Top Stories - Posted by Jocelyn Duffy-Carnegie Mellon on Monday, March 28, 2011 9:29 - 0 Comments
How neurons hear above the din
CARNEGIE MELLON (US) — Much like a person trying to be heard across a crowded room, billions of neurons in the brain need to figure out how to get their message heard over all the chatter.
Neurons communicate by sending out electrical impulses called action potentials or “spikes” that code information much like Morse code with only dots and no dashes. Groups of neurons can choose to communicate information in one of two ways: by spiking simultaneously or by spiking separately.
“Neurons face a universal communications conundrum. They can speak together and be heard far and wide, or they can speak individually and say more,” explains Nathan Urban, distinguished professor of life sciences at Carnegie Mellon University. “Both are important. We wanted to find out how neurons choose between these strategies.”
To find out, Urban and Brent Doiron, assistant professor of mathematics at the University of Pittsburgh, and doctoral student Sonya Grihar looked at mitral cell neurons in the brain’s olfactory bulb—the part of the brain that sorts out smells and a common model for studying global information processing.
The research, is reported online in the journal Proceedings of the National Academy of Sciences (PNAS).
Using slice electrophysiology and computer simulations, they found that the brain had a clever strategy for ensuring that the neurons’ message was being heard.
Over the short time scale of a few milliseconds, the brain engaged its inhibitory circuitry to make the neurons fire in synchrony. This simultaneous, correlated firing creates a loud, but simple, signal, much like a crowd at a sporting event chanting, “Let’s go team!”
Over short time intervals, individual neurons produced the same short message, increasing the effectiveness with which activity was transmitted to other brain areas. In both human and neuronal communication alike, this collective communication works well for simple messages, but not for longer or more complex messages that contain more intricate information.
The neurons studied used longer timescales (around one second) to convey these more complex concepts. Over longer time intervals, the inhibitory circuitry generated a form of competition between neurons, so that the more strongly activated neurons silenced the activity of weakly activated neurons, enhancing the differences in their firing rates and making their activity less correlated.
Each neuron was able to communicate a different piece of information about the stimulus without being drowned out by the chatter of competing neurons. It would be like being in a group where each person spoke in turn. The room would be much quieter than a sports arena and the immediate audience would be able to listen and learn much more complex information.
“Across biology, from genetics to ecology, systems must simultaneously complete multiple functions,” Urban says. “The solution we found in neuroscience can be applied to other systems to try to understand how they manage competing demands.”
The study was funded by the National Institute on Deafness and Other Communications Disorders, the National Institutes of Health and the National Science Foundation.
More news from Carnegie Mellon University: www.cmu.edu/news/