Sensations evoked by microstimulation of single mechanoreceptive afferents innervating the human face and mouth.

Intraneural microneurography and microstimulation were performed on single afferent axons in the inferior alveolar and lingual nerves innervating the face, teeth, labial, or oral mucosa. Using natural mechanical stimuli, 35 single mechanoreceptive afferents were characterized with respect to unit type [fast adapting type I (FA I), FA hair, slowly adapting type I and II (SA I and SA II), periodontal, and deep tongue units] as well as size and shape of the receptive field. All afferents were subsequently microstimulated with pulse trains at 30 Hz lasting 1.0 s. Afferents recordings whose were stable thereafter were also tested with single pulses and pulse trains at 5 and 60 Hz. The results revealed that electrical stimulation of single FA I, FA hair, and SA I afferents from the orofacial region can evoke a percept that is spatially matched to the afferent's receptive field and consistent with the afferent's response properties as observed on natural mechanical stimulation. Stimulation of FA afferents typically evoked sensations that were vibratory in nature; whereas those of SA I afferents were felt as constant pressure. These afferents terminate superficially in the orofacial tissues and seem to have a particularly powerful access to perceptual levels. In contrast, microstimulation of single periodontal, SA II, and deep tongue afferents failed to evoke a sensation that matched the receptive field of the afferent. These afferents terminate more deeply in the tissues, are often active in the absence of external stimulation, and probably access perceptual levels only when multiple afferents are stimulated. It is suggested that the spontaneously active afferents that monitor tension in collagen fibers (SA II and periodontal afferents) may have the role to register the mechanical state of the soft tissues, which has been hypothesized to help maintain the body's representation in the central somatosensory system.

Functional properties of low-threshold mechanoreceptive afferents in the human labial mucosa.

We used microneurography to investigate the functional properties of low-threshold mechanoreceptive afferents innervating the oral mucosa of the inside of the lower lip. Impulse responses were recorded from the inferior alveolar nerve of four human subjects. The threshold force and receptive field boundaries were identified for 19 single mechanoreceptive afferents using thin filaments (von Frey hairs) that applied known forces to the mucosa. Most of the receptive fields were located close to the corners of the mouth. Twelve of the afferents were slowly adapting (SA) and the remaining seven units were fast adapting (FA). Two types of slowly adapting responses were observed, SA I and SA II. Four of the six SA II units were spontaneously active. The geometric mean value of the receptive field sizes was 4.20 mm(2) for the SA I units, 5.65 mm(2) for the SA II units, and 5.60 mm(2) for the FA I units. None of the FA afferents showed response properties characteristic of Pacinian-corpuscle type afferents (FA II units). All afferents showed low force threshold between 0.06 and 1 mN. The properties of the mechanoreceptors supplying the human labial mucosa appear more similar to those of the vermilion and facial skin of the lower lip than those supplying the mucosa of the dorsal tongue.

Encoding of spatial location by posterior parietal neurons.

The cortex of the inferior parietal lobule in primates is important for spatial perception and spatially oriented behavior. Recordings of single neurons in this area in behaving monkeys showed that the visual sensitivity of the retinotopic receptive fields changes systematically with the angle of gaze. The activity of many of the neurons can be largely described by the product of a gain factor that is a function of the eye position and the response profile of the visual receptive field. This operation produces an eye position-dependent tuning for locations in head-centered coordinate space.

Sensory retraining following orthognathic surgery: effect on threshold measures of sensory function.

The purpose of this analysis was to examine the effect of sensory retraining on sensory function after bilateral sagittal split osteotomy (BSSO). A total of 186 subjects were enrolled in a multi-centre double-blind two parallel group stratified block randomized clinical trial. Subjects were randomized to group immediately after surgery. Threshold measures for contact detection, two-point discrimination and two-point perception were obtained on the chin before and 1, 3 and 6 months and 1 and 2 years after surgery. The ratio of each threshold measure (post-surgery value/pre-surgery value) was calculated to characterize subjects' impairment. A general linear mixed model was fit for the impairment to examine the effect of the sensory retraining before and after adjusting for demographic, surgical and psychological factors. On average, two-point perception was less impaired in subjects who were retrained than in those who were not retrained (P = 0.04). Significant recovery continued up to 6 months after surgery for contact detection and two-point perception and up to 24 months for two-point discrimination. Older subjects experienced more impairment in two-point discrimination than younger subjects (P = 0.009). Subjects who received maxillary surgery in addition to mandibular surgery experienced more impairment on the chin in both two-point discrimination (P = 0.0003) and perception (P = 0.0013) than subjects who received mandibular surgery only. Psychological factors did not explain additional variability in subjects' impairment post-surgery. These finding indicate that a simple non-invasive exercise programme initiated shortly after orthognathic surgery can alter the way patients experience or respond to tactile stimulation long after the exercise regimen has stopped.

Effect of facial sensory re-training on sensory thresholds.

Nearly 100% of patients experience trauma to the trigeminal nerve during orthognathic surgery, impairing sensation and sensory function on the face. In a recent randomized clinical trial, people who performed sensory re-training exercises reported less difficulty related to residual numbness and decreased lip sensitivity than those who performed standard opening exercises only. We hypothesized that re-training reduces the impaired performance on neurosensory tests of tactile function that is commonly observed post-surgically. We analyzed thresholds for contact detection, two-point discrimination, and two-point perception, obtained during the clinical trial before and at 1, 3, and 6 months after surgery, to assess tactile detection and discriminative sensitivities, and subjective interpretation of tactile stimulation, respectively. Post-surgery, the retrained persons exhibited less impairment, on average, than non-retrained persons only in two-point perception (P < 0.025), suggesting that retrained persons experienced or interpreted the tactile stimuli differently than did non-retrained persons.

Facial altered sensation and sensory impairment after orthognathic surgery.

The aim of this study was to determine whether impairment of sensory functions after trigeminal nerve injury differs in severity among patients who report qualitatively different altered sensations. Data were obtained from 184 patients. Before and at 1, 3 and 6 months after orthognathic surgery, patients were grouped as having no altered sensation, negative sensations only (hypoaesthetic), mixed sensations (negative+active), or active sensations only (paraesthetic or dysaesthetic). Bias-free estimates of contact detection and two-point discrimination were obtained to assess, via ANOVA, whether patients in the four groups exhibited different levels of sensory impairment. Impairment in contact detection and two-point discrimination was found to differ significantly among the groups at 6 months but not at 1 month. At 6 months, patients who reported negative sensations only exhibited the greatest impairment, on average, in contact detection; in contrast, patients who reported mixed sensations exhibited the greatest impairment in two-point discrimination. The least residual impairment at 6 months was observed in patients who reported no altered sensation. It is recommended that clinical judgments regarding nerve injury-associated sensory dysfunction should not be based on threshold testing results without consideration of patients' subjective reports of altered sensation.

Auto-adjusting mandibular repositioning device for in-home use.

Obstructive Sleep Apnea (OSA) is a form of respiratory dysfunction that affects 20% of adults in the world. Among the first-line treatments that are used to mitigate the effects of OSA are continuous positive airway pressure (CPAP) and mandibular repositioning devices (MRD). Although CPAP provides a more efficacious therapy than MRDs, recent studies suggest that both are comparable in overall effectiveness due to greater patient preference and adherence to MRD therapy. In this paper, we present the Auto-Positioner, a novel add-on for MRDs that adjusts the extent to which the mandible (lower jaw) is advanced in response to respiratory signals indicating labored breathing during sleep, and to changes in sleeping position known to affect individual patient's airway patency.

Psychophysical assessment of the affective components of non-painful touch.

A novel psychophysical procedure for the evaluation of the affective components of touch was developed. A fabric material was stroked across the test site at a controlled direction and velocity, after which the subject provided a numerical estimate of pleasantness. Significant differences were detected for the sites tested (FACE vs ARM), the fabric materials used (VELVET, COTTON and PLASTIC MESH), and the velocity of motion (0.5, 5 and 50 cm/s). Attesting to their validity, estimates of pleasantness correlated negatively with estimates of unpleasantness obtained for the same stimuli. Moreover, subjects were reasonably consistent in their ratings upon stimulus replication. These findings demonstrate that the hedonic qualities of touch can be psychophysically evaluated, and that valid and reliable estimates are obtained.

Capturing the spatial percepts evoked by moving tactile stimuli: a novel approach.

Forced-choice procedures are conventionally used to study the percepts evoked by stimuli that move across the skin and enable an unbiased estimation of subjects' sensory capacities. These procedures, however, require subjects to assign complicated percepts to one of a small number of experimenter-defined response categories, none of which may satisfactorily describe the perceptual experience. To address this limitation, we developed a psychophysical approach, which graphically captures spatial information about a moving stimulus in a holistic manner. Briefly summarized, the stimulus object controlled for location, velocity, direction and distance is moved across the skin of a blind-folded subject, after which the subject draws its path on a life-size, two-dimensional photograph of the body region stimulated. Using this approach, we demonstrated that the drawings contain perceptually relevant information, estimates of direction discrimination and subjective traverse length derived from the drawings closely parallel data obtained with forced-choice and magnitude estimation methods, respectively, and generate comparable psychophysical functions of stimulus velocity. In addition, information is represented in the complex shapes of the curves and in the locations at which they are drawn. Analyses of these latter features support the hypothesis that non-sensory factors (individual subject biases) also affect the drawings.

Assessment of the capacity of human subjects and S-I neurons to distinguish opposing directions of stimulus motion across the skin.

The ability of human subjects and the capacities of single S-I neurons of macaque monkeys to distinguish opposing directions of movement over the skin were investigated by employing experimental paradigms and data analyses based on sensory decision theory (SDT). It is shown that these techniques can be utilized to provide behavioral and neurophysiological indices of directional sensitivity which have the same metric, and are amenable to statistical tests for significance. The influences of 3 different paradigms and modes of relative operating characteristic (ROC) curve construction on SDT indices of human cutaneous directional sensitivity were investigated. Response latency (RL) was used as an objective indication of certainty in all 3 paradigms; in one of the 3 paradigms the subject also rated the certainty of each report. The SDT indices of cutaneous directional sensitivity and response bias were shown to be independent of the paradigm and mode of ROC curve construction investigated, and the SDT 'Gaussian-equal variance' hypothesis was concluded to be consistent with the data provided by all 3 paradigms. A considerable amount of inter-subject as well as intra-subject variability in human cutaneous directional sensitivity is demonstrated for all subjects tested. This variability appears to be an attribute of the processes underlying the sensing of stimulus direction since it is present even when stimulus conditions are maintained constant. Experimental designs were developed which account for this variability, thus allowing detection and quantitation of the influence of variations in stimulus conditions on human directional sensitivity. It is demonstrated that for S-I neurons, an ROC curve can be generated from the responses to multiple replications of opposing directions of movement across the receptive field. The large number of stimulus presentations required to estimate directional sensitivity from ROC curves involves a prolonged period of single neuron recording that is difficult to achieve even under ideal experimental conditions. It is shown that one can obtain a reliable estimate of single neuron directional sensitivity (i.e. delta'e) using relatively few stimulus replications when mean firing rate is assumed to represent that aspect of the neural response carrying information about stimulus direction. These indices allow assessment of the selectivity of single S-I neurons for direction as stimulus parameters are varied. Examples are provided which show (utilizing delta'e) that those stimulus conditions evoking maximal firing rates from S-I neurons are often not optimal for signalling direction of movement across the skin.

Factors influencing cutaneous directional sensitivity: a correlative psychophysical and neurophysiological investigation.

The effects of 4 parameters of moving tactile stimuli (i.e., velocity, traverse length, position and orientation) on human cutaneous directional sensitivity and on the behavior of directionally sensitive neurons in S-I of unanesthetized macaque monkeys are studied. The experimental paradigms and approaches to data analysis are based on sensory decision theory (SDT), and provide indices of single neuron and of perceptual cutaneous direction sensitivity that can be compared. Human cutaneous directional sensitivity is shown to be maximal when the stimuli move at velocities between 5 and 30 cm/s, and to fall off either at lower or higher velocities. The neurophysiological studies of the effects of velocity reveal a heterogeneity in the population of directionally sensitive S-I neurons. Some neurons are shown to exhibit maximal directional sensitivity at velocities between 5 and 30 cm/s, whereas others possess maximal directional sensitivity at lower velocities (i.e., less than 5 cm/s). Human cutaneous directional sensitivity is determined at each of 5 different forelimb regions. The data reveal that a pronounced gradient in human cutaneous directional sensitivity exists along the proximodistal axis of the forelimb, with the greatest sensitivity existing at the most distal forelimb site studied. The companion neurophysiological studies reveal that a change in the position of the moving stimulus within the receptive field of an individual directionally sensitive S-I neuron is usually accompanied by a change in the magnitude of its directional sensitivity. Two major classes of directionally sensitive S-I neurons can be distinguished on the basis of the in-field variations in directional sensitivity they exhibit. For one neuron class, preferred direction remains the same at all regions within the receptive field; these are termed 'direction invariant neurons' and they appear to be capable of signalling direction of motion unambiguously under most of the experimental conditions used in this study. For the neurons of the second class, preferred direction varies with the position of the stimulus within the receptive field; these are termed 'direction variant' neurons. Direction variant S-I neurons signal movement toward or away from a given point within the receptive field. As a consequence, a reversal in cutaneous directional sensitivity within their receptive fields can typically be demonstrated. For every direction variant neuron studied the receptive field position at which cutaneous directional sensitivity reversed was located over a joint.(ABSTRACT TRUNCATED AT 400 WORDS)

Spatial and gender-dependent variations in perioral pinprick sensitivity.

Twenty-eight right-handed young adults participated in a sensory testing experiment to evaluate pinprick sensitivity at ten spatially matched sites on the right and left sides of the face. Stimuli were provided by a sharp-pointed dental explorer on which a rubber eraser had been positioned to minimize variations in the extent to which the skin was indented. Sharpness was defined as the magnitude at which abrupt, localized pricking/stinging sensations were evoked. A magnitude matching procedure was used to reduce among-subject variability in the data. Specifically, each estimate of sharpness was adjusted (i.e., divided) by the subject's mean estimate of the brightness of a visual stimulus. Prior to data collection, subjects were carefully instructed on the use of a common numerical scale for assignment of values of sharpness and brightness. Repeated-measures analysis of variance of the adjusted estimates of sharpness revealed a non-significant effect of gender (p > 0.4), a highly significant effect of side (p < 0.0001), and a highly significant effect of test site (p < 0.0001). Pinprick percepts were sharper on the left side of the face than on the right. Moreover, the vermilion of the upper lip exhibited the greatest sensitivity to pinprick; the vermilion of the lower lip exhibited the least sensitivity. These results suggest that use of a patient's sensitivity to pinprick during clinical neurosensory examination must be undertaken in an informed manner. A conclusion of pathological alteration in sensation can be made only after consideration of the normal spatial variations in the percept of sharpness.

Effects of traverse length on human perioral directional sensitivity.

The capacity of 8 neurologically healthy adults to distinguish direction of motion on the skin overlying the mental foramen was determined. The velocity, orientation, and the length and width of skin traversed by the moving tactile stimuli were precisely controlled. Directional sensitivity, d', was found to depend on both stimulus velocity and the length of skin traversed. Since the relationship between d' and velocity at each traverse length was well described by a generalized gamma function, it was possible to quantitatively characterize the effects of changes in traverse length on the relationship between d' and velocity. Specifically, peak (i.e., maximal) directional sensitivity increased as the length of skin traversed was increased, yet the velocity which resulted in peak directional sensitivity (i.e., the optimal or model velocity) remained invariant over the range of traverse lengths investigated (0.35-1.0 cm). The effect of stimulus velocity on directional sensitivity was least at the longest traverse lengths used. The generalized gamma function model fit the relationship between directional sensitivity and velocity equally well at all traverse lengths studied. The results lead us to anticipate that stimuli of the type used in this study should prove valuable for the detection and quantification of disturbances in orofacial tactile spatiotemporal integration in patients with peripheral nerve injury.

Effects of trauma to the mandibular nerve on human perioral directional sensitivity.

The capacity of 4 patients who had previously experienced trauma to their mandibular nerves to distinguish opposing directions of tactile motion over the distribution of the mental nerve was compared to that of 8 neurologically normal adults. Brushing stimuli were delivered to the perioral region and were precisely controlled for their velocity, the length of skin traversed, the width of skin contacted, and the orientation and direction of motion. A temporal, 2-alternative, forced choice method was used to obtain estimates of directional sensitivity, d'. It was discovered that impairment in cutaneous directional sensitivity could be readily detected within areas of hypaesthesia. Although directional sensitivity was found to increase linearly with the length of skin traversed for both the patients and the neurologically normal adults, the slope and the x-intercept of the linear relationship differed between the two groups. The difference in the slope suggests that direction discrimination within the hypaesthetic areas is relatively insensitive to changes in the length of skin traversed. The difference in the x-intercept suggests that a greater length of skin must be traversed before any information about direction is made available at the hypaesthetic sites. The dependency of the capacity of neurologically normal and impaired individuals to process information about direction of tactile motion on the length of skin traversed and the velocity of stimulation suggests that a high degree of stimulus control is required for the detection and quantification of subtle neurosensory deficits.

Gender-, side- and site-dependent variations in human perioral spatial resolution.

Twenty-eight right-handed, young adults participated in a sensory testing experiment to evaluate spatial resolution at 10 positionally matched sites on the right- and left-hand sides of the face. An adaptive psychophysical (i.e. tracking) procedure was used to estimate the threshold spatial separation for perceiving two points of contact at each site. Estimates of the threshold at one site on both sides of the face were also obtained with a method-of-limits procedure similar to that employed for clinical evaluation of patients. In addition, each individual was asked to rate (i) his(her) overall facial sensitivity to touch and (ii) the degree to which he(she) could discern subtle changes in lip, cheek and chin position during speech, chewing and facial expression. Analysis of the estimates of the threshold separation obtained with the tracking procedure revealed a significant effect of gender (p < 0.04) and of site (p < 0.001). Females were more spatially sensitive than males: average threshold separations were 1.55 mm less. Most notably, the threshold increased ninefold with distance posterolaterally from the oral opening. The vermilion of the upper lip was the most spatially sensitive site (population geometric mean = 2.4 mm) and the preauricular skin the least spatially sensitive site (20.9 mm). Significant effects of side and of interactions among gender, side and site were not observed. The estimates obtained with the method-of-limits procedure were very similar to those obtained with the tracking procedure: the latter were 0.67 mm less on the average. Individuals' ratings of overall facial sensitivity to touch were similar for males and females (p > 0.70). Females, however, reported greater ability to discern subtle changes in lip, cheek and chin position than males (p < 0.03). The ratings of this sensory function correlated negatively with the estimates of the threshold separation on the vermilion of the upper lip (p < 0.03).

Three-dimensional nasolabial displacement during movement in repaired cleft lip and palate patients.

The objective of this study was two-fold: (1) to explore the suitability of a novel modified Procrustes fit method to adjust data for head motion during instructed facial movements, and (2) to compare the adjusted data among repaired unilateral (n = 4) and bilateral (n = 5) cleft lip and palate patients and noncleft control subjects (n = 50). Using a video-based tracking system, three-dimensional displacement of 14 well-defined nasolabial landmarks was measured during four set facial animations without controlling for head motion. The modified Procrustes fit method eliminated the contributions of head motion by matching the most stable landmarks of each video-recorded frame of the face during function to frames at rest. Its effectiveness was found to approximate that of a previous method (i.e., use of a maxillary occlusal splint to which stable dentition-based markers were attached). Data from both the unilateral and bilateral cleft lip and palate patients fell outside the normal range of maximum displacements and of asymmetry, and individual patients demonstrated greater right-versus-left asymmetry in maximum displacement than did individual noncleft subjects. It is concluded that the modified Procrustes fit method is fast, is easy to apply, and allows subjects to move the head naturally without the inconvenience of a splint while facial movement data are being collected. Results obtained using this method support the view that facial movements in cleft patients may be severely hampered and that assessment of facial animation should be strongly considered when contemplating surgical lip revisions.

The response to sudden change in vocal tract resistance during stop consonant production.

The speech respiratory system is configured in ways that tend to maximize its ability to respond to changes in the airway environment. Intraoral pressures remain at levels sufficient to generate reliably recognized consonant sounds even in the presence of structural deficits such as velopharyngeal inadequacy. Similar respiratory compensations occur when bite blocks and bleed valves are used to vent airway pressures. The purpose of the present study was to determine the sensitivity of the monitoring system psychophysically and to assess its physiological response to sudden, unanticipated perturbations. Twenty adults were asked to produce the utterance/pa/, and a calibrated perturbator valve permitted air to escape from the oral cavity on randomly selected productions. Respiratory responses were recorded using PERCI-SARS instrumentation. The results indicated that sudden openings of 0.14 cm2 (SD = 0.04) were detected by speakers. Compensatory respiratory responses to suprathreshold pressure-venting occurred rapidly (i.e., 27 ms [SD = 8]) after valve opening. Although peak pressure and area under the pressure pulse fell with valve opening, the magnitude of pressure was nevertheless sufficient for sound generation. Measurements of the slope of the rise in intraoral pressure after subthreshold pressure-venting in 10 participants were compared to measurements obtained from an-elastic model of the upper airway. The data demonstrated a significant difference between vented and unvented conditions for the model, but not the participants. This suggests that elastic recoil is actively and unconsciously controlled in humans to compensate for losses in airway pressure during speech.

Dental research priorities and availability of research opportunities for dental students.

The American Student Dental Association surveyed 69 dental deans representing schools in the United States, Canada, and Puerto Rico to assess the priority of research and the role of dental students in research activity. Student interest, curricular requirements, potential funding, and opportunities available, as related to dental research, were topics included on the questionnaire. The results indicate that although the percentage of dental students seeking research involvement is small, opportunities and financial support for research are available in most dental schools as part of the regular curriculum.

A longitudinal study of the association between tooth loss and age-related hearing loss.

The purpose of this study was to investigate cross-sectional and longitudinal associations between hearing acuity and tooth loss in 1156 US veterans taking part in the Veterans Affairs' Normative Aging (NAS) and Dental Longitudinal (DLS) Studies in the Boston, MA, area. The mean age was 48 years (SD = 8.9), 5.3% were edentulous, and 15.4% had < 17 teeth at baseline. Hearing acuity was determined by puretone, air- and bone-conduction audiometry, and speech discrimination tests at triennial examinations over a 20-year follow-up period. Hearing decline was defined as a change from baseline in the average puretone air-conduction thresholds of > or = 20 dB at 0.25, 0.5, 1, 2, 3, 4, 6, and 8 kHz. The explanatory variables of interest were change since baseline in dentate status (cut points at < 1, < 17, and < 20 teeth), and in the number of teeth lost (linear). Linear and logistic regression models--which controlled for baseline audiological status, age, air-bone gap, and otoscopic examination at current visit--showed that subjects who went from having > or = 17 to < 17 teeth had 1.64 times (95% CI, 1.24-2.17) as high odds of having hearing decline as those with no change in their dentate status. For every tooth lost since baseline, there was a 1.04 times as high odds (95% CI, 1.02-1.06) for hearing decline, when additional baseline and time-varying covariates were taken into account in the model.

Food oral processing: conversion of food structure to textural perception.

Food oral processing includes all muscle activities, jaw movements, and tongue movements that contribute to preparing food for swallowing. Simultaneously, during the transformation of food structure to a bolus, a cognitive representation of food texture is formed. These physiological signals detected during oral processing are highly complex and dynamic in nature because food structure changes continuously due to mechanical and biochemical breakdown coupled with the lubricating action of saliva. Multiple and different sensations are perceived at different stages of the process. Although much work has focused on factors that determine mechanical (e.g., rheological and fracture) and sensory properties of foods, far less attention has been paid to linking food transformations that occur during oral processing with sensory perception of texture. Understanding how food structure influences specific patterns of oral processing and how these patterns relate to specific textural properties and their cognitive representations facilitates the design of foods that are nutritious, healthy, and enjoyable.