Grating Orientation Task Research Articles

Evaluation of sterile glove usage on digital tactile sensitivity using the Grating Orientation Task.

Surgical glove use may be associated with a decrease in tactile sensitivity, with thicker gloves or double-gloving techniques further altering sensation. This study evaluates digital tactile sensitivity by use of a Grating Orientation Task (GOT) with multiple sterile gloving techniques (no gloves, single standard gloving, double standard gloving, orthopedic gloves, and micro-thickness gloves). Each participant performed the GOT at increasing grating widths until correctly noting orientation in ≥8 of 10 trials with multiple glove types or double-gloving technique. Glove order was randomly assigned and participants were blinded to the orientation and dome size. All gloves except micro-thickness gloves showed increased threshold sensitivity values (i.e. worse fingertip sensitivity) when compared to control (micro:control, p = 0.105, others:control, p < 0.05). Single-layer gloves showed no significant difference in sensitivity when compared to orthopedic (p = 0.06) or double-layer latex gloves (p = 0.26). Standard latex gloves decreased fingertip sensitivity when evaluated with the GOT. Double-layer and orthopedic latex gloves do not decrease sensitivity when compared with single-layer gloving. Micro-thickness gloves may provide similar tactile sensitivity to no surgical glove.

Development and validation of child’s food texture preference questionnaire and associations with oral tactile sensitivity and food fussiness in children

This study aimed to 1) develop a parent-reported child’s food texture preference questionnaire, 2) assess content validity and inter-rater reliability among parent-, child-report and the child report after tasting and 3) validate the questionnaire with oral tactile acuity and food fussiness in 5 to 12-year-old Australian children. Parents rated their child’s preference for 29 pairs of foods selected as they were different in texture but similar in other sensory attributes. A subset of these food pairs (10 pairs) was used for child reported preference and preference after tasting (4 pairs). Content validity was rated by 7 experts and expressed as the content validation index for items. Grating orientation task was used to measure oral tactile sensitivity. Parents reported fussiness on the Children’s Eating Behavior Questionnaire fussiness subscale. A total of 154 caregivers and 251 children (129 boys, 122 girls) participated. Content validation resulted in the elimination of 9 items. Child-rated texture preference was positively correlated with preference after tasting (r = 0.55) and parent-reported scores (r = 0.31). A moderate positive correlation was found between preference after tasting and parent reported scores (r = 0.20). Child's food texture preference was positively associated with child’s age (p < 0.05) but not correlated with measured oral tactile sensitivity or food fussiness. This is the first study to evaluate content validity and inter-rater reliability of parent-report child’s food texture preference measure. There still remains opportunities for improvements of both food texture preference measure and oral tactile sensitivity.

Oral acuity, particle size sensitivity, and food texture preferences in an older adult population

Changes in sensory sensitivity occur as we age but changes in food texture sensitivity in the older adult population remain poorly understood. The objective of this study was to describe the relationship between oral tactile acuity, mouth behaviour, and particle size sensitivity and their potential influence on preferred food textures in older adults. Older adults (n = 79; mean age = 69.7 yrs) participated in an evaluation of oral health and texture perception through survey measurements of mouth behaviour, and preferred food textures. Oral tactile acuity was assessed using the Grating Orientation Task (GOT) with three grating sizes (0.5, 0.75, and 1.5 mm). Food particle sensitivity was evaluated through a difference-from-control (DFC) sensory assessment of ground quinoa mixed into yogurt, utilizing three particle size ranges (<75, 150–250, and 500–600 μm). The results revealed that the sample containing 500–600 mm particle sizes yielded a higher difference (DFC) score compared to the samples with < 75 μm and 150–250 μm particles (p < 0.05). However, no significant relationship (p > 0.05) was found between the R-indices obtained from the GOT assessments and DFC scores, indicating no association between oral tactile acuity and particle size sensitivity. Liking ofcreamy, leafy, slippery, sticky, with skins,andcombinationfood textures was significantly positively associated with the 0.5 mm GOT tool R-index values, suggesting higher oral acuity influences liking of specific food textures. Significant differences (p < 0.05) were present in liking of food textures among different mouth behaviour groups. These results suggest that texture perception and sensitivity influence texture acceptance in older adults.

Less might be more: 1 mA but not 1.5 mA of tDCS improves tactile orientation discrimination

BackgroundTranscranial direct current stimulation (tDCS) is a frequently used brain stimulation method; however, studies on tactile perception using tDCS are inconsistent, which might be explained by the variations in endogenous and exogenous parameters that influence tDCS. ObjectivesWe aimed to investigate the effect of one of these endogenous parameters—the tDCS amplitude—on tactile perception. MethodsWe conducted this experiment on 28 undergraduates/graduates aged 18–36 years. In separate sessions, participants received 20 min of 1 mA or 1.5 mA current tDCS in a counterbalanced order. Half of the participants received anodal tDCS of the left SI coupled with cathodal tDCS of the right SI, and this montage was reversed for the other half. Pre- and post-tDCS tactile discrimination performance was assessed using the Grating Orientation Task (GOT). In this task, plastic domes with gratings of different widths cut into their surfaces are placed on the fingertip, and participants have to rate the orientation of the gratings. ResultsLinear modeling with amplitude, dome, and session as within factors and montage as between factors revealed the following: significant main effects of grating width, montage, and session and a marginally significant interaction effect of session and amplitude. Posthoc t-tests indicated that performance in GOT improved after 1 mA but not 1.5 mA tDCS independent of the montage pattern of the electrodes. ConclusionIncreasing the stimulation amplitude from 1 mA to 1.5 mA does not facilitate the tDCS effect on GOT performance. On the contrary, the effect seemed more robust for the lower-current amplitude.

The effects of transcranial electrical stimulation of the left dorsolateral prefrontal cortex on tactile spatial discrimination performance

The dorsolateral prefrontal cortex (DLPFC) plays a key role in tactile perceptual discrimination performance. Both transcranial random noise stimulation (tRNS) and anodal transcranial pulsed current stimulation (tPCS) have been shown to modulate neural activity in cortical regions. In this study, we aimed to determine whether tRNS and anodal tPCS over the left DLPFC would improve tactile perceptual discrimination performance of the right index finger in healthy neurological individuals. Subjects underwent a grating orientation task before, immediately after, and 30 min after applying tRNS in Experiment 1 or anodal tPCS in Experiment 2. tRNS application on the left DLPFC tended to enhance tactile perceptual discrimination performance. In contrast, the application of anodal tPCS over the left DLPFC did not affect tactile perceptual discrimination performance. These findings indicate that transcranial electrical stimulation to the left DLPFC may improve tactile perceptual discrimination performance, with effects that depend on stimulus modality.

A protocol for tactile function assessment using JVP domes: Feasibility study and preliminary results.

Touch is a crucial sense for perceiving the spatial characteristics of objects. The JVP dome was developed to evaluate tactile spatial acuity using a grating orientation task. There were few studies depicting sequences and details for the entire task, including practice, training, and testing sessions. Therefore, we proposed and elaborated a protocol for the grating orientation task using the staircase method, which required fewer testing trials compared with the method of constant stimuli. Twenty-three healthy participants were enrolled in this experiment. The JVP domes with 11 different groove widths were used. Tactile discrimination thresholds were estimated using a two-down-one-up staircase method. The experiment comprised practice, training, and testing sessions, conducted by trained examiners who performed grating stimulation on participants' index fingerpads. All participants passed the required accuracy in the practice and training sessions. Eight transition points were obtained in the testing session for each participant. The tactile discrimination thresholds were determined from the last six transition points. We obtained the mean tactile discrimination threshold as 1.8±0.75mm (n=23). The results demonstrated that the proposed protocol was successfully applied to assess tactile discrimination thresholds. The present study investigated the protocol of grating orientation tasks requiring a small number of testing trials with the assurance of the task quality. The feasibility study and preliminary results indicated the potentiality of this protocol for future clinical application.

The perception of affective and discriminative touch in blind individuals

Enhanced tactile acuity in blindness is among the most widely reported results of neuroplasticity following prolonged visual deprivation. However, tactile submodalities other than discriminative touch are profoundly understudied in blind individuals. Here, we examined the influence of blindness on two tactile submodalities, affective and discriminative touch, the former being vital for social functioning and emotional processing. We tested 36 blind individuals and 36 age- and sex-matched sighted volunteers. In Experiment 1, we measured the perception of affective tactile signals by asking participants to rate the pleasantness of touch delivered on the palm (nonhairy skin, sparsely innervated with C tactile [CT] fibers) or the forearm (hairy skin, densely innervated with CT fibers) in a CT-optimal versus a CT-nonoptimal manner using a paradigm grounded in studies on tactile sensory neurophysiology. In Experiment 2, we implemented a classic task assessing discriminative touch abilities, the grating orientation task. We found that blind individuals rated the touch as more pleasant when delivered on the palm than on the forearm, while the opposite pattern was observed for sighted participants, who rated stimulation on the forearm as more pleasant than stimulation on the palm. We also replicated the previous findings showing enhanced discriminative tactile acuity in blind individuals. Altogether, our results suggest that blind individuals might experience affective touch differently than sighted individuals, with relatively greater pleasantness perceived on the palm. These results provide a broader insight into somatosensory perception in blind individuals, for the first time taking into consideration the socioemotional aspect of touch.

Active tactile discrimination is coupled with and modulated by the cardiac cycle.

Perception and cognition are modulated by the phase of the cardiac signal in which the stimuli are presented. This has been shown by locking the presentation of stimuli to distinct cardiac phases. However, in everyday life sensory information is not presented in this passive and phase-locked manner, instead we actively move and control our sensors to perceive the world. Whether active sensing is coupled and modulated with the cardiac cycle remains largely unknown. Here, we recorded the electrocardiograms of human participants while they actively performed a tactile grating orientation task. We show that the duration of subjects' touch varied as a function of the cardiac phase in which they initiated it. Touches initiated in the systole phase were held for longer periods of time than touches initiated in the diastole phase. This effect was most pronounced when elongating the duration of the touches to sense the most difficult gratings. Conversely, while touches in the control condition were coupled to the cardiac cycle, their length did not vary as a function of the phase in which these were initiated. Our results reveal that we actively spend more time sensing during systole periods, the cardiac phase associated with lower perceptual sensitivity (vs. diastole). In line with interoceptive inference accounts, these results indicate that we actively adjust the acquisition of sense data to our internal bodily cycles.

Effect of Transcranial Electrical Stimulation over the Posterior Parietal Cortex on Tactile Spatial Discrimination Performance

The intraparietal sulcus region, which is part of the posterior parietal cortex (PPC), has been shown to play an important role in discriminating object shapes using the fingers. Transcranial random noise stimulation (tRNS) and anodal transcranial pulsed current stimulation (tPCS) are noninvasive strategies widely used to modulate neural activity in cortical regions. Therefore, we investigated the effects of tRNS and anodal tPCS applied to left or right PPC on the tactile discrimination performance of the right index finger in 20 neurologically healthy subjects. A grating orientation task (GOT) was performed before and immediately after delivering tRNS (stimulus frequency 0.1–640 Hz) in Experiment 1 or anodal tPCS (pulse width 50 ms and inter-pulse interval 5 ms) in Experiment 2. Performing tRNS over the right PPC significantly improved discrimination performance on the GOT. Subjects were classified into low and high baseline performance groups. Conducting tRNS over the left PPC significantly reduced the GOT discrimination performance in the high-performance group. By contrast, anodal tPCS delivered to the PPC of the left and right hemispheres had no significant effect on the tactile GOT discrimination performance of the right hand. We show that transcranial electric stimulation over the PPC may improve tactile perception but the effect depends on stimulus modality, parameters, and on the stimulated hemisphere.

Grating orientation task trial numbers for short- and long-term tactile discrimination learning

Perceptual learning generally improves with training intensity, but the number of training trials sufficient for transient and long-term improvement in tactile grating orientation task (GOT) discrimination has not been systematically studied. To define reliable trial numbers for tactile discrimination learning, we compared tactile orientation discrimination performance of the right-finger following 200 and 400 training trials. Fifty-one neurologically healthy subjects were recruited. Tactile spatial acuity for orientation (parallel or orthogonal to the long axis of the finger) across different grating frequencies was assessed before, immediately after, 30 min after, and 24 h after sessions consisting of 200 training trials (50/block × 4 blocks), 400 training trials (50/block × 8 blocks), or no training (sham control). Both the 200- and 400-trial training conditions reduced the grating orientation discrimination threshold at 24 h after training. In contrast, the control condition had no effect on the grating orientation discrimination threshold. There was a negative correlation between the baseline grating orientation discrimination threshold and training-induced change in threshold (improvement) following both 200 and 400 trials. Fewer GOT trials (200) substantially prolong tactile discrimination learning, presumably by promoting the consolidation of the underlying neuroplastic mechanisms. In this widely used perceptual learning paradigm, 200 and 400 training trials appear effective for inducing short-term and long-term perceptual memory.

Development and application of specific questions to classify a child as food texture sensitive.

Understanding food texture sensitivity in children is important in guiding food selection. The objective of this work was to develop a short questionnaire that could be completed by parents in nonclinical settings to provide a categorization for food texture sensitivity in children. This study evaluated the distribution of children as texture sensitive (TS) or non-texture sensitive (NTS) and the predictive validity of these questions to explain rejection of specific food textures. Three sets of survey data were examined, including data from a home-use test (HUT) in children with and without Down syndrome (DS), and lingual tactile sensitivity measured by grating orientation task (GOT). From three parent-completed surveys, the use of the questionnaire yielded a similar distribution of children in the TS category (16-22%) as previously reported. TS children (4-36 months) were more likely to reject specific food textures, including chewy, hard, lumpy, and "tough meat" (p < .05). A higher percentage of children with a diagnosis of DS were TS (36.9%). Children who were TS showed increased negative behaviors to foods and ate less than NTS children. In older children (5-12 years), TS children were fussier than NTS children (p < .001). Lingual tactile sensitivity was not significantly different by TS/NTS categorization (p=.458). This study demonstrated that the use of these five questions specific to food texture provides a useful tool in categorizing a child as TS/NTS, with this information being useful in selecting preferred food textures. Future studies involving these TS questions should perform psychometric assessments and measures of criterion validity using other questionnaires.

Grating orientation task: A screening tool for determination of oral tactile acuity in children

Oral tactile sensitivity is logically linked to food texture perception. However, there is currently no widely accepted method to determine oral tactile sensitivity, particularly in children. The aim of this study was to determine the suitability of the grating orientation task to measure tactile acuity in a large and diverse sample of 5–12-year-old children. A total of 1817 Australian children (921 boys, 896 girls) participated. Three grating widths (0.5, 0.75 and 1.25 mm) and two square sizes (1 cm2 and 2 cm2) were utilized. Grating squares were presented in random order, 8 times total either vertically or horizontally on the tongue, and children were asked to identify the orientation of groove and sureness of their responses. Oral tactile sensitivity was calculated as R-index values. Spearman’s correlation coefficients and one-way ANOVA were performed to investigate correlations and statistical differences between R-index values and child’s characteristics. Overall, 1 cm2 grating square in 0.5 mm groove width effectively discriminated oral tactile acuity in the sample of children, showing a near ideal normal distribution of R-index (p = 0.97 by Shapiro-Wilk test). Oral tactile acuity was not significantly different by age, age group, gender or BMIz (p > 0.05). No relationship was found between oral tactile acuity and BMI (r = -0.03) or waist circumference (r = 0.01). The measured R-index was highly correlated to the R Index without the surety question (Accuracy index, r = 0.86). The study illustrated that grating orientation task is a simple suitable method to measure in oral tactile acuity in children.

Hemoglobin, Body Mass Index, and Age as Risk Factors for Paclitaxel- and Oxaliplatin-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating adverse effect of neurotoxic cancer treatments including taxanes and platinum agents. Limited knowledge exists of potential prechemotherapy factors associated with CIPN development. To identify the association of pretreatment blood-based and clinical factors with CIPN persistence in patients who received paclitaxel or oxaliplatin. This cohort study assessed pretreatment blood-based clinical factors and demographic characteristics of 333 patients treated with paclitaxel and oxaliplatin chemotherapy at urban multicenter cancer clinics and academic institutions in Australia between September 2015 and February 2020. Comprehensive neuropathy assessments were undertaken 3 to 12 months posttreatment. Posttreatment CIPN severity was compared with blood-based factors within 30 days prior to commencing chemotherapy. Data were analyzed between March and December 2020. Paclitaxel or oxaliplatin chemotherapy. CIPN was measured using composite neurological grading scales, nerve conduction studies, and assessments of fine motor skills (grooved pegboard test), sensory function (grating orientation test and 2-point discrimination), and patient-reported outcomes. Independent samples t tests and Mann-Whitney U tests with post hoc Bonferroni correction were used to compare CIPN between patients according to blood-based factor normative ranges. Linear regression was used to identify blood-based and clinical associations with CIPN development. The study included 333 participants (266 [79.9%] women; median [interquartile range] age, 58 [18] years) who were consecutively recruited and referred (228 treated with paclitaxel, 105 treated with oxaliplatin; 138 [41.4%] with breast cancer, 83 [24.9%] with colorectal cancer). Most participants had grade 1 CIPN or higher (238 [71.5%] participants). Participants with low hemoglobin pretreatment had worse CIPN posttreatment (median [IQR] composite neurological grading scale score, 5 [2-8] vs 4 [1-6]; P = .002; grooved pegboard mean [SD] time, 84.2 [28.7] vs 72.9 [21.1] seconds; P = .002; grating orientation task, 4.8 [2.8] vs 3.9 [1.8] mm; P = .03; 2-point discrimination, 45% vs 28%; P = .01), with no other impairments outside normative ranges associated with CIPN. In the multivariable model, several factors were associated with worse CIPN (F4,315 = 18.6; P < .001; r2 = .19) including for lower hemoglobin (β = -0.47; 95% CI, -0.73 to -0.21; P < .001), higher body mass index (β = 0.08; 95% CI, 0.02 to 0.12; P = .007), older age (β = 0.08; 95% CI, 0.06 to 0.11; P < .001), and female sex (β = -1.08; 95% CI, -1.76 to -0.16; P = .01). The results of this cohort study suggest that participants with low pretreatment hemoglobin, higher body mass index, older age, and female sex were more likely to develop paclitaxel- or oxaliplatin-induced CIPN posttreatment. Future research should investigate prospectively whether these risk factors are associated with a higher incidence of CIPN development.

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.

A Mechanical Stimulation Glove to Induce Hebbian Plasticity at the Fingertip

Repetitive sensory stimulation of the fingertip induces Hebbian plasticity in the sensorimotor cortex that benefits the tactile and motor behavior of the hand in healthy younger adults, older adults, and patients. To use this method outside the laboratory, robust and portable stimulation systems are needed that allow prolonged stimulation phases over several hours without compromising on signal intensity or personal mobility. Here, we introduce two stimulation gloves that apply finger- and frequency-specific mechanical stimulation to individual fingertips over prolonged periods. The stimulators are built into commercially available cotton gloves and apply stimulation either via loudspeaker membranes or via linear resonant actuators (LRAs). We tested the efficiency of both gloves to induce Hebbian plasticity in younger adults by using two established measures of tactile performance, the grating orientation task (GOT), and the two-point discrimination task (2PDT). Both tests were performed before and after 3 h of sensory finger stimulation using one of either glove system. As a control condition, a non-stimulated finger was tested in both tasks before and after stimulation. The results show no significant effect of sensory stimulation on GOT thresholds, but a significant decrease in the 2PDT thresholds after compared to before the training at the stimulated finger only. The loudspeaker membrane improved performance in the 2PDT in 10/16 participants, whereas the LRA improved performance in the 2PDT in 13/16 participants. Stimulation gloves with built-in modules may be used in future larger-scale cohort studies on sensorimotor plasticity, rehabilitation, and learning.

Comparison of transcranial electrical stimulation regimens for effects on inhibitory circuit activity in primary somatosensory cortex and tactile spatial discrimination performance

Transcranial electrical stimulation (tES) can be used to modulate inhibitory circuits in primary somatosensory cortex, resulting in improved somatosensory function. However, efficacy may depend on the specific stimulus modality and patterns. For instance, transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), and transcranial pulsed current stimulation (tPCS) were found to stably and effectively modulate neuronal excitability, while anodal transcranial direct current stimulation (tDCS) appeared less effective overall but with substantial response heterogeneity among subjects. Therefore, we compared the effects of tES applied to primary somatosensory cortex on somatosensory evoked potential paired-pulse depression (SEP-PPD) and tactile discrimination performance in 17 neurologically healthy subjects. In Experiment 1, somatosensory evoked potential N20/P25_SEP-PPD, N20_SEP-PPD, and P25_SEP-PPD responses were assessed before and immediately after anodal tDCS, tACS (stimulation frequency, 140 Hz), tRNS (stimulation frequency, 0.1–640 Hz), anodal tPCS (pulse width, 50 ms; inter-pulse interval, 5 ms), and sham stimulation applied to primary somatosensory cortex. In Experiment 2, a grating orientation task (GOT) was performed before and immediately after the same anodal tDCS, tRNS, anodal tPCS, and sham stimulation regimens. Anodal tDCS and anodal tPCS decreased N20_SEP-PPD, and tRNS increased the first N20 SEP amplitude. Furthermore, tRNS and anodal tPCS decreased GOT discrimination threshold (improved performance). These results suggest that tRNS and anodal tPCS can improve sensory perception by modulating neuronal activity in primary somatosensory cortex.

Effects of Temporary Functional Deafferentation in Chronic Stroke Patients: Who Profits More?

Temporary functional deafferentation (TFD) by an anesthetic cream on the stroke-affected forearm was shown to improve sensorimotor abilities of stroke patients. The present study investigated different predictors for sensorimotor improvements during TFD and indicated outcome differences between patients grouped in subcortical lesions only and lesions with any cortical involvement. Thirty-four chronic stroke patients were temporarily deafferented on the more affected forearm by an anesthetic cream. Somatosensory performance was assessed using von Frey Hair and grating orientation task; motor performance was assessed by a shape-sorter-drum task. Seven potential predictors were entered into three linear multiple regression models. Furthermore, effects of TFD on outcome variables for the two groups (cortical versus subcortical lesion) were compared. Sex and sensory deficit were significant predictors for changes in motor function while age accounted for changes in grating orienting task. Males, patients with a stronger sensory deficit, and older patients profited more. None of the potential predictors made significant contributions to changes in threshold for touch. Furthermore, there were no differences in sensorimotor improvement between lesion site groups. The effects of TFD together with the low predictability of the investigated parameters suggest that characteristics of patients alone are not suitable to exclude some patients from TFD.

Inhibitory Mechanisms in Primary Somatosensory Cortex Mediate the Effects of Peripheral Electrical Stimulation on Tactile Spatial Discrimination

Selective afferent activation can be used to improve somatosensory function, possibly by altering cortical inhibitory circuit activity. Peripheral electrical stimulation (PES) is widely used to induce selective afferent activation, and its effect may depend on PES intensity. Therefore, we investigated the effects of high- and low-intensity PES applied to the right index finger on tactile discrimination performance and cortical somatosensory-evoked potential paired-pulse depression (SEP-PPD) in 25 neurologically healthy subjects. In Experiment 1, a grating orientation task (GOT) was performed before and immediately after local high- and low-intensity PES (both delivered as 1-s, 20-Hz trains of 0.2-ms electrical pulses at 5-s intervals). In Experiment 2, PPD of SEP components N20/P25_SEP-PPD, N20_SEP-PPD and P25_SEP-PPD, respectively, were assessed before and immediately after high- and low-intensity PES. Improved GOT discrimination performance after high-intensity PES (reduced discrimination threshold) was associated with lower baseline performance (higher baseline discrimination threshold). Subjects were classified into low and high (baseline) GOT performance groups. Improved GOT discrimination performance in the low GOT performance group was significantly associated with a greater N20_SEP-PPD decrease (weaker PPD). Subjects were also classified into GOT improvement and GOT decrement groups. High-intensity PES decreased N20_SEP-PPD in the GOT improvement group but increased N20_SEP-PPD in the GOT decrement group. Furthermore, a greater decrease in GOT discrimination threshold was significantly associated with a greater N20_SEP-PPD decrease in the GOT improvement group. These results suggest that high-intensity PES can improve somatosensory perception in subjects with low baseline function by modulating cortical inhibitory circuits in primary somatosensory cortex.

Exploring Behavioral Correlates of Afferent Inhibition.

(1) Background: Afferent inhibition is the attenuation of the muscle response evoked from transcranial magnetic stimulation (TMS) by a prior conditioning electrical stimulus to a peripheral nerve. It is unclear whether the magnitude of afferent inhibition relates to sensation and movement; (2) Methods: 24 healthy, young adults were tested. Short-latency afferent inhibition (SAI) and long-latency afferent inhibition (LAI) were obtained following median and digital nerve stimulation. Temporal tactile acuity was assessed with a temporal order judgement (TOJ) task, spatial tactile acuity was assessed using a grating orientation task (GOT), and fine manual dexterity was assessed with the Pegboard task; (3) Results: Correlation analyses revealed no association between the magnitude of SAI or LAI with performance on the TOJ, GOT, or Pegboard tasks; (4) Conclusion: The magnitude of SAI and LAI does not relate to performance on the sensory and motor tasks tested. Future studies are needed to better understand whether the afferent inhibition phenomenon relates to human behavior.

Fast-adapting mechanoreceptors are important for force control in precision grip but not for sensorimotor memory.

Sensory feedback from cutaneous mechanoreceptors in the fingertips is important in effective object manipulation, allowing appropriate scaling of grip and load forces during precision grip. However, the role of mechanoreceptor subtypes in these tasks remains incompletely understood. To address this issue, psychophysical tasks that may specifically assess function of type I fast-adapting (FAI) and slowly adapting (SAI) mechanoreceptors were used with object manipulation experiments to examine the regulation of grip force control in an experimental model of graded reduction in tactile sensitivity (healthy volunteers wearing 2 layers of latex gloves). With gloves, tactile sensitivity decreased significantly from 1.9 ± 0.4 to 12.3 ± 2.2 μm in the Bumps task assessing function of FAI afferents but not in a grating orientation task assessing SAI afferents (1.6 ± 0.1 to 1.8 ± 0.2 mm). Six axis force/torque sensors measured peak grip (PGF) and load (PLF) forces generated by the fingertips during a grip-lift task. With gloves there was a significant increase of PGF (14 ± 6%), PLF (17 ± 5%), and grip and load force rates (26 ± 8%, 20 ± 8%). A variable-weight series task was used to examine sensorimotor memory. There was a 20% increase in PGF when the lift of a light object was preceded by a heavy relative to a light object. This relationship was not significantly altered when lifting with gloves, suggesting that the addition of gloves did not change sensorimotor memory effects. We conclude that FAI fibers may be important for the online force scaling but not for the buildup of a sensorimotor memory.