October 28, 2013
Dendrites In Brain Act As Mini-Neural Computers
Brett Smith for redOrbit.com - Your Universe Online
Initially thought of as a simple means of sending signals in the brain, new research, published on Sunday in the journal Nature, has revealed that the dendrite sections of neurons are capable of processing 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, an assistant professor in the UNC School of Medicine.
"Imagine you're reverse engineering a piece of alien technology, and what you thought was simple wiring turns out to be transistors that compute information," Smith continued. "That's what this finding is like. The implications are exciting to think about."
Axons, the wire-like part of neurons, are where the nerve cells typically generate electrical impulses, but many of the same molecules that sustain axonal impulses are also present in dendrites, or the ‘heads’ of nerve cells. Previous studies using brain tissue have shown that dendrites are capable of using those molecules to create electrical spikes on their own, but the role of these dendritic impulses in normal brain activity was unclear.
In the new study, Smith’s team discovered that dendrites act as mini-neural computers, processing neuronal input signals on their own.
To reach this conclusion, the team conducted a series of experiments that took years to complete and spanned two continents. The scientists used electrophysiology techniques to essentially "listen" in on the electrical signaling process of a neuronal dendrite in the brain of a mouse. The method required the scientists to delicately attach a microscopic glass pipette electrode to the mouse neuron.
"Attaching the pipette to a dendrite is tremendously technically challenging," Smith said. "You can't approach the dendrite from any direction. And you can't see the dendrite. So you have to do this blind. It's like fishing if all you can see is the electrical trace of a fish."
"You just go for it and see if you can hit a dendrite," he said. "Most of the time you can't."
Once the pipette was attached, the researchers took electrical recordings from within the brains of anesthetized and awake mice. As the mice saw visual stimuli on a computer screen, the researchers observed a strange pattern of electrical signals in the dendrite.
The researchers then discovered that the dendritic spikes happened selectively, depending on the visual stimulus, an indication of the dendrites processing information about what the mouse was seeing.
To provide visual proof of their discovery, the researchers filled neurons with calcium dye, which gave an optical readout of activity. This showed that dendrites fired electrical impulses while other sections of the neuron did not, meaning that the spikes were being produced within the dendrites.
Study author Tiago Branco, created a model of neurons and discovered that known mechanisms could explain the dendritic spiking, further validating the team’s interpretation of the data.
"All the data pointed to the same conclusion," Smith said. "The dendrites are not passive integrators of sensory-driven input; they seem to be a computational unit as well."
Smith said the team plans to see what this newly discovered dendritic role may play in brain circuitry.