In a paper published April 6 in Nature, Simons Collaboration on the Global Brain (SCGB) Investigators Matteo Carandini, Kenneth D. Harris and their team gained insight into the relationship between individual neurons and the larger neural populations in which they reside in an effort to understand how information is encoded in neural circuits.
By studying the visual cortex of mice and monkeys, they found that neighboring neurons vary in how influenced they are by the firing of the larger population of neurons. Some neurons are strongly coupled to their neighbors, whereas others are weakly coupled, a discovery that may shed light on the global activity of neural populations.
Neurons in the cerebral cortex operate like members of a large orchestra: Some act as the choristers who support the main tune, while others are soloists playing separate melodies, and these roles tend not to change, explain the researchers. Each neuron can be categorized in terms of its ‘population coupling,’ a measurement that characterizes the extent to which the activity of that individual neuron relates to the larger population of neurons, determining whether it is a chorister or a soloist.
“The findings represent a previously unappreciated dimension by which we can characterize neurons,” explains Carandini. “It’s new and simple and it has clear biological backing: Neurons that ‘sing with the choir’ receive more incoming synaptic inputs than ‘soloist’ neurons.”
The discovery that chorister neurons typically receive more synaptic inputs than soloist neurons allows neuroscientists to interpret the joint activity of large populations of neurons without having exact knowledge of the intricate wiring that connects them.
“One might have thought that describing the activity of thousands of neurons would be impossible without computing the millions of correlations between each pair of cells,” says Harris. “This discovery gives us a powerful tool moving forward, to understand complex circuits through simpler analysis.”
The Simons Foundation funds both Carandini and Harris in this collaborative project. Through work together in their joint laboratory, the researchers believe that this one simple principle of population coupling will bring scientists closer to understanding the workings of the brain’s billions of neurons.
“A key goal of neuroscience is to understand how any single neuron relates to the global activity patterns that underlie perception, cognition and action. We discovered that this relationship can be described, at least to a first approximation, in a very simple way,” says Harris.
Now, Carandini and Harris are making new recordings of brain activity to more thoroughly understand the functional consequences of a neuron being a chorister or a soloist. “This is exciting work, but it is just the beginning,” says Harris.