Neurons And The Sense Of Touch
October 26, 2012

Sense Of Touch Comes Down To The Neurons

Michael Harper for — Your Universe Online

The sense of touch is perhaps the most basic, most elementary of the senses. It´s how many living things learn, move and explore. Yet, according to W. Daniel Tracey, PhD, there´s still plenty left to be discovered when it comes to the sense of touch.

“On a molecular level, touch is the most poorly understood of the senses,” said Dr. Tracey who is an associate professor of anesthesiology at Duke University Medical Center. Dr. Tracey also authored a paper detailing his work in pinpointing specific neurons which are crucial to the sense of touch.

These neurons are fairly easy to find, as they´re covered in thin spikes. Dr. Tracey also believes these spikes are used to determine force.

This paper was published on October 25th in the journal Current Biology and details these spiked neurons found in fruit fly larvae. It is also the first paper to be able to describe what these spiked sensory neurons are capable of.

“While there are many types of touch sensor neurons, we still don´t know how these neurons respond to force,” said Dr. Tracey in a statement.

Dr. Tracey and his team conducted their study on fruit flies to identify the way these insects responded to touch. These fruit flies worked as an accurate, yet small, analog as they use touch to explore, sense danger and more, just as humans do. Working with such a small candidate meant small tools needed to be employed. The team used an eyelash to stroke the fruit flies, measuring their response to the soft touches.

During their research, the Duke team discovered the fruit flies had many specialized sensory neurons which acted as touch sensors, specifically the class II and class III multidentritic neurons.

With these neurons identified, the team could then silence them genetically in order to study how the flies would respond with these neurons out of commission. With these sensors silenced, the fruit flies´ sense of touch was impaired. Turning these neurons on again repaired their senses.

It´s these class III cells which bear the long, narrow spikes, called filopedia. The researchers believe these long filopedia act as a sort of antenna for cells to gauge their environment. Neurons which had more filopedia on the surface were more sensitive to force, while those with fewer spikes were less sensitive to force.

Dr. Tracey and his team were not able to find a correlation between the length of the filopedia and the sensitivity to force, however.

“Our discoveries in fruit fly larvae give us really important clues as to where we should look in the genes of mammals to better understand the sense of touch,” said Dr. Tracey.

“We do not yet know if humans will present similar structures, but further studies may shed light on the sense of touch in our species.”

With a better understanding of the sense of touch on a molecular level, doctors could one day better treat patients who have issues with pain or their sense of touch. Some patients with chronic pain can be crippled by even the lightest touch. Understanding why such signals are being sent to the brain could be the first step in treating these conditions.

“By learning more about touch sensing, we can begin to explore why these neurons become so responsive to stimuli, and how it is that these signals become painful. We might - in the long run - help people with chronic pain issues in new ways by looking at the underlying molecular mechanisms,” concluded Dr. Tracey.