Temporal discrimination of two passive movements in humans: a new psychophysical approach to assessing kinaesthesia

Percutaneous electrical stimulation of the motor point of the first dorsal interosseous muscle (FDI) was used to produce a non-painful contraction of the FDI muscle that caused index finger abduction movement but no radiating cutaneous paraesthesias or sharp sensations localized to joints. Pairs of stimuli separated by different time intervals were given and subjects were asked to report whether they perceived a single or a double index finger abduction movement. The threshold value was the shortest interval for which the subjects reported two separate index finger abduction movements. Temporal discrimination movement thresholds (TDMT) were measured for both right and left hand. To assess the possible role of muscle and cutaneous afferents in temporal discrimination, we investigated the effects of high-frequency (20 Hz) electrical stimulation of the right ulnar and radial nerves on TDMT. In humans, muscle afferents from FDI are supplied by the ulnar nerve whereas the cutaneous territory overlying the muscle and joint is supplied by the radial and median nerves. Threshold values were not significantly different for right (75.1 ms) and left (75.6 ms) hands. During ulnar and to a lesser extent during radial nerve stimulation, TDMT values were significantly increased (119.2 and 93.5 ms, respectively) compared with baseline conditions (78.0 ms) whereas no changes were observed during median nerve stimulation (80.5 ms). These results suggest that muscle, and in part cutaneous, afferents contribute to temporal discrimination of a dual movement. The technique may provide a useful way of measuring temporal discrimination of kinaesthetic inputs in humans.     

Somatosensory function in boys with ADHD and tactile defensiveness

In this study, we tested for deficits in somatosensory function in boys with Attention Deficit Hyperactivity Disorder (ADHD) and tactile defensiveness (TD). The subjects were 67 boys with ADHD, sub-typed as TD (ADHD+TD+) or non TD (ADHD+TD-), matched with 60 "typical" children in the control group. Sixty nine percent of the boys with ADHD were categorized as TD. The groups were compared on three measures: (a) performance scores on subtests of the Sensory Integration and Praxis Test, (b) measurements of the Somatosensory Evoked Potential (SEP) and (c) ratings of the children's affective responses during tactile stimulation. Both ADHD groups differed from the control group on most study measures. No significant differences were found between the two ADHD subgroups on threshold and perceptual tests scores, except for Finger Identification. However, the TD+ group demonstrated significantly higher central SEP amplitudes than did the TD- group. Together, the results support claims that TD is related to central processing of somatosensory information, but not to anomalous tactile perception, with the exception of Finger Identification.     

Effect of whole body vibration exercise on muscle strength and proprioception in females with knee osteoarthritis

The purpose of this study was to assess the effect of whole body vibration (WBV) exercise on muscle strength and proprioception in female patients with osteoarthritis in the knee (knee-OA). A single blinded, randomised, controlled trial was performed in an outpatient clinic on 52 female patients diagnosed with knee-OA (mean age 60.4 years ± 9.6). They were randomly assigned to one of 3 groups: 1. WBV-exercise on a stable platform (VibM; n = 17 (mean age, 61.5 ± 9.2)), WBV-exercise on a balance board (VibF; n = 18 (mean age, 58.7 ± 11.0)), or control group (Con; n = 18 (mean age, 61.1 ± 8.5)).The WBV groups trained twice a week for 8 weeks, with a progressively increasing intensity. The WBV groups performed unloaded static WBV exercise.The following were measured: knee muscle strength (extension/flexion) and proprioception (threshold for detection of passive movement (TDPM)). Self-reported disease status was measured using WOMAC.It was found that muscle strength increased significantly (p < 0.001) in VibM compared to Con. Isometric knee-extension significantly increased (p = 0.021) in VibM compared to Con. TDPM was significantly improved (p = 0.033) in VibF compared to Con, while there was a tendency (p = 0.051) for VibM to perform better compared to Con. There were no effects in the self-reported disease status measures.This study showed that the WBV-exercise regime on a stable platform (VibM) yielded increased muscle strength, while the WBV-exercise on a balance board (VibF) showed improved TDPM. The WBV-exercise is a time-saving and safe method for rehabilitation of women with knee-OA.     

Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle

Whereas the acuity of the position sense at the ankle can be disturbed by muscle fatigue, it recently also has been shown to be improved, under normal ankle neuromuscular state, through the use of an artificial tongue-placed tactile biofeedback. The underlying principle of this biofeedback consisted of supplying individuals with supplementary information about the position of their matching ankle position relative to their reference ankle position through electrotactile stimulation of the tongue. Within this context, the purpose of the present experiment was to investigate whether this biofeedback could mitigate the deleterious effect of muscle fatigue on joint position sense at the ankle. To address this objective, sixteen young healthy university students were asked to perform an active ankle-matching task in two conditions of No-fatigue and Fatigue of the ankle muscles and two conditions of No-biofeedback and Biofeedback. Measures of the overall accuracy and the variability of the positioning were determined using the absolute error and the variable error, respectively. Results showed that the availability of the biofeedback allowed the subjects to suppress the deleterious effects of muscle fatigue on joint position sense at the ankle. In the context of sensory re-weighting process, these findings suggested that the central nervous system was able to integrate and increase the relative contribution of the artificial tongue-placed tactile biofeedback to compensate for a proprioceptive degradation at the ankle.     

The Ia afferent feedback of a given movement evokes the illusion of the same movement when returned to the subject via muscle tendon vibration

The aim of the present study was to further investigate the contribution of primary muscle spindle feedback to proprioception and higher brain functions, such as movement trajectory recognition. For this purpose, complex illusory movements were evoked in subjects by applying patterns of muscle tendon vibration mimicking the natural Ia afferent pattern. Ia afferent messages were previously recorded using microneurographic method from the six main muscle groups acting on the ankle joint during imposed “writing like” movements. The mean Ia afferent pattern was calculated for each muscle group and used as a template to pilot each vibrator. Eleven different vibratory patterns were applied to ten volunteers. Subjects were asked both to copy the perceived illusory movements by hand on a digitizing tablet and to recognize and name the corresponding graphic symbol. The results show that the Ia afferent feedback of a given movement evokes the illusion of the same movement when it is applied to the subject via the appropriate pattern of muscle tendon vibration. The geometry and the kinematic parameters of the imposed and illusory movements are very similar and the so-called “two-thirds power law” is present in the reproduction of the vibration-induced illusory movements. Vibrations within the “natural” frequency range of Ia fibres firing (around 30 Hz) produce clear illusions of movements in all the tested subjects. In addition, increasing the mean frequency of the vibration patterns resulted in a linear increase in the size of the illusory movements. Lastly, the subjects were able to recognize and name the symbols evoked by the vibration-induced primary muscle spindle afferent patterns in 83% of the trials. These findings suggest that the “proprioceptive signature” of a given movement is associated with the corresponding “perceptual signature”. The neural mechanisms possibly underlying the sensory to perceptual transformation are discussed in the general framework of “the neuronal population vector model”.     

Motor performance changes induced by muscle vibration

The possibility that mechanical stimulation of selected muscles can act directly on the nervous system inducing persistent changes of motor performances was explored. On the basis of literature, stimulating parameters were chosen to stimulate the central nervous system and to avoid muscle fibre injuries. A sinusoidal mechanical vibration was applied, for three consecutive days, on the quadriceps muscle in seven subjects that performed a muscular contraction (VC). The same stimulation paradigm was applied on seven subjects in relaxed muscle condition (VR) and seven subjects were not treated at all (NV). Two sessions (PRE and POST) of isometric and isotonic tests were performed separated for 21 days, in all studied groups 7 days before and 15 days after stimulation, whilst an isokinetic test was performed on VC only. In the isometric test, the time of force development showed a significant decrease only in VC (POST vs PRE mean 27.8%, P < 0.05). In the isotonic test, the subjects’ had to perform a fatiguing leg extension against a load. In this condition, the fatigue resistance increased greatly in VC (mean 40.3%, P < 0.001), increased slightly in VR and there was no difference in NV. In Isokinetic test, at several angular velocities, significantly less time was required to reach the force peak (mean 20.2% P < 0.05). The findings could be ascribed to plastic changes in proprioceptive processing, leading to an improvement in knee joint control. Such action delineates a new tool in sports training and in motor rehabilitation.     

Leminscal and extralemniscal thalamic lesions and tactile discrimination in the rat

Summary Rats with lesions centered in the ventrobasal nuclear complex, the parafascicular-centrum median complex, or the posterior nuclear group were compared to each other and to control groups with and without thalamic damage on a battery of five two-choice tactile discriminations. Almost all animals mastered the first four discriminations, although many rats with lesions did not learn the discrimination with the least difference between positive and negative stimuli. Statistical analyses revealed differences in the raw scores and in the frequency of deviant scores between animals with lesions of the ventrobasal complex and controls, as well as between rats with parafascicular damage and controls. Animals with damage in the posterior nuclear group also showed some deficits on the problems. Histological analyses revealed possible differences in lesion size and locus for ventrobasal and parafascicular animals that did and did not master the series of tactile discriminations. Results are interpreted in terms of the roles of lemniscal and extralemniscal systems in somatic sensation and performance.This investigation was supported by National Science Foundation Grant GB-12374 and by Biomedical Sciences Support Grant FR-07 054 from the General Research Support Branch, Division of Research Resources, Bureau of Health Professions, Education and Manpower Training, National Institute of Health.     

Integration of visual and tactile stimuli: top-down influences require time

In a visuotactile congruency task, a distracting flash of light presented near a tactile target can influence speeded judgments of tactile location. Localization of the tactile target is more rapid when the elevation of the visual distractor is congruent with the tactile stimulus than when it is incongruent. The goal of the present study was to examine the degree of control that can be exerted on the process proposed to integrate the visual and tactile stimuli. To this end, the proportion of spatially congruent items was manipulated across blocks of trials. A robust congruency effect was observed across three experiments. There was no effect of proportion congruency (varied between 75 and 11% congruent) when the visual event was presented only 30 ms prior to the tactile event. When this lead-time was increased to 100 ms there was a significant increase in the congruency effect, for errors, in the high proportion congruent conditions (experiment 3). We conclude that with sufficient lead-time, top-down influence can be exerted in this task, however, when presented at near simultaneity, visuotactile integration is independent of top-down effects.These data were previously presented at the fifth IMRF in Sitges, Spain, June 2–5, 2004 .     

ERP correlates of tactile spatial attention differ under intra- and intermodal conditions

To investigate whether the mechanisms underlying endogenous tactile spatial attention differ under pure tactile compared to mixed modality conditions event-related brain potentials (ERPs) were recorded to bilateral tactile and visual cues and tactile imperative stimuli. In the cue-stimulus interval the anterior directing attention negativity (ADAN) was present contralateral to the side of the attentional shift. Importantly, under pure tactile conditions this component persisted until imperative stimulus onset, while it diminished under intermodal conditions. Furthermore, post-tactile stimulus onset attentional modulations were present for the P100 component and later latencies under intermodal conditions. In contrast, under pure tactile conditions attentional modulations only emerged for the N140 component and later latencies. It is suggested that mechanisms underlying attentional orienting and selection are not entirely supramodal but depend in part on the modalities involved.     

Changes in head and neck position affect elbow joint position sense

Changes in the position of the head and neck have been shown to introduce a systematic deviation in the end-point error of an upper limb pointing task. Although previous authors have attributed this to alteration of perceived target location, no studies have explored the effect of changes in head and neck position on the perception of limb position. This study investigated whether changes in head and neck position affect a specific component of movement performance, that is, the accuracy of joint position sense (JPS) at the elbow. Elbow JPS was tested with the neck in four positions: neutral, flexion, rotation and combined flexion/rotation. A target angle was presented passively with the neck in neutral, after a rest period; this angle was reproduced actively with the head and neck in one of the test positions. The potential effects of distraction from head movement were controlled for by performing a movement control in which the head and neck were in neutral for the presentation and reproduction of the target angle, but moved into flexion during the rest period. The absolute and variable joint position errors (JPE) were greater when the target angle was reproduced with the neck in the flexion, rotation, and combined flexion/rotation than when the head and neck were in neutral. This study suggests that the reduced accuracy previously seen in pointing tasks with changes in head position may be partly because of errors in the interpretation of arm position.     

An anisotropy of human tactile sensitivity and its relation to the visual oblique effect

Summary The ability of humans to detect striated stimuli on the distal phalanges was found to be highly anisotropic. Observers were much more sensitive to stripes presented in the proximal-distal orientation than to stripes in any other orientation. This tactile anisotropy was contrasted with the well-known visual anisotropy in which sensitivity is greatest for stripes at the horizontal and vertical orientations. We suggest that both the tactile anisotropy and the visual anisotropy are caused by corresponding anisotropies in the distribution of preferred orientations of orientation-selective neurons with in the respective modalities.     

Improved differentiation of tactile activations in human secondary somatosensory cortex and thalamus using cardiac-triggered fMRI

Functional magnetic resonance imaging (fMRI) can reveal human brain activations with high precision. The accuracy may, however, be impaired by movement and deformation of brain tissue associated with cardiac pulsations. Here we corrected for such artifacts by time-locking the fMRI data acquisition to the cardiac cycle in ten subjects who received tactile stimuli to their lips, fingers, and toes. The imaged brain areas covered the parietal operculum and the thalamus, including the secondary somatosensory cortex (SII) bilaterally. Variance of the blood-oxygen-level-dependent signal decreased on average by 38–40% in the SII cortex and by 26% in the thalamus during cardiac triggering compared with conventional imaging. Consequently, statistically significant responses were seen both in the SII cortex and in the ventroposterior thalamus in a larger number of subjects. At the cortical level, the activation pattern revealed two distinct representations for both fingers and toes in the SII region, and the more medial representations were detected with enhanced clarity during cardiac-triggered imaging. In the group-level analysis, the thalamic response to finger stimulation was seen with cardiac triggering, only.     

Images of tactile intimacy in same-sex dyads elicit larger P2 and LPC amplitudes

There is considerable behavioral evidence suggesting that the tactile intimacy between same-sex dyads might be viewed negatively. However, there is no electrophysiological evidence. In order to address this issue, event-related potentials (ERP) were recorded when both male and female participants were asked to evaluate whether the behaviors in same-sex dyads were appropriate or not. Both participant groups responded faster when they evaluated intimate pictures showing two males. The female participants were more inclined to tolerate female same-sex intimate pictures than the male participants. The deflections of P2 (150-250 ms) and LPC (400-600 ms) were significantly amplified in the intimate condition than in the non-intimate one, indicating that same-sex intimate pictures elicited negative emotions in participants. The female intimate pictures elicited larger LPC (600-900 ms) than the male intimate pictures only in the case of the female participants, indicating that female participants might enjoy in same-sex interactions as the dyads shown in the picture, and greater processing resources were required in evaluating processes. Above all, behavioral and electrophysiological scalp data provided the evidence that the tactile intimacy between same-sex dyads was viewed negatively.     

Goal directed motor behavior and its adaptation following reversed tactile perception in man

Summary When two adjacent fingers are crossed over each other and two tactile stimuli are touched to the two crossed fingertips, the two stimuli are perceived to be inverted in space. This phenomenon of tactile reversal was used in the present work to study the sensorimotor transformation occurring in goal directed motor behavior. When the subjects had to perform a movement toward a tactile stimulus (target) in tactile reversal conditions, the stimulus directed movements were performed wrongly, that is, away from the target. However, not all the subjects perceived a complete inversion of the stimuli; in this case, the target stimulus was perceived to be on the same side as its actual position, although with an error. In these conditions, the stimulus directed movements were performed correctly, that is, toward the target. These results show that the illusory spatial perception of the stimuli controls motor behavior on the basis of the amount of the perceptual error. Within the first hour of training, several compensatory responses occurred so as to produce correct motor performance. Despite this motor learning, reversed tactile perception remained reversed. Therefore, what subjects learned was the execution of the movements opposite to those necessary for reaching the target stimulus, without any change in perception. In the context of theories concerning the relationship between motor learning and perceptual adaptation, the present study shows that, with this experimental paradigm, motor learning during the first hour was mainly cognitive and did not have short-term effects upon perceptual processes.     

Cue‐locked lateralized components in a tactile spatial attention task: Evidence for a functional dissociation between ADAN and LSN

ERP studies investigating the control processes responsible for spatial orienting in touch have consistently observed that the anterior directing attention negativity (ADAN) elicited by an attention‐directing cue is followed by a sustained negativity contralateral to the cued hand. Recent evidence suggested that the later negativity, labeled late somatotopic negativity (LSN), might reflect distinct neurocognitive processes from those associated with the ADAN. To investigate the functional meaning of the ADAN and LSN components, we measured ERPs elicited by bilateral tactile cues indicating to covertly shift tactile attention to the left or right hand. Participants performed two spatial attention tasks that differed only for the difficulty of the target/nontarget discrimination at attended locations. The LSN but not the ADAN was sensitive to our experimental manipulation of task difficulty, suggesting that this component might reflect sensory‐specific preparatory processes prior to a forthcoming tactile stimulus.     

Space-independent modality-driven attentional capture in auditory,tactile and visual systems

Extending previous evidence for attentional shifts across auditory and visual modalities without the confound of the two modalities originating at different locations (Turatto et al. 2002), we investigated attention shifts between auditory and tactile modalities, and between tactile and visual modalities. Two stimuli (S₁ and S₂), either in the same or in different modalities, were delivered from the same spatial source and were separated by a variable temporal gap. S₁ was task irrelevant, whereas S₂ required a speeded discrimination. Results showed that modality switching is detrimental independently of the stimulated modality as long as the temporal lag between S₁ and S₂ is short enough that there is not time to switch attention before S₂ is delivered. We observed automatic, modality-driven, attentional capture, with ipsimodal trials leading to faster response times than crossmodal trials. The present results cannot be accounted for by spatial artifacts, response priming or criterion shifts, and are interpreted as the consequence of a space-independent attentional shift across sensory modalities.The research was supported by grants from CNR and MURST to C.U.     

Attenuation of somatosensory evoked potentials by acupuncture and tactile skin stimulation in man

The effects of acupuncture and tactile skin stimulation on somatosensory evoked potentials (SEPs), elicited by the median nerve stimulation, were investigated in healthy subjects. Acupuncture needles were inserted into either Hegu plus Shousanli, Hegu plus Waiguan, or Shousanli positions ipsilateral to the median nerve stimulation. Tactile skin stimulation was applied to either the ulnar side of the palm, or the dorsal surface of the hand or forearm ipsilaterally to the nerve stimulation. It was found that acupuncture significantly suppressed the amplitude of P22 and P40, and that the tactile skin stimulation of the ulnar side of the palm significantly suppressed the amplitude of P22 and P40, but that the peak latencies were not affected. Dipole tracing analysis showed that the location and vector direction of P22 were not changed but the vector moment of P22 was changed by both acupuncture and tactile stimulation. Based on these findings the suppressive effect of acupuncture and skin stimulation on P22 was proposed to be due to the afferent inhibition in the somatosensory cortex. Although the suppressive mechanism of P40 by tactile skin stimulation seemed to be similar to that of P22, the suppression of P40 by acupuncture appeared to include different mechanisms.     

Effect of tactile stimulation pulse characteristics on sensation threshold and power consumption

The psychophysical responses of human subjects to vibratory tactile stimulation of the skin were investigated experimentally. The parameters, of the waveform important to the minimization of power consumed by the tactile array of electromechanical vibrators and the maximization of the skin sensitivity to the stimulus were explored to develop optimum stimulation. Parameters investigated included the amplitude, frequency, and duty cycle of the current waveform used to drive the vibrators as well as the number of pulses per stimulating burst and the recovery time between bursts. Graphical techniques were used to determine, the optimal combination of the parameters which gave a stimulus that excited the skin to above tactile threshold while maintaining at a relative minimum the power required for the stimulus. The optimal stimulation waveform contains a burst of 10 rectangular pulses of 4% duty cycle separated by a period of nonstimulation of 2 s. Such a waveform can elicit a sensitivity of 29.4 mA⁻¹ consuming only 55 μW of power.     

Directing visual attention with spatially informative and spatially noninformative tactile cues

We investigated the tactile cuing of visual spatial attention using spatially-informative (75% valid) and spatially-noninformative (25% valid) tactile cues. The participants performed a visual change detection task following the presentation of a tactile spatial cue on their back whose location corresponded to one of the four visual quadrants on a computer monitor. The participants were explicitly instructed to use the spatially-informative tactile cues but to ignore the spatially-noninformative cues. In addition to reaction time data, participants’ eye-gaze was monitored as a measure of overt visual attention. The results showed that the spatially-informative tactile cues resulted in initial saccades toward the cued visual quadrants, and significantly reduced the visual change detection latencies. When spatially-noninformative tactile cues were used, the participants were largely successful at ignoring them as indicated by a saccade distribution that was independent of the quadrant that was cued, as well as the lack of a significant change in search time as compared to the baseline measure of no tactile cuing. The eye-gaze data revealed that the participants could not always completely ignore the spatially-noninformative tactile cues. Our results suggest that the tactile cuing of visual attention is natural but not automatic when the tactile cue and visual target are not collocated spatially, and that it takes effort to ignore the cues even when they are known to provide no useful information. In addition, our results confirm previous findings that spatially-informative tactile cues are especially effective at directing overt visual attention to locations that are not typically monitored visually, such as the bottom of a computer screen or the rearview mirror in an automobile.