Rethinking the brain’s circuitry

A series of studies conducted by Randy Bruno, PhD, and Christine Constantinople, PhD, of Columbia University’s Department of Neuroscience, topples convention by showing that sensory information travels to two places at once: not only to the brain’s mid-layer (where most axons lead), but also directly to its deeper layers. The study appears in the June 28, 2013, edition of the journal Science.

A) Since the 1950s, the cortex has been thought to be a collection of modules, or “columns,” the layers of which sequentially process information before handing it off to another column. (B) This study shows that sensory signals are instead copied to two targets (L4 and L5B) and that the upper and lower halves of the cortex are independent. The “top brain” and “bottom brain,” which contain different types of cells, are able to influence behavior via completely different neural pathways. (Credit: Image credit: Christine Constantinople, PhD/Randy Bruno, PhD/Columbia University Medical Center)

For decades, scientists have thought that sensory information is relayed from the skin, eyes, and ears to the thalamus and then processed in the six-layered cerebral cortex in serial fashion: first in the middle layer (layer 4), then in the upper layers (2 and 3), and finally in the deeper layers (5 and 6.) This model of signals moving through a layered “column” was largely based on anatomy, following the direction of axons—the wires of the nervous system.

“Our findings challenge dogma,” said Dr. Bruno, assistant professor of neuroscience and a faculty member at Columbia’s new Mortimer B. Zuckerman Mind Brain Behavior Institute and the Kavli Institute for Brain Science. “They open up a different way of thinking about how the cerebral cortex does what it does, which includes not only processing sight, sound, and touch but higher functions such as speech, decision-making, and abstract thought.”

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