Tactile Acuity Research Articles

Pain intensity attenuates movement control of the lumbar spine in low back pain

Introduction: Pain intensity attenuates muscular activity, proprioception, and tactile acuity, with consequent changes of joint kinematics. People suffering from low back pain (LBP) frequently show movement control impairments of the lumbar spine in sagittal plane. This cross-sectional, observational study investigated if the intensity of LBP attenuates lumbar movement control. The hypothesis was that lumbar movement control becomes more limited with increased pain intensity. Methods: The effect of LBP intensity, measured with a numeric rating scale (NRS), on lumbar movement control was tested using three movement control tests. The lumbar range of motion (ROM), the ratio of lumbar and hip ROM as indicators of direction specific movement control, and the recurrence and determinism of repetitive lumbar movement patterns were assessed in ninety-four persons suffering from LBP of different intensity and measured with an inertial measurement unit system. Generalized linear models were fitted for each outcome. Results: Lumbar ROM (+0.03°, p=0.24) and ratio of lumbar and hip ROM (0.01, p=0.84) were unaffected by LBP intensity. Each one point increase on the NRS resulted in a decrease of recurrence and determinism of lumbar movement patterns (−3.11 to −0.06, p⩽0.05). Discussion: Our results indicate changes in movement control in people suffering from LBP. Whether decreased recurrence and determinism of lumbar movement patterns are intensifiers of LBP intensity or a consequence thereof should be addressed in a future prospective study.

Dissociable routes for personal and interpersonal visual enhancement of touch

Seeing a hand can enhance tactile acuity on the hand, even when tactile stimulation is not visible. This visual enhancement of touch (VET) occurs both when participants see their own hand (personal VET), and when they see another person's hand (interpersonal VET). Interpersonal VET occurs irrespective of where the viewed hand appears, while personal VET is eliminated when visual and proprioceptive signals about the location of one's own hand are incongruent. This suggests that the neural mechanisms for VET may differ according to ownership of the seen hand. We used continuous theta-burst transcranial magnetic stimulation (TMS) to disrupt either the human ventral intraparietal area (hVIP), which integrates tactile, proprioceptive, and visual information about one's own body, or the extrastriate body area (EBA), which processes visual body information irrespective of ownership. Participants then judged the orientation of tactile gratings applied to their hand while viewing images of their own hand, another person's hand, or a non-body object on a screen placed over their actual hand. Disrupting the hVIP attenuated personal VET but did not affect interpersonal VET, suggesting the hVIP is only involved in VET when one's own hand is seen. Disrupting the EBA reduced both personal and interpersonal VET, suggesting it is common to both routes.

The two dimensions of the body representation in women suffering from Anorexia Nervosa

A core symptom of Anorexia Nervosa (AN) is a severe alteration of body representations. Evidence from somatoperception studies point to a generic disturbances of somatosensory components of body representations. Here we have investigated whether AN patients (N=18) and controls differed in the perception of tactile stimuli differently oriented along the body axes. We tested the hypothesis that patients perceive and represent their body selectively larger in only one dimension. To this aim we used elementary tactile measures for tactile acuity (Von Frey's test and two-point discrimination thresholds – 2PD) and tactile discrimination measures. The rationale is based on the assumption that AN patients have a wider body representation, and that tactile body representation tasks (Tactile Distance task) oriented across the bodies (horizontally) are influenced by distorted body representations compared with tactile stimuli oriented along the bodies (vertically) which should not be influenced by body representations. Results showed that patients judged horizontal tactile stimuli significantly wider than the same stimuli oriented vertically.These results suggest that human brain perceives things differently based on body representations and that the beliefs concerning body size influence the specific somatosensory process of tactile experience.

Enhanced tactile acuity through mental states.

Bodily training typically evokes behavioral and perceptual gains, enforcing neuroplastic processes and affecting neural representations. We investigated the effect on somatosensory perception of a three-day Zen meditation exercise, a purely mental intervention. Tactile spatial discrimination of the right index finger was persistently improved by only 6 hours of mental–sensory focusing on this finger, suggesting that intrinsic brain activity created by mental states can alter perception and behavior similarly to external stimulation.

Effects of mirror visual feedback and spinal mobilisations on pain and tactile acuity: a randomised controlled trial

Effects of mirror visual feedback and spinal mobilisations on pain and tactile acuity: a randomised controlled trial

Factors influencing tactile spatial acuity of knee regions in healthy individuals

Factors influencing tactile spatial acuity of knee regions in healthy individuals

Tactile Acuity among Commercial Motorcyclists in Uturu, Nigeria

Tactile Acuity among Commercial Motorcyclists in Uturu, Nigeria

Pain sensitivity and tactile spatial acuity are altered in healthy musicians as in chronic pain patients.

Extensive training of repetitive and highly skilled movements, as it occurs in professional classical musicians, may lead to changes in tactile sensitivity and corresponding cortical reorganization of somatosensory cortices. It is also known that professional musicians frequently experience musculoskeletal pain and pain-related symptoms during their careers. The present study aimed at understanding the complex interaction between chronic pain and music training with respect to somatosensory processing. For this purpose, tactile thresholds (mechanical detection, grating orientation, two-point discrimination) and subjective ratings to thermal and pressure pain stimuli were assessed in 17 professional musicians with chronic pain, 30 pain-free musicians, 20 non-musicians with chronic pain, and 18 pain-free non-musicians. We found that pain-free musicians displayed greater touch sensitivity (i.e., lower mechanical detection thresholds), lower tactile spatial acuity (i.e., higher grating orientation thresholds) and increased pain sensitivity to pressure and heat compared to pain-free non-musicians. Moreover, we also found that musicians and non-musicians with chronic pain presented lower tactile spatial acuity and increased pain sensitivity to pressure and heat compared to pain-free non-musicians. The significant increment of pain sensitivity together with decreased spatial discrimination in pain-free musicians and the similarity of results found in chronic pain patients, suggests that the extensive training of repetitive and highly skilled movements in classical musicians could be considered as a risk factor for developing chronic pain, probably due to use-dependent plastic changes elicited in somatosensory pathways.

The effect of motor control and tactile acuity training on patients with non-specific low back pain and movement control impairment

Movement control impairment is a clinical subgroup of non-specific low back pain which can be assessed reliably. There is a strong correlation between tactile acuity and movement control suggesting these two treatments might have additive effects. The first research aim was to determine if patients with a motor control impairment demonstrated improvement in outcome with combined tactile acuity and motor control training. The second aim was to determine if tactile acuity training enhanced the effect of motor control training. The primary study was a single-arm cohort study conducted in three physiotherapy practices in the German-speaking part of Switzerland. 40 patients (23 males and 17 females) suffering from non-specific low back pain (NSLBP) and movement control impairment were treated. Patients were assessed at baseline and immediately post treatment. Treatment included exercises to lumbopelvic control and graphesthesia training to improve tactile acuity. Treatment effects were evaluated using the Roland Morris disability questionnaire (RMQ) and the patient-specific functional scale (PSFS). The performance on a set of six movement control tests and lumbar two-point discrimination were also assessed. The results of this cohort study were compared with a historic control group which was comparable with the primary study but included only motor control exercises. All the outcomes improved significantly with the combined training (RMQ - 2.2 pts., PSFS - 2.8 pts.; MCTB - 2.02 pts. & TPD - 17.07 mm; all p < 0.05). In comparison to the outcomes of the historic control, there was no significant differences in movement control, patient-specific functional complaints or disability between the groups. The results of this study, based on a before and after intervention comparison, showed that outcome improved significantly following combined tactile acuity and motor control training. However, compared to an earlier study, the tactile acuity training did not have an additional effect to the results. The use of historical controls does not control for allocation bias and the results obtained here require verification in a randomized controlled trial.

Bodily illusions disrupt tactile sensations.

To accurately interpret tactile information, the brain needs to have an accurate representation of the body to which to refer the sensations. Despite this, body representation has only recently been incorporated into the study of tactile perception. Here, we investigate whether distortions of body representation affect tactile sensations. We perceptually altered the length of the arm and the width of the waist using a tendon vibration illusion and measured spatial acuity and sensitivity. Surprisingly, we found reduction in both tactile acuity and sensitivity thresholds when the arm or waist was perceptually altered, which indicates a general disruption of low-level tactile processing. We postulate that the disruptive changes correspond to the preliminary stage as the body representation starts to change and may give new insights into sensory processing in people with long-term or sudden abnormal body representation such as are found in eating disorders or following amputation.

Movement restriction does not modulate sensory and perceptual effects of exercise-induced arm pain.

Movement restriction has been proposed as an important modulator of changes in sensory and perceptual function and motor imagery performance that are observed in musculoskeletal pain syndromes. There are no empirical data to support this view. The primary objective of this experiment was to determine the effects of movement restriction on local and widespread sensory, perceptual and motor imagery changes after exercise-induced muscular pain. Further objectives were to investigate whether changes in sensory perception are correlated with pain intensity and tactile acuity or motor imagery performance. In forty healthy volunteers, delayed onset muscle soreness (DOMS) of the non-dominant elbow flexors was induced using eccentric contractions until exhaustion. Participants were then randomised into two groups: a movement restriction group (wearing a sling) or a control group (not wearing a sling). Sensory and perceptual functions were measured using a range of sensory tests and a motor imagery performance task (left/right limb judgements). Movement restriction did not modulate any of the measures. We found concurrent mechanical hypoesthesia (p < 0.01), reduced tactile acuity (p = 0.02) and pressure hyperalgesia (p < 0.01) at the painful side. We found evidence of widespread pressure hyperalgesia. Impaired tactile acuity was associated with a decrease in pain threshold to pressure (r = -0.34, p = 0.03). Motor imagery performance was unchanged (p > 0.35) by pain or movement restriction. Short-term movement restriction did not influence local and widespread sensory changes induced by experimentally induced muscular pain.

Short-term visual deprivation, tactile acuity, and haptic solid shape discrimination.

Previous psychophysical studies have reported conflicting results concerning the effects of short-term visual deprivation upon tactile acuity. Some studies have found that 45 to 90 minutes of total light deprivation produce significant improvements in participants' tactile acuity as measured with a grating orientation discrimination task. In contrast, a single 2011 study found no such improvement while attempting to replicate these earlier findings. A primary goal of the current experiment was to resolve this discrepancy in the literature by evaluating the effects of a 90-minute period of total light deprivation upon tactile grating orientation discrimination. We also evaluated the potential effect of short-term deprivation upon haptic 3-D shape discrimination using a set of naturally-shaped solid objects. According to previous research, short-term deprivation enhances performance in a tactile 2-D shape discrimination task – perhaps a similar improvement also occurs for haptic 3-D shape discrimination. The results of the current investigation demonstrate that not only does short-term visual deprivation not enhance tactile acuity, it additionally has no effect upon haptic 3-D shape discrimination. While visual deprivation had no effect in our study, there was a significant effect of experience and learning for the grating orientation task – the participants' tactile acuity improved over time, independent of whether they had, or had not, experienced visual deprivation.

Resting BOLD fluctuations in the primary somatosensory cortex correlate with tactile acuity

Sensory perception, including 2-point discrimination (2ptD), is tightly linked to cortical processing of tactile stimuli in primary somatosensory cortices. While the role of cortical activity in response to a tactile stimulus has been widely investigated, the role of baseline cortical activity is largely unknown. Using resting state fMRI we investigated the relationship between local BOLD fluctuations in the primary somatosensory cortex (the representational field of the hand) and 2ptD of the corresponding index finger (right and left). Cortical activity was measured using fractional amplitudes of the low frequency BOLD fluctuations (fALFF) and synchronicity using regional homogeneity (ReHo) of the S1 hand region during rest. 2ptD correlated with higher ReHo values in the representational areas of the contralateral S1 cortex (left hand: p = .028; right hand: p = .049). 2ptD additionally correlated with higher fALFF in the representational area of the left hand (p = .007) and showed a trend for a significant correlation in the representational area of the right hand (p = .051). Thus, higher BOLD amplitudes and synchronicity at rest, as measures of cortical activity and synchronicity, respectively, are related to better tactile discrimination abilities of the contralateral hand. Our findings extend the relationship seen between spontaneous BOLD fluctuations and sensory perception.

C-02 * Sensory and Motor Deficits in Spanish Speaking Individuals with Schizophrenia

Objective: Research suggests individuals with schizophrenia (SZ) present with sensory and motor deficits. In Puerto Rico, comprehensive neuropsychological assessment of SZ occurs infrequently, so further investigation of sensory and motor deficits is needed. This study examined sensory and motor functions in a sample of Hispanic normal adults and individuals with SZ using specific test items from the Dean-Woodcock Sensory and Motor Battery (DWSMB). Method: The sample consisted of 81 Spanish speaking individuals (40% female; mean age = 36.0 years) divided into normal control (NC: n = 59) and SZ groups (n = 22). The DWSMB was administered in Spanish to all participants. It consists of nine tests that assess auditory, visual, and tactile acuity, and nine tests that measures gross and fine motor skills, balance, expressive speech, grip strength, coordination, and lateral preference (35 items total). Results: t-tests comparing groups on the 35 DWSMB items indicated the SZ group performed significantly worse than controls on 21 items after controlling for multiple comparisons (t's ranged from 3.54 to 8.39). These included visual acuity and confrontation, naming, auditory acuity, palm writing, gait and station, Romberg test, construction, and coordination. Conclusion(s): Findings suggest sensory and motor deficits identified in English speaking individuals with schizophrenia were also present in this Hispanic sample, and that the DWSMB is useful for evaluation of these deficits. We were unable to determine whether these deficits were a primary feature of SZ itself, or might be caused by secondary influences (e.g., antipsychotic medication effects). Additional research is necessary to address this matter.

Age and strength influences on lingual tactile acuity.

Sensory motor interactions are a topic of interest in understanding the processing activities that take place in the mouth during eating and swallowing. In this paper, we explore a test of sensory acuity in the mouth, in which the tongue is used to "read" embossed letters on Teflon strips. Our questions were to determine whether sensory acuity for this task declines with age, or with age-related reductions in tongue strength. We determined that older people perform this task with less accuracy, suggesting some changes in oral sensory function with age. However, these changes were not related to tongue strength. The findings suggest that strength does not play a major role in the kind of sensory discrimination task tested in this study.

Mechanotransduction in epidermal Merkel cells.

The cellular and molecular basis of vertebrate touch reception remains least understood among the traditional five senses. Somatosensory afferents that innervate the skin encode distinct tactile qualities, such as flutter, slip, and pressure. Gentle touch is thought to be transduced by somatosensory afferents whose tactile end organs selectively filter mechanical stimuli. These tactile end organs comprise afferent terminals in association with non-neuronal cell types such as Merkel cells, keratinocytes, and Schwann cells. An open question is whether these non-neuronal cells serve primarily as passive mechanical filters or whether they actively participate in mechanosensory transduction. This question has been most extensively studied in Merkel cells, which are epidermal cells that complex with sensory afferents in regions of high tactile acuity such as fingertips, whisker follicles, and touch domes. Merkel cell-neurite complexes mediate slowly adapting type I (SAI) responses, which encode sustained pressure and represent object features with high fidelity. How Merkel cells contribute to unique SAI firing patterns has been debated for decades; however, three recent studies in rodent models provide some direct answers. First, whole-cell recordings demonstrate that Merkel cells are touch-sensitive cells with fast, mechanically activated currents that require Piezo2. Second, optogenetics and intact recordings show that Merkel cells mediate sustained SAI firing. Finally, loss-of-function studies in transgenic mouse models reveal that SAI afferents are also touch sensitive. Together, these studies identify molecular mechanisms of mechanotransduction in Merkel cells, reveal unexpected functions for these cells in touch, and support a revised, two-receptor site model of mechanosensory transduction.

Are tactile acuity and clinical symptoms related to differences in perceived body image in patients with chronic nonspecific lower back pain?

Clinically, perceived image of the lower back and the two-point discrimination (TPD) test are used as markers for evaluating alterations of cortical reorganization. The purpose of the present study was to examine whether TPD and selected clinical findings are different in subgroups of individuals with chronic nonspecific lower back pain (CNLBP) based on body image drawings. Forty-two patients with CNLBP and seventeen healthy individuals were recruited. Perceived body image, TPD and clinical profiles was measured. Of the patients with CNLBP, 42.8% had a normal perceived body image, 28.5% an expanded image, and 28.5% a shrunken image. The TPD distance threshold was significantly larger for the expanded subgroup (13.3 ± 6.8 mm) compared with the control (5.5 ± 3.8 mm; Difference, 7.8; 95%CI, 1.83 to 13.66; p < 0.05) and normal subgroups (4.5 ± 5.5 mm; Difference, 8.8; 95%CI, 2.90 to 14.59; p < 0.05). No significant differences in pain intensity, duration of pain, Roland Morris Disability Questionnaire (RDQ), and Pain Catastrophizing Scale (PCS) scores were found between three body image subgroups. Our results suggest that TPD is increased in patients who report an expanded perceived image of the lower back compared with healthy individuals and patients who report a normal image. The effectiveness of new rehabilitation techniques may be evaluated by assessing perceived image of the lower back and TPD values for patients with CNLBP before and after treatment.

P885: Resting BOLD fluctuations in the primary somatosensory cortex correlate with tactile acuity

P885: Resting BOLD fluctuations in the primary somatosensory cortex correlate with tactile acuity

Whole-body mapping of spatial acuity for pain and touch.

ObjectiveTactile spatial acuity is routinely tested in neurology to assess the state of the dorsal column system. In contrast, spatial acuity for pain is not assessed, having never been systematically characterized. More than a century after the initial description of tactile acuity across the body, we provide the first systematic whole-body mapping of spatial acuity for pain.MethodsWe evaluated the 2-point discrimination thresholds for both nociceptive-selective and tactile stimuli across several skin regions. Thresholds were estimated using pairs of simultaneous stimuli, and also using successive stimuli.Results and interpretationThese two approaches produced convergent results. The fingertip was the area of highest spatial acuity, for both pain and touch. On the glabrous skin of the hand, the gradient of spatial acuity for pain followed that observed for touch. On the hairy skin of the upper limb, spatial acuity for pain and touch followed opposite proximal–distal gradients, consistent with the known innervation density of this body territory. Finally, by testing spatial acuity for pain in a rare participant completely lacking Aβ fibers, we demonstrate that spatial acuity for pain does not rely on a functioning system of tactile primary afferents. This study represents the first systematic characterization of spatial acuity for pain across multiple regions of the body surface. Ann Neurol 2014;75:917–924

Show me the skin! Does seeing the back enhance tactile acuity at the back?

A growing body of literature associates musculoskeletal disorders with cortical reorganisation. One condition in which reorganisation is established and treatments that ‘train the brain’ are being widely used is chronic back pain. Recent evidence suggests that treatments that involve tactile training are more effective if they incorporate multisensory mechanisms, most obviously vision. With regard to back pain however, we must first determine if tactile function is enhanced by incorporating other modalities. A series of three cross-over experiments were conducted in healthy pain-free subjects to determine whether tactile acuity is enhanced when participants can see the skin of their back during testing. An initial randomised cross-over experiment suggested tactile acuity was significantly enhanced when participants could see their backs (t(25) = −4.226, p < 0.001, r = 0.65). However, a second replication experiment was not corroborative. Both the second (F(3,66) = 1.00, p = 0.398) and third (t(9) = 0.969, p = 0.358) experiments suggested that seeing the back did not significantly affect tactile acuity, confirming that our initial results were likely due to chance. The principle that visual feedback improves tactile acuity at the hand does not apply to the back. These results strongly suggest that attempts to enhance tactile training by incorporating vision will not offer the benefit to treatment of back pain that has been observed for treatment of hand pain.