27 October 2013
Brain's processing power vastly underestimated, suggests new study
by Will Parker
In work that could change the way we think about how neural circuitry functions in the brain, scientists have shown that dendrites, long thought to be passive wiring in the brain, actually process information. "Suddenly, it's as if the processing power of the brain is much greater than we had originally thought," said study author Spencer Smith, from the University of North Carolina.
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body of the neuron from which the dendrites project. Smith's team's findings, published in the journal Nature, indicate that dendrites actively process neuronal input signals themselves, effectively acting as mini computers.
Previous research using dissected brain tissue had demonstrated that, like neurons, dendrites could generate electrical spikes themselves, but it was unclear whether normal brain activity involved those dendritic spikes. For example, could dendritic spikes be involved in how we see?
Smith's investigations required a series of intricate experiments that spanned two continents, beginning in study co-author Michael Hausser's lab at University College London, and completed at the University of North Carolina.
The scientists used patch-clamp electrophysiology to attach a microscopic glass pipette electrode, filled with a physiological solution, to a neuronal dendrite in the brain of a mouse. The idea being, to directly "listen" in on the electrical signaling process.
Once the pipette was attached to a dendrite, Smith's team took electrical recordings from individual dendrites within the brains of anesthetized and awake mice. As the mice viewed visual stimuli on a computer screen, the researchers saw an unusual pattern of electrical signals - bursts of spikes - in the dendrite.
The researchers found that the dendritic spikes occurred selectively, depending on the visual stimulus, indicating that the dendrites processed information about what the animal was seeing.
To provide visual evidence of their finding, the team filled neurons with calcium dye, which provided an optical tell-tale of spiking. This revealed that dendrites fired spikes while other parts of the neuron did not, indicating that the spikes were the result of local processing within the dendrites.
"All the data pointed to the same conclusion," Smith summarized. "The dendrites are not passive integrators of sensory-driven input; they seem to be a computational unit as well."
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