New study reveals contrasts in how groups of neurons function during decision making

July 19, 2017, Harvard Medical School
Fluorescence changes (flashes) indicate spiking activity in a field of cortical neurons. Credit: Harvey Lab/HMS.

By training mice to perform a sound identification task in a virtual reality maze, researchers at Harvard Medical School and the Istituto Italiano di Tecnologia (IIT) have identified striking contrasts in how groups of neurons in different cortex regions of the brain function during decision making.

The findings, published in Nature on July 19, shed light on potential neural mechanisms involved in working memory and decision making.

"Our study is a step toward thinking of the brain not in terms of the activity of individual , but rather what is special about neurons when they work together," said co-senior study author Christopher Harvey, assistant professor of neurobiology at HMS. "Revealing how populations of neurons work and what emergent properties might arise helps us better understand the mechanisms that underlie complex brain functions."

To investigate how populations of neurons work together in different regions of the brain, Harvey and his colleagues—including lead study author Caroline Runyan, postdoctoral fellow in neurobiology at HMS, and Eugenio Piasini and Stefano Panzeri of the IIT—trained mice to perform a simple task in a environment.

Running on a spherical ball that floats on a cushion of air, the mice navigated through a T-shaped maze that was projected on a screen in front of them. They were presented with a sound, and had to report whether that sound originated from their left or right side by turning in that direction at the T-intersection.

Better together

As the mice performed this task, the team recorded the activity of groups of neurons, roughly 50 at a time, from the auditory —which processes sound stimuli—and the posterior parietal cortex—which receives information from the auditory cortex and other sensory regions, and is associated with more complex cognitive functions.

Using newly developed computational techniques that allowed them to analyze the simultaneous influence that each neuron had on the activity of its neighbors, the team found that populations of neurons in the auditory cortex tended to work independently of each other, with each neuron having little influence on others. In contrast, populations of neurons in the posterior parietal cortex greatly influenced one another, and appeared to work cooperatively.

The activity of is brief, but populations of neurons working together can carry information for longer periods by being active at different time points. In the , the strong cooperative activity allowed groups of neurons to carry information about the sound identification task for up to a second. Groups of neurons in the auditory cortex carried information for only a few hundred milliseconds.

"The transient activation of neurons in the is great for representing sound, which fluctuates rapidly," Harvey said. "But we think that parietal cortex neurons work together on the longer timescale that we observed because they need to integrate information over time to make the best possible choice."

In support of this hypothesis, the team found mice were more likely to make the correct choice while navigating the maze in trials where parietal cortex neurons seemed to be working better as a group, with stronger coupling in the activity of neurons. In trials with weaker coupling, mice seemed more likely to make an incorrect choice.

While the activity of individual neurons has been studied for decades, recent advances in technology have allowed neuroscientists to begin to investigate large groups of neurons simultaneously. The results of this study, Harvey said, are important for deciphering how populations of neurons interact with one another and revealing emergent properties such as varying timescales of activity, which informs the study of higher cognitive functions.

"Our hope is if we can understand the network and synaptic mechanisms responsible for the differences between the parietal and auditory cortices, it might lead to insight on the mechanisms that underlie short-term, or working, memory," Harvey said. "I think the more we start to develop tools and ways to think about populations of neurons, the more we are going to be able to understand about the brain."

Explore further: Coupling of movement and vision

More information: Caroline A. Runyan et al, Distinct timescales of population coding across cortex, Nature (2017). DOI: 10.1038/nature23020

Related Stories

Coupling of movement and vision

June 22, 2017
In a study published in Cell, Georg Keller and his group shed light on neural circuits in the cortex that underlie the integration of movement and visual feedback. They identified a mechanism in the visual cortex responsible ...

Egocentric hearing: Study clarifies how we can tell where a sound is coming from

June 15, 2017
A new UCL and University of Nottingham study has found that most neurons in the brain's auditory cortex detect where a sound is coming from relative to the head, but some are tuned to a sound source's actual position in the ...

Scientists demonstrate the existence of 'social neurons'

May 25, 2017
The existence of new "social" neurons has just been demonstrated by scientists from the Institut de neurosciences des systèmes (Aix-Marseille University / INSERM), the Laboratoire de psychologie sociale et cognitive (Université ...

Mouse study suggests how hearing a warning sound turns into fearing it over time

June 22, 2017
The music from the movie "Jaws" is a sound that many people have learned to associate with a fear of sharks. Just hearing the music can cause the sensation of this fear to surface, but neuroscientists do not have a full understanding ...

Neuroscientists map brain cell activity that occurs during the delay between sensation and action

September 8, 2016
A UC Santa Barbara researcher studying how the brain uses perception of the environment to guide action has a new understanding of the neural circuits responsible for transforming sensation into movement.

Researchers uncover brain circuitry central to reward-seeking behavior

February 22, 2017
The prefrontal cortex, a large and recently evolved structure that wraps the front of the brain, has powerful "executive" control over behavior, particularly in humans. The details of how it exerts that control have been ...

Recommended for you

New technique helps uncover changes in ALS neurons

June 22, 2018
Northwestern Medicine scientists have discovered that some neurons affected by amyotrophic lateral sclerosis (ALS) display hypo-excitability, using a new method to measure electrical activity in cells, according to a study ...

Broken shuttle may interfere with learning in major brain disorders

June 22, 2018
Unable to carry signals based on sights and sounds to the genes that record memories, a broken shuttle protein may hinder learning in patients with intellectual disability, schizophrenia, and autism.

Watching stem cells repair spinal cord in real time

June 22, 2018
Monash University researchers have restored movement and regenerated nerves using stem cells in zebra fish where the spinal cord is severely damaged.

Scientists discover how brain signals travel to drive language performance

June 21, 2018
Effective verbal communication depends on one's ability to retrieve and select the appropriate words to convey an intended meaning. For many, this process is instinctive, but for someone who has suffered a stroke or another ...

'Antifreeze' molecules may stop and reverse damage from brain injuries

June 21, 2018
The key to better treatments for brain injuries and disease may lie in the molecules charged with preventing the clumping of specific proteins associated with cognitive decline and other neurological problems, researchers ...

Scientists discover fundamental rule of brain plasticity

June 21, 2018
Our brains are famously flexible, or "plastic," because neurons can do new things by forging new or stronger connections with other neurons. But if some connections strengthen, neuroscientists have reasoned, neurons must ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.