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Scientists probe functional connectivity among neurons in auditory cortex gives rise to map of acoustic space

September 22, 2017

"If you did this experiment in the visual cortex, you would see that the connectivity is the same regardless of which way you cut the slice," explains Oviedo. "But in our experiments in the auditory cortex slices, we found that there was a qualitative difference in the connectivity between slices cut along the tonotopic axis vs. those cut perpendicular to it."

There was an even more striking divergence from the visual cortex-and presumably the other cortical regions. As demonstrated by a Nobel Prize-winning discovery in 1962, in the visual cortex, the neurons that share the same input source (or respond to the same signal) are organized into columns. As Oviedo puts it, "all neurons within a column in the vertical cortex are tuned to the same position in space and are more likely to communicate with other neurons from within the same column."

Analogously, in the auditory cortex, neurons within a column are expected to be tuned to the same frequency. So the scientists were especially surprised to find that for a given neuron in this region, the dominant input signal didn't come from within its column but from outside it.

"It comes from neurons that we think are tuned to higher frequencies," elaborates Zador. "This is the first example of the neuronal organizing principle not following the columnar pattern, but rather an out-of-column pattern." Discovering this unexpected, out-of-column source of information for a neuron in the auditory complex adds a new twist to their research, which is focused on understanding auditory function in terms of the underlying circuitry and how this is altered in disorders such as autism.

"With this study, we've moved beyond having only a conceptual notion of the functional difference between the two axes by actually finding correlates for this difference at the level of the neuronal microcircuits in this region," he explains.

Source: Cold Spring Harbor Laboratory