A Study on the Effectiveness of Information Obtained from Long-term
Observation of Somatosensory Sensitivity
A JISAIHAN1) ORCID:0000-0002-3485-0965, OHNO Yuko1)2) ORCID:0000-0002-3469-6793, UEMURA Nana2), IMAINahoko2), SHIMIZU Yuuna2), ENNKA Moe2), MORITA Rika2), WAKABAYASHI Kurumi2),
SUGIMOTO Nanasa2), FUKUSHIMA Miki2), FURUKAWA Tatsumi1), YOSHIMURA Shin'ichi1),
TONOIKE Mitsuo1) ORCID:0000-0001-8322-2212
1) Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.
2) School of Media Informatics, Mukogawa Women’s University, Nishinomiya, Hyogo, Japan.
Correspondence: u188236b@ecs.osaka-u.ac.jp <A JISAIHAN>

Keywords: Somatosensory sensitivity, Abnormalities detection, Pre-symptomatic health management
Abstract: In this study, the somatosensory sensitivity ofthe toe thumbs of healthy adults was measured for morethan 14 weeks using a device that records the distancetraveled by the skin-contact probe in micrometers when thesubject senses the probe's movement and presses theresponse button. The results showed that the variation in
the somatosensory sensitivity of the subjects was about 10to 20 micrometers, and the reproducibility of themeasurements was confirmed. When the sensitivity of only
one or both legs worsened during the observation period,
it was found that there was a reason, such as an injury, poor
physical condition, or taking analgesics. This study
confirms that somatosensory sensitivity can be quantified
and introduced into health care.

1. Background
In an aging society, nursing support covers not only
patients in the hospital but also routine healthmanagement at home and the population living in thecommunity. Routine health management requires somenon-invasive indicators, is easy to measure, and is able
to detect early and small abnormalities. We focused on
somatosensory sensitivity.
Small changes insomatosensory sensitivity, such as numbness anddiscomfort in the fingertips, are some of the mostcommon and important information reported by patientsand are often cited as a precursor to various diseases,
health conditions, and pre-illness states. However, thesehave been recorded qualitatively as patients' subjective
complaints and have not been fully utilized for the early
detection of abnormalities.
In this study, we report on what information can beobtained by long-term observation of somatosensory
sensitivity using a device that can measure somaticsensation down to the micrometer level. It also
discussed how these measurements can help in healthmanagement, particularly in pre-symptomatic healthmanagement, a condition that maintains homeostasis.
2. Device for Measuring Somatic Sensation
The somatic sensation is measured with a skin sensory
sensitivity threshold test device, planter foot sensationtesting instrument, i.e., PFS tester (Fig.1) [1][2]. The
probe travel distance and the increment can be set

Fig. 1PFS tester

arbitrarily by 1 micrometer. The time between the probe
starting to move and the subject pressing the button is
also recorded as a response time in milliseconds. The
somatosensory sensitivity is the shortest probe traveled
distance when the subject has answered correctly threetimes in a row.
3. Experimental Methods
Using a PFS tester, the sensitivity of the toe thumb wasmeasured repeatedly in nine healthy women, ages 19 to27, for more than 14 weeks. Each time during theexperiment, subjects were interviewed about changes intheir daily habits, physical condition, and the type ofshoes they wear, such as high heels or sneakers. Thechanges in toe-thumb sensory sensitivity and theresponse time were examined in terms of intra- andinter-individual variability and the observed rapidchanges.
4. Results & Discussion(1) Long-term repeated measurements of toe-thumbsensory sensitivity
Figure 2 shows the change in repeated measures of toethumb sensitivity in three subjects over a year and a half.
The scale on the vertical axis is 10μm. The most stablesubject’s inter-individual variability was in the 10μm

range. At 69 weeks, her sensitivity deteriorated by10μm; however, the sensitivity has improved again.

Fig 2 Long-term repeated measurement of the plantar
sensory sensitivity in 3 subjects

Of the nine subjects measured over a 14-week period,
six had remained mostly stable sensitivity, and there was
not much difference in the measurement between theleft and right legs. The change of sensitivity was in therange of 10 to 20 micrometers throughout the examinedperiod. The remaining three had periods when thesensitivity of left-right difference suddenly increased, orthat of both legs worsened. According to the results ofinterviews at such periods, a subject had broken one leg,and one had back pain. In such cases, the healthy leg’s
sensitivity showed worse than usual, which implied thatthe healthy side of the leg was also under strain,
protecting the sick side. In the cases where thesensitivities of both legs worsened, this seemed to be
due to the wearing of high heels and lack of exercise.
After the subject switched from high heels to athleticshoes for exercise, the plantar sensation improved inapproximately one week.
In healthy people, the sensitivity of the left and rightlegs shows almost the same value and similarfluctuation. If sensitivity is "poor for one's age" or"suddenly deteriorates", it may be associated withillnesses, poor health conditions, or using a kind ofanalgesics; improvements in these conditions often
seemed to recover to better sensitivity. Dulling of the toe
sensation is a common symptom in diabetics, andmedical specialists said that early detection of blunted
sensation could lead to medical attention and prevent
diabetes aggravation. It is reported that many cancer
patients undergoing chemotherapy complain of
discomfort of cutaneous sensation in their fingertips. If
the discomfort is detected earlier, the quality of life of
the treatment may be improved. These are to be future
research. Finally, we would like to mention some caseswith excessive good somatosensory sensitivity, such asaround 5 micrometers, they responded in the interviews
that they were a little depressed or stressed. A personwith too much sensitivity also needs to be examined.

(2) The relation between the somatosensory sensitivity
and the response time
The time taken from sensing "this might be the probe
movement" to pressing the response button is also
recorded as response time in the PFS tester. The value
and the variability in response time seemed morechallenging to investigate than somatosensory
sensitivity. In the study, for example, one subject’s
response time changed from 0.413 msec, 0.285 msec,
and 0.399 msec as the probe traveled distance from theshortest to the longest. The other one’s response timevaried from 0.592 msec, 0.414 msec, and 0.731 msec.
We expected the response time would gradually shorten
as the probe traveled distance increased and the probe
movement became easier to recognize, but in fact, many
subjects showed the fastest response at the secondlength. A short response time would mean that thesubject pressed the button without hesitation, i.e., thesubject recognized the probe movement clearly. In caseof a longer response time, the subject might need moretime to identify if the probe has moved. Or it might takea long time for the brain to issue the command for theaction of pushing the button, or it might take time forthe brain to take action after receiving the command.
These would be investigated in the future using
neuroscientific methods [3].
(3) For the nursing support and early detection of theabnormalities
The conventional method used to examine cutaneous
sensory abnormalities is the test with a SemmesWeinstein monofilament set, which consists of 20 pentype testing devices with monofilaments of different
thicknesses attached to the tip of the pen. The examiner
lowers the device to the test site until the filament
deflects, and the subject responds whether he/she felt itor not. This test is said to need more accuracy andreproducibility. Because it was essentially information
based on the patient's subjective sensations, somaticsensation has long been treated insufficiently.
Measuring the somatosensory sensitivity with the PFS
tester on the micrometer order can detect small and/or
rapid abnormalities and lead to pre-symptomatic healthmanagement, a condition that maintains homeostasis.
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