Biomedical subjects

R Grasso

Publications and source records attributed to R Grasso.

At least 37 records · Page 2Linked to original sources

PubMed1999

Effect of gaze on postural responses to neck proprioceptive and vestibular stimulation in humans.

1. We studied the effect of gaze orientation on postural responses evoked by vibration of neck dorsal muscles or by galvanic stimulation of the vestibular system during quiet standing in healthy humans. Various gaze orientations were obtained by different combinations of horizontal head-on-feet (-90, -45, 0, 45, 90 deg) and eye-in-orbit (-30, 0, 30 deg) positions. The instantaneous centre of foot pressure was recorded with a force platform. 2. With a symmetrical position of the vibrator relative to the spine, neck muscle vibration elicited a body sway in the direction of the head naso-occipital axis when the eyes were aligned with it. The same result was obtained both during head rotations and when the head and trunk were rotated together. 3. For lateral eye deviations, the direction of the body sway was aligned with gaze orientation. The effect of gaze was present both with eyes open and eyes closed. After long-lasting (1 min) lateral fixation of the target the effect of gaze decreased significantly. 4. Postural responses to galvanic vestibular stimulation tended to occur orthogonal to the head naso-occipital axis (towards the anodal ear) but in eight of the 11 subjects the responses were also biased by the direction of gaze. 5. The prominent effect of gaze in reorienting automatic postural reactions indicates that both neck proprioceptive and vestibular stimuli are processed in the context of visual control of posture. The results point out the importance of a viewer-centred frame of reference for processing multisensory information.

Adult↗

PubMed1999

Replication of passive whole-body linear displacements from inertial cues. Facts and mechanisms.

Using path integration, normal subjects should be able to compute the distance of a traveled path even from the sole inertial sensory input. Blindfolded subjects were submitted to a passive linear forward displacement along 2 to 10 m. Their task was to replicate the traveled distance, still blindfolded, by driving the vehicle they were seated upon using a joystick that controlled linear speed. Subjects replicated both the length and the velocity profile of the passive travel, suggesting that a dynamic record of experienced motion is stored in memory. Even when the replication of passive motion dynamics was made impossible, the subjects could still replicate the displacement. The results are explained by a dynamic feedback model that performs a running comparison between the perceived instantaneous displacement of the ongoing motion and the displacement derived from a spatiotemporal record of perceived passive motion. A multimodal acceleration-related sensory input is transformed into a displacement-related perception through double time-integration.

Adult↗

PubMed1999

Basal ganglia and gait control: apomorphine administration and internal pallidum stimulation in Parkinson's disease.

Gait coordination was analyzed (four-camera 100 Hz ELITE system) in two groups of idiopathic Parkinson disease (PD) patients. Five patients underwent continuous infusion of apomorphine and were recorded in two different sessions (APO OFF and APO ON) in the same day. Three patients with a previous chronic electrode implantation in both internal globi pallidi (GPi) were recorded in the same experimental session with the electrodes on and off (STIM ON and STIM OFF). The orientation of both the trunk and the lower-limb segments was described with respect to the vertical in the sagittal plane. Lower-limb inter-segmental coordination was evaluated by analyzing the co-variation between thigh, shank, and foot elevation angles by means of orthogonal planar regression. At least 30 gait cycles per experimental condition were processed. We found that the trunk was bent forward in STIM OFF, whereas it was better aligned with the vertical in STIM ON in both PD groups. The legs never fully extended during the gait cycle in STIM OFF, whereas they extended before heel strike in STIM ON. The multisegmental coordination of the lower limb changed almost in parallel with the changes in trunk orientation. In STIM OFF, both the shape and the spatial orientation of the planar gait loops (thigh angle vs. shank angle vs. foot angle) differed from those of physiological locomotion, whereas in STIM ON the gait loop tended to resume features closer to the control. Switching the electrodes on and off in patients with GPi electrodes resulted in quasi-parallel changes of the trunk inclination and of the planar gait loop. The bulk of the data suggest that the basal-ganglia circuitry may be relevant in locomotion by providing an appropriate spatio-temporal framework for the control of posture and movement in a gravity-based body-centered frame of reference. Pallido-thalamic and/or pallido-mesencephalic pathways may influence the timing of the inter-segmental coordination for gait.

Aged↗

PubMed1999

Non-specific directional adaptation to asymmetrical visual-vestibular stimulation.

Subjective estimates of passive whole-body rotations in darkness were evaluated before and after exposure to asymmetrical incoherent visual-vestibular stimulation (VVS). Two subjects who showed large capacity for adaptation to symmetrical incoherent VVS were enrolled in the study. Strikingly, after 45 min of asymmetrical left-right VVS, perception of rotation decreased equally for rotations to the right and to the left indicating that the calibration of vestibular sensory input for spatial orientation did not undergo a directional specific control.

Acoustic Stimulation↗

PubMed1999

Manometric study of hiatal hernia and its correlation with esophageal peristalsis.

The pathogenesis of gastroesophageal reflux disease (GERD) is considered multifactorial, but alterations of the esophagogastric junction (EGJ) and hiatal hernia play a prominent role. The correlations between hiatal hernia and the other pathogenetic factors are as yet unclear, and they need to be investigated by a methodological approach based on new anatomic and functional criteria. Our aim was to study, by stationary manometry, the relationships between small reducible hiatal hernia, identified by endoscopy, and esophageal peristalsis, in patients with and without GERD. According to the absence or presence of esophagitis (E), and the absence or presence of hiatal hernia (H), 58 subjects were divided into four groups: controls 10; H 14; E 10; and HE 24. Stationary manometry was performed by the rapid pull-through (RPT) technique, with catheter water perfused, to study the lower esophageal high pressure zone [lower esophageal sphincter (LES) and diaphragmatic crura] and the parameters of esophageal peristalsis. In patients with hiatal hernia, the various combinations of peak and/or deflection of manometric line pressure identified five EGJ profiles, only one of which reveals (by one-peak profile due to superimposed LES and diaphragmatic crura) the reducibility of the hernia. The frequency of the five profiles was calculated in the HE and H groups: a two-peak profile was significantly more prevalent in these patients, although less so in the group with esophagitis. In E patients the distal amplitude and the distal propagation of esophageal waves were significantly lower than in the other three groups (P < 0.05 vs controls and group HE; P < 0.01 vs group H). Furthermore, the distal amplitude was significantly higher in the group H than in the HE (P < 0.01). Our results show a better definition of hiatal hernia morphology, via the RPT technique, disclosing five pressure profiles. In addition, a significant link was found between small reducible hiatal hernia without GERD and wave amplitude of the distal esophagus. The amplification of peristaltic clearing may be considered the initial protective process against acid reflux; the breakdown of this mechanism may trigger the pathological sequence of GERD.

Adult↗

PubMed1998

Eye-head coordination for the steering of locomotion in humans: an anticipatory synergy.

We investigated head and gaze orientation in six healthy volunteers walking along 90 degrees corner trajectories, both at light and with eyes closed. We found that head and eyes systematically deviated toward the future direction of the curved trajectory. Anticipation lead was about 1 s. Strikingly, the same behaviour was observed in darkness. In backward (BW) locomotion along the trajectory (from end- to start-point), gaze deviated toward the opposite direction, such that the forward locomotor pattern did not appear time-reversed. Orienting movements displayed higher amplitude, reproducibility and time lead in the forward (FW) direction at light. We suggest that anticipatory orienting synergies belong to the behavioural repertoire of human navigation and may reflect the need to prepare a stable reference frame for intended action.

Adult↗

PubMed1998

Development of anticipatory orienting strategies during locomotor tasks in children.

Some basic problems related to the development of goal-directed locomotion in humans are reviewed here. A preliminary study is presented which was aimed at investigating the emergence of anticipatory head orienting strategies during goal-directed locomotion in children. Eight children ranging from 3.5 to 8 years had to walk along a 90 degrees right corner trajectory to reach a goal, both in light and in darkness. The instantaneous orientation in space of the head, trunk, hips and left foot antero/posterior axes was computed by means of an ELITE four-TV camera, 100 Hz system. The results showed that predictive head orienting movements can occur also in the youngest children. The head starts to rotate toward the goal before the corner point of the trajectory is reached. In children, the head peak rotation coincides with the trajectory corner while in adults the peak is attained before. In children, the walking speed is largely decreased in darkness. The results suggest that feedforward control of goal-directed locomotion appears very early in gait development and becomes increasingly important afterwards.

Adult↗

PubMed1998

Motor patterns for human gait: backward versus forward locomotion.

Seven healthy subjects walked forward (FW) and backward (BW) at different freely chosen speeds, while their motion, ground reaction forces, and electromyographic (EMG) activity from lower limb muscles were recorded. We considered the time course of the elevation angles of the thigh, shank, and foot segments in the sagittal plane, the anatomic angles of the hip, knee, and ankle joints, the vertical and longitudinal ground reaction forces, and the rectified EMGs. The elevation angles were the most reproducible variables across trials in each walking direction. After normalizing the time course of each variable over the gait cycle duration, the waveforms of all elevation angles in BW gait were essentially time reversed relative to the corresponding waveforms in FW gait. Moreover, the changes of the thigh, shank, and foot elevation covaried along a plane during the whole gait cycle in both FW and BW directions. Cross-correlation analysis revealed that the phase coupling among these elevation angles is maintained with a simple reversal of the delay on the reversal of walking direction. The extent of FW-BW correspondence also was good for the hip angle, but it was smaller for the knee and ankle angles and for the ground reaction forces. The EMG patterns were drastically different in the two movement directions as was the organization of the muscular synergies measured by cross-correlation analysis. Moreover, at any given speed, the mean EMG activity over the gait cycle was generally higher in BW than in FW gait, suggesting a greater level of energy expenditure in the former task. We argue that conservation of kinematic templates across gait reversal at the expense of a complete reorganization of muscle synergies does not arise from biomechanical constraints but may reflect a behavioral goal achieved by the central networks involved in the control of locomotion.

Adult↗

PubMed1997

The contribution of otoliths and semicircular canals to the perception of two-dimensional passive whole-body motion in humans.

1. Perception of two-dimensional (2-D) whole-body passive motion in the horizontal plane was studied in twelve blindfolded healthy volunteers: pure rotation in place (180 deg), linear motion (4.5 m) and a semicircular trajectory (radius, 1.5 m; angular acceleration, 0.2 rad s-2) were applied in random sequence by means of a remote-controlled robot equipped with a racing-car seat. The seat orientation in the horizontal plane was controlled by the experimenter, independent of the robot trajectory. Thus different degrees of otolith-canal interaction were obtained. The maximal linear acceleration during the semicircular trajectory was 0.1 g; however, the linear acceleration vector was complex as it rotated relative to the subject's head. 2. In the first of two sessions, subjects were instructed to maintain an angular pointer oriented towards a remote (15 m) previously seen target during the passive movements. In the second session they had to make a drawing of the path of the perceived trajectory, after the movement was finished. 3. The results showed that, on average, the movement of the pointer matched the dynamics of the rotatory component of the 2-D motion well. This suggests that, in the range of linear accelerations used in this study, no appreciable influence of otolith input on canal-mediated perception of angular motion occurred. 4. The curvature of the drawn paths was mostly explained by the input to the semicircular canals. Subjects' reconstruction of motion did not account for the directional dynamics of the input to the otoliths occurring during passive motion. 5. This finding proves that reconstructing trajectory in space does not imply a mathematically perfect transformation of the linear and angular motion-related inputs into a Cartesian or polar 2-D representation. Physiological constraints on the interaction between motion direction and change of heading play an important role in motion perception.

Acceleration↗

PubMed1997

Does low-frequency variability of heart period reflect a specific parasympathetic mechanism?

Low frequency (LF, approximately 0.1 Hz) spontaneous oscillations of heart period in humans have been attributed to and correlated with the sympathetic efferent control of the heart. However, this interpretation is controversial, because sympathetic blockade does not suppress these oscillations, while parasympathetic blockade strongly affects them. The sympathetic origin of LF of arterial pressure, on the contrary, has been convincingly demonstrated. Four 10 min cycle-by-cycle time series of R-R interval (RR), and systolic (SAP) and diastolic (DAP) arterial pressure were produced by automatic analysis of data obtained with non-invasive methods in 10 healthy humans during supine rest and while standing, both before and after beta 1-selective blockade (atenolol). Time series were analysed by autoregressive transfer function analysis. beta-blockade failed to induce systematic changes on the power of the LF peak of RR, in any condition. The coherence between RR and SAP in the same region remained high (0.77 +/- 0.03) and a constantly negative phase (approximately 50-60 degrees, corresponding to a delay of 1-2 heart beats of RR on SAP) was always seen. beta-blockade decreased the power of the LF peak of SAP, increased the transfer function gain between SAP and RR at LF, and the HF power of RR. We conclude that LF oscillations of RR are not directly generated by the sympathetic drive to the heart but reflect mainly the parasympathetic activity. The results suggest that the LF oscillations of the vagal outflow, and of RR, are generated by the baroreceptor reflex, driven by sympathetically-induced blood pressure LF waves.

Adrenergic beta-Antagonists↗

PubMed1997

Circular trajectory formation during blind locomotion: a test for path integration and motor memory.

Eight healthy subjects were asked to walk blindfolded along circular paths of different radii after several practice trials with vision. Their task was to stop after completing two full revolutions. They always walked counter-clockwise (CCW) in (a) a control condition (CONTROL), including the instructions mentioned above, (b) with the further instruction to count backwards in twos (MENTAL), (c) with the instruction to count loudly (LOUD). The movement of two markers lying along the head naso-occipital axis was recorded by means of an ELITE system. Total walked distance (DISTANCE), total head turning angle (ANGLE) and average radius (RADIUS) of the trajectories performed were measured. All subjects were able to perform approximately circular trajectories. They consistently overshot the ideal radius independently of the condition and circle size, undershot the total angle and overshot total distance. The LOUD condition induced greater errors in the performance but only on total distance (P<0.05). A strong correlation was found between the errors in radius and total distance but not between distance and total angle. Principal components analysis suggested that radius and distance share a common source of errors while total angle produced independent errors. The results indicate that (a) circular trajectories can be generated starting from spatial and/or motor memory, without the aid of visual information; (b) the task needs some attentional control and does not involve simple automatic processing of afferent information; (c) different sensory information or different processing modes are probably involved in the estimation of the curvature and length of the walked path on the one hand, and of the total rotation angle on the other.

Adult↗

PubMed1997

Spatial orientation in humans: perception of angular whole-body displacements in two-dimensional trajectories.

Vestibular perception of whole-body passive rotation in the horizontal plane was studied by applying two-dimensional (2D) motion to eight blindfolded healthy volunteers: pure rotations in place, corner-like trajectories and arcs of a circular trajectory were randomly applied by means of a remotely controlled robot. Angles embedded in the 2D trajectories were 45 degrees, 90 degrees, 135 degrees and 180 degrees. Stimulation of semicircular canals was the same for all trajectories but was accompanied by concurrent otolith stimulation during circular motion. Subjects participated in two successive experimental sessions. In the first session they were instructed to use a pointer to reproduce the total angular displacement after the motion (REPRODUCTION); in the second session they had to keep pointing towards a remote (15 m) memorised target during the motion (TRACKING). In REPRODUCTION subjects tended to overestimate their rotation angle by 28 +/- 11% (mean +/- SD). There was no systematic effect of the trajectory. Overestimation also occurred when subjects were required to rotate in darkness by 180 degrees (by controlling a joystick). In TRACKING there was virtually no overestimation (6 +/- 17%) and the movement of the pointer matched the dynamics of angular motion. We conclude that (a) the brain can separate and memorise the angular component of complex 2D motion; however, a large inter-individual variability in estimating its amplitude exists; (b) in the range of linear accelerations used in the study, no appreciable effect of otolith-canal perceptual interaction was shown; (c) angular displacements can be dynamically transformed into matched pointing movements; (d) overestimation seems to be typical of delayed judgements of angular displacement and of self-controlled rotations in place. This could be due to the characteristics of the physiological calibration of the vestibular input.

Humans↗

PubMed1997

Integration of somatosensory and vestibular inputs in perceiving the direction of passive whole-body motion.

We investigated the contribution of somatosensory and vestibular inputs in the detection of the direction of linear whole-body displacement (1.5 m) at low levels of linear acceleration (peak acceleration 0.2 m/s2), in normal subjects. Subjects sat on a mobile robot wearing opaque goggles and headphones. They indicated the direction of motion by using a laser pointer held by the right hand at the level of the chin. Adaptation to a long-lasting static head turn (45 degrees to the right) was used to modify the perceived head orientation relative to the trunk. After about 15 min the head and trunk were perceived to be aligned with each other. After adaptation subjects pointed in the same direction as in the control condition in spite of the change in the perception of the head orientation. Because space orientated reactions to vestibular stimuli were previously shown to be coded in the perceived head reference frame, these results indicate that somatosensory cues are also integrated in the perception of linear motion. Unexpectedly, after adaptation, trunk and head perceived orientations were attracted toward the direction of the imposed motion. This suggests that the internal representation of body configuration depends also upon available cues from the extrapersonal space.

Head↗

PubMed1997

Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties.

According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by passive transport can be used to build a dynamic as well as a static representation of the traveled path. We found a close quantitative similarity between the present findings on distance reproduction and those obtained from active locomotion experiments in which the same paradigm was used. This resemblance suggests that the two types of navigation tasks draw on common physiological processes and extends the relevance of our results to naturally occurring path integration.

Acceleration↗

PubMed1996

The predictive brain: anticipatory control of head direction for the steering of locomotion.

The control of head direction in humans walking along planned circular trajectories was investigated in this study. Five healthy volunteers were asked to walk at a constant speed along circular trajectories in the light and while blindfolded. Head and walking directions were analysed on a real-time basis. Head direction systematically anticipated changes in the direction of locomotion (by about 200 ms). The anticipation interval depended on the curvature of the circle. In the light, head orientation was deviated with respect to the walking direction, toward the inner concavity of the performed trajectory. The results suggest that head direction is controlled on a step-by-step basis in a predictive fashion. A 'go where you look' strategy seems to underlie steering along circular trajectories.

Adult↗

PubMed1996

Quantitative analysis of human walking trajectory on a circular path in darkness.

Thirteen normal (eight young and five older) subjects and a patient who was removed left sided acoustic neurinoma were tested to walk blindfolded along circular paths. They were asked to walk completing two revolutions and to stop when they judged they had returned to the initial position with their head faced to the initial directions. Movements of two markers on the subjects head were recorded by three dimensional motion analyzing system (ELITE system) at 50 Hz which allowed us to measure (a) total walked distance, (b) average radius of the trajectory, and (c) cumulative angle of rotation. Eight young subjects were tested on three circles with radii 0.5, 0.9, and 1.15 m, in two conditions (control, and with mental arythmetic), only to clockwise direction. Five older subjects and a patient were tested on a circle of 0.9 m radius in two conditions, but to both directions, counterclockwise and clockwise. Walked trajectories of young subjects were smooth, whereas those of older subjects tended to be polygonal. Young subjects overshot the ideal distance (6.6%) and ideal radius (9.5%), whereas they undershot the ideal angle (5.1%). There was no effect of circle size or condition on these variables. On the other hand, there was a significant effect of condition on average radius in the older group. The performance of older subjects seemed to be affected by the concurrent mental task. Comparing the counterclockwise walk, the older subjects undershot the turning angle much more than the young subjects which suggest deficits in the vestibular function with aging. The patient showed larger radius and smaller angle while she turned to the healthy side (clockwise) than to the affected side (counterclockwise). Lack of unilateral vestibular information seemed to have affected the circular walking trajectory.

Adult↗

PubMed1995

Spatial memory of body linear displacement: what is being stored?

The ability to evaluate traveled distance is common to most animal species. Head trajectory in space is measured on the basis of the converging signals of the visual, vestibular, and somatosensory systems, together with efferent copies of motor commands. Recent evidence from human studies has shown that head trajectory in space can be stored in spatial memory. A fundamental question, however, remains unanswered: How is movement stored? In this study, humans who were asked to reproduce passive linear whole-body displacement distances while blindfolded were also able to reproduce velocity profiles. This finding suggests that a spatiotemporal dynamic pattern of motion is stored and can be retrieved with the use of vestibular and somesthetic cues.

Acceleration↗

PubMed1995

Arterial baroreceptors are not essential for low frequency oscillation of arterial pressure.

Cardiovascular parameters exhibit spontaneous oscillations at the respiratory frequency, and in the low frequency range (LF < 0.20 Hz). Although LF is attributed to the sympathetic control, the mechanism responsible for the oscillation, whether instability of the baroreflex loop, or activity of a central nervous system pattern generator, is controversial. To answer this question, time series of arterial blood pressure, heart period and left external iliac blood flow from chloralose-anaesthetised dogs were examined by standard statistics as well as by autoregressive spectral and cross-spectral analysis. The circulation to the left hind-limb was isolated and connected to a constant-pressure perfusing system, to obtain mechanical uncoupling from the central circulation. Three steady-state conditions were studied. A device inserted into the common carotid arteries allowed the carotid sinus region to be in continuity with the animal's arterial system (CONTROL) or perfused at constant pressure by an external source (CAROTID BUFFER); bilateral cervical vagotomy was also performed (VAGI CUT). Intra-individual (beat-to-beat) variability of each parameter was evaluated by standard deviation (SD) of time series in the three conditions. The average SD of heart period was reduced in CAROTID BUFFER and in VAGI CUT; the SDs of arterial pressure and iliac flow were not changed by these interventions. Autospectra of iliac flow time series in CONTROL showed a prominent peak at 0.05 +/- 0.04 Hz (mean +/- SD of all experiments), accounting for 90 +/- 11% of the total variance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗