Scientists have found that dendrites, the branch-like projections of neurons, act as mini-neural computers - actively processing information to multiply the brain's computing power.
Dendrites were thought to be passive wiring in the brain but researchers at the University of North Carolina at Chapel Hill with their colleagues have shown that these dendrites do more than relay information from one neuron to the next.
"Suddenly, it's as if the processing power of the brain is much greater than we had originally thought," said Spencer Smith, an assistant professor in the UNC School of Medicine.
The findings could change the way scientists think about long-standing scientific models of how neural circuitry functions in the brain, while also helping researchers better understand neurological disorders.
Axons are where neurons conventionally generate electrical spikes, but many of the same molecules that support axonal spikes are also present in the dendrites.
Previous research using dissected brain tissue had demonstrated that dendrites can use those molecules to 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 team found that dendrites effectively act as mini-neural computers, actively processing neuronal input signals themselves.
Researchers 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 was to directly "listen" in on the electrical signalling process.
Once the pipette was attached to a dendrite, Smith's team took electrical recordings from individual dendrites within the brains of anaesthetised 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.
Smith's team then 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, Smith's team filled neurons with calcium dye, which provided an optical readout of spiking.
This revealed that dendrites fired spikes while other parts of the neuron did not, meaning that the spikes were the result of local processing within the dendrites.
"All the data pointed to the same conclusion. The dendrites are not passive integrators of sensory-driven input; they seem to be a computational unit as well," Smith said.
The findings were published in the journal Nature.
