfering scatterers that contain sensory information to bias what the mouse thinks is the next target. These experiments will allow them to develop a more accurate understanding of working memory representations.

Financing: This research was funded by the Wellcome Trust, the Gatsby Foundation and the University of Basel.

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About this memory research news

author: April Cashin Garbutt
source: Sainsbury’s Welcome Center
Contact: April Cashin Garbutt – Sainsbury’s Welcome Center
picture: The image is in the public domain

original search: open access.
Cortical feedback loops connect distributed representations of working memoryby Ivan Voitov et al. temper nature


Summary

Cortical feedback loops connect distributed representations of working memory

Working memory – the brain’s ability to take in information and use it flexibly to direct behavior – is a key component of cognition. Although activity related to working memory has been observed in many brain regions, how neural populations actually represent working memory and the mechanisms by which this activity is maintained remain unclear.

Here we describe the neural execution of visual working memory in rats as alternating between a non-sample delayed-matching task and a simple discrimination task that does not require working memory but has the same stimulus, movement, and reward statistics.

Transient optogenetic disruptions revealed that distributed regions of the neocortex were selectively required to maintain working memory. Population activity in the AM visual area and the M2 motor area during the delay period was dominated by low-dimensional structured dynamics, however, that was independent of working memory.

Instead, working memory representations were included in the high-dimensional population activity, present in both cortical regions, and persisted throughout the delay between stimulus, and the expected behavioral responses during the working memory task.

To test whether the distributed nature of working memory depends on reciprocal interactions between cortical areas, we silenced one cortical area (AM or M2) while recording feedback it received from the other.

Transient disruption of any region selectively disrupts interregional communication of working memory. Therefore, mutually correlated areas maintain high-dimensional representations associated with working memory.

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