For the first time, scientists have been able to record a neuronal dendrite processing an optical signal from an intact brain. It sheds new light on dendrites and how the brain processes images.
The new recordings, taken from the brains of mice, may mean that dendrites are far more complex and vital for processing incoming signals than previously thought. It's a breakthrough that could contribute to our understanding of how the brain analyzes a visual scene.
Using a patch pipette - or a glass electrode with a very fine tip - scientists captured images and made electrical recordings of the dendrite processing visual signals. The patch pipette is "just small enough to sneak inside the cell," says Michael Häusser, a neuroscientist at University College London and a co-author of the paper, which is published in the journal Nature.
The technique is a new application of research by two Germans, Erwin Neher and Bert Sakmann, who won the Nobel Prize in Medicine in 1991 for their work in this area.
"It's kind of remained a secret because these dendrites are so small," says Häusser.
Dendrites are the tree-like projections at the end of a brain cell that capture the electrical impulses from stimuli and send them to the cell body. They are less than 1 micron in diameter - about a hundredth the diameter of a human hair.
Häusser and his colleagues showed mice a series of images of black-and-white stripes, also known as "grating," in various orientations.
Animal brains make distinctions in orientation of shapes, such as stripes, to help decode their environment
A half century earlier, neuroscientists had proven that in mice, certain groups of neurons respond to a particular orientation of stripes (for example, vertical), while other groups of neurons respond to other orientations (such as diagonal).
Neurons in other species - and humans as well - also display this feature.
Häusser told DW that a person looking at a map, for example, will have to make such visual distinctions to be able to interpret it.
"It helps us to understand how the brain is picking apart a visual scene," he says.
The recordings, made by a team of neuroscientists from Cambridge University, University College London and the University of North Carolina at Chapel Hill, shed further light on how visual signals are processed by neurons - or brain cells.
Dendrites were long considered passive conduits for such information. But the new recordings show that dendrites are far more sophisticated than originally thought.
"We found that the dendrites provide an attuned response - they already do the processing for a cell in a particular way," Häusser says.
The recordings indicate that dendrites act as an important computing element, priming the information that the soma, or cell body, then processes and delivers to the rest of the brain's network.
It's led Häusser to describe dendrites as "mini-computers."
The team is the first to record an optical impulse going through a dendrite from an intact brain.
"It's helped to crack this 50-year-old mystery of how the cells compute the orientation of the stimulus," says Häusser.