“The organization of the cortex does not look as pretty as it does in the textbooks,” says Dr. Kanold, Assistant Professor of Biology at the University of Maryland, and lead scientist on a new study of the auditory cortex. “Things are a lot messier than expected.”
Dr. Kanold and his team published their report on auditory processing in the January 31 online edition of Nature Neuroscience.
“[Discrete sampling] is like showing someone who wants to know how America looks, ‘Here is one person from New York City and one person from California.’ You don’t get a very good picture of what the country looks like from that sampling,” says Kanold, originally from Germany.
Kanold’s team employed a new technique to observe all the neurons across a broad swath of the auditory cortex. Using a dye that glows when calcium levels rise, indicating active neurons, the team shone a laser on areas of the cortex and measured the neuronal activity of hundreds of neurons in activated by simple tones at different frequencies.
Left: Dyed Brain Regions; Right: Frequency Response
According to Dr. Andrew King, Professor of Neurophysiology at the University of Oxford, “The functional organization of the auditory cortex has remained unclear and a matter of some controversy, despite the efforts of many labs over a number of years. The approach used by Dr. Kanold and colleagues is an important advance in this field.”
“We discovered that the organization of the cortex does not look as pretty as it does in the textbooks, which surprised us,” explains Kanold. “Things are a lot messier than expected. And we don’t see evidence of the maps previously proposed using less precise techniques.”
This messiness could hint at a brain that is far more adaptable than previously thought. “These results may rewrite our classical views of how cortical circuits are organized and what functions they serve,” suggests Dr. Shihab Shamma, whose own work had used discrete microelectrodes to map the auditory cortex.
Kanold’s team looked at both how neurons receive sound information (the inputs), and how they process it (the outputs). “Neighboring neurons do their own thing by creating different outputs,” Kanold says, a finding which overturns conventional models. “You can imagine that you and your neighbor both receive water to your houses from the same pipe, but you do different things with it — you might cook with it while your neighbor waters the lawn. You can’t assume that they are doing the same thing just because they are neighbors.”
Dr. Kanold, an expert in neuroplasticity, sees a benefit to this randomness. “Each individual neuron is getting inputs from a wide range of frequencies, and by selecting which frequencies they are strongly responding to, they might be very easily able to shift their function,” he says. This might help explain how we are quickly able to tune in to different auditory information (paying attention at one moment to the car radio, and at the next to a question from the back seat).
