Duke researchers have found that the way rodents process sensory information at signaling pathways, previously thought to be linear, is intermixed.
The study was conducted by a number of neurobiology researchers under Fan Wang, associate professor of neurobiology at the School of Medicine. Wang’s lab focuses on neural circuits and sensation processing, examining how rodents respond to their environments. The recent results have disproven a widely accepted idea about how the nervous system relays sensory information—the “labeled line theory.”
The labeled line theory implies that the same type of sensory information is relayed to a specific station within the neural pathway, said postdoctoral researcher Katsuyasu Sakurai, lead researcher of the article published in the October issue of Cell Reports.
The lab has demonstrated that second order neurons receive at least two different kinds of sensory information, neurobiology postdoctoral fellow Jun Takato said. The study reports a “one-to-many and many-to one” connectivity scheme for how tactile information is processed. The researchers found that sensory information is mixed at the first relay station to the brain in the mouse trigeminal system, which closely resembles the sensory system in primates.
Transgenic mice were used in the research because of the ability to genetically label the different types of neurons and visualize the wiring diagram of the whisker touch sensory system, Sakurai said.
“In our study, two different kind of sensory neurons, slowly and rapidly adapting neurons, are tagged with two different genes,” Takato said.
Takato added that the researchers next take thin brain sections and immunostain the tags then analyze the images and examine the overlap of the different fluorescent labels. By visualizing different sensory neurons, the group was able to examine whether single second order neurons receive two different kinds of sensory information.
The Nicolelis Lab of the Duke University Medical Center also investigates sensory signaling as an integral part of its neuroprosthetics research. Postdoctoral fellow Eric Thomson, who works in the lab, said that the Nicolelis Lab has found similar results without the same level of molecular and anatomical detail that Sakurai’s paper shows.
“Their study shows that the brain is much more messy, that from very early levels it is mixing different sources of information into a more integrated picture of what is happening in the world,” Thomson said.
The recently published research was supported partially with grants from the National Institutes of Health and has applications for the general public.
Takato said the findings can be applied to the generation of better artificial sensors for people with certain handicaps.
“It would be wonderful if handicapped people can feel what they touch through their prosthetics,” Takato said.
To allow people to touch and feel with artificial limbs, prosthetics would need to be designed with sensors that provide virtual tactile feedback to the brain of the user, Thomson noted.
“Learning about the architecture of the tactile processing system should be very helpful for determining how best to construct such feedback systems,” Thomson said.
Sakurai said the study focuses solely on the organization of two different types of mechano-sensors, but it is not a holistic understanding of the neuronal circuit. There are also other neurons that help facilitate natural tactile behaviors.
“I would like to understand how this kind of tactile information is processed within the neural circuit by manipulating those neurons,” Sakurai said.
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