RESUMO
We studied the effect of walking on a horizontally rotating disk (circular treadmill) on the stepping test in seven normal subjects. Subjects walked for 2 hours on the perimeter of the treadmill with eyes open while remaining stationary in space. Then, off the treadmill, they attempted to step in place with eyes closed for 50 paces without turning. All subjects exhibited post-treadmill turning in the same direction as that of the previous walking relative to the treadmill. Post-treadmill average angular velocities were 207 to 880 deg/min greater than pretreadmill values. No subject experienced any sensation of motion relative to ground or space. The stepping test may no longer be considered a specific indicator of vestibulospinal function.
Assuntos
Teste de Esforço , Atividade Motora/fisiologia , Medula Espinal/fisiologia , Núcleos Vestibulares/fisiologia , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , RotaçãoRESUMO
Recent studies identified an adaptive "Podokinetic" (PK) sensory motor system involved in sensing and controlling spatial orientation during locomotion, by referencing body orientation to the space-stable stance foot. This paper investigates the interaction of vestibular and PK systems by asking blindfolded subjects to 'step-in-place' (i.e. without turning) after exposing them to a unidirectional post-rotational vestibular stimulus. Six of the nine subjects consistently began by vigorously propelling themselves round in the direction of preceding turntable rotation, but notably without any sensation of turning. In all these subjects the speed of this PK-induced rotation progressively declined to zero over about the next 30 sec and then reversed direction with increasing speed for about 50 sec. Thereafter the speed of rotation declined slowly to zero over the next 4 to 5 minutes. Since the PK-generated body rotation presumably feeds back into the vestibular-PK drive, we formulated a closed loop model of the combined system to investigate the complex nature of the behavioral response. The simulated response of this model closely resembled the experimental data, suggesting that there is indeed a functionally closed loop operating between the vestibular and podokinetic systems in natural life.
Assuntos
Movimento/fisiologia , Equilíbrio Postural/fisiologia , Percepção Espacial/fisiologia , Nervo Vestibular/fisiologia , Adulto , Vias Aferentes/fisiologia , Idoso , Vias Eferentes/fisiologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Orientação/fisiologia , Desempenho Psicomotor/fisiologia , Rotação , Privação Sensorial/fisiologia , Comportamento Espacial/fisiologia , Vestíbulo do Labirinto/fisiologiaRESUMO
After prolonged stepping in place relative to space over the center of a rotating turntable, blindfolded subjects cannot step on the stationary platform without unknowingly turning themselves relative to space, a phenomenon termed podokinetic after rotation (PKAR). We asked what role the resulting vestibular stimulation might play in the expression of this form of PKAR. A method of servo-stabilizing the body relative to space during PKAR was devised to compare PKAR expression with and without significant vestibular stimulation. Simulated estimates of average central vestibular response profiles were obtained by passing the averaged unidirectional body angular velocity profiles relative to space through a first-order model of the canal system (tau=15 s). Such simulation results suggested that during normal PKAR performed on a stationary platform, the average central vestibular response would likely rise to peak levels equivalent to that induced by about 9 degrees /s within the frequency range of natural head movement. In the servo-stabilized condition, the simulated response was reduced to insignificant levels. Experimental results demonstrated that in the unstabilized condition the rate of rise of PKAR angular velocity was roughly four times slower than in the stabilized condition. We conclude that the normal expression of PKAR conducted on a stationary platform tends to be substantially slowed by interaction with an unperceived vestibular response.
Assuntos
Pé/fisiologia , Percepção/fisiologia , Equilíbrio Postural/fisiologia , Vestíbulo do Labirinto/fisiologia , Fenômenos Biomecânicos , Interpretação Estatística de Dados , HumanosRESUMO
Previous studies investigated adaptive properties of a podokinetic (PK) system that senses and controls angular movement of the trunk relative to the stance foot when walking around a curved trajectory or during rotational stepping on the spot. In particular, after adaptively modifying the PK system by prolonged stepping-in-place over the axis of a horizontally rotating platform, blind-folded subjects could no longer step in place on firm ground. When trying to do so they invariably rotated themselves relative to space without perceiving their rotation, a phenomenon termed podokinetic after-rotation (PKAR). It is well known that normal rotational stepping generates a specifically podokinetic component of compensatory nystagmus which is independent of the VOR. The present study investigated whether during PKAR this podokinetic component of oculomotor activity follows the somatosensory correlate of actually stepping around, or the cognitive intent or percept of 'no rotation'. Experiments were conducted in two phases on five normal human subjects. In the first phase, the normal passively induced VOR was compared with the combined VOR and PK oculomotor response induced by intentional rotational stepping on the spot. In both cases the angular stimulus was a 2-min rotation at 15 degrees/s. Subtraction of the decaying VOR from the actively induced combined response revealed a constant podokinetic nystagmus with slow-phase velocity gain of about 0.4 maintained throughout this period. The PK and VOR response components appeared to sum linearly. In the second phase, we measured oculomotor activity during PKAR, when the blindfolded subjects involuntarily rotated themselves at around 15 degrees/s while attempting to step-in-place after the podokinetic adaptation procedure noted above. The striking result of the second phase of experiments was that, although an apparently normal decaying VOR was present, the maintained PK component of response was consistently absent, despite an essentially normal physical pattern of rotational stepping. Thus, in the adapted state, non-vestibular oculomotor activity followed the cognitive intent or percept of 'no rotation', rather than the prevailing somatosensory-motor activity of the lower limbs. The finding points to an important cognitive element in this form of oculomotor control.
Assuntos
Adaptação Fisiológica/fisiologia , Marcha/fisiologia , Nervo Oculomotor/fisiologia , Reflexo Vestíbulo-Ocular/fisiologia , Adulto , Idoso , Cognição/fisiologia , Movimentos Oculares/fisiologia , Movimentos da Cabeça/fisiologia , Humanos , Pessoa de Meia-Idade , Percepção de Movimento/fisiologia , Orientação/fisiologia , Desempenho Psicomotor/fisiologia , Rotação , Privação Sensorial/fisiologiaRESUMO
Previous studies showed that after stepping-in-place on a rotating turntable, blindfolded subjects cannot step-in-place on firm ground. Instead they involuntarily turn themselves relative to space in the same direction as they were turning relative to the rotating turntable. This phenomenon has been termed podokinetic after-rotation (PKAR). PKAR comprises a brief exponentially rising phase of response during the first 2 min followed by a prolonged second phase of slow exponential decline during the next 28 min. Here we ask whether PKAR is modified in patients with compensated unilateral vestibular loss. Eleven patients who had previous vestibular ablation underwent (1) a Fukuda-like control stepping test, (2) podokinetic adaptation to 30 min of stepping in place on the centre of a turntable rotating at 45 deg/s and (3) PKAR. Control tests showed that the blindfolded patients had no significant rotational bias while stepping-in-place on the ground for 1 min. After 30 min of adaptation, the 2-min rising phase of PKAR was indistinguishable from normal. In contrast, the subsequent 28-min phase of exponential decline showed a lesion-dependent asymmetry. PKAR had significantly higher mean velocities toward the side of the lesion than away from the lesion. The observed PKAR asymmetry may signify occult residual static vestibular imbalance.
Assuntos
Percepção de Movimento , Atividade Motora , Percepção Espacial , Doenças Vestibulares/fisiopatologia , Adulto , Humanos , Pessoa de Meia-Idade , Rotação , Fatores de TempoRESUMO
Eight human subjects were exposed to 2 h of walking on the perimeter of a horizontally rotating disc with the body remaining still in space. After adaptation to this experience subjects were blindfolded and asked to walk straight ahead on firm ground. When doing so all subjects generated curved walking trajectories of radii ranging from 65 to 200 inches and angular velocities from 7 to 20 deg/s. Subsequent trials over the next half hour revealed retained, but decreasing, trajectory curvature. Angular velocities associated with these trajectories were well above vestibular sensory threshold, yet all subjects consistently perceived themselves as walking straight ahead. The blindfolded subjects were also asked to propel themselves in a straight line in a wheel chair. Post-adaptation wheel chair trajectories showed no change from those before adaptation. Hence we infer that it was the relation between somatosensory/motor elements of gait and the perception of trunk rotation that had been remodelled during walking on the turning disc. This novel form of adaptive plasticity presumably serves to maintain optimal values of central neural parameters that control the trajectory of locomotion. The findings may have significant implications for the diagnosis and rehabilitation of locomotor and vestibular disorders.
Assuntos
Adaptação Fisiológica/fisiologia , Locomoção/fisiologia , Plasticidade Neuronal/fisiologia , Orientação/fisiologia , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Percepção Espacial/fisiologia , Caminhada , Cadeiras de RodasRESUMO
The increasing demand for sterilization as a permanent and effective form of birth control leads one to consider the various methods available to achieve this end. Tubal cauterization and excision by laparoscopy appears to be a safe, efficient method.The technique used is carefully reviewed step by step. The absence of major complications in this series of 115 consecutive laparoscopies certainly supports the safety of the procedure. The low morbidity, short hospital stay and minimal time required appeal particularly to the working mother. The absence of an abdominal scar is also much appreciated. The procedure, when used for investigation of infertility, provides far more information than other current methods.
Assuntos
Infertilidade Feminina/diagnóstico , Laparoscopia , Esterilização Tubária , Adulto , Eletrocoagulação , Feminino , Humanos , Laparoscópios , Métodos , Esterilização Tubária/instrumentação , Instrumentos CirúrgicosRESUMO
We asked whether podokinetic adaptation to walking on a circular treadmill transfers to different forms of locomotion. Subjects were blindfolded and asked to walk straight across the floor, in the forward and backward directions, following podokinetic (PK) stimulation that consisted of 30 min of forward walking-in-place on the perimeter of a disk rotating in the clockwise direction. During both forward and backward walking following forward-walking PK stimulation, subjects involuntarily walked along curved trajectories at angular velocities well above vestibular threshold, although they perceived that they were walking along straight paths. The curved paths of forward and backward walking were indistinguishable from one another. Transfer of PK adaptations acquired during forward walking on the turntable to backward walking trials suggests that the PK system controls general locomotor trajectory. Adaptation of the system thus influences forms of locomotion other than that used during acquisition of the adaptation. This transfer also supports the concept that forward and backward walking are controlled by neural networks that share common elements. An interesting feature of the transfer of PK adaptation is that for both forward and backward walking, subjects turned in a counterclockwise direction. As such, the direction of relative rotation between the trunk and feet was maintained for both forward and backward walking. However, the relationship of the lower extremities to the center of rotation was not preserved. The left limb was the inner leg during PK stimulation and forward walking after adaptation, but the left leg was the outer leg during backward walking. These results suggest that PK adaptation affects general locomotor trajectory via a remodeling of the rotational relationship between the trunk and the feet.
Assuntos
Adaptação Fisiológica/fisiologia , Marcha/fisiologia , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Desempenho Psicomotor/fisiologia , Vestíbulo do Labirinto/fisiologia , Caminhada/fisiologiaRESUMO
Previous studies demonstrated an aftereffect of walking on a rotating treadmill, involving inadvertent circular navigation with eyes closed [podokinetic after-rotation (PKAR)]. We compared PKAR following unilateral and bilateral podokinetic (PK) stimulation to determine whether the left and right legs could be independently adapted. Each subject performed two sessions of PK stimulation, stepping in place with one foot on either side of the axis of a rotating disk. Subjects experienced bilateral stimulation (i.e., both left and right feet stepped on the rotating disk) in one session and unilateral stimulation (i.e., the left foot stepped on the rotating disk and the right foot stepped on a stationary surface) in the other. Following stimulation, we recorded foot lift-off and touchdown times and pelvic angular velocity while subjects stepped in place on a stationary surface. PKAR velocity following unilateral stimulation was lower than that following bilateral stimulation. Following bilateral stimulation, pelvic rotation was in the counterclockwise (CCW) direction during single-limb support on both the left and right sides. Immediately following left unilateral stimulation, subjects demonstrated CCW pelvic rotation during left single-limb support but not during right single-limb support. Across the first 13 strides, the difference between left and right sides diminished; pelvic angular velocity was then CCW during single-limb support on both sides. This suggests that both the adapted left and the unadapted right limb influenced the final PKAR response with information from the two limbs being integrated over the first few strides.
Assuntos
Lateralidade Funcional/fisiologia , Marcha/fisiologia , Postura/fisiologia , Adaptação Fisiológica/fisiologia , Adulto , Idoso , Fenômenos Biomecânicos , Humanos , Pessoa de Meia-Idade , Caminhada/fisiologiaRESUMO
Following stepping in-place on the surface of a rotating circular treadmill, a subject attempting to step in-place or walk in a straight line across the floor without vision will rotate relative to space. This adaptation, termed podokinetic after-rotation (PKAR), transfers to backward walking following forward walking on the rotating disk. We asked whether adaptation obtained during stepping in-place on the rotating disk would transfer to hopping on both feet. We hypothesized that subjects would demonstrate PKAR during both hopping and stepping, adding support to the hypothesis that PKAR is a centrally mediated adaptation of general locomotor trajectory that is not specific to the form of locomotion used while on the rotating disk. Subjects demonstrated PKAR during both hopping and stepping after stepping in-place on the rotating disk. The time courses of PKAR during hopping and stepping were similar, although the angular velocity amplitude of PKAR was lower in hopping than in stepping. This difference in amplitude suggests an incomplete transfer of PKAR.
Assuntos
Adaptação Fisiológica/fisiologia , Marcha/fisiologia , Adulto , Idoso , Feminino , Lateralidade Funcional/fisiologia , Humanos , Masculino , Pessoa de Meia-Idade , Caminhada/fisiologiaRESUMO
The present study characterizes a previously reported adaptive phenomenon in a somatosensory-motor system involved in directional control of locomotor trajectory through foot contact with the floor. We call this the "podokinetic" (PK) system. Podokinetic adaptation was induced in six subjects by stepping in-place over the axis of a horizontally rotating disc over a range of disc angular velocities (11.25-90 degrees/s) and durations (7.5-60 min). After adaptation, subjects were blindfolded and attempted to step in-place on the floor without turning. Instead they all rotated relative to space. The rate of the "podokinetic afterrotation" (PKAR) was linearly related to stimulus amplitude up to 45 degrees/s, and the ratio of initial PKAR velocity to that of the adaptive stimulus was approximately 1:3. PKAR exhibited exponential decay, which was composed of "short-" and "long-term" components with "discharging" time constants on the order of 6-12 min and 1-2 h, respectively. The effect of stimulus duration on PKAR revealed a "charging" time constant that approximated that of the short-term component. A significant suppression of PKAR occurred during the 1 st min of the postadaptive response, suggesting functional interaction between the PK and vestibular systems during the period of vestibular stimulation. During PKAR subjects perceived no self-rotation, indicating that perception as well as locomotor control of spatial orientation were remodeled by adaptation of the PK system.