Somatosensory Cues Research Articles

Influence of dance training on challenging postural control task

BackgroundPrevious studies have shown that dance training affects postural control, particularly during challenging tasks. However, it is still unknown whether dance training also affects the ability to use vestibular, somatosensory, and visual cues, thus leading to postural control differences. ObjectiveThe main goal of the present study was to evaluate the influence of dance training on sensory weighting during static postural control. MethodThe center of pressure of 24 participants was recorded (12 dancers and 12 control non-dancers) using a force platform as well as the modified Clinical Test of Sensory Organization in Balance (mCTISB). ResultsThe results suggest that dancers perform significantly better than controls in conditions where somatosensory cues are disturbed. Moreover, a significant negative correlation between vestibular frequency band and training intensity was observed, along with, a significant positive correlation between visual frequency band and training intensity. SignificanceThis research outlines dancers’ increased ability to modulate sensory weighting differently than non-dancers during postural task where somatosensory cues are reduced.

Mathematical models for dynamic, multisensory spatial orientation perception.

Mathematical models have been proposed for how the brain interprets sensory information to produce estimates of self-orientation and self-motion. This process, spatial orientation perception, requires dynamically integrating multiple sensory modalities, including visual, vestibular, and somatosensory cues. Here, we review the progress in mathematical modeling of spatial orientation perception, focusing on dynamic multisensory models, and the experimental paradigms in which they have been validated. These models are primarily "black box" or "as if" models for how the brain processes spatial orientation cues. Yet, they have been effective scientifically, in making quantitative hypotheses that can be empirically assessed, and operationally, in investigating aircraft pilot disorientation, for example. The primary family of models considered, the observer model, implements estimation theory approaches, hypothesizing that internal models (i.e., neural systems replicating the behavior/dynamics of physical systems) are used to produce expected sensory measurements. Expected signals are then compared to actual sensory afference, yielding sensory conflict, which is weighted to drive central perceptions of gravity, angular velocity, and translation. This approach effectively predicts a wide range of experimental scenarios using a small set of fixed free parameters. We conclude with limitations and applications of existing mathematical models and important areas of future work.

Critical Role of Somatosensation in Postural Control Following Spaceflight: Vestibularly Deficient Astronauts Are Not Able to Maintain Upright Stance During Compromised Somatosensation.

The free-fall of orbital spaceflight effectively removes the gravitational vector used as a primary spatial orientation reference on Earth. Sustained absence of this reference drives adaptive changes in the internal perception-action models of the central nervous system (CNS), most notably in the processing of the vestibular otolith inputs. Upon landing, the return of the gravitational signal triggers a re-adaptation that restores terrestrial performance; however, during this period, the individual suffers from a functional vestibular deficiency. Here we provide evidence of a transient increase of the weighting of somatosensory inputs in postural control while the CNS resolves these vestibular deficiencies. Postural control performance was measured before and after spaceflight in 11 Shuttle astronauts and 11 matched controls and nine elderly who did not experience spaceflight. A quiet-stance paradigm was used that eliminated vision, modulated the lower extremity somatosensory cues by subtly modulating the orientation of the support surface beneath feet of subjects in all groups. Additionally, in astronauts and matched controls, we challenged the vestibular system with dynamic head tilts. Postural stability on the landing day (R+0) was substantially decreased for trials with absent visual and altered somatosensory cues, especially those also requiring dynamic head tilts ( ± 5° @ 0.33 Hz) during which 20/22 trials ended prematurely with a fall. In contrast, none of the astronauts fell during eyes-closed, dynamic head tilt trials with unaltered somatosensory cues, and only 3/22 trials resulted in falls with eyes-closed and altered somatosensory cues, but static upright head orientation. Furthermore, postural control performance of astronauts was either statistically not different or worse than that of healthy elderly subjects during the most challenging vestibular conditions on R+0. Overall, our results demonstrate a transient reweighting of sensory cues associated with microgravity-induced vestibular deficiencies, with a significant increase in reliance on somatosensory cues, which can provide an effective reference even without vision and with dynamic vestibular challenges. The translation of these results to aging population suggests that elderly individuals with visual and vestibular deficits may benefit from therapeutic interventions enhancing sensorimotor-integration to improve balance and reduce the risk of falling.

A Conditioned Place Preference Protocol for Measuring Incubation of Craving in Rats.

A major cause of repeated relapses is a craving for the drug. Drug craving increases progressively during the abstinence period, a phenomenon termed incubation of drug craving. Here, we describe a morphine conditioned place preference (CPP) protocol for measuring the incubation of craving in rats. In this protocol, a CPP paradigm mainly employing somatosensory cues is used to establish a long-term reward memory of morphine. A three-chamber CPP box that differs in the texture of the chamber floor is constructed. First, the animals are tested for their baseline preference to the two side chambers for three consecutive days. Then, they are injected intraperitoneally with morphine/saline and put into their non-preferred/preferred chamber for 45 min. After 6 days of conditioning, their preference to the side chambers is tested for 15 min at different time points after the last conditioning session. With this paradigm, the reward memory of morphine could last for at least 18 days. To test whether the above-mentioned protocol can model increased craving, the number of entrances into the two side chambers are counted during the abstinence period. The results show that the entrances increased, suggesting that the CPP paradigm could mimic the incubation of craving. Future studies can employ this model to study neural mechanisms underlying long-term memory and incubation of craving.

A Conditioned Place Preference Protocol for Measuring Incubation of Craving in Rats

A major cause of repeated relapses is a craving for the drug. Drug craving increases progressively during the abstinence period, a phenomenon termed incubation of drug craving. Here, we describe a morphine conditioned place preference (CPP) protocol for measuring the incubation of craving in rats. In this protocol, a CPP paradigm mainly employing somatosensory cues is used to establish a long-term reward memory of morphine. A three-chamber CPP box that differs in the texture of the chamber floor is constructed. First, the animals are tested for their baseline preference to the two side chambers for three consecutive days. Then, they are injected intraperitoneally with morphine/saline and put into their non-preferred/preferred chamber for 45 min. After 6 days of conditioning, their preference to the side chambers is tested for 15 min at different time points after the last conditioning session. With this paradigm, the reward memory of morphine could last for at least 18 days. To test whether the above-mentioned protocol can model increased craving, the number of entrances into the two side chambers are counted during the abstinence period. The results show that the entrances increased, suggesting that the CPP paradigm could mimic the incubation of craving. Future studies can employ this model to study neural mechanisms underlying long-term memory and incubation of craving.

Balance in multiple sclerosis: relationship to central brain regions.

Dizziness, postural instability, and ataxia are among the most debilitating symptoms of multiple sclerosis (MS), reflecting, in large part, dysfunctional integration of visual, somatosensory, and vestibular sensory cues. However, the role of MS-related supratentorial lesions in producing such symptoms is poorly understood. In this study, motor control test (MCT) and dynamic sensory organization test (SOT) scores of 58 MS patients were compared to those of 72 healthy controls; correlations were determined between the MS scores of 49 patients and lesion volumes within 26 brain regions. Depending upon platform excursion direction and magnitude, MCT latencies, which were longer in MS patients than controls (p < 0.0001), were correlated with lesion volumes in the cortex, medial frontal lobes, temporal lobes, and parietal opercula (r's ranging from 0.20 to 0.39). SOT test scores were also impacted by MS and correlated with lesions in these same brain regions as well as within the superior frontal lobe (r's ranging from - 0.28 to - 0.40). The strongest and most consistent correlations occurred for the most challenging tasks in which incongruent visual and proprioceptive feedback were given. This study demonstrates that supratentorial lesion volumes are associated with quantitative balance measures in MS, in accord with the concept that balance relies upon highly convergent and multimodal neural pathways involving the skin, muscles, joints, eyes, and vestibular system.

Random-amplitude sinusoidal linear acceleration causes greater vestibular modulation of skin sympathetic nerve activity than constant-amplitude acceleration.

We tested the hypothesis that random variations in the magnitude of sinusoidal linear acceleration cause greater modulation of skin sympathetic nerve activity (SSNA), but not muscle sympathetic nerve activity (MSNA), than sinusoidal stimuli of the same frequency but constant amplitude. Subjects (n = 22) were seated in a sealed room mounted on a linear motor that could deliver peak sinusoidal accelerations of 30mG in the antero-posterior direction. Subjects sat on a padded chair with their neck and head supported vertically, thereby minimizing somatosensory cues, facing the direction of motion in the anterior direction. Each block of sinusoidal motion was delivered at 0.2Hz, either with a constant-amplitude (root mean square 14 mG) or randomly fluctuating amplitudes of the same mean amplitude. MSNA (n = 12) and SSNA (n = 10) were recorded via tungsten microelectrodes inserted into muscle or cutaneous fascicles of the common peroneal nerve. Cross-correlation analysis was used to measure the magnitude of vestibular modulation. The modulation index for SSNA was significantly higher during delivery of random vs constant-amplitude acceleration (31.4 ± 1.9 vs 24.5 ± 2.5%), but there was no significant difference in the modulation indices for MSNA (28.8 ± 2.9 vs 33.4 ± 4.1%). We conclude that the pattern of vestibular stimulation affects the magnitude of modulation of sympathetic outflow to skin but not to muscle. Presumably, this is related to the subperceptual development of nausea, which is known to be associated with greater vestibular modulation of SSNA but not MSNA.

Top-Down Control of Alpha Phase Adjustment in Anticipation of Temporally Predictable Visual Stimuli.

Alpha oscillations (8-14 Hz) are proposed to represent an active mechanism of functional inhibition of neuronal processing. Specifically, alpha oscillations are associated with pulses of inhibition repeating every ∼100 msec. Whether alpha phase, similar to alpha power, is under top-down control remains unclear. Moreover, the sources of such putative top-down phase control are unknown. We designed a cross-modal (visual/auditory) attention study in which we used magnetoencephalography to record the brain activity from 34 healthy participants. In each trial, a somatosensory cue indicated whether to attend to either the visual or auditory domain. The timing of the stimulus onset was predictable across trials. We found that, when visual information was attended, anticipatory alpha power was reduced in visual areas, whereas the phase adjusted just before the stimulus onset. Performance in each modality was predicted by the phase of the alpha oscillations previous to stimulus onset. Alpha oscillations in the left pFC appeared to lead the adjustment of alpha phase in visual areas. Finally, alpha phase modulated stimulus-induced gamma activity. Our results confirm that alpha phase can be top-down adjusted in anticipation of predictable stimuli and improve performance. Phase adjustment of the alpha rhythm might serve as a neurophysiological resource for optimizing visual processing when temporal predictions are possible and there is considerable competition between target and distracting stimuli.

Hands-off Ultrasound Technique: Utilizing Simultaneous Modeling to Enhance Ultrasound Training.

Image acquisition can be a challenging component of obtaining ultrasound proficiency. To assist with obtaining the correct image, instructors may take the transducer away or guide the learner's hand. However, this passive form of learning has been suggested to be much less valuable, as it removes learner autonomy and somatosensory cueing. This paper describes the hands-off ultrasound technique, a simultaneous modeling teaching strategy using multimodal feedback to improve ultrasound image acquisition.

Learning dynamic balancing in the roll plane with and without gravitational cues.

We determined the relative contributions of gravity-dependent positional cues and motion cues to the learning of roll balance control. We hypothesized that gravity-dependent otolith and somatosensory shear forces related to body orientation would yield better initial performance, more rapid learning, and better retention. Blindfolded subjects rode in a device programmed to roll with inverted pendulum dynamics in a vertical (UPRIGHT) or horizontal plane (SUPINE), and used a joystick to align themselves with the direction of balance. Each subject completed five blocks of four 100s long trials on two consecutive days in one of four groups (n=10 per group): Group 1, UPRIGHT balancing both days; Group 2, SUPINE both days; Group 3, UPRIGHT then SUPINE; and Group 4, SUPINE then UPRIGHT. On Day 1, UPRIGHT subjects showed better initial performance and greater improvement in performance than SUPINE subjects, who showed improvements only in having fewer deviations exceeding ±60deg from the direction of balance. Subjects tested UPRIGHT on both days showed full retention of learning across days and additional Day 2 learning, but subjects tested SUPINE on both days showed partial retention of their marginal learning from Day 1 and little improvement on Day 2. Subjects tested SUPINE on Day 2 after being tested UPRIGHT on Day 1 showed no better performance than subjects tested SUPINE on Day 1. By contrast, there was transfer from SUPINE on Day 1 to UPRIGHT on Day 2. We conclude that absence of gravitationally dependent otolith and somatosensory cues degrades balance performance.

The somatosensory-evoked potential in reaction time is gated and elicited earlier when the motor response to a somatosensory cue is faster.

The aim of this study was to investigate whether the somatosensory-evoked potential (SEP) is gated and elicited earlier when a motor response to a somatosensory stimulus is faster. In healthy humans, the left index finger and thumb were pinched in response to a somatosensory stimulus administered over the left median nerve. The SEP elicited by this stimulus when producing a fast motor response was compared with that when producing a slow motor response. The amplitudes of N18 and frontal P40 when producing a fast motor response were smaller than those when producing a slow motor response. The latencies of frontal P22 and P40 when producing a fast motor response were shorter than those when producing a slow motor response. These findings indicated that the responses of the primary sensory and frontal areas elicited by a somatosensory stimulus are gated and that the responses of the frontal areas elicited by this stimulus occur earlier when a motor response to this stimulus is faster. The enhanced efficiency or increased speed of the stimulus identification process may be related to the gating and early onset of the SEP components when producing a fast motor response.

Multisensory control of a straight locomotor trajectory.

Locomotor steering is contingent upon orienting oneself spatially in the environment. When the head is turned while walking, the optic flow projected onto the retina is a complex pattern comprising of a translational and a rotational component. We have created a unique paradigm to simulate different optic flows in a virtual environment. We hypothesized that non-visual (vestibular and somatosensory) cues are required for proper control of a straight trajectory while walking. This research study included 9 healthy young subjects walking in a large physical space (40×25m2) while the virtual environment is viewed in a helmet-mounted display. They were instructed to walk straight in the physical world while being exposed to three conditions: (1) self-initiated active head turns (AHT: 40° right, left, or none); (2) visually simulated head turns (SHT); and (3) visually simulated head turns with no target element (SHT_NT). Conditions 1 and 2 involved an eye-level target which subjects were instructed to fixate, whereas condition 3 was similar to condition 2 but with no target. Identical retinal flow patterns were present in the AHT and SHT conditions whereas non-visual cues differed in that a head rotation was sensed only in AHT but not in SHT. Body motions were captured by a 12-camera Vicon system. Horizontal orientations of the head and body segments, as well as the trajectory of the body's centre of mass were analyzed. SHT and SNT_NT yielded similar results. Heading and body segment orientations changed in the direction opposite to the head turns in SHT conditions. Heading remained unchanged across head turn directions in AHT. Results suggest that non-visual information is used in the control of heading while being exposed to changing rotational optic flows. The small magnitude of the changes in SHT conditions suggests that the CNS can re-weight relevant sources of information to minimize heading errors in the presence of sensory conflicts.

Preparation for reaction time tasks in multiple sclerosis

Background Sensorimotor integration can be assessed using simple reaction time tasks to somatosensory stimuli (ssRT). Tasks performed to stimuli applied to the contralateral hemibody would reveal interhemispheric transfer of information (IHT) across corpus callosum, while tasks performed when a startling-auditory stimulus (SAS) is presented together with the somatosensory cue would reveal the level of subcortical motor preparation. We studied both preparation and IHT in MS patients in whom callosal pathways and subcortical structures may be particularly involved. Methods In 13 controls and 20 mildly disabled relapsing-remitting MS patients, we studied ssRT for voluntary wrist-extension to ipsilateral and contralateral low intensity electrical stimuli, applied to the index finger. Percentage delay (PD) of contralateral vs ipsilateral responses was calculated as a measure of IHT. StartReact trials were performed applying randomly a SAS in ssRT trials (20%). Percentage shortening (SAS-Short) with respect to ssRT was calculated as a measure of the effectiveness of preparation. Motor conduction time (MCT) was assessed by recording the motor-evoked potentials to TMS. Results In controls, mean PD of contralateral responses was 105.7% longer than for ipsilateral responses. In StartReact trials, the mean SAS-Short was 29.7% for ipsilateral and 23.3% for contralateral responses. With respect to controls, patients had no differences in PD (105.4%) but showed significantly lower SAS-Short for ipsilateral (23.4%; p = 0.02) and contralateral trials (10.9%; p = 0.005). Contralateral SAS-Short was inversely correlated with MCT (r = −0.294). Two patients had abnormally delayed orbiculari-oculi responses to SAS. Conclusions Patients with MS have defective subcortical motor preparation that is worse when IHT sensorimotor integration is required.

Enhanced mirror activity in 'crossed' reaction time tasks in multiple sclerosis.

Execution of unimanual voluntary motor tasks requires appropriate inhibitory control over contralateral motor output. Such inhibition should involve interhemispheric connections, which are often damaged in multiple sclerosis (MS). Twenty mildly-disabled MS patients and 13 healthy subjects performed ipsilateral and contralateral wrist-extension reactions (IR and CR, respectively) to a unilateral somatosensory cue, the latter condition requiring necessarily interhemispheric transfer of information. Prevalence, persistence, latency and amount of mirror electromyographic activity (mEMG) were calculated in each study group, as well as diffusion-tensor-imaging measures of damage in corpus callosum and brainstem for correlation with mEMG. Healthy subjects and patients showed mEMG more often in CR than in IR. In CR tasks, mEMG was larger, more persistent and occurred more often at a shorter latency with respect to voluntary reaction in patients than in healthy subjects (p<0.05 for all). Patients with mEMG had significantly higher diffusivity values of damage in corpus callosum and lower brainstem volumes than patients without mEMG (p<0.05 for all). MS patients show deficient inhibition of unintended mEMG in 'crossed' reaction time tasks. Enhanced mEMG in MS may be due to microstructural axonal damage and atrophy in inhibitory commissural connections of the corpus callosum and brainstem.

Visual gravity contributes to subjective first-person perspective.

A fundamental component of conscious experience involves a first-person perspective (1PP), characterized by the experience of being a subject and of being directed at the world. Extending earlier work on multisensory perceptual mechanisms of 1PP, we here asked whether the experienced direction of the 1PP (i.e. the spatial direction of subjective experience of the world) depends on visual-tactile-vestibular conflicts, including the direction of gravity. Sixteen healthy subjects in supine position received visuo-tactile synchronous or asynchronous stroking to induce a full-body illusion. In the critical manipulation, we presented gravitational visual object motion directed toward or away from the participant’s body and thus congruent or incongruent with respect to the direction of vestibular and somatosensory gravitational cues. The results showed that multisensory gravitational conflict induced within-subject changes of the experienced direction of the 1PP that depended on the direction of visual gravitational cues. Participants experienced more often a downward direction of their 1PP (incongruent with respect to the participant’s physical body posture) when visual object motion was directed away rather than towards the participant’s body. These downward-directed 1PP experiences positively correlated with measures of elevated self-location. Together, these results show that visual gravitational cues contribute to the experienced direction of the 1PP, defining the subjective location and perspective from where humans experience to perceive the world.

Temporoparietal encoding of space and time during vestibular-guided orientation.

When we walk in our environment, we readily determine our travelled distance and location using visual cues. In the dark, estimating travelled distance uses a combination of somatosensory and vestibular (i.e., inertial) cues. The observed inability of patients with complete peripheral vestibular failure to update their angular travelled distance during active or passive turns in the dark implies a privileged role for vestibular cues during human angular orientation. As vestibular signals only provide inertial cues of self-motion (e.g., velocity, °/s), the brain must convert motion information to distance information (a process called 'path integration') to maintain our spatial orientation during self-motion in the dark. It is unknown, however, what brain areas are involved in converting vestibular-motion signals to those that enable such vestibular-spatial orientation. Hence, using voxel-based lesion-symptom mapping techniques, we explored the effect of acute right hemisphere lesions in 18 patients on perceived angular position, velocity and motion duration during whole-body angular rotations in the dark. First, compared to healthy controls' spatial orientation performance, we found that of the 18 acute stroke patients tested, only the four patients with damage to the temporoparietal junction showed impaired spatial orientation performance for leftward (contralesional) compared to rightward (ipsilesional) rotations. Second, only patients with temporoparietal junction damage showed a congruent underestimation in both their travelled distance (perceived as shorter) and motion duration (perceived as briefer) for leftward compared to rightward rotations. All 18 lesion patients tested showed normal self-motion perception. These data suggest that the cerebral cortical regions mediating vestibular-motion ('am I moving?') and vestibular-spatial perception ('where am I?') are distinct. Furthermore, the congruent contralesional deficit in time (motion duration) and position perception, seen only in temporoparietal junction patients, may reflect a common neural substrate in the temporoparietal junction that mediates the encoding of motion duration and travelled distance during vestibular-guided navigation. Alternatively, the deficits in timing and spatial orientation with temporoparietal junction lesions could be functionally linked, implying that the temporoparietal junction may act as a cortical temporal integrator, combining estimates of self-motion velocity over time to derive an estimate of travelled distance. This intriguing possibility predicts that timing abnormalities could lead to spatial disorientation.

Partnered Dancing to Improve Mobility for People With Parkinson's Disease.

Partnered Dancing to Improve Mobility for People With Parkinson's Disease.

When touch predicts pain: predictive tactile cues modulate perceived intensity of painful stimulation independent of expectancy

AimsNon-nociceptive somatosensory input, such as tactile or proprioceptive information, always precedes nociceptive input during a painful event. This relationship provides clear opportunities for predictive associative learning, which may shape future painful experiences. In this differential classical conditioning study we tested whether pain-associated tactile cues (conditioned stimuli; CS) could alter the perceived intensity of painful stimulation, and whether this depends on duration of the CS—seeing that CS duration might allow or prevent conscious expectation. MethodsSubjects underwent a classical differential conditioning task in which a tactile cue at location A (CS+) preceded painful electrical stimulation at location B (UShigh), whereas a tactile cue at location C (CS−) preceded non-painful electrical stimulation at location B (USlow). At test, we compared the pain evoked by a moderately painful stimulus (USmed) when preceded by either the CS+ or CS−. CS duration was manipulated between subjects. Participants were assigned to one of three groups: Long CS (4s, allowing conscious expectation), Short CS (110ms) and CS-US indistinguishable (20ms), preventing conscious expectation). We hypothesised that more pain would be evoked by the US when preceded by the CS+ relative to the CS-, and that the effect would be independent of CS duration. ResultsFifty-four healthy participants (31 females, age=26, SD=9) were included in the analysis. The hypotheses were supported in that more intense pain was evoked by the USmed when paired with the tactile CS+, than when paired with the tactile CS-; mean difference 3mm on a 150mm VAS (CI 0.4–4.8mm). CS duration did not moderate the effect. The effect was greater in those participants where calibration was optimal, as indicated by a relatively more painful UShigh. ConclusionWe conclude that pain-associated tactile cues can influence pain, and that this effect is not dependent on stimulus duration. This suggests that explicit expectation is not a requirement for predictive cues to modulate pain. That the presence of the CS+ resulted in only a 5.3% higher intensity rating compared with the CS− may reflect a limitation of laboratory studies, where a limited number of trials, an artificial context and the use of experimental pain are likely to reveal only glimpses of what is clinically possible. ImplicationsPain-associated visual and auditory cues have been shown to enhance pain in laboratory and clinical scenarios, supposedly by influencing expectation of impending harm. We show that pain-associated somatosensory cues can also modulate pain and that this can occur independently of expectation. This points to a larger potential role for associative learning in the development and treatment of pain than has previously been considered. We suggest that research into associative mechanisms underpinning pain, as distinct from those that link pain to pain-related fear and avoidance, is worthwhile.

Vestibular modulation of muscle sympathetic nerve activity by the utricle during sub-perceptual sinusoidal linear acceleration in humans

We assessed the capacity for the vestibular utricle to modulate muscle sympathetic nerve activity (MSNA) during sinusoidal linear acceleration at amplitudes extending from imperceptible to clearly perceptible. Subjects (n = 16) were seated in a sealed room, eliminating visual cues, mounted on a linear motor that could deliver peak sinusoidal accelerations of 30 mG in the antero-posterior direction. Subjects sat on a padded chair with their neck and head supported vertically, thereby minimizing somatosensory cues, facing the direction of motion in the anterior direction. Each block of sinusoidal motion was applied at a time unknown to subjects and in a random order of amplitudes (1.25, 2.5, 5, 10, 20 and 30 mG), at a constant frequency of 0.2 Hz. MSNA was recorded via tungsten microelectrodes inserted into muscle fascicles of the common peroneal nerve. Subjects used a linear potentiometer aligned to the axis of motion to indicate any perceived movement, which was compared with the accelerometer signal of actual room movement. On average, 67 % correct detection of movement did not occur until 6.5 mG, with correct knowledge of the direction of movement at ~10 mG. Cross-correlation analysis revealed potent sinusoidal modulation of MSNA even at accelerations subjects could not perceive (1.25–5 mG). The modulation index showed a positive linear increase with acceleration amplitude, such that the modulation was significantly higher (25.3 ± 3.7 %) at 30 mG than at 1.25 mG (15.5 ± 1.2 %). We conclude that selective activation of the vestibular utricle causes a pronounced modulation of MSNA, even at levels well below perceptual threshold, and provides further evidence in support of the importance of vestibulosympathetic reflexes in human cardiovascular control.

Prospective gait changes as a function of shifting perceptions of slipperiness: effects of visual and somatosensory cues

Forty participants, ages 18–45 years, rated perceived slipperiness before and after walking on five different floors under three different surface conditions. The before-ratings were taken as a proxy for visual cues to slipperiness, while after-ratings were taken as a proxy for somatosensory feedback received while walking on the surface. Before and after ratings of slipperiness were used to predict gait parameters, as a function of trial, during repeated walking. Effects of after-ratings of slipperiness were observed beginning on the second trial, and continued through the fifth trial, while effects of before-ratings of slipperiness were most apparent on the first trial. When perceived slipperiness increased (or decreased) from before to after walking on the surface, gait became more (or less) protective across trials. It is concluded that both visual cues, as well as somatosensory feedback, are used in the prospective control of gait.Practitioner Summary: Effects of visual and somatosensory cues to slipperiness on gait were disentangled using floor surfaces varying in the slipperiness suggested by those cues. Visually based ratings of slipperiness predicted gait parameters on earlier trials, while somatosensory-based ratings predicted gait parameters on subsequent trials. Flooring design should provide reliable information regarding slipperiness.