The relationship between tactile thresholds and histology in the human finger

The Effects of Ageing on Tactile Function in Humans

Ageing is accompanied by a steady decline in touch sensitivity and acuity. Conversely, pleasant touch, such as experienced during a caress, is even more pleasant in old age. There are many physiological changes that might explain these perceptual changes, but researchers have not yet identified any specific mechanisms. Here, we review both the perceptual and structural changes to the touch system that are associated with ageing. The structural changes include reduced elasticity of the skin in older people, as well as reduced numbers and altered morphology of skin tactile receptors. Effects of ageing on the peripheral and central nervous systems include demyelination, which affects the timing of neural signals, as well as reduced numbers of peripheral nerve fibres. The ageing brain also undergoes complex changes in blood flow, metabolism, plasticity, neurotransmitter function, and, for touch, the body map in primary somatosensory cortex. Although several studies have attempted to find a direct link between perceptual and structural changes, this has proved surprisingly elusive. We also highlight the need for more evidence regarding age-related changes in peripheral nerve function in the hairy skin, as well as the social and emotional aspects of touch.

Contact Pressure Level Indication Using Stepped Output Tactile Sensors

In this article, we report on a novel diaphragm-type tactile pressure sensor that produces stepwise output currents depending on varying low contact pressures. When contact pressures are applied to the stepped output tactile sensor (SOTS), the sensor's suspended diaphragm makes contact with the substrate, which completes a circuit by connecting resistive current paths. Then the contact area, and therefore the number of current paths, would determine the stepped output current produced. This mechanism allows SOTS to have high signal-to-noise ratio (>20 dB) in the 3-500 Hz frequency range at contact pressures below 15 kPa. Moreover, since the sensor's operation does not depend on a material's pressure-dependent electrical properties, the SOTS is able to demonstrate high reproducibility and reliability. By forming a 4 × 4 array of SOTS with a surface bump structure, we demonstrated shear sensing as well as surface (1 × 1 cm²) pressure mapping capabilities.

Intraepidermal nerve fiber density at the distal leg: a worldwide normative reference study

The diagnostic reliability of skin biopsy in small fiber neuropathy depends on the availability of normative reference values. We performed a multicenter study to assess the normative values of intraepidermal nerve fiber (IENF) density at distal leg stratified by age deciles. Eight skin biopsy laboratories from Europe, USA, and Asia submitted eligible data. Inclusion criteria of raw data were healthy subjects 18 years or older; known age and gender; 3-mm skin biopsy performed 10-cm above the lateral malleolus; bright-field immunohistochemistry protocol, and quantification of linear IENF density in three 50-µm sections according to published guidelines. Data on height and weight were recorded, and body mass index (BMI) was calculated in subjects with both available data. Normative IENF density reference values were calculated through quantile regression analysis; influence of height, weight, or BMI was determined by regression analyses. IENF densities from 550 participants (285 women, 265 men) were pooled. We found a significant age-dependent decrease of IENF density in both genders (women p < 0.001; men p = 0.002). Height, weight, or BMI did not influence the calculated 5th percentile IENF normative densities in both genders. Our study provides IENF density normative reference values at the distal leg to be used in clinical practice.

Aging effects on joint proprioception: the role of physical activity in proprioception preservation

Throughout the human life span the functions of several physiological systems dramatically change, including proprioception. Impaired proprioception leads to less accurate detection of body position changes increasing the risk of fall, and to abnormal joint biomechanics during functional activities so, over a period of time, degenerative joint disease may result. Altered neuromuscular control of the lower limb and consequently poor balance resulting from changes in the proprioceptive function could be related to the high incidence of harmful falls that occur in old age subjects. There is evidence of proprioception deterioration with aging. Regular physical activity seems to be a beneficial strategy to preserve proprioception and prevent falls among older subjects. Some studies have demonstrated that the regular physical activity can attenuate age-related decline in proprioception. This paper reviews the evidence of age effects on joint proprioception. We will discuss the possible mechanisms behind these effects and the role of regular physical activity in the attenuation of age-related decline in proprioception.

Repetitive motion in perception of tactile sensation in the fingers of string players

Little is known about the mechanisms that underlie the pathophysiology involved in the development of cumulative trauma disorders. Musicians, specifically string players, may be a useful model to examine the cumulative effects of repetitive motion given the highly attended movements of their left hands and the stereotypical grasp of their right hands. Musculoskeletal disorders related to playing are experienced by 39% to 87% of musicians, making musicians a potentially good model for the study of factors involved in development of cumulative trauma disorders. Sensory thresholds for two-point discrimination and light touch were measured in all phalanges of each digit, of each hand. Comparisons were made within and between a control group of 10 nonmusicians who did not engage in repetitive motion and 10 healthy musicians who did. There were 5 violinists, 2 violists, and 3 cellists. The Non-musician group perceived two-points and light touch at significantly lower thresholds in the proximal phalanges of the left hand than the right hand. Significant differences were not present between right and left hands for the means of distal, middle, and proximal phalanges of the Musician group. This lack of significant difference may be due to higher sensory thresholds associated with repetitive use of the left hand of the musicians.

Localization of mechanosensitive channel TRPV4 in mouse skin

A transient receptor potential (TRP) family, TRPV4, is a calcium-permeable swell-activated channel, playing a role in cutaneous mechanosensation. To elucidate the localization in the mechanosensitive endings, we found with immunohistochemistry in mice that TRPV4 was expressed both by small (low threshold) and large (high threshold) dorsal root ganglia neurons. In addition to free nerve endings, TRPV4 was specifically located at cutaneous mechanosensory terminals co-localized with neurofilament 200, including Meissner, Merkel, penicillate and intraepidermal terminals but not including hair follicle palisades. The distribution suggests that the sensation of pressure by mechanosensitive TRPV4 channel is transmitted through A- as well as C-fiber.

The relationship of the number of Meissner's corpuscles to dermatoglyphic characters and finger size

This study investigated the relationships between the density of Meissner's corpuscles and the dermatoglyphic characteristics of human fingers. Dermatoglyphic prints and tissue samples were collected from the index (II) and ring (IV) fingers of 28 cadavers from the Medical School, University of Adelaide. Pattern types, pattern intensity, total ridge count and ridge breadth, were determined for each sample and the density of Meissner's corpuscles established by recording the mean number of Meissner's corpuscles underlying a 10 mm long line on the skin surface. No relationship was found between the density of Meissner's corpuscles and pattern type, pattern intensity or total ridge count. Negative correlations were found for the density of Meissner's corpuscles with both ridge width and size of fingers. Males were found to have significantly larger fingers, larger ridge breadth, and a lower density of Meissner's corpuscles per 10 mm compared with females. However, there was no difference between the total number of Meissner's corpuscles per finger in males and females. No significant differences were found in either the density of Meissner's corpuscles between antimeres or between the index and ring fingers. These results suggest that for both the left and right hand in males and females, there is a similar number of Meissner's corpuscles for both the index and ring fingers.

Transport and localization of the DEG/ENaC ion channel BNaC1alpha to peripheral mechanosensory terminals of dorsal root ganglia neurons

Mammalian brain sodium channel (BNaC, also known as BNC/ASIC) proteins form acid-sensitive and amiloride-blockable sodium channels that are related to putative mechanosensory channels. Certain BNaC isoforms are expressed exclusively in dorsal root ganglia (DRG) and have been proposed to form the ion channels mediating tissue acidosis-induced pain. With antibody labeling, we find that the BNaC1alpha isoform is expressed by most large DRG neurons (low-threshold mechanosensors not involved in acid-induced nociception) and few small nociceptor neurons (which include high-threshold mechanoreceptors). BNaC1alpha is transported from DRG cell bodies to sensory terminals in the periphery, but not to the spinal cord, and is located specifically at specialized cutaneous mechanosensory terminals, including Meissner, Merkel, penicillate, reticular, lanceolate, and hair follicle palisades as well as some intraepidermal and free myelinated nerve endings. Accordingly, BNaC1alpha channels might participate in the transduction of touch and painful mechanical stimuli.

Transport and localization of the DEG/ENaC ion channel BNaC1alpha to peripheral mechanosensory terminals of dorsal root ganglia neurons

Mammalian brain sodium channel (BNaC, also known as BNC/ASIC) proteins form acid-sensitive and amiloride-blockable sodium channels that are related to putative mechanosensory channels. Certain BNaC isoforms are expressed exclusively in dorsal root ganglia (DRG) and have been proposed to form the ion channels mediating tissue acidosis-induced pain. With antibody labeling, we find that the BNaC1alpha isoform is expressed by most large DRG neurons (low-threshold mechanosensors not involved in acid-induced nociception) and few small nociceptor neurons (which include high-threshold mechanoreceptors). BNaC1alpha is transported from DRG cell bodies to sensory terminals in the periphery, but not to the spinal cord, and is located specifically at specialized cutaneous mechanosensory terminals, including Meissner, Merkel, penicillate, reticular, lanceolate, and hair follicle palisades as well as some intraepidermal and free myelinated nerve endings. Accordingly, BNaC1alpha channels might participate in the transduction of touch and painful mechanical stimuli.

Multiunit neural responses to strong finger pulp vibration. II. Comparison with tactile sensory thresholds

In a companion microneurographic study (Schmidt et al. 1990) maximal multiunit sensory responses to finger pulp vibration were compared with maximal responses evoked by electrical stimulation of the digital nerve. It was found that the MR/ER ratio, i.e. the ratio between the magnitudes of the responses to mechanical and electrical stimulation, decreased with increasing age. The shape of this age-related decline in the ratio corresponded well with the decrease in the number of Meissner corpuscles found in histological studies. In the present study the tactile sensory detection thresholds were measured in the same subjects that participated in the companion study and the relationship between these thresholds and the MR/ER ratios was examined. The tactile sensory detection threshold increased with age. A weak negative correlation was found between the threshold and the ratio. However, after compensation for common age-mediated effects, this negative correlation disappeared. Thus, the results indicate that measurement of tactile sensory detection thresholds and determination of MR/ER ratios may complement each other, giving an indication of different types of derangement of the mechanoreceptive system.

Depth sense aesthesiometry: an advance in the clinical assessment of sensation in the hands

Fingertip depth sense threshold has been examined in fifty normal subjects using the simple pocket aesthesiometer invented by Renfrew. Index fingers possessed the lowest thresholds and little fingers the highest, whilst there were no significant differences between the same fingers of either hand. Sex and age (at least up to 70 years) had no significant influence on depth sense threshold, but thickened skin and low intelligence tended to raise thresholds. Fingertip depth sense thresholds were then compared with the results of conventional sensory testing in fifty patients with sensory symptoms in the hands. The depth sense threshold of affected fingers was more often abnormal than were the results of clinical tests for light touch appreciation, joint position sense and two-point discrimination. Depth sense aesthesiometry is recommended as a simple, sensitive and quantifiable routine technique for the evaluation of sensory disturbance in the hands.

The relation of tactile thresholds to histology in the fingers of elderly people

Touch thresholds in a group of elderly people were determined for three sites on the little finger. They were found to be raised by some two and a half times in each site, in comparison with a group of young subjects. An age-associated reduction in the number of Meissner corpuscles also was observed, but it is suggested that this may reflect a general reduction in peripheral innervation and may not be necessarily directly related to the decrease in tactile sensitivity. No significant sex differences were found either in sensory thresholds, or in the population density of corpuscles.