Age-related changes in cutaneous sensation in the healthy human hand

The effect of nitrile gloves on temperature perception during hot water immersion

INTRODUCTION

Scalds account for 40 % of burn injuries in developed countries, with a subset occurring during caregiving activities, particularly when gloves are worn. Gloves, a standard precaution against infection and body fluid exposure, may impair sensory feedback critical for detecting temperature changes, potentially increasing the risk of burns during personal care tasks.

METHODS

This study investigated the impact of glove use on heat perception. Twelve healthy participants (6 male, 6 female) immersed their index fingers in water baths set at 40°C, 45°C, 50°C, 55°C, and 60°C. Heat perception thresholds were assessed under three conditions: no gloves, single gloves, and double gloves. Participants withdrew their fingers upon feeling discomfort, and the withdrawal temperatures were recorded.

RESULTS

Our trial showed that gloves significantly delayed heat discomfort detection, with the longest delays observed at 50°C and 55°C when double gloves were worn. Wearing a single glove raised the discomfort threshold by approximately 5°C, while double gloves increased it by 10°C. This logarithmic relationship between temperature and perception delay indicates a substantial sensory alteration, especially at higher temperatures.

CONCLUSION

The findings underscore the heightened risk of scald injuries in vulnerable individuals due to delayed heat detection caused by gloves. Awareness of altered temperature thresholds during glove use is essential to prevent burns during caregiving tasks, particularly in activities requiring precise temperature assessment, such as bathing or showering. Enhanced education and preventive measures are crucial for ensuring safety in these contexts.

Touch inhibits cold: non-contact cooling suggests a thermotactile gating mechanism

Skin stimuli reach the brain via multiple neural channels specific for different stimulus types. These channels interact in the spinal cord, typically through inhibition. Inter-channel interactions can be investigated by selectively stimulating one channel and comparing the sensations that result when another sensory channel is or is not concurrently stimulated. Applying this logic to thermal-mechanical interactions proves difficult, because most existing thermal stimulators involve skin contact. We used a novel non-tactile stimulator for focal cooling (9 mm2) by using thermal imaging of skin temperature as a feedback signal to regulate exposure to a dry-ice source. We could then investigate how touch modulates cold sensation by delivering cooling to the human hand dorsum in either the presence or absence of light touch. Across three signal detection experiments, we found that sensitivity to cooling was significantly reduced by touch. This reduction was specific to touch, as it did not occur when presenting auditory signals instead of the tactile input, making explanations based on distraction or attention unlikely. Our findings suggest that touch inhibits cold perception, recalling interactions of touch and pain previously described by Pain Gate Theory.

Nerve conduction, latency, and its association with hand function in young men

INTRODUCTION

The median and ulnar nerves have been suggested to play a significant role in hand function; however, there are insufficient data to determine the strength of this association. This study aimed to investigate the correlation between hand function as measured with the Grooved pegboard test (GPT) and conduction velocity and latency of the median and ulnar nerves.

METHODS

We collected convenience samples in the College of Medicine, KSAU-HS. We used GPT to characterize hand function and performed measured nerve conduction velocity (NCV) and latency of the ulnar and median nerves of both hands. We used the Edinburgh handedness inventory (EHI) to determine hand dominance.

RESULTS

We recruited 28 healthy medical students aged 20-29 years (mean: 21.46 ± 1.62 years). Most were right-handed (n = 25, 89.3%), with a mean EHI score of 302 ± 210. The mean GPT time was significantly faster in the dominant (65.5 ± 6.4 s) than in the non-dominant (75.0 ± 9.6 s) hand. The NCV for the ulnar nerve of the dominant hand was significantly correlated with GPT (r = -0.52, p = 0.005) while median nerve was not correlated (0.24, p = 0.21). Regression analysis and collinearity test showed that the ulnar NCV explained 20% of the variance in GPT of the dominant hand (R2 = 0.203, p = 0.016).

CONCLUSION

The ulnar nerve conduction velocity, explained 20% of the variance in GPT times of the young men. Performance on this biomarker of neurological health seems to be more influenced by other factors in healthy young individuals.

Assessing the severity of carpal tunnel syndrome during physical examination by measuring two-point discrimination: Post-hoc analysis of prospectively collected data

INTRODUCTION

Carpal tunnel syndrome (CTS) commonly presents after distal radius fractures. Assessing its degree of severity is essential to therapeutic decision-making - i.e. operative vs. conservative treatment. The role of the two-point discrimination (2PD) has not yet been evaluated as a potential indicator of severity during physical examination. Therefore, in our cross-sectional study, we aimed to find a correlation between 2PD values and disease severity, based on the gold-standard electromyography and electroneurography (EMG-ENG) and ultrasonography findings.

METHODS

We conducted a post-hoc analysis of prospectively assessed CTS patients for 2PD values. We analyzed the correlation between 2PD and EMG-ENG measurement results, patient characteristics, nerve ultrasonography, and relevant CTS questionnaires. CTS severity was determined by EMG-ENG results. The Pearson correlation was calculated between variables.

RESULTS

The study included 81 patients. The three pre-determined EMG-ENG severity categories showed a significant correlation between both 2PD values and 2PD severity categories (r= 0.29 [0.07-0.48] and r= 0.26 [0.03-0.45]). Distal sensory latency and conduction velocity values correlated significantly with 2PD categories. However, the correlation coefficients (r= 0.25 [0.02-0.46] and r=-0.24 [-0.37-0.07]) were low. The 2PD severity categories showed no significant correlation with the severity assessed by nerve ultrasound (r=-0.07 [-0.38-0.25]). The 2PD values showed a significant correlation between the values of the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire (r= 0.3 [0.06-0.51]). We concluded that the best cut-off value for differentiating severe from non-severe CTS was at the 9.5 mm 2PD cut-off value (sensitivity = 0.65 [0.45-0.81], specificity = 0.71[0.58-0.82], AUC = 0.71 [0.59-0.83]).

CONCLUSION

There is a significant correlation between 2PD values and the severity of carpal tunnel syndrome as determined by EMG-ENG; however, they are not interchangeable. Based on the results of our study, we propose that measuring two-point discrimination may be a quick and easy, reliable and cost-effective screening method to assess the severity of carpal tunnel syndrome following distal radius fractures.

Age related changes in skin sensitivity assessed with smartphone vibration testing

The capacity to perceive tactile input at the fingertips, referred to as tactile sensitivity, is known to diminish with age due to regressive changes to mechanoreceptor density and morphology. Sensitivity is measured as perceptual responses to stimuli of varying intensity. Contrary to traditional sensitivity monitoring instruments, smartphones are uniquely suited for remote assessment and have shown to deliver highly calibrated stimuli along a broad spectrum of intensity, which may improve test reliability. The aim of this study was to evaluate a vibration-emitting smartphone application, the Vibratus App, as a mode of estimating tactile sensory thresholds in the aging adult. The peripheral nerve function of 40 neurologically healthy volunteers (ages 18-71) was measured using monofilaments, a 128-Hz tuning fork, the Vibratus App, and nerve conduction studies (NCS). Between group differences were analyzed to determine each measurement's sensitivity to age. Spearman correlation coefficients depicted the associative strength between hand-held measurements and sensory nerve action potential (SNAP) amplitude. Inter-rater reliability of traditional instruments and the software-operated smartphone were assessed by intraclass correlation coefficient (ICC2,k). Measurements taken with Vibratus App were significantly different between age groups (p < 0.001). The inter-rater reliability of monofilament, smartphone vibration, and tuning fork testing was moderate to good (ICC2,k = 0.65, 0.69, and 0.79, respectively). The findings of this study support further investigation of smartphones as sensitivity monitoring devices for at home monitoring of skin sensitivity.

Relations between tactile sensitivity of the finger, arm, and cheek skin over the lifespan showing decline only on the finger

Touch sensitivity generally declines with age, contributing to loss of manual dexterity and tactile function. We investigated how touch changes over the lifespan, using different tests and on three body sites. We used a classical test of force detection sensitivity, where calibrated monofilaments were applied passively to the right index finger pad, forearm, and cheek. In addition, at the index, we used an active touch spatial discrimination task, developed by our group. Spatial discrimination was estimated through participants' ability to evaluate the distance between parallel bands printed on acrylic plates. Data were collected from 96 healthy women, aged 20-75 years. Force detection and tactile spatial discrimination on the index deteriorated significantly with age; however, no change was found for tactile detection on the forearm or cheek. Tactile detection on the cheek remained remarkably highly sensitive throughout life. There was a significant positive relationship between force detection and spatial discrimination on the index. Further, force detection on the forearm was significantly associated with detection on the index and cheek. Our results suggest a decrease in touch perception with age on the index finger pad, yet a preservation of tactile sensitivity in hairy skin. This opens discussion about the impact of daily activities upon the glabrous hand skin and on the function of hairs in tactile sensitivity. We highlight the need for new methods in evaluating tactile sensitivity on hairy skin.

Two-Point Discrimination for Upper Extremity and Face in Healthy Young Adults: A Cross-Sectional Study

BACKGROUND AND AIM

The threshold values of two-point discrimination (TPD) provide a numerical measure of tactile acuity. Normal reference values are needed to decide whether sensory variability is within normal sensorial limits. The study aimed to determine the upper extremity and face threshold values in healthy young adults.

MATERIALS AND METHODS

Static TPD thresholds of 67 healthy young adults aged 18-35 years were assessed. Eight skin areas in the face and upper extremity on the dominant side were assessed using a "method of limits" approach with an aesthesiometer. Differences between genders were examined with the Mann-Whitney U test. The Spearman correlation analysis investigated the relationship between age and TPD measurements.

RESULTS

TPD values ranged between 4.66 and 19.16 mm and 1.33-68.66 mm in the face and upper extremity, respectively, in the participants with a mean age of 23.83 ± 4.66 years. Fingertips and the area over the lateral mandibula showed the greatest sensitivity. The threshold values of TPD showed both interindividual and intraindividual variability. There was no statistical difference in the TPD values according to gender in any of the measured areas, and there was no relationship between age and TPD test values.

CONCLUSIONS

The threshold values of TPD have clinical applicability in various diseases affecting the sensation of the upper extremity and/or face. These data may help the detection of early sensory loss.

Skin viscoelasticity effects on the periodic mechanical stimuli propagation between skin layers

Our daily lives are constantly surrounded by dynamic stimuli, and our skin is deformed in a time-dependent manner. Although skin plays an important role in transmitting stimuli received at the surface to mechanoreceptors, few studies have investigated how differences in skin viscoelasticity affect the mechanical stimuli propagation in the skin. Therefore, using a finite element model, we evaluated the effects and trends of changes in the stiffness and viscoelasticity of the skin on the propagation of mechanical quantities between skin layers where mechanoreceptors are present when subjected to periodic stimuli. First, we constructed a new, sophisticated mathematical model of skin viscoelasticity based on the history-dependent deformation behavior of human skin obtained experimentally. We were able to construct a skin model that thoroughly reproduced the actual human skin deformation behavior at oscillations as fast as 10 Hz by setting viscoelastic parameters with a short time constant (0.001-0.006 s). Then, we calculated how skin material parameters affect the propagation of the mechanical quantities in the skin during the history-dependent skin deformation response to periodic stimuli. The finite element analysis showed that not only stiffness but also viscoelasticity markedly affected the mechanical stimuli propagation in the skin, and the effect differed depending on the layer. In particular, greater immediate responsiveness of the dermis contributed to greater propagation of the mechanical stimulus. Our results indicate that more attention needs to be given to the differences in the time-dependent intradermal mechanical stimuli propagation caused by individual's skin viscoelasticity.

Changes in sensitivity and hedonic rating to transcutaneous electrical nerve stimulation following COVID-19

COVID-19 affects not only the respiratory system but also other biological systems such as the nervous system. Usually, these changes are reported based on the patient's subjective description. The aim of our study, therefore, was to objectively determine the effect that the SARS-CoV-2 virus and COVID-19 disease has on sensory threshold and the hedonic and subjective perception of an electrical stimulus. The sensory threshold was tested on the inner forearm by applying non-invasive transcutaneous electrical nerve stimulation (TENS) with 100 Hz and 100 µs parameters and a biphasic current waveform. The study involved 211 participants, aged 22-79 years, with a mean age of 56.9 ± 12.1 years. There were 131 subjects in the COVID group, while the NON-COVID group, the control group, was matched to the COVID group in terms of gender, age, body mass index and presence of chronic diseases. The research was carried out in 2022. Sensory sensitivity was highest in the group that had suffered with COVID-19. The median sensory sensitivity was 11 mA in the COVID group and 14 mA (p < 0.001) in the NON-COVID group, however, the current sensitivity threshold decreased over time (R = 0.52, p < 0.001). Post COVID-19, the electrical stimulus was more often perceived as unpleasant: COVID versus NON-COVID (23% vs. 3%, p < 0.001) and as a different sensation to tingling (27% vs. 2%, p < 0.001). Post-COVID-19 patients have a lower sensory threshold, the electrical stimulus is more often described as unpleasant and in subjective feelings it is more often described as pinching. The differences between COVID and NON-COVID decrease with time since the onset of COVID symptoms.

Reduced tactile sensitivity is associated with mild cognitive impairment

BACKGROUND

Sensory impairment has been related to age-associated cognitive decline. While these associations were investigated primarily in the auditory and visual domain, other senses such as touch have rarely been studied. Thus, it remains open whether these results are specific for particular sensory domains, or rather point to a fundamental role of sensory deficits in cognitive decline.

METHODS

Data from 31 participants with mild cognitive impairment (MCI), 46 participants with frailty, and 23 non-clinical control participants (NCCs) were included. We assessed sensory function using visual acuity and contrast sensitivity, hearing threshold, and mechanical detection threshold. Cognitive function in participants with MCI was assessed using associative memory performance. Group differences on sensory thresholds were tested using analyses of covariance with age, sex, and years of education as covariates. Associations between measures within participants with MCI were evaluated using Spearman correlations.

FINDINGS

We found a significant difference in mechanical detection threshold between the groups (p < 0.001, η2 = 0.18). Participants with MCI showed significantly reduced tactile sensitivity compared to participants with frailty and NCCs. In participants with MCI, lower associative memory performance was significantly related to reduced tactile sensitivity (rs = 0.39, p = 0.031) and auditory acuity (rs = 0.41, p = 0.022).

INTERPRETATION

Our results indicate that reduced tactile sensitivity is related to cognitive decline. Prospective studies should investigate the age-related alterations of multimodal sensory processes and their contribution to dementia-related processes.

FUNDING

Deutsche Forschungsgemeinschaft (FL 156/41-1) and a grant of the Hector-Stiftung II, Weinheim, Germany.

Stratum corneum compliance enhances tactile sensitivity through increasing skin deformation: A study protocol for a randomized controlled trial

BACKGROUND

Tactile sensation plays a crucial role in object manipulation, communication, and even emotional well-being. It has been reported that the deformability of skin (also described as skin compliance) that shows a large mechanical response to stimuli is associated with high tactile sensitivity. However, although the compliance of the stratum corneum, the outermost layer of skin, can change daily due to skin care and environmental factors, few studies have quantified the effect of the stratum corneum on tactile sensation.

AIMS

We investigated the changes in tactile sensitivity resulting from skin hydration and identified corresponding alterations in the compliance of the stratum corneum.

METHODS

A randomized controlled trial was conducted. Participants were randomly assigned to an intervention group (n = 20) that had a moisturizing cream applied to their cheeks or a control group (n = 19) that had Milli-Q water applied to their cheeks. Tactile discrimination performance was assessed using psychophysical techniques before and after application. The water content, mechanical response characteristics, and penetration of PEG/PPG-17/4 dimethyl ether from the cream in the stratum corneum were evaluated to identify hydration effects. Skin deformations occurring during tactile sensation were measured concurrently using a suction device employed for tactile stimulation.

RESULTS

Tactile sensitivity was increased in participants who had cream applied to the skin surface, while no significant change was observed in participants who received Milli-Q water. The improved discrimination of tactile stimulus intensity was directly related to the magnitude of skin displacement. The higher water content of the stratum corneum due to cream application decreased the dynamic modulus of elasticity of the stratum corneum and increased the skin's extensibility in response to tactile stimuli.

CONCLUSIONS

Hydrating the stratum corneum significantly enhances tactile sensitivity and is accompanied by an increase in skin extensibility, a factor in tactile intensity perception. The compliance of the thin stratum corneum layer plays a crucial role in tactile experiences that involve skin stretching.

An individual's skin stiffness predicts their tactile discrimination of compliance

Individual differences in tactile acuity have been correlated with age, gender and finger size, whereas the role of the skin's stiffness has been underexplored. Using an approach to image the 3-D deformation of the skin surface during contact with transparent elastic objects, we evaluate a cohort of 40 young participants, who present a diverse range of finger size, skin stiffness and fingerprint ridge breadth. The results indicate that skin stiffness generally correlates with finger size, although individuals with relatively softer skin can better discriminate compliant objects. Analysis of contact at the skin surface reveals that softer skin generates more prominent patterns of deformation, in particular greater rates of change in contact area, which correlate with higher rates of perceptual discrimination of compliance, regardless of finger size. Moreover, upon applying hyaluronic acid to soften individuals' skin, we observe immediate, marked and systematic changes in skin deformation and consequent improvements in perceptual acuity in differentiating compliance. Together, the combination of 3-D imaging of the skin surface, biomechanics measurements, multivariate regression and clustering, and psychophysical experiments show that subtle distinctions in skin stiffness modulate the mechanical signalling of touch and shape individual differences in perceptual acuity. KEY POINTS: Although declines in tactile acuity with ageing are a function of multiple factors, for younger people, the current working hypothesis has been that smaller fingers are better at informing perceptual discrimination because of a higher density of neural afferents. To decouple relative impacts on tactile acuity of skin properties of finger size, skin stiffness, and fingerprint ridge breadth, we combined 3-D imaging of skin surface deformation, biomechanical measurements, multivariate regression and clustering, and psychophysics. The results indicate that skin stiffness generally correlates with finger size, although it more robustly correlates with and predicts an individual's perceptual acuity. In particular, more elastic skin generates higher rates of deformation, which correlate with perceptual discrimination, shown most dramatically by softening each participant's skin with hyaluronic acid. In refining the current working hypothesis, we show the skin's stiffness strongly shapes the signalling of touch and modulates individual differences in perceptual acuity.

Digital nerve injury: to repair or not?

BACKGROUND

There are very few studies comparing patients with and without repair after digital nerve injury. It is still controversial whether digital nerve repair is necessary.

AIMS

The aim of this study was to evaluate the long-term clinical outcomes of patients with unilateral isolated digital nerve injury who underwent surgical repair and those who did not.

METHODS

Seventy-four patients with unilateral digital nerve injury were included in the study. Of these, the patients who underwent surgical repair were determined as group A (n = 42), the patients without repair as group B (n = 32), and the groups were divided into subgroups according to injury levels. Results were evaluated with a minimum follow-up of 24 months.

RESULTS

When the S2PD results were evaluated overall, it was found that those who had digital nerve repair (group A) had significantly better outcomes compared to those without repair (group B) (p = 0.012). When the subgroups were evaluated according to the injury localization, no significant difference was observed at the distal levels, while it was observed that the patients who underwent repair in the proximal levels showed significantly better results (p = 0.003, p = 0.012).

CONCLUSION

In this study, it was seen that there was no difference between the results of repair and non-repair of unilateral nerve injuries distal to the middle level of the middle phalanx, but repair is required in injuries proximal to this level.

Longitudinal multiparametric MRI of traumatic spinal cord injury in animal models

Multi-parametric MRI (mpMRI) technology enables non-invasive and quantitative assessments of the structural, molecular, and functional characteristics of various neurological diseases. Despite the recognized importance of studying spinal cord pathology, mpMRI applications in spinal cord research have been somewhat limited, partly due to technical challenges associated with spine imaging. However, advances in imaging techniques and improved image quality now allow longitudinal investigations of a comprehensive range of spinal cord pathological features by exploiting different endogenous MRI contrasts. This review summarizes the use of mpMRI techniques including blood oxygenation level-dependent (BOLD) functional MRI (fMRI), diffusion tensor imaging (DTI), quantitative magnetization transfer (qMT), and chemical exchange saturation transfer (CEST) MRI in monitoring different aspects of spinal cord pathology. These aspects include cyst formation and axonal disruption, demyelination and remyelination, changes in the excitability of spinal grey matter and the integrity of intrinsic functional circuits, and non-specific molecular changes associated with secondary injury and neuroinflammation. These approaches are illustrated with reference to a nonhuman primate (NHP) model of traumatic cervical spinal cord injuries (SCI). We highlight the benefits of using NHP SCI models to guide future studies of human spinal cord pathology, and demonstrate how mpMRI can capture distinctive features of spinal cord pathology that were previously inaccessible. Furthermore, the development of mechanism-based MRI biomarkers from mpMRI studies can provide clinically useful imaging indices for understanding the mechanisms by which injured spinal cords progress and repair. These biomarkers can assist in the diagnosis, prognosis, and evaluation of therapies for SCI patients, potentially leading to improved outcomes.

Aging exerts a limited influence on the perception of self-generated and externally generated touch

Touch generated by our voluntary movements is attenuated both at the perceptual and neural levels compared with touch of the same intensity delivered to our body by another person or machine. This somatosensory attenuation phenomenon relies on the integration of somatosensory input and predictions about the somatosensory consequences of our actions. Previous studies have reported increased somatosensory attenuation in elderly people, proposing an overreliance on sensorimotor predictions to compensate for age-related declines in somatosensory perception; however, recent results have challenged this direct relationship. In a preregistered study, we used a force-discrimination task to assess whether aging increases somatosensory attenuation and whether this increase is explained by decreased somatosensory precision in elderly individuals. Although 94% of our sample (n = 108, 21-77 yr old) perceived their self-generated touches as weaker than externally generated touches of identical intensity (somatosensory attenuation) regardless of age, we did not find a significant increase in somatosensory attenuation in our elderly participants (65-77 yr old), but a trend when considering only the oldest subset (69-77 yr old). Moreover, we did not observe a significant age-related decline in somatosensory precision or a significant relationship of age with somatosensory attenuation. Together, our results suggest that aging exerts a limited influence on the perception of self-generated and externally generated touch and indicate a less direct relationship between somatosensory precision and attenuation in the elderly individuals than previously proposed.NEW & NOTEWORTHY Self-generated touch is attenuated compared with externally generated touch of identical intensity. This somatosensory attenuation has been previously shown to be increased in elderly participants, but it remains unclear whether it is related to age-related somatosensory decline. In our preregistered study, we observed a trend for increased somatosensory attenuation in our oldest participants (≥69 yr), but we found no evidence of an age-related decline in somatosensory function or a relationship of age with somatosensory attenuation.

An individual's skin stiffness predicts their tactile acuity

Individual differences in tactile acuity have been correlated with age, gender, and finger size, while the role of the skin's stiffness has been underexplored. Using an approach to image the 3-D deformation of the skin surface while in contact with transparent elastic objects, we evaluate a cohort of 40 young participants, who present a diverse range of finger size, skin stiffness, and fingerprint ridge breadth. The results indicate that skin stiffness generally correlates with finger size, although individuals with relatively softer skin can better discriminate compliant objects. Analysis of contact at the skin surface reveals that softer skin generates more prominent patterns of deformation, in particular greater rates of change in contact area, which correlate with higher rates of perceptual discrimination, regardless of finger size. Moreover, upon applying hyaluronic acid to soften individuals' skin, we observe immediate, marked and systematic changes in skin deformation and consequent improvements in perceptual acuity. Together, the combination of 3-D imaging of the skin surface, biomechanics measurements, multivariate regression and clustering, and psychophysical experiments show that subtle distinctions in skin stiffness modulate the mechanical signaling of touch and shape individual differences in perceptual acuity.

Applying cosmetic oil with added aromatic compounds improves tactile sensitivity and skin properties

Tactile sensitivity generally decreases with aging and is associated with impairments in skin properties. Products that hydrate the skin can combat touch deficits and aromatic compounds have been shown to improve skin mechanical properties. Thus, we tested a base cosmetic oil against a perfumed oil, applied to the skin of females aged 40-60 years, on tactile sensitivity and skin properties after repeated application. Tactile detection thresholds were assessed using calibrated monofilaments applied at the index finger, palm, forearm, and cheek. Spatial discrimination on the finger was assessed using pairs of plates with different inter-band spaces. These tests were performed before and after 1 month of base or perfumed oil use. We found that tactile detection thresholds and spatial discrimination improved only in perfumed oil group. A complementary immunohistological study using human skin was conducted to estimate the expression of olfactory receptor OR2A4 and elastic fiber length. Further, the expression of OR2A4 intensity and the length of elastic fibers increased significantly with oil application, where larger effects were seen with the perfumed oil. We conclude that the application of a perfumed oil may be of additional benefit and could repair, and even prevent, tactile decline with aging by ameliorating skin condition.

Healthy Human Laryngopharyngeal Sensory Innervation Density Correlates with Age

OBJECTIVE

Somatosensory feedback from upper airway structures is essential for swallowing and airway defense but little is known about the identities and distributions of human upper airway neurons. Furthermore, whether sensory innervation modifies with aging is unknown. In this study, we quantify neuronal and chemosensory cell density in upper airway structures and correlate with age.

METHODS

Participants underwent biopsies from base of tongue, lateral and midline pharyngeal wall, epiglottis, and arytenoids (N = 25 13 female/12 male; 20-80 years, mean 51.4 years without clinical diagnosis of dysphagia or clinical indication for biopsy). Tissue sections were labeled with antibodies for all neurons, myelinated neurons, and chemosensory cells. Densities of lamina propria innervation, epithelial innervation, solitary chemosensory cells, and taste buds were calculated and correlated with age.

RESULTS

Arytenoid had the highest density of innervation and chemosensory cells across all measures compared to other sites. Taste buds were frequently observed in arytenoid and epiglottis. Base of tongue, lateral pharynx, and midline posterior pharynx had minimal innervation and few chemosensory cells. Epithelial innervation was present primarily in close proximity to chemosensory cells and taste buds. Overall innervation and myelinated fibers in the arytenoid lamina propria decline with aging.

CONCLUSION

Findings establish the architecture of healthy adult sensory innervation and demonstrate the varied distribution of laryngopharyngeal innervation, necessary steps toward understanding the sensory basis for swallowing and airway defense. We also document age-related decline in arytenoid innervation density. These findings suggest that sensory afferent denervation of the upper airway may be a contributing factor to presbyphagia.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:773-784, 2023.

A Systematic Review of Navigation Assistance Systems for People With Dementia

Technological developments provide solutions to alleviate the tremendous impact on the health and autonomy due to the impact of dementia on navigation abilities. We systematically reviewed the literature on devices tested to provide assistance to people with dementia during indoor, outdoor and virtual navigation (PROSPERO ID number: 215585). Medline and Scopus databases were searched from inception. Our aim was to summarize the results from the literature to guide future developments. Twenty-three articles were included in our study. Three types of information were extracted from these studies. First, the types of navigation advice the devices provided were assessed through: (i) the sensorial modality of presentation, e.g., visual and tactile stimuli, (ii) the navigation content, e.g., landmarks, and (iii) the timing of presentation, e.g., systematically at intersections. Second, we analyzed the technology that the devices were based on, e.g., smartphone. Third, the experimental methodology used to assess the devices and the navigation outcome was evaluated. We report and discuss the results from the literature based on these three main characteristics. Finally, based on these considerations, recommendations are drawn, challenges are identified and potential solutions are suggested. Augmented reality-based devices, intelligent tutoring systems and social support should particularly further be explored.

Effects of Presence Rate of the Palmaris Longus Tendon on Wrist Proprioception and Grip Strength

INTRODUCTION

The palmaris longus muscle displays a great variation in terms of incidence and shape. This study has documented the incidence ratio of this muscle among the students at Bolu Abant İzzet Baysal University, Faculty of Medicine, and has revealed the effects of its presence on wrist proprioception and grip strength.

METHODS

A total of 101 students between the ages of 18 and 25 were included in the study. Age, height, weight, body mass index (BMI), and dominant upper extremity of the individuals were recorded. After the presence of palmaris longus tendon (PLT) was determined by using the Schaeffer's test, wrist proprioception was evaluated by using a digital inclinometer, and grip strength was evaluated by using a hand dynamometer.

RESULTS

PLT absence rates were evaluated separately as right and left, and it was found as 16.8% and 17.8%. No correlation was found between the dominant upper extremity and BMI and the presence of PLT. The presence or absence of PLT has no effect on grip strength and wrist proprioception.  Conclusion: PLT is used in many clinical areas, such as reconstructive and cosmetic surgery, graft applications, tendon repairs, ptosis correction operations, and ligament stabilization. We think there will be no significant loss in the sense of proprioception and grip strength in the absence of PLT.

Horses' Tactile Reactivity Differs According to the Type of Work: The Example of Equine-Assisted Intervention

Tactile perception in humans varies between individuals and could depend on extrinsic factors such as working activity. In animals, there is no study relating the influence of animals' work and their tactile reactivity per se. We investigated horses' tactile reactivity using von Frey filament in different body areas and compared horses working only in equine-assisted interventions (EAI), in riding school (RS) lessons, and in both activities (EAI-RS). We further compared tactile actions by people with or without mental and/or developmental disorders during brushing sessions. The results indicated that EAI horses showed higher tactile reactivity compared to EAI-RS and RS horses, both in terms of number of reactions overall, and especially when the test involved thin filaments. All horses showed high tactile reactivity when tested on the stifle, and this was particularly true for EAI horses. These differences could be related to humans' actions, as participants diagnosed with disorders brushed more the hindquarters and showed more fragmented actions. This study opens new lines of thought on the influence of EAI working activity on horses' tactile reactivity, and hence, on horses' sensory perception. Tactile reactivity outside work, may be directly (via tactile stimulations) or indirectly (via the welfare state), influenced by working conditions.

Skin properties and afferent density in the deterioration of tactile spatial acuity with age

Tactile sensitivity is affected by age, as shown by the deterioration of spatial acuity assessed with the two-point discrimination task. This is assumed to be partly a result of age-related changes of the peripheral somatosensory system. In particular, in the elderly, the density of mechanoreceptive afferents decreases with age and the skin tends to become drier, less elastic and less stiff. To assess to what degree mechanoreceptor density, skin hydration, elasticity and stiffness can account for the deterioration of tactile spatial sensitivity observed in the elderly, several approaches were combined, including psychophysics, measurements of finger properties, modelling and simulation of the response of first-order tactile neurons. Psychophysics confirmed that the Elderly group has lower tactile acuity than the Young group. Correlation and commonality analysis showed that age was the most important factor in explaining decreases in behavioural performance. Biological elasticity, hydration and finger pad area were also involved. These results were consistent with the outcome of simulations showing that lower afferent density and lower Young's modulus (i.e. lower stiffness) negatively affected the tactile encoding of stimulus information. Simulations revealed that these changes resulted in a lower build-up of task-relevant stimulus information. Importantly, the reduction in discrimination performance with age in the simulation was less than that observed in the psychophysical testing, indicating that there are additional peripheral as well as central factors responsible for age-related changes in tactile discrimination. KEY POINTS: Ageing effects on tactile perception involve the deterioration of spatial sensitivity, although the contribution of central and peripheral factors is not clear. We combined psychophysics, measurements of finger properties, modelling and simulation of the response of first-order tactile neurons to investigate to what extent skin elasticity, stiffness, hydration, finger pad area and afferent density can account for the lower spatial sensitivity observed in the elderly. Correlation and commonality analysis revealed that age was the most important factor to predict behavioural performance. Skin biological elasticity, hydration and finger pad area contributed to a lesser extent. The simulation of first-order tactile neuron responses indicated that reduction in afferent density plays a major role in the deterioration of tactile spatial acuity. Simulations also showed that lower skin stiffness and lower afferent density affect the build-up of stimulus information and the response of SA1 (i.e. type 1 slowly adapting fibres) and RA1 (i.e. type 1 rapidly adapting fibres) afferent fibres.

Alpha-Lipoic Acid Supplementation Restores Early Age-Related Sensory and Endothelial Dysfunction in the Skin

Many changes characterize skin aging, and the resulting dysfunctions still constitute a real challenge for our society. The aim of this study was to compare the skin aging of two rat strains, Wistar and Brown Norway (BN), considered as "poorly aging" and "healthy aging" models, respectively, and to assess the effect of alpha-lipoic acid (LPA), especially on skin microcirculation. To this purpose, various skin characteristics were studied at 6, 12, and 24 months and compared to the results of LPA treatment performed at 12 or 24 months. Skin aging occurred in both strains, but we showed an early occurrence of different age-related disorders in the Wistar strain compared to BN strain, especially regarding weight gain, glycemia dysregulation, basal skin perfusion, endothelial function, and skin resistance to low pressure. LPA treatment tended to improve skin resistance to low pressure in BN but not in Wistar despite the improvement of basal skin perfusion, endothelial function, and skin sensory sensitivity. Overall, this study confirmed the healthier aging of BN compared to Wistar strain and the positive effect of LPA on both general state and skin microcirculation.

Age-dependent increase of cytoskeletal components in sensory axons in human skin

Aging is a complex process characterized by several molecular and cellular imbalances. The composition and stability of the neuronal cytoskeleton is essential for the maintenance of homeostasis, especially in long neurites. Using human skin biopsies containing sensory axons from a cohort of healthy individuals, we investigate alterations in cytoskeletal content and sensory axon caliber during aging via quantitative immunostainings. Cytoskeletal components show an increase with aging in both sexes, while elevation in axon diameter is only evident in males. Transcriptomic data from aging males illustrate various patterns in gene expression during aging. Together, the data suggest gender-specific changes during aging in peripheral sensory axons, possibly influencing cytoskeletal functionality and axonal caliber. These changes may cumulatively increase susceptibility of aged individuals to neurodegenerative diseases.

Newborn and elderly skin: two fragile skins at higher risk of pressure injury

Skin is a key organ maintaining internal homeostasis by performing many functions such as water loss prevention, body temperature regulation and protection from noxious substance absorption, microorganism intrusion and physical trauma. Skin ageing has been well studied and it is well known that physiological changes in the elderly result in higher skin fragility favouring the onset of skin diseases. For example, prolonged and/or high-intensity pressure may suppress local blood flow more easily, disturbing cell metabolism and inducing pressure injury (PI) formation. Pressure injuries (PIs) represent a significant problem worldwide and their prevalence remains too high. A higher PI prevalence is correlated with an elderly population. Newborn skin evolution has been less studied, but some data also report a higher PI prevalence in this population compared to older children, and several authors also consider this skin as physiologically fragile. In this review, we compare the characteristics of newborn and elderly skin in order to determine common features that may explain their fragility, especially regarding PI risk. We show that, despite differences in appearance, they share many common features leading to higher fragility to shear and pressure forces, not only at the structural level but also at the cellular and molecular level and in terms of physiology. Both newborn and elderly skin have: (i) a thinner epidermis; (ii) a thinner dermis containing a less-resistant collagen network, a higher collagen III:collagen I ratio and less elastin; (iii) a flatter dermal-epidermal junction (DEJ) with lower anchoring systems; and (iv) a thinner hypodermis, resulting in lower mechanical resistance to skin damage when pressure or shear forces are applied. At the molecular level, reduced expression of transforming growth factor β (TGFβ) and its receptor TGFβ receptor II (TβRII) is involved in the decreased production and/or increased degradation of various dermal extracellular matrix (ECM) components. Epidermal fragility also involves a higher skin pH which decreases the activity of key enzymes inducing ceramide deficiency and reduced barrier protection. This seems to be correlated with higher PI prevalence in some situations. Some data also suggest that stratum corneum (SC) dryness, which may disturb cell metabolism, also increases the risk of PI formation. Besides this structural fragility, several skin functions are also less efficient. Low applied pressures induce skin vessel vasodilation via a mechanism called pressure-induced vasodilation (PIV). Individuals lacking a normal PIV response show an early decrease in cutaneous blood flow in response to the application of very low pressures, reflecting vascular fragility of the skin that increases the risk of ulceration. Due to changes in endothelial function, skin PIV ability decreases during skin ageing, putting it at higher risk of PI formation. In newborns, some data lead us to hypothesize that the nitric oxide (NO) pathway is not fully functional at birth, which may partly explain the higher risk of PI formation in newborns. In the elderly, a lower PIV ability results from impaired functionality of skin innervation, in particular that of C-fibres which are involved in both touch and pain sensation and the PIV mechanism. In newborns, skin sensitivity differs from adults due to nerve system immaturity, but the role of this in PIV remains to be determined.

Development and Trial of a Prototype Device for Sensorimotor Therapy in Patients with Distal Radius Fractures

This study examined the clinical feasibility of a prototype device (development name: Ghost) for facilitating range of motion (RoM) recovery in the acute phase in patients with distal radius fractures (DRF). The Ghost device involves the administration of a combination of vibratory and visual stimuli. We divided the patients into the Ghost (n = 10) and control group (n = 4; tendon vibration only) groups. The experimental interventions were administered between the day after surgery and day 7 postoperatively. Traditional hand therapy was provided to both groups once daily from day 7 until day 84 postoperatively and once a week from day 84 until the end of the intervention period. Because vibratory stimulation makes the patient focus on wrist flexion, the primary outcome was the arc of wrist flexion-extension on the injured side, which was measured on days 7, 14, 28, 42, 56, 70, and 84. Analysis of covariance was applied using a bootstrap method to evaluate changes over time and compare them between the groups. Analyses was performed after stratification by age and body mass index. Both interventions improved RoM over time in patients with DRF. Results showed that Ghost has greater efficacy for improving wrist RoM in DRF patients than vibration alone. Treatment with Ghost can result in good RoM improvement during the acute phase of DRF in young patients and those with and normal or low body mass index. Further study is needed to verify our findings and assess the extent of RoM recovery.

Effects of tendon vibration and age on force reproduction task performed with wrist flexors

The sense of force is suggested to rely in part on proprioceptive inputs when assessed with a force reproduction task. The age-related alterations in proprioceptive system could, therefore, alter the sense of force. This study investigated the effects of tendon vibration on a force reproduction task performed with the wrist flexors in 18 young (20-40 year) and 18 older adults (60-90 year). Participants matched a target force (5% or 20% of their maximal force) with visual feedback of the force produced (target phase), and reproduced the target force without visual feedback (reproduction phase) after a 5-s rest period with or without vibration. The force reproduction error was expressed as the ratio between the force produced during the reproduction and the target phases. For the trials with vibration, the error was expressed as the ratio between the force produced during the reproduction phase performed with and without vibration. Tactile acuity was assessed with a two-point discrimination test. The error was greater at 5% than at 20% contraction intensity (p < 0.001), and in older [56.5 (32.2)%; mean (SD)] than in young adults [33.5 (13.6)%] at 5% (p = 0.002) but not 20% target (p = 0.46). Tendon vibration had a greater effect at 5% than 20% contraction intensity, and in older [41.7 (32.4)%, p < 0.001] than young adults [20.0 (16.1)%]. Tactile acuity was lesser in older than young adults (p < 0.001). The results support the contribution of proprioception in the sense of force, and highlight a decrease in performance with ageing restricted to low-force contractions.

Cutaneous Sensitivity Across Regions of the Foot Sole and Dorsum are Influenced by Foot Posture

Understanding the processing of tactile information is crucial for the development of biofeedback interventions that target cutaneous mechanoreceptors. Mechanics of the skin have been shown to influence cutaneous tactile sensitivity. It has been established that foot skin mechanics are altered due to foot posture, but whether these changes affect cutaneous sensitivity are unknown. The purpose of this study was to investigate the potential effect of posture-mediated skin deformation about the ankle joint on perceptual measures of foot skin sensitivity. Participants (N = 20) underwent perceptual skin sensitivity testing on either the foot sole (N = 10) or dorsum (N = 10) with the foot positioned in maximal dorsiflexion/toe extension, maximal plantarflexion/toe flexion, and a neutral foot posture. Perceptual tests included touch sensitivity, stretch sensitivity, and spatial acuity. Regional differences in touch sensitivity were found across the foot sole (p < 0.001) and dorsum (p < 0.001). Touch sensitivity also significantly increased in postures where the skin was compressed (p = 0.001). Regional differences in spatial acuity were found on the foot sole (p = 0.002) but not dorsum (p = 0.666). Spatial acuity was not significantly altered by posture across the foot sole and dorsum, other than an increase in sensitivity at the medial arch in the dorsiflexion posture (p = 0.006). Posture*site interactions were found for stretch sensitivity on the foot sole and dorsum in both the transverse and longitudinal directions (p < 0.005). Stretch sensitivity increased in postures where the skin was pre-stretched on both the foot sole and dorsum. Changes in sensitivity across locations and postures were believed to occur due to concurrent changes in skin mechanics, such as skin hardness and thickness, which follows our previous findings. Future cutaneous biofeedback interventions should be applied with an awareness of these changes in skin sensitivity, to maximize their effectiveness for foot sole and dorsum input.

Subjective touch sensitivity leads to behavioral shifts in oral food texture sensitivity and awareness

Neurotypical individuals have subjective sensitivity differences that may overlap with more heavily studied clinical populations. However, it is not known whether these subjective differences in sensory sensitivity are modality specific, or lead to behavioral shifts. In our experiment, we measured the oral touch sensitivity and food texture awareness differences in two neurotypical groups having either a high or low subjective sensitivity in touch modality. To measure oral touch sensitivity, individuals performed discrimination tasks across three types of stimuli (liquid, semisolid, and solid). Next, they performed two sorting exercises for two texture-centric food products: cookies and crackers. The stimuli that required low oral processing (liquid) were discriminated at higher rates by participants with high subjective sensitivity. Additionally, discrimination strategies between several foods in the same product space were different across the groups, and each group used attributes other than food texture as differentiating characteristics. The results show subjective touch sensitivity influences behavior (sensitivity and awareness). However, we show that the relationship between subjective touch sensitivity and behavior generalizes beyond just touch to other sensory modalities.

The organizational principles of de-differentiated topographic maps in somatosensory cortex

Topographic maps are a fundamental feature of cortex architecture in the mammalian brain. One common theory is that the de-differentiation of topographic maps links to impairments in everyday behavior due to less precise functional map readouts. Here, we tested this theory by characterizing de-differentiated topographic maps in primary somatosensory cortex (SI) of younger and older adults by means of ultra-high resolution functional magnetic resonance imaging together with perceptual finger individuation and hand motor performance. Older adults' SI maps showed similar amplitude and size to younger adults' maps, but presented with less representational similarity between distant fingers. Larger population receptive field sizes in older adults' maps did not correlate with behavior, whereas reduced cortical distances between D2 and D3 related to worse finger individuation but better motor performance. Our data uncover the drawbacks of a simple de-differentiation model of topographic map function, and motivate the introduction of feature-based models of cortical reorganization.

The impact of movement sonification on haptic perception changes with aging

Combining multisensory sources is crucial to interact with our environment, especially for older people who are facing sensory declines. Here, we examined the influence of textured sounds on haptic exploration of artificial textures in healthy younger and older adults by combining a tactile device (ultrasonic display) with synthetized textured sounds. Participants had to discriminate simulated textures with their right index while they were distracted by three disturbing, more or less textured sounds. These sounds were presented as a real-time auditory feedback based on finger movement sonification and thus gave the sensation that the sounds were produced by the haptic exploration. Finger movement velocity increased across both groups in presence of textured sounds (Rubbing or Squeaking) compared to a non-textured (Neutral) sound. While young adults had the same discrimination threshold, regardless of the sound added, the older adults were more disturbed by the presence of the textured sounds with respect to the Neutral sound. Overall, these findings suggest that irrelevant auditory information was taken into account by all participants, but was appropriately segregated from tactile information by young adults. Older adults failed to segregate auditory information, supporting the hypothesis of general facilitation of multisensory integration with aging.

Deciphering Sounds Through Patterns of Vibration on the Skin

Sensory substitution refers to the concept of feeding information to the brain via an atypical sensory pathway. We here examined the degree to which participants (deaf and hard of hearing) can learn to identify sounds that are algorithmically translated into spatiotemporal patterns of vibration on the skin of the wrist. In a three-alternative forced choice task, participants could determine the identity of up to 95% and on average 70% of the stimuli simply by the spatial pattern of vibrations on the skin. Performance improved significantly over the course of 1 month. Younger participants tended to score better, possibly because of higher brain plasticity, more sensitive skin, or better skills at playing digital games. Similar results were obtained with pattern discrimination, in which a pattern representing the sound of one word was presented to the skin, followed by that of a second word. Participants answered whether the word was the same or different. With minimal difference pairs (distinguished by only one phoneme, such as "house" and "mouse"), the best performance was 83% (average of 62%), while with non-minimal pairs (such as "house" and "zip") the best performance was 100% (average of 70%). Collectively, these results demonstrate that participants are capable of using the channel of the skin to interpret auditory stimuli, opening the way for low-cost, wearable sensory substitution for the deaf and hard of hearing communities.

Predictors of Hand Function Following Digit Replantation: Quantitative Review and Meta-Analysis

Background: Digit replantation affords the opportunity to restore hand function following amputation. To date, however, few studies have evaluated functional outcomes following replantation. Therefore, it was the objective of this study to perform a meta-analysis to better characterize the predictors of hand function. Methods: A literature search was performed using the PubMed database to identify studies that focused on digit amputation/replantation and functional outcomes. Studies were evaluated for patient- and injury-related factors and their respective effects on clinical outcomes of sensation, grip strength, and Disabilities of the Arm, Shoulder, and Hand (DASH) scores. Statistical analysis was conducted across the pooled data set to identify significant trends. Results: Twenty-eight studies representing 618 replanted digits were included in this study. We found the average grip strength was 78.7% (relative to contralateral), the average 2-point discrimination (2PD) was 7.8 mm, and the average DASH score was 12.81. After conducting statistical analysis, we found patients with more proximal injuries had lower grip strength scores (P < .05). We found 2PD scores were influenced by age, mechanism of injury, and amputation level (P < .05). Finally, we found DASH scores after replantation were predicted by mechanism of injury and level of amputation (P < .05). The following variables did not influence outcomes: gender, tobacco use, ischemia time, and digit number. Conclusions: Digit replant does not restore premorbid hand function but does result in adequate hand function. Expected functional outcomes following replant should be considered in the decision-making process. These data can help risk-stratify patients, guide postreplant expectations, and influence the decision for replantation.

Improvements and Degradation to Spatial Tactile Acuity Among Blind and Deaf Individuals

Cross-modal reorganization takes place for sensory cortices when there is no more primary input. For instance, the visual cortex in blind individuals which receives no visual input starts responding to auditory and tactile stimuli. Reorganization may improve or degrade processing of other modality inputs, via bottom-up compensational processes and top-down updating. In two experiments, we measured the spatial tactile response in a large sample of early- (N = 49) and late-blind (N = 51) individuals with varying levels of Braille proficiencies, and early-deaf (N = 69) with varying levels of hearing devices against separate hearing and sighted controls. Spatial tactile responses were measured using a standard gradient orientation task on two locations, the finger and tongue. Experiments show limited to no advantage in passive tactile response for blind individuals and degradation for deaf individuals at the finger. However, the use of hearing devices decreased the tactile impairment in early-deaf individuals. Also, no differences in age-related decline in both sensory-impaired groups were shown. Results show less tactile acuity differences between blind and sighted than previously reported, but supports recent reports of tactile impairment among the early-deaf.

Effects of tDCS on Tactile Perception Depend on Tactile Expertise in Both Musicians and Non-Musicians

Brain plasticity in the somatosensory cortex and tactile performance can be facilitated by brain stimulation. Here, we investigated the effects of transcranial direct current stimulation (tDCS) on tactile perception in musicians and non-musicians to elucidate how tDCS-effects might depend on tactile expertise. On three separate days, 17 semi-professional musicians (e.g., piano or violin players) and 16 non-musicians aged 18-27 years received 15 min of 1 mA anodal (a-tDCS), cathodal (c-tDCS) or sham tDCS in a pseudorandomized design. Pre and post tDCS, tactile sensitivity (Touch Detection Task; TDT) and discrimination performance (Grating Orientation Task; GOT) were assessed. For further analysis, the weekly hours of instrument-playing and computer-typing were combined into a "tactile experience" variable. For GOT, but not TDT, a significant group effect at baseline was revealed with musicians performing better than non-musicians. TDT thresholds were significantly reduced after a-tDCS but not c-tDCS or sham stimulation. While both musicians' and non-musicians' performance improved after anodal stimulation, neither musical nor tactile expertise was directly associated with the magnitude of this improvement. Low performers in TDT with high tactile experience profited most from a-tDCS. We conclude that tactile expertise may facilitate somatosensory cortical plasticity and tactile learning in low performers.

Modelling the effects of age-related morphological and mechanical skin changes on the stimulation of tactile mechanoreceptors

Our sense of fine touch deteriorates as we age, a phenomenon typically associated with neurological changes to the skin. However, geometric and material changes to the skin may also play an important role on tactile perception and have not been studied in detail. Here, a finite element model is utilised to assess the extent to which age-related structural changes to the skin influence the tactile stimuli experienced by the mechanoreceptors. A numerical, hyperelastic, four-layered skin model was developed to simulate sliding of the finger against a rigid surface. The strain, deviatoric stress and strain energy density were recorded at the sites of the Merkel and Meissner receptors, whilst parameters of the model were systematically varied to simulate age-related geometric and material skin changes. The simulations comprise changes in skin layer stiffness, flattening of the dermal-epidermal junction and thinning of the dermis. It was found that the stiffness of the skin layers has a substantial effect on the stimulus magnitudes recorded at mechanoreceptors. Additionally, reducing the thickness of the dermis has a substantial effect on the Merkel disc whilst the Meissner corpuscle is particularly affected by flattening of the dermal epidermal junction. In order to represent aged skin, a model comprising a combination of ageing manifestations revealed a decrease in stimulus magnitudes at both mechanoreceptor sites. The result from the combined model differed from the sum of effects of the individually tested ageing manifestations, indicating that the individual effects of ageing cannot be linearly superimposed. Each manifestation of ageing results in a decreased stimulation intensity at the Meissner Corpuscle site, suggesting that ageing reduces the proportion of stimuli meeting the receptor amplitude detection threshold. This model therefore offers an additional biomechanical explanation for tactile perceptive degradation amongst the elderly. Applications of the developed model are in the evaluation of cosmetics products aimed at mitigating the effects of ageing, e.g. through skin hydration and administration of antioxidants, as well as in the design of products with improved tactile sensation, e.g. through the optimisation of materials and surface textures.

Simultaneous use of sensory stimulation and motor exercise improves the manual skills of educable children with mental retardation at preprimary and primary school levels

Background: Children with mental retardation have various clinical problems. They mostly have motor delay and sensory deficit. Neurorehabilitation focuses on restoring remaining abilities. Thus, the present study was designed to study the effects of simultaneous use of sensory-motor therapy on manual skills of children with mental retardation. Methods: In this study, 120 educable boys and girls with mental retardation (9-12 years) were selected from 2 preprimary and primary exceptional centers in Tehran using stratified sampling method considering the geographical dispersion. The participants were divided into 2 equal trial and control groups using simple random sampling. Lincoln-Oseretsky Motor Development Scale, Purdue Pegboard test, and Handwriting Legibility Checklist of Persian Language were used. Simultaneous sensory stimulations and motor exercises were used for 3 one-hour weekly sessions for 12 consecutive weeks. Pre and posttests were done for evaluation. Using parametric paired and independent samples t tests, the findings were analyzed in SPSS 23. Results: The manual skills significantly improved following therapeutic use of simultaneous sensory stimulation and motor exercise (p=0.001). In the control group, the pre and post evaluation difference was not significant (p=0.813) Conclusion: Based on the findings of this study, simultaneous use of sensory-motor techniques can have better clinical results in the trial group compared to the control group. Thus, these types of techniques should be used more in clinics. However, further studies are needed for more comparison between separate applications of these techniques.

Hand-Feel Touch Cues and Their Influences on Consumer Perception and Behavior with Respect to Food Products: A Review

There has been a great deal of research investigating intrinsic/extrinsic cues and their influences on consumer perception and purchasing decisions at points of sale, product usage, and consumption. Consumers create expectations toward a food product through sensory information extracted from its surface (intrinsic cues) or packaging (extrinsic cues) at retail stores. Packaging is one of the important extrinsic cues that can modulate consumer perception, liking, and decision making of a product. For example, handling a product packaging during consumption, even just touching the packaging while opening or holding it during consumption, may result in a consumer expectation of the package content. Although hand-feel touch cues are an integral part of the food consumption experience, as can be observed in such an instance, little has been known about their influences on consumer perception, acceptability, and purchase behavior of food products. This review therefore provided a better understanding about hand-feel touch cues and their influences in the context of food and beverage experience with a focus on (1) an overview of touch as a sensory modality, (2) factors influencing hand-feel perception, (3) influences of hand-feel touch cues on the perception of other sensory modalities, and (4) the effects of hand-feel touch cues on emotional responses and purchase behavior.

Outcomes of surgical repair of a single digital nerve in adults

Current standard management of a cut digital nerve is end-to-end microsurgical nerve coaptation where possible. A recent systematic review of adult digital nerve injuries that were either repaired or left unrepaired showed that the evidence for good nerve recovery or improved function following nerve repair is poor. In the 30 studies included, only 24% of repaired nerves regained sensory recovery close to or equivalent to estimated pre-injury levels. Neuroma rates were the same in those nerves repaired (4.6%) and those not repaired (5%). Questions under debate include proper assessment methods of outcomes, decision making for repair or no repair to different fingers or the thumb, levels of injury, age, and hand dominance. This review summarizes the major evidence available and debates the surgical dogma that surrounds this injury.

Long Term Cosmetic Application Improves Tactile Discrimination in the Elderly; a New Psychophysical Approach

Introduction: Tactile sensitivity is impaired in older adults, which contributes to the loss of manual dexterity and mobility function. The reliability of classical psychophysical tests, such as two-point gap discrimination, has been questioned. Here we tested a new method to determine tactile acuity during dynamic touch, which is more functional than static touch. The aim was to validate a method providing a high level of discrimination of tactile acuity in the elderly.

Methods: We tested the ability of subjects to evaluate the distance between bands printed on poly-methyl-methacrylate (PMMA) sheets. Pairs of sheets were compared in two groups of participants aged from 60 to 74 years; the test group was required to apply a cosmetic foam with an active ingredient on both their hands twice a day for 1 month, the control group had an identical task but used the same cosmetic foam without any active ingredient. The tests were run in a double-blind, placebo-controlled study.

Results: The tactile discrimination threshold decreased by 83 μm after 1 month of cosmetic application in the group using the active ingredient, while it was unchanged in the control group.

Discussion: The test presented here provided highly accurate results and should be useful to determine tactile performance. It allows the monitoring of tactile rehabilitation and/or skin treatments used to restore tactile acuity in the elderly.

The upper limb Physiological Profile Assessment: Description, reliability, normative values and criterion validity

A progressive decline in upper limb function is associated with ageing and disease. In this cross-sectional study we assessed the performance of 367 healthy individuals aged of 20 to 95 years across a battery of upper limb clinical tests, which we have termed the upper limb Physiological Profile Assessment (PPA). The upper limb PPA was designed to quantify the performance of the multiple physiological domains important for adequate function in the upper extremities. Included are tests of muscle strength, unilateral movement and dexterity, position sense, skin sensation, bimanual coordination, arm stability, along with a functional task. We report age and gender normative values for each test. Test-retest reliability ranged from good to excellent in all tests (intra-class correlation coefficients from 0.65 to 0.98) with the exception of position sense (0.31). Ten of the thirteen tests revealed differences in performance between males and females, twelve showed a decline in performance with increasing age, and eight discriminated between older people with and without upper limb functional impairment. Furthermore, most tests showed good external validity with respect to age, an upper limb functional test and self-reported function. This profiling approach provides a reference range for clinical groups with upper limb sensory and motor impairments and may assist in identifying undiagnosed deficits in the general population. Furthermore, the tests are sufficiently reliable to detect motor impairments in people with compromised upper limb function and evaluate the effectiveness of interventions.

Age-Related Changes in Vibro-Tactile EEG Response and Its Implications in BCI Applications: A Comparison Between Older and Younger Populations

The rapid increase in the number of older adults around the world is accelerating research in applications to support age-related conditions, such as brain-computer interface (BCI) applications for post-stroke neurorehabilitation. The signal processing algorithms for electroencephalogram (EEG) and other physiological signals that are currently used in BCI have been developed on data from much younger populations. It is unclear how age-related changes may affect the EEG signal and therefore the use of BCI by older adults. This research investigated the EEG response to vibro-tactile stimulation from 11 younger (21.7±2.76 years old) and 11 older (72.0±8.07 years old) subjects. The results showed that: 1) the spatial patterns of cortical activation in older subjects were significantly different from those of younger subjects, with markedly reduced lateralization; 2) there is a general power reduction of the EEG measured from older subjects. The average left vs. right BCI performance accuracy of older subjects was 66.4±5.70%, 15.9% lower than that of the younger subjects (82.3±12.4%) and statistically significantly different (t(10)= -3.57, p= 0.005). Future research should further investigate age-differences that may exist in electrophysiology and take these into consideration when developing applications that target the older population.

Effects of age and individual experiences on tactile perception over the life span in women

Tactile perception results from the interplay of peripheral and central mechanisms for detection and sensation of objects and the discrimination and evaluation of their size, shapes, and surface characteristics. For different tasks, we investigated this interaction between more bottom-up stimulus-driven and rather top-down attention-related and cognitive processes in tactile perception. Moreover, we were interested in effects of age and tactile experiences on this interaction. 299 right-handed women participated in our study and were divided into five age groups: 18-25 years (N = 77), 30-45 years (N = 76), 50-65 years (N = 62), 66-75 years (N = 63) and older than 75 years (N = 21). They filled a questionnaire on tactile experiences and rated their skin as either very dry, dry, normal, or oily. Further they performed three tactile tests with the left and right index fingers. Sensitivity for touch stimuli was assessed with von Frey filaments. A sand paper test was used to examine texture discrimination performance. Spatial discrimination was investigated with a tactile Landolt ring test. Multivariate ANOVA confirmed a linear decline in tactile perceptual skills with age (F(3, 279) = 76.740; p < .000; pEta² = 0.452), starting in early adulthood. Largest age effects were found for the Landolt ring test and smallest age effects for the Sand paper test, indicating different aging slopes. Tactile experiences had a positive effect on tactile performance (F (3,279) = 4.450; p = .005; pEta² = 0.046) and univariate ANOVA confirmed this effect for the sand paper and the Landolt ring test, but not for the von Frey test. Using structural equation modelling, we confirmed two dimensions of tactile performance; one related to more peripheral or early sensory cortical (bottom-up) processes (i.e., sensitivity) and one more associated with cognitive or evaluative (top-down) processes (i.e., perception). Interestingly, the top-down processes were stronger influenced by age than bottom-up ones, suggesting that age-related deficits in tactile performance are mainly caused by a decline of central perceptive-evaluative capacities rather than by reduced sensitivity.

Sensory-specific impairment among older people. An investigation using both sensory thresholds and subjective measures across the five senses

Age-related sensory impairment is a slow and gradual progress, which affects multiple modalities. Two contradictory hypotheses exist about the age-related decline of sensory thresholds. The common factor theory assumes one underlying factor-which accounts for the loss of several sensory modalities simultaneously-and the specific factor theory predicts that the sensory decline is uncorrelated between different modalities. In this study, we aimed to explore whether (i) there is a common factor of sensory thresholds in older people, (ii) older people assume that sensory decline in one modality also affects other modalities, (iii) there is a relation between sensory threshold and the subjective assessment of sensory function. This was accomplished by collecting both threshold measures and self-reported ratings for smell, hearing, taste, vision, and touch function in a group of 104 older people (mean age: 67.2 years; SD: 9.85; range: 50-100 years). Results indicated that there was no common factor of sensory thresholds, hence an impairment in one modality did not necessarily imply a shortfall in other modalities. In contrast, our results suggested one or two common factor(s) for the participants' ratings. Participants who reported a diminished function in one sense tended to generalize this rating to the other senses as well. The correspondence between subjective ratings and sensory thresholds was relatively good for vision and audition, although no correlations were observed for the other domains. These findings have implications for clinicians, suggesting that subjective measures should be combined with sensory threshold measurements when evaluating sensory dysfunction. Also, these data convey a positive message for older people and their physicians by showing that loss in one sensory modality does not necessarily generalize to losses across all sensory modalities.

Peg-manipulation capabilities of middle-aged adults have a greater influence on pegboard times than those of young and old adults

Declines in manual dexterity are frequently quantified as the time it takes to complete the grooved pegboard test. The test requires individuals to manipulate 25 pegs, one at a time, by removing them from a well and inserting them into a prescribed hole. The manipulation of each peg involves four phases: selection, transport, insertion, and return. The purpose of our study was to compare the times to complete the four phases of peg manipulation and the forces applied to the pegboard during peg insertion as young, middle-aged, and old adults performed the grooved pegboard test. The relative significance of the peg-manipulation attributes for 30 young (24.0 ± 4.4 years), 15 middle-aged (46.5 ± 6.5 years), and 15 old (70.4 ± 4.0 years) adults was assessed with a multiple-regression analysis. The grooved pegboard test was performed on a force plate. Pegboard times for the old adults (81 ± 17 s) were longer than those for young (56 ± 7 s) and middle-aged (58 ± 11 s) adults. Regression analysis indicated that the explanatory variables for the pegboard times of young (R² = 0.33) and middle-aged (R² = 0.78) adults were the times for the peg insertion and return phases, whereas the predictors for old adults (R² = 0.49) were the times for the peg selection and transport phases. The relative influence of peg-manipulation capabilities on a pegboard test of manual dexterity was greater for middle-aged adults than for young and old adults.