The functioning of memory depends on the interaction between the brain

Summary: Scientists show how visual working memory is stored in interconnected regions of the brain in mice.

A source: Sainsbury Wellcome Centre

How does the brain remember a phone number before dialing it? Working memory is an important component of cognition, allowing the brain to temporarily remember information and use it to guide future behavior.

Although many previous studies have revealed the involvement of multiple brain regions, until now it remained unclear how these multiple regions interact to represent and maintain working memory.

In a new study published today natureNeuroscientists from the Sainsbury Wellcome Center at UCL studied interactions between the two brains involved in visual working memory in mice.

The team found that communication between these two working memory areas, the parietal cortex and the premotor cortex, depends on moment-to-moment time scales.

“There are different types of working memory and for the past 40 years scientists have been trying to work out how these are represented in the brain.

“In particular, sensory working memory has been difficult to study because many other processes, such as timing, motor preparation and reward anticipation, are occurring simultaneously during standard laboratory tasks,” said Dr. Ivan Voitov, a researcher in the Mrsic-Flogel lab and first author on the paper.

To overcome this challenge, the SWC researchers compared a memory-dependent task with a simple working memory-independent task. In a working memory task, mice were presented with a sensory stimulus and then had to match the stimulus they had seen before a delay with the next stimulus.

This meant that during the delay, the mice had to have a representation of the first stimulus in their working memory in order to successfully complete the task and receive the reward. In contrast, in a memory-independent task, the mice’s decision regarding the secondary stimulus was unrelated to the primary stimulus.

By contrasting these two tasks, the researchers were able to observe a portion of neural activity that was dependent on working memory, as opposed to natural activity related to the working environment.

They found that most neural activity is unrelated to working memory, and that working memory representations are embedded in “high-dimensional” modes of activity, meaning instead that small fluctuations around the average firing of individual cells carry working memory information.

To understand how these representations are stored in the brain, neuroscientists used a technique called optogenetics to selectively silence certain parts of the brain during a delay, and observed that the mice were impaired in what they remembered.

Interestingly, they found that erasing working memory representations in either parietal or premotor cortical regions resulted in similar deficits in mice’s ability to recall the previous stimulus, suggesting that these representations were dependent on each other during the delay.

To test this hypothesis, researchers interrupted one area and recorded activity that fed back into another area. When they disrupted the parietal cortex, the activity reported in the anterior motor cortex and parietal cortex was almost unchanged in terms of mean activity.

They found that most neural activity is unrelated to working memory, and that working memory representations are embedded in “high-dimensional” modes of activity, meaning instead that small fluctuations around the average firing of individual cells carry working memory information. Image is in the public domain

However, the representation of working memory activity is particularly impaired. This was also true in the reverse experiment, where they disrupted the premotor cortex, looked at the parietal cortex, and observed cortical-cortical connectivity that is characteristic of working memory.

“By recording and manipulating long-range circuits in the brain, we discovered that working memory resides in interdependent patterns of activity in interconnected cortical regions, thereby maintaining working memory through instantaneous connections,” said Professor Tom Missick. Flogel. , director of the Sainsbury Wellcome Center and co-author of the paper.

The next step for researchers is to look for shared activity patterns between these regions. They also plan to study more complex working memory tasks that modulate specific information stored in working memory beyond its power.

To do this, neuroscientists use mixers that contain sensory information that directs the mouse to what it thinks is the next target. Such experiments allow them to gain a deeper understanding of working memory representations.

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

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Author: April Cashin-Garbutt
A source: Sainsbury Wellcome Centre
The connection: April Cashin-Garbutt – Sainsbury’s Salam Centre
Photo: Image is in the public domain

Original research: Open access.
“Cortical feedback loops link distributed representations of working memory” by Ivan Voitov et al. nature


Cortical feedback loops link distributed representations of working memory

Working memory—the brain’s ability to flexibly use information to assimilate information and direct behavior—is an important component of cognition. Although activity associated with working memory has been observed in several brain regions, how neuronal populations actually represent working memory and the mechanisms by which this activity is maintained remain unclear.

Here, we describe the neural implementation of visual working memory in mice alternating between a delayed-to-sample mismatch task and a simple discrimination task that does not require working memory but has the same stimulus, movement, and reward statistics.

Transient optogenetic inactivations have shown that distributed regions of the neocortex are selectively required for working memory storage. Population activity in visual area AM and premotor area M2 was dominated by orderly low-dimensional dynamics during the delay period, but was independent of working memory.

Instead, working memory representations are embedded in high-dimensional population activity, present in both cortical regions, persisting during the interstimulus delay period, and predicting behavioral responses during a working memory task.

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

Transient inactivation of both regions resulted in selective impairment of interregional connectivity in working memory. Therefore, interconnected cortical regions maintain connected high-dimensional representations of working memory.

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