Somatosensory Cues Research Articles

Spatial aspects of bodily self-consciousness

Visual, somatosensory, and perspectival cues normally provide congruent information about where the self is experienced. Separating those cues by virtual reality techniques, recent studies found that self-location was systematically biased to where a visual–tactile event was seen. Here we developed a novel, repeatable and implicit measure of self-location to compare and extend previous protocols. We investigated illusory self-location and associated phenomenological aspects in a lying body position that facilitates clinically observed abnormal self-location (as on out-of-body experiences). The results confirm that the self is located to where touch is seen. This leads to either predictable lowering or elevation of self-localization, and the latter was accompanied by sensations of floating, as during out-of-body experiences. Using a novel measurement we show that the unitary and localized character of the self can be experimentally separated from both the origin of the visual perspective and the location of the seen body, which is compatible with clinical data.

Role of Vestibular Input in Triggering and Modulating Postural Responses in Unilateral and Bilateral Vestibular Loss Patients

The aim of this study was to determine whether the greater medial-lateral (ML) instability observed in patients with compensated unilateral vestibular loss (UVL), tested on a seesaw platform with eyes closed, is task-dependent. UVL patients, categorized into three groups according to time since lesion (1 week, 1 month and 1 year), bilateral vestibular loss patients and age-matched healthy control subjects were tested in three dynamic postural tasks. These tasks involved different supports – a seesaw platform (Satel), a platform generating horizontal linear translations (Synapsys) and foam rubber placed on a static platform – each requiring different somatosensory cues to maintain equilibrium. Displacements of the subjects’ center of pressure in both the anterior-posterior (AP) and ML directions were recorded by strain gauges within the platforms. Only tests performed with eyes closed were analyzed. Bilateral vestibular loss patients fell during foam and seesaw trials but not on the platform generating translations. We previously reported that UVL patients had greater postural oscillations on the seesaw platform in the ML compared to AP direction. In this study, we show similar ML/AP differences in patient performance on foam when standing with ‘feet close together’. In contrast, these differences were not found when patients were tested on linear translation or on foam standing with feet apart. In conclusion, the postural performance of patients with vestibular loss depends on the exact task used to measure postural stability. UVL patients are less stable when subjected to movement in the ML direction because of the biomechanical constraints of the tasks and/or the availability of proprioceptive information.

Space and motion discomfort and abnormal balance control in patients with anxiety disorders

Objective: Previous research suggested that panic disorder with agoraphobia is associated with abnormalities on vestibular and balance function tests. The purpose of this study was to further examine psychiatric correlates...

One second interval production task during post-rotatory sensation

Temporal intervals production of one second was found to be more variable during self-motion compared to no motion situations. Moreover, the temporal intervals production rhythm during self-motion deceleration decreased whereas it increased during self-motion acceleration, whatever the direction of motion. As somatosensory cues were not excluded in this previous experiment, we now examined whether the same temporal perturbation would occur without variable somatosensory information. In order to isolate the contribution of the vestibular system from that of the somatosensory system, the participants were required to perform a one second temporal interval production task (pressing a button each second) during the post-rotatory illusion following self-rotation. The intervals produced during the vestibular illusion were compared to those produced before the imposed rotation and during self-motion. The production regularity was affected as the temporal intervals were more variable with vestibular stimulation (real and illusory self-motion) than without. Furthermore, during post-rotatory illusion, the production rhythm decreased along the trial, as it was observed during self-motion deceleration. These findings suggest that vestibular stimulation (even vestibular illusion) impaired time estimation.

Laterodorsal nucleus of the thalamus: A processor of somatosensory inputs.

The laterodorsal (LD) nucleus of the thalamus has been considered a "higher order" nucleus that provides inputs to limbic cortical areas. Although its functions are largely unknown, it is often considered to be involved in spatial learning and memory. Here we provide evidence that LD is part of a hitherto unknown pathway for processing somatosensory information. Juxtacellular and extracellular recordings from LD neurons reveal that they respond to vibrissa stimulation with short latency (median = 7 ms) and large magnitude responses (median = 1.2 spikes/stimulus). Most neurons (62%) had large receptive fields, responding to six and more individual vibrissae. Electrical stimulation of the trigeminal nucleus interpolaris (SpVi) evoked short latency responses (median = 3.8 ms) in vibrissa-responsive LD neurons. Labeling produced by anterograde and retrograde neuroanatomical tracers confirmed that LD neurons receive direct inputs from SpVi. Electrophysiological and neuroanatomical analyses revealed also that LD projects upon the cingulate and retrosplenial cortex, but has only sparse projections to the barrel cortex. These findings suggest that LD is part of a novel processing stream involved in spatial orientation and learning related to somatosensory cues.

Effects of alcohol exposure during development on play behavior and c-Fos expression in response to play behavior

Developmental exposure to alcohol can produce characteristic physiological and cognitive deficits, often termed Fetal Alcohol Spectrum Disorder (FASD). More recently, social deficits have been shown to occur both in FASD and animal models of FASD; the behavioral and neural bases of these deficits remain to be determined. It was hypothesized that changes in sensory processing may in part underlie the social deficits seen in FASD. This study used a rat model of FASD and social play, a behavior critical to adult social functioning, to begin to examine this hypothesis. Somatosensory cues from dorsal contact to the nape of the neck, critical to the initiation of pinning, were systematically degraded by administration of different doses of xylocaine, a topical anesthetic. Neuronal activity after 1 h of play was assessed by measurement of c-Fos immunoreactivity (IR) in different brain regions. Ethanol-exposed rats showed an increased frequency of pinning during social play and were more sensitive to the degradation of somatosensory cues compared to the control groups, suggesting difficulties in processing somatosensory cues. Neuronal activity in the somatosensory cortex induced by play was significantly decreased in the ethanol-exposed group compared to the non-treated group. The c-Fos IR in the nucleus accumbens was altered in a sexually dimorphic manner in the ethanol-exposed group. Thus, the behavioral and brain measures are consistent with the hypothesis that ethanol exposure during development induces alterations in social play via deficits in processing somatosensory cues that are important to social play.

A rehabilitation tool for functional balance using altered gravity and virtual reality

BackgroundThere is a need for effective and early functional rehabilitation of patients with gait and balance problems including those with spinal cord injury, neurological diseases and recovering from hip fractures, a common consequence of falls especially in the elderly population. Gait training in these patients using partial body weight support (BWS) on a treadmill, a technique that involves unloading the subject through a harness, improves walking better than training with full weight bearing. One problem with this technique not commonly acknowledged is that the harness provides external support that essentially eliminates associated postural adjustments (APAs) required for independent gait. We have developed a device to address this issue and conducted a training study for proof of concept of efficacy.MethodsWe present a tool that can enhance the concept of BWS training by allowing natural APAs to occur mediolaterally. While in a supine position in a 90 deg tilted environment built around a modified hospital bed, subjects wear a backpack frame that is freely moving on air-bearings (cf. puck on an air hockey table) and attached through a cable to a pneumatic cylinder that provides a load that can be set to emulate various G-like loads. Veridical visual input is provided through two 3-D automultiscopic displays that allow glasses free 3-D vision representing a virtual surrounding environment that may be acquired from sites chosen by the patient. Two groups of 12 healthy subjects were exposed to either strength training alone or a combination of strength and balance training in such a tilted environment over a period of four weeks.ResultsIsokinetic strength measured during upright squat extension improved similarly in both groups. Measures of balance assessed in upright showed statistically significant improvements only when balance was part of the training in the tilted environment. Postural measures indicated less reliance on visual and/or increased use of somatosensory cues after training.ConclusionUpright balance function can be improved following balance specific training performed in a supine position in an environment providing the perception of an upright position with respect to gravity. Future studies will implement this concept in patients.

Temporal facilitation of gaze in the presence of postural reactions triggered by sudden surface perturbations

Saccadic reaction times can be shortened by an additional sensory modality (e.g. auditory, tactile) presented in temporal proximity to the triggering cue. Whereas somatosensory cues given by sudden perturbations of the support surface can trigger appropriate postural adjustments to maintain upright stance, it is not known how gaze executions are affected by the dual task of maintaining upright balance while redirecting gaze. It was hypothesized that the onset latency of gaze movements toward visual targets will be shortened by sudden surface perturbations following visual target shifts to prompt a stable visual anchor for postural stabilization. Eight subjects stood on a movable platform with gaze fixated on a central target 2 m directly in front, and were instructed to shift their gaze to lateral targets located along a 63° arc to the right and left. The trials began with the central target lit followed randomly by either the right, left or center target. Fifty or 250 ms following this target shift, balance was perturbed by a sudden yaw movement of the support surface (15.5° over 210 ms at 130°/s), with no stepping or large arm reactions observed. The latency of the gaze shifts was significantly shortened (by ∼72 ms) when executed simultaneously with a surface perturbation. A decrease in excitation latency was also observed in the cervical paraspinals and sternocleidomastoid muscles. Postural responses in the ankle and knee muscles were not affected by gaze shifts. Pelvic horizontal angular motion closely followed surface motion whereas head motion was influenced by gaze shifts. During the combined gaze shift and surface motion conditions, thorax movement excursion was larger and not correlated with either the surface motion or visual target shift. In conclusion, postural adjustments in response to sudden surface yaws facilitate voluntary gaze shift execution and this enhancement may result from the sensory fusion of somatosensory and visual information.

Parietal disruption impairs reflexive spatial attention within and between sensory modalities

Reflexive spatial attention is critical for controlling perception and action. An established body of evidence suggests that mechanisms of spatial attention operate both within and between sensory modalities; however the attentional mechanisms that link modalities in the human brain are unclear. Here we used transcranial magnetic stimulation (TMS) to explore the role of the parietal cortex in coordinating reflexive shifts of spatial attention between vision and touch. In two experiments, healthy participants localised visual and somatosensory targets that were preceded by non-informative visual or somatosensory spatial cues. To determine the role of parietal cortex in spatial orienting, TMS was delivered synchronously with cue onset for 100ms. Results revealed a critical role of the right angular gyrus and supramarginal gyrus in reflexive orienting to visual and somatosensory targets that followed a somatosensory cue. In contrast, the same TMS protocol was ineffective in modulating reflexive orienting based on visual cues. This dependence on cue modality may reflect subcortical redundancy of visual orienting mechanisms. Overall, our results indicate a critical role of the inferior parietal cortex in mediating reflexive shifts of attention within and between sensory modalities.

The change of postural gain scaling by constrained somatosensory cues(1C3 Musculo-Skeletal Biomechanics III)

The change of postural gain scaling by constrained somatosensory cues(1C3 Musculo-Skeletal Biomechanics III)

Perception of longitudinal body axis in microgravity during parabolic flight

It has been proposed that an internal representation of body vertical has a prominent role in spatial orientation. This investigation investigated the ability of human subjects to accurately locate their longitudinal body axis (an imaginary straight body midline running from head to toes) while free-floating in microgravity. Subjects were tested in-flight, as well as on ground in normal gravity in both the upright and supine orientations to provide baseline measurements. The subjects wore a goggle device and were in total darkness. They used knobs to rotate two luminous lines until they were parallel to the subjective direction of their longitudinal body axis, in the roll (right/left) and the pitch (forward/backward) planes. Results showed that the error between the perceived and the objective direction of the longitudinal body axis was significantly larger in microgravity than in normal gravity. This error in this egocentric frame of reference is presumably due to the absence of somatosensory cues when free-floating. Mechanical pressure on the chest using an airbag reduced the error in perception of the longitudinal body axis in microgravity, thus improving spatial orientation.

Changing lanes: inertial cues and explicit path information facilitate steering performance when visual feedback is removed

Can driver steering behaviors, such as a lane change, be executed without visual feedback? In a recent study with a fixed-base driving simulator, drivers failed to execute the return phase of a lane change when steering without vision, resulting in systematic final heading errors biased in the direction of the lane change. Here we challenge the generality of that finding. Suppose that, when asked to perform a lane (position) change, drivers fail to recognize that a heading change is required to make a lateral position change. However, given an explicit path, the necessary heading changes become apparent. Here we demonstrate that when heading requirements are made explicit, drivers appropriately implement the return phase. More importantly, by using an electric vehicle outfitted with a portable virtual reality system, we also show that valid inertial information (i.e., vestibular and somatosensory cues) enables accurate steering behavior when vision is absent. Thus, the failure to properly execute a lane change in a driving simulator without a moving base does not present a fundamental problem for feed-forward driving behavior.

The effect of rhythmic somatosensory cueing on gait in patients with Parkinson's disease

Background and aims Gait and gait related activities in patients with Parkinson's disease (PD) can be improved with rhythmic auditory cueing (e.g. a metronome). In the context of a large European study, a portable prototype cueing device was developed to provide an alternative for rhythmic auditory cueing: rhythmic somatosensory cueing (RSC, a miniature vibrating cylinder attached to the wrist). We investigated whether PD patients could adapt their walking pattern using RSC under conditions of changing walking speed and the presence of potentially distracting visual flow while walking on a treadmill. Methods A total of 17 patients with PD participated (mean age 63.4 ± 10.3 years; Hoehn-Yahr score 2.5 ± 0.9, mean Unified Parkinson's Disease Rating Scale score 49.8 ± 13.7, mean disease duration 7.7 ± 5.1 years). They performed systematic walking speed manipulations under 4 conditions in a random order: (1) no cue, no visual flow, (2) no cue, visual flow, (3) cue, no visual flow and (4) cue, visual flow. Visual flow in the form of a virtual corridor that moved at the current walking speed was projected on a 2 × 2 m rear-projection screen. The cueing rhythm was set at − 10% of preferred stride frequency at each speed. Stride frequency was assessed using peaks in the trajectories of thigh sagittal plane segmental angles. Results Walking with RSC resulted in lower stride frequencies, and thus larger step lengths ( p-values < 0.05), regardless of walking speed. The presence of visual flow did not impair the use of RSC, as evidenced by the lack of differences between conditions 3 and 4 ( p > 0.05). Conclusion Rhythmic somatosensory cueing may be a viable alternative for auditory cueing and is robust to changes in walking speed and visual distractors.

Time Course and Magnitude of Illusory Translation Perception During Off-Vertical Axis Rotation

Human spatial orientation relies on vision, somatosensory cues, and signals from the semicircular canals and the otoliths. The canals measure rotation, whereas the otoliths are linear accelerometers, sensitive to tilt and translation. To disambiguate the otolith signal, two main hypotheses have been proposed: frequency segregation and canal-otolith interaction. So far these models were based mainly on oculomotor behavior. In this study we investigated their applicability to human self-motion perception. Six subjects were rotated in yaw about an off-vertical axis (OVAR) at various speeds and tilt angles, in darkness. During the rotation, subjects indicated at regular intervals whether a briefly presented dot moved faster or slower than their perceived self-motion. Based on such responses, we determined the time course of the self-motion percept and characterized its steady state by a psychometric function. The psychophysical results were consistent with anecdotal reports. All subjects initially sensed rotation, but then gradually developed a percept of being translated along a cone. The rotation percept could be described by a decaying exponential with a time constant of about 20 s. Translation percept magnitude typically followed a delayed increasing exponential with delays up to 50 s and a time constant of about 15 s. The asymptotic magnitude of perceived translation increased with rotation speed and tilt angle, but never exceeded 14 cm/s. These results were most consistent with predictions of the canal-otolith-interaction model, but required parameter values that differed from the original proposal. We conclude that canal-otolith interaction is an important governing principle for self-motion perception that can be deployed flexibly, dependent on stimulus conditions.

Effects of external rhythmical cueing on gait in patients with Parkinson's disease: a systematic review

To critically review studies evaluating the effects of external rhythmical cueing on gait in patients with Parkinson's disease. Articles published from 1966 to January 2005 were searched by two physiotherapists in MEDLINE, PiCarta, PEDRo, Cochrane, DocOnline, CINAHL and SUMSEARCH. To be included, articles had to investigate the effects of external rhythmical cueing (i.e., auditory, visual or tactile cueing) on gait parameters in patients with idiopathic Parkinson's disease. Both controlled and noncontrolled studies were included. Based on the type of design and methodological quality a meta-analysis or best-evidence synthesis was applied. Twenty-four studies (total number of patients = 626) out of the 159 screened studies were evaluated in this systematic review. Two out of 24 were randomized controlled trails (RCT), both of high methodological quality. One RCT did not focus specifically on external rhythmical cueing of individual patients with Parkinson's disease, but on group exercises in general, including walking with cues. All other studies were pre-experimental studies. Best-evidence synthesis showed strong evidence for improving walking speed with the help of auditory cues. Insufficient evidence was found for the effectiveness of visual and somatosensory cueing. Only one high-quality study, specifically focused on the effects of auditory rhythmical cueing, suggesting that the walking speed of patients with Parkinson's disease can be positively influenced. However, it is unclear whether positive effects identified in the laboratory can be generalized to improved activities of daily living (ADLs) and reduced frequency of falls in the community. In addition, the sustainability of a cueing training programme remains uncertain.

The influence of dynamic visual cues for postural control in children aged 7–12 years

Young children rely heavily on vision for postural control during the transition to walking. Although by 10 years of age, children have automatic postural responses similar to adults, it is not clear when the integration of sensory inputs becomes fully developed. The purpose of this study was to examine this transition in the sensory integration process in children aged 7-12 years. Healthy children and adults stood on a fixed or sway-referenced support surface while viewing full-field optic flow scenes that moved sinusoidally (0.1 and 0.25 Hz) in an anterior-posterior direction. Center of pressure was recorded, and measures of sway amplitude and phase were calculated at each stimulus frequency. Children and adults had significant postural responses during approximately two-thirds of the trials. In adults, there was a 90% decrease in sway on the fixed surface compared with the sway-referenced surface, but only a 50% decrease in children. The phase between the optic flow stimulus and postural response in children led that of adults by 52 degrees at 0.1 Hz and by 15 degrees at 0.25 Hz. Adults and children aged 7-12 years have similar ability to use dynamic visual cues for postural control. However, 7-12-year-old children do not utilize somatosensory cues to stabilize posture to the same extent as adults when visual and somatosensory cues are conflicting.

Neuronal activity in primary motor cortex differs when monkeys perform somatosensory and visually guided wrist movements

This study was designed to investigate how activity patterns of primary motor cortical (MI) neurons change when monkeys perform the same movements guided by somatosensory and/or visual cues. Two adult male rhesus monkeys were trained to make wrist extensions and flexions after holding a steady position during an instructed delay period lasting 0.5-2.0 s. Monkeys held against a 0.07 Nm load that opposed flexion movements. Wrist movements were guided by vibratory cues (VIB-trials), visual cues (VIS-trials), or both in combination (COM-trials). Extracellular recordings of 188 MI neurons were made during all three paradigms. Individual neurons were counted twice, once for each movement direction, yielding 376 cases. All neurons had significant task-related activity (TRA) changes relative to delay period activity during at least one of the three paradigms. TRA was analyzed to determine if it was different as a function of the sensory cue(s) that initiated movement and that specified movement endpoints. Cases were grouped by whether the TRA changes were greater in VIB- or VIS-trials; this defined their "bias". One hundred and eighteen cases (31.4%) had greater TRA changes in VIB-trials (Vb-neurons), whereas 185 (49.2%) showed greater TRA changes in VIS-trials (Vs-neurons). The remaining 73 cases (19.4%) had similar TRA changes in VIB- and VIS-trials (Nb-neurons). For Vb- and Vs-neurons, earlier TRA onsets and greater TRA changes were observed in the trials for which these neurons were biased. During the COM-trials, the TRA was intermediate. During the trials for which the activity was not biased, the TRA was the least. For Nb-neurons, no significant TRA differences were observed across paradigms. TRA changes of MI neurons may represent movement planning-related inputs from other central, presumably cortical, sources as well as contribute to motor outflow from the cortex. These data suggest that Vb- and Vs-neurons are affected differently by somatosensory- and visually related central inputs, resulting in different TRAs, even for essentially identical movements. Such differences may depend not only on the type of sensory information that initiates movement but also whether that information specifies movement endpoints or might interfere with movement monitoring.

The sensorimotor transformation of cross-modal spatial information in the anterior intraparietal sulcus as revealed by functional MRI

The parietal cortex in monkeys and humans has been shown to play an important role in the transformation of sensory information to motor commands. However, it is still unclear whether in humans, these areas are divided functionally into subregions based on different combinations of sensory and motor modalities. To identify subregions in the parietal cortex involved in the sensorimotor information transformation between different modalities, functional MRI was used to examine brain areas activated during tasks requiring different sensorimotor transformations—i.e., various combinations of eye (saccade) or finger movements triggered by visual or somatosensory cues. We then compared the activations between cross-modal conditions (eye movements triggered by somatosensory cues and finger movements triggered by visual cues) and intramodal (eye movements triggered by visual cues and finger movements triggered by somatosensory cues) conditions. Although the parietal cortex was involved in all tasks regardless of sensorimotor combinations, the only region activated to a greater degree in the cross-modal conditions compared to the intramodal conditions was the anterior portion of the intraparietal sulcus (a-IPS). The results suggest that the a-IPS plays an important role in the sensorimotor transformation of cross-modal spatial information.

Effect of compliance on haptic perception of curvature

The haptic sense of geometric properties such as the curvature of a contour is derived from somatosensory cues about the motions and forces experienced during exploratory actions. This study addressed the question of whether compliance, the relationship between force and displacement, influences haptic perception of curvature. Subjects traced a curved 30 cm long compliant contour by grasping the handle of a manipulandum and reported whether the contour curved towards or away from them. The contour at which there was equal probability of responding either way was taken to represent one that was sensed as being straight. The compliance of the contour was varied, being constant, greatest in the middle or greatest at the ends. Subjects exhibited a bias in what they sensed to be a straight edge. However, the actual handpath that was judged to be straight did not vary across the three compliance profiles. Our results rule out a hypothetical strategy in which an intended motion is planned and the actual trajectory is then inferred by sensing force feedback. Another strategy in which the force against the contour is controlled and the handpath is inferred from proprioceptive feedback is more consistent with the observations.

Imagination of body rotation can induce eye movements

ObjectiveSeveral studies have shown that spatiotemporal aspects of motion are stored and can be retrieved with the use of vestibular and somatosensory cues. The purpose of this study was to examine whether intentional imagination of body rotation can induce oculomotor activity similar to the typical vestibulo-ocular reflex (VOR).Material and MethodsNormal subjects without known vestibular and/or oculometric abnormalities were instructed to imagine a sensation of accelerating body rotation in the horizontal plane (rightward or leftward) while sitting in darkness with closed eyes, using only vestibular and somatosensory cues and not imaginary visual cues. Eye movements were recorded during the imagery session and also during a full, routine electronystagmography (ENG) test. All subjects selected for this study showed normal results in the ENG test, and none of them had gaze-evoked or end-point nystagmus.ResultsIn response to imaginary rotations, horizontal eye movements were found in 91/121 recordings (75%) in 10 subjects. A typical pattern of nystagmus (0.3–3 Hz, 3–30°/s maximal speed of slow component) was recorded in 53% of mental rightward rotations and 49% of leftward rotations. The fast component was always in the direction of the imaginary rotation (similar to a normal VOR). Other types of eye movement comprised either contralateral eye drift (≈17% of trials) or macro square waves. In 25% of the recordings no definite eye movements could be detected during the mental maneuvers.ConclusionThese mentally induced eye movements seem to be due to a cortical process which can affect the normal input to the brainstem nuclei. A possible mechanism is discussed. This phenomenon may serve as an objective measurement of mental activity, may be used for testing the cognitive resources of patients and can probably be used for enhancing the rehabilitation process after acute vestibular insult.