Assessment of Midline Lingual Point-Pressure Somatosensation Using Von Frey Hair Monofilaments

This protocol is significant because it allows researchers to easily assess point pressure sensation on the midline tongue giving us insights into each individuals’sensory profile. This technique can be performed anywhere using simple, portable equipment. These devices are easy to use and easy to clean and are also relatively time and cost efficient.

The purpose of using this technique is to understand how point pressure sensation changes across the adult life span. Because disorders can cause changes but so can age and lifestyle choices. We use this method to assess oral sensation in relation to food preferences and eating behavior but it could also be used to study speech clarity and swallowing disorders.

Demonstrating the procedure will be Jenn Brodock and Molly Higgins graduate students at Penn State. To set up the experiment place the monofilaments with the indicated target forces onto a table so that each target level can be easily read and seat the participant in a comfortable chair with a glass of water within arms reach. Then instruct the participant that during the experiment they will be asked to close their eyes and stick out their tongue and that they are encouraged to take a sip of water every five to ten trials or after the first incorrect response.

To perform a detection threshold estimate inform the participant that they will hear trial one and trial two and feel a point of pressure on the tongue during one of the trials. If the participant thinks they feel a point of pressure in trial one the participant should put up one finger. If the participant thinks they feel a point of pressure in trial two the participant should put up two fingers.

If the participant is not sure the participant should give their best guess. Pressure should always be applied in one of the two trials. To identify the starting point for testing have the participant close their eyes and say trial one and pause.

Then say trial two and pause. Be sure to deliver the pressure in one of the trials such that the monofilament is pressed to the tongue’s surface until the monofilament buckles. Then hold for a second and release.

It is important that the monofilament be applied in the same manner on each trial using a smooth and deliberate motion. Use a random number generator to create a series of one and two trials so that the stimuli will be presented randomly in trial one or trial two without following a pattern. Be sure to be deliberate and intentional when applying the pressure such that the stimulus is always clearly delivered in trial one or trial two with a one second pause before and after when the trial number is said and when the stimulus is delivered.

Record the participant’s response after each evaluation. To complete discrimination threshold testing inform the participant that they will still hear trial one and trial two but that this time pressure will be applied in both trials. If the participant thinks that they feel the stronger point of pressure in trial one the participant should put up one finger.

If the participant thinks they feel the stronger point of pressure in trial two the participant should put up two fingers. If the participant is not sure the participant should give their best guess. Begin the test at three monofilament levels above the detection threshold estimate stopping point and use the target stimulus and the monofilament immediately below the threshold in force as the two discrimination stimuli.

Then have the participant to close their eyes or ask the participant to close their eyes and start the trials delivering the weaker and stronger stimuli in a randomized order after clearly stating trial one and trial two. At the end of the experiment place the nylon end of each monofilament in a folded 70%alcohol prep pad and gently squeeze the pieces of pad together while pulling the monofilament through. Then allow the disinfected monofilaments to dry in the open position before closing and storing the monofilaments in a clean, dry environment away from direct sunlight.

In this representative analysis 51 participants completed the detection threshold estimate testing and a total of 107 participants completed the discrimination threshold estimate testing. Evaluation of the midline lingual point pressure detection threshold estimate in relation to the participant age revealed that participants across this healthy age span demonstrated low thresholds for point pressure detection. Assessment of the midline lingual point pressure discrimination threshold estimate by participant age showed that the participants across this healthy age span demonstrated a greater variability in the discrimination threshold estimate compared to the detection threshold estimates.

It is essential to remember which monofilament you are delivering and how many times you have delivered it so you know when to change the stimulus or stop testing. Multiple additional methods would be well suited to follow this technique particularly if you are interested in how point pressure sensation relates to food preferences or motor behaviors like speech and swallowing.