Researchers found that "branch-like projections of the neurons" called dendrites don't just deliver information between neurons, they process it as well.
"Suddenly, it's as if the processing power of the brain is much greater than we had originally thought," Spencer Smith, PhD, an assistant professor in the UNC School of Medicine, said in a University of North Carolina, Chapel Hill news release.
Neurons generate electrical spikes in neurons, but many of these axonal spike-supporting molecules can also be found it dendrites. The dendrites are believed to also have to ability to generate electrical spikes through these molecules.
The research team set out to see if the brain used the dendrite spikes. They concluded the dendrites do in fact act as "mini-neural computers," and are able to process input signals on their own.
The team 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 researchers hoped to be able to directly "listen" to the electrical process with a two-photon microscope system that Smith built himself.
"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 but all you can see is the electrical trace of a fish. [And you can't use bait.] You just go for it and see if you can hit a dendrite. Most of the time you can't."
When the team finally succeeded in attaching the pipette they were able to take electrical recordings of individual recording within the anesthetized but awake mice's brains. The recordings were taken as the mouse watched visual stimuli on a screen.
The recordings showed unusual spikes and patterns in the dendrite's electrical signal. They found the activity corresponded with what the mouse was seeing, suggesting the dendrites were processing the visual stimuli.
The team tested their theory even further by filling the neurons with calcium dye, which created an "optical readout of spiking." Since some parts of the dendrite fired spikes and others did not, the team concluded "the spikes were the result of local processing within the dendrites."
"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."
The study was published in the journal Nature.
