Study Finds Mechanism That Controls Brain's Information Flow

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Understanding how information flows within and between various brain regions is one of the many unsolved mysteries of neuroscience. Recently, a team of neuroscientists broke new ground by pinpointing a unique mechanism that operates like a "switchboard" in the cerebral cortex and appears to control the flow of sensory information in the mammalian brain.

This trailblazing study was conducted on active and alert mice by researchers at New York University's Langone Medical Center and its Neuroscience Institute. The March 2017 paper was published yesterday in the journal Science.

During this study, the NYU researchers found that specialized nerve cells—called "somatostatin-expressing interneurons" (also known as Sst interneurons)—play a pivotal role in controlling how information flows through somatosensory cortices in the active mouse brain.

In recent years, other studies on inhibitory interneurons have shown that these specialized nerve cells play a key role in sensorimotor integration, selective attention, and reinforcement encoding.

Interneurons are distributed throughout six distinct layers within the cerebral cortex. Previous research on interneurons in living mammalian brains during active wakefulness has been restricted to the top layers of the neocortex due to technological limits of microscopy.

For this pioneering study, the NYU researchers were able to probe into the deepest layers of the cerebral cortex and record the activity of inhibitory interneurons using a revolutionary optical-tagging technique they developed called "channelrhodopsin-assisted patching."

Neurons in the cerebral cortex have long been known to play a key role in sensory perception, learning, and memory formation. That said, according to the researchers, their new study is the first to identify the layer-specific "switchboard" mechanism of Sst interneurons in the cerebral cortex.

In an article for The Scientist, neuroscientist Massimo Scanziani of the University of California, San Diego (who wasn't involved in this research) described the study by saying, "It is an outstanding example of circuit analysis and a real experimental tour de force."

Cortical Interneurons Display Layer-Specific Activities

In a statement, senior study investigator Bernardo Rudy, professor of neuroscience and physiology at NYU Langone said,

"We have long wondered how the cerebral cortex can process and integrate separate information lines coming in from different brain structures, or from other areas of the cortex, and how it sorts out what information is relevant at any given moment. We now know that Sst interneurons operate like a switchboard that controls the flow of these information lines.”

Mice and rats are primarily nocturnal animals who rely on their whiskers to map out their environments and to choreograph movements in the darkness. A mouse's whiskers and the process of "whisking" are its most important sensory organ. Because mice rely so heavily on whisking, the study of nerve cell activity linked to whiskers during both active and passive brain states is an ideal model for neuroscientists to monitor shifts in interneuron processing modes.

Rudy and colleagues found that when a mouse is navigating its environment and whisking, some of the Sst interneurons turn on while others turn off. This was a breakthrough discovery.

More specifically, the team pinpointed that the cerebral cortex contains a diverse subset of Sst interneurons that project into different layers of the neocortex. Interestingly, the activity of these Sst interneurons changes when a mouse shifts from a resting state (not moving its whiskers) to an active state of whisking.

Notably, in order for a mouse to make informed decisions that guide its movements appropriately, the Sst interneurons appear to selectively boost or block the cortical flow of sensory information.

These findings advance neuroscientific understanding of how the cerebral cortex in mice (and speculatively humans) processes sensory information. Co-lead study investigator William Muñoz, says the team's findings could lead to drug therapies for conditions where the senses are disrupted, such as autism spectrum disorders (ASD), Alzheimer's disease, and schizophrenia.

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In future studies, the NYU research team plans to investigate and analyze the activities of Sst interneurons and other kinds of neurons in the cerebral cortex during more complex behaviors.