A new study has revealed that it’s not the size or shape that but the way neuron responds to incoming stimuli that sets one neuron apart from another. Carnegie Mellon University researchers have said that this diversity is critical to overall brain function and essential in how neurons process complex stimuli and code information.
"I think neuroscientists have, at an intuitive level, recognised the variability between neurons, but we swept it under the rug because we didn’t consider that diversity could be a feature. Rather, we looked at it as a fundamental reflection of the imprecision of biology," Nature quoted Nathan N. Urban of CMU’s Department of Biological Sciences as saying.
"We wanted to reconsider that notion. Perhaps this diversity is important — maybe it serves some function," he said.
Urban and Krishnan Padmanabhan of CMU tested single neurons'' responses to a complex stimulus. By placing an electrical probe into individual excitatory neurons called mitral cells and exposing them to a complex computer-controlled noise stimulus, the researchers were able to determine how each cell responded.
They found that out of the dozens of neurons they tested, no two had the exact same response. While the researchers believed that these results were striking on their own, it led them to wonder whether or not the neurons were giving a messy version of a single response, or if they were each providing different pieces of information about the stimulus.
To test their hypothesis, the CMU researchers used a tool called spike-triggered averaging that allowed them to determine what feature of the stimulus causes each neuron to respond.
They found that some responded to rapid changes in the stimulus and others to slower changes; still other neurons responded when the input signal changed in a regular or rhythmic way.
The researchers then computed the information contained in the outputs of highly diverse sets of neurons and compared it to that of groups of more similar neurons.
They found that the heterogeneous groups of neurons transmitted two times as much information about the stimulus than the homogeneous group.
"A population in which each member is a little different in terms of what they can do is a more efficient and more effective population. It’s like a baseball team — if you want to win, you shouldn’t put nine pitchers on the field," Urban said.
Aside from its role in information coding, the researchers believe neuronal diversity also could play a role in neurological disorders like epilepsy, Parkinson’s disease and schizophrenia. The findings were published in Nature Neuroscience.