RESUMEN
Sensory input from the semicircular canals (SCC) and otolith organs is centrally combined with signals from other sensory modalities to continuously update the internal estimate of self-motion. Constant velocity vertical on-axis rotation leads to decay of the nystagmus response from the horizontal SCC and of perceived angular velocity (PAV), and when the rotation stops, a similar oppositely directed post-rotatory response occurs. Case reports and electrical stimulation studies suggest an involvement of the temporo-peri-Sylvian vestibular cortex in generating the PAV. Here, we transiently inhibited the right superior temporal gyrus (STG) by use of continuous theta-burst stimulation (cTBS) and predicted an accelerated decay of PAV compared to controls (n = 5 control session first, n = 1 cTBS session first). Constant velocity (100°/s) vertical on-axis rotations were applied over 75 s before (1 block) and after (3 blocks) cTBS over the right STG in six subjects. Breaks between the rotations (75 s) were initiated by abrupt stops. By use of a rotating potentiometer, subjects indicated the PAV during and after the chair rotations. Simultaneously eye positions were recorded using a scleral search coil. One subject was excluded for per-rotary analysis. Early after cTBS, the post-rotary PAV decay time constant (DTC) was significantly (9.4 ± 5.7 vs. 13.6 ± 5.9 s; p = 0.049) reduced (no directionality to this effect observed). Overall, post-rotary PAV showed a trend toward shortened DTC compared to the control trials (p = 0.086) in the first 25 min after cTBS, while per-rotary PAV was not significantly changed. Per-rotary and post-rotary aVOR DTC were not significantly changed after cTBS (p > 0.05). These findings support the hypothesis that the right STG is involved in mediating self-motion perception and can be modulated by cTBS.
Asunto(s)
Movimientos Oculares/fisiología , Percepción de Movimiento/fisiología , Reflejo Vestibuloocular/fisiología , Lóbulo Temporal/fisiología , Estimulación Magnética Transcraneal , Aceleración , Adulto , Anciano , Interpretación Estadística de Datos , Femenino , Humanos , Modelos Lineales , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Corteza Motora/fisiología , Músculo Esquelético/fisiología , Membrana Otolítica/fisiología , Estimulación Física , Proyectos Piloto , Rotación , Encuestas y CuestionariosRESUMEN
Previous studies reported linear drift of perceived vertical for brief (≤10 min) observation periods. Here, we repeated estimates of direction of gravity up to 60 min to evaluate whether the drift is sustained, shows saturation or even reverses over time. Fifteen healthy human subjects repetitively adjusted a luminous line along subjective visual vertical (SVV) and horizontal (SVH) over periods of 5 min (constituting one block). We obtained seven blocks within 60 min in each subject for SVV and SVH. In between the first six blocks, subjects remained in darkness for 5 min each, whereas the lights were briefly turned on before block 7. We noted significantly (p < 0.05) increased errors in perceived direction of gravity by block 2 (SVV) and 3 (SVH). These increases disappeared after turning on the lights before block 7. Focusing on blocks 2-6, significant drift started from similar offset positions and pointed to the same direction in a majority of runs in 9/15 (SVV) and 11/15 (SVH) subjects. When pooling data from all blocks, orthogonality of errors was lost in all subjects. Trial-to-trial variability remained stable over the seven runs for SVV and SVH. Only when pooling all runs, precision was significantly (p < 0.05) higher for the SVH. Our findings suggest that perceived direction of gravity continues to fluctuate over extended recording periods with individuals showing unique patterns of direction-specific drift while variability remains stable. As subjects were upright during the entire experiment and as drift persisted over several blocks, sensory adaptation seems unlikely. We therefore favor a central origin of this kind of drift.
Asunto(s)
Oscuridad , Gravitación , Desempeño Psicomotor/fisiología , Percepción Espacial/fisiología , Adulto , Femenino , Humanos , Masculino , Estimulación Luminosa/métodos , Factores de Tiempo , Percepción Visual/fisiología , Adulto JovenRESUMEN
Here we investigated how well internal estimates of direction of gravity are preserved over time and if the subjective visual vertical (SVV) and horizontal (SVH) can be used inter-changeably. Fourteen human subjects repetitively aligned a luminous line to SVV, SVH or subjective visual oblique (± 45°) over 5 min in otherwise complete darkness and also in dim light. Both accuracy (i.e., the degree of veracity as reflected by the median adjustment error) and precision (i.e., the degree of reproducability as reflected by the trial-to-trial variability) of adjustments along the principle axes were significantly higher than along the oblique axes. Orthogonality was only preserved in a minority of subjects. Adjustments were significantly different between SVV vs. SVH (7/14 subjects) and between ±45° vs. -45° (12/14) in darkness and in 6/14 and 14/14 subjects, respectively, in dim light. In darkness, significant drifts over 5min were observed in a majority of trials (33/56). Both accuracy and precision were higher if more time was taken to make the adjustment. These results introduce important caveats when interpreting studies related to graviception. The test re-test reliability of SVV and SVH can be influenced by drift of the internal estimate of gravity. Based on spectral density analysis we found a noise pattern consistent with 1/fß noise, indicating that at least part of the trial-to-trial dynamics observed in our experiments is due to the dependence of the serial adjustments over time. Furthermore, using results from the SVV and SVH inter-changeably may be misleading as many subjects do not show orthogonality. The poor fidelity of perceived ± 45° indicates that the brain has limited ability to estimate oblique angles.
Asunto(s)
Sensación de Gravedad/fisiología , Orientación/fisiología , Desempeño Psicomotor/fisiología , Percepción Visual/fisiología , Adulto , Femenino , Humanos , Masculino , Fenómenos Fisiológicos Oculares , Reproducibilidad de los Resultados , Proyectos de Investigación , Conducta Espacial/fisiología , Factores de Tiempo , Adulto JovenRESUMEN
We investigated the perception of self-rotation using constant-velocity chair rotations. Subjects signalled self motion during three independent tasks (1) by pushing a button when rotation was first sensed, when velocity reached a peak, when velocity began to decrease, and when velocity reached zero, (2) by rotating a disc to match the perceived motion of the body, or (3) by changing the static position of the dial such that a bigger change in its position correlated with a larger perceived velocity. All three tasks gave a consistent quantitative measure of perceived angular velocity. We found a delay in the time at which peak velocity of self-rotation was perceived (2-5 s) relative to the beginning or to the end of chair rotation. In addition the decay of the perception of self-rotation was preceded by a sensed constant-velocity interval or plateau (9-14 s). This delay in the rise of self-motion perception, and the plateau for the maximum perceived velocity, contrasts with the rapid rise and the immediate decay of the angular vestibuloocular reflex (aVOR). This difference suggests that the sensory signal from the semicircular canals undergoes additional neural processing, beyond the contribution of the velocity-storage mechanism of the aVOR, to compute the percept of self-motion.
Asunto(s)
Percepción de Movimiento/fisiología , Postura , Propiocepción/fisiología , Aceleración , Adulto , Femenino , Gravitación , Humanos , Masculino , Persona de Mediana Edad , Movimiento (Física) , Reflejo Vestibuloocular/fisiología , Rotación , Adulto JovenRESUMEN
We have investigated the effects of mental set on predictive capabilities using a saccade square-wave tracking paradigm with ten normal subjects, comparing three amplitudes (10, 20, and 40 degrees ) and five inter-stimulus intervals (ISIs) (400, 500, 625, 1000, and 2000 ms). Subjects were instructed simply to "follow the lights" (passive, reflexive instruction) or explicitly "move your eyes in time with the lights" (active, volitional instruction). Saccades were defined as reflexive (latency>100 ms), predictive (-200 msAsunto(s)
Cognición/fisiología
, Desempeño Psicomotor/fisiología
, Movimientos Sacádicos/fisiología
, Adulto
, Interpretación Estadística de Datos
, Femenino
, Humanos
, Imagen por Resonancia Magnética
, Masculino
, Persona de Mediana Edad
, Estimulación Luminosa
RESUMEN
Predictive saccade tracking (targets stepping back and forth at frequencies of 1.25 = 1.0 Hz) and self-paced saccades between two stationary targets were measured in patients with cerebellar degeneration and in normal subjects. Cerebellar patients produced similar predictive latencies and generated the same percentage of predictive saccades as did normal subjects. Only the variability in the self-paced saccade paradigm was different between the groups.
Asunto(s)
Movimientos Sacádicos/fisiología , Ataxias Espinocerebelosas/fisiopatología , Degeneraciones Espinocerebelosas/fisiopatología , Adulto , Anciano , Humanos , Persona de Mediana Edad , Tiempo de Reacción , Valores de ReferenciaRESUMEN
BACKGROUND: We used ocular motor paradigms to examine whether or not saccades are impaired in individuals with high functioning autism (HFA). METHODS: We recorded eye movements in patients with HFA (n=11), and in normal adolescents (n=11) on anti-saccade, memory-guided saccade (MGS), predictive saccade and gap/overlap tasks. RESULTS: Compared with the normal subjects, patients with HFA had (1) a significantly higher percentage of directional errors on the anti-saccade task (63.2% versus 26.6%), (2) a significantly higher percentage of response suppression errors on a MGS task (60.3% versus 29.5%) and (3) a significantly lower percentage of predictive eye movements on a predictive saccade task. They also showed longer latencies on a MGS task and for all conditions tested on a gap/null/overlap task (fixation target extinguished before, simultaneously, or after the new peripheral target appeared). When the latencies during the gap condition were subtracted from the latencies in the overlap condition, there was no difference between patients and normals. CONCLUSIONS: Abnormalities in ocular motor function in patients with HFA provide preliminary evidence for involvement of a number of brain regions in HFA including the dorsolateral prefrontal cortex (dlPFC) and the frontal eye fields (FEFs) and possibly the basal ganglia and parietal lobes.
Asunto(s)
Trastorno Autístico/psicología , Trastornos de la Motilidad Ocular/etiología , Adolescente , Trastorno Autístico/complicaciones , Niño , Femenino , Fijación Ocular , Lateralidad Funcional/fisiología , Humanos , Masculino , Estimulación Luminosa , Corteza Prefrontal/fisiología , Desempeño Psicomotor/fisiología , Movimientos Sacádicos/fisiología , Campos Visuales/fisiologíaRESUMEN
BACKGROUND: Prevailing hypotheses suggest that attention deficit hyperactivity disorder (ADHD) is secondary to dysfunction of motor intentional systems mediated by prefrontal circuitry. Oculomotor paradigms provide a mechanism for examining and localizing dysfunction at the interface between movement and cognition. OBJECTIVE: Three different saccade tasks (reflexive or prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and the execution of eye movements, including motor response preparation, response inhibition, and working memory. METHODS: The study included 19 children with ADHD, divided into two groups: a group of 8 children on methylphenidate at the time of testing and a group of 11 children not taking any psychoactive medication. Results from the two groups were compared with those from 25 age- and gender-matched normal control children. RESULTS: Both groups of children with ADHD made significantly more directional errors than did controls on the antisaccade task and significantly more anticipatory errors than did controls on the memory-guided saccade task, findings that are consistent with deficits in response inhibition. There were no significant differences in prosaccade latency, although unmedicated children with ADHD showed significantly greater variability in latency on the prosaccade task than did controls. On the memory-guided saccade task there were no significant differences in saccade accuracy; however, unmedicated children with ADHD showed longer saccade latency than did either controls or medicated children with ADHD. CONCLUSIONS: Oculomotor findings suggest that deficits in prefrontal functions, in particular response inhibition, contribute to behavioral abnormalities observed in ADHD. Findings also suggest that the administration of methylphenidate is associated with improvements in the consistency of motor response. Although there were no observed improvements in response inhibition with methylphenidate, conclusions await a design in which subjects complete testing both on and off medication.
Asunto(s)
Trastorno por Déficit de Atención con Hiperactividad/fisiopatología , Músculos Oculomotores/fisiopatología , Movimientos Sacádicos/fisiología , Adolescente , Niño , Femenino , Humanos , Masculino , Tiempo de Reacción/fisiologíaRESUMEN
PURPOSE: To establish an objective Hess screen test that allows a simultaneous and binocular analysis of all three axes of eye rotation. METHODS: In orthotropic and strabismic human subjects, both eyes were recorded with dual scleral search coils in a three-field magnetic system. Before mounting the search coil annuli on the eyes, the voltage offsets of each channel and the relative magnitudes of the three magnetic fields were determined. For calibration, subjects were only required to fix monocularly on a single reference target. During fixation of targets on the Hess screen by the uncovered eye, the three-dimensional eye position of both the occluded and the viewing eye was simultaneously measured. RESULTS: For clinical interpretation, an easy to understand graphical description of the three-dimensional Hess screen test was developed. Positions of orthotropic and strabismic eyes tended to follow Listing's law, which in both eyes allowed the determination of the primary position, that is, the position of gaze from which pure horizontal and pure vertical movements do not lead to an ocular rotation about the line-of-sight. To a first approximation, the location of primary position is a result of the summation of the individual rotation axes of the six extraocular muscles and thus can be used to infer which muscle is paretic. CONCLUSIONS: The three-dimensional Hess screen test with binocular dual search coils in a three-field magnetic system is an objective method to assess the ocular alignment in three dimensions with high precision. From these recordings, the clinician can relate deviations of primary position to specific eye muscle palsies.
Asunto(s)
Técnicas de Diagnóstico Oftalmológico , Trastornos de la Motilidad Ocular/diagnóstico , Músculos Oculomotores/patología , Visión Binocular , Algoritmos , Técnicas de Diagnóstico Oftalmológico/instrumentación , Fijación Ocular , Humanos , MagnetismoRESUMEN
OBJECTIVE: To assess saccadic eye movements in boys with Tourette syndrome (TS) with and without attention-deficit hyperactivity disorder (ADHD), comparing performance with that of an age-matched group of male controls. METHOD: Three different saccade tasks (prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and execution of eye movements, including motor response preparation, response inhibition, and working memory. The study included 14 boys with TS without ADHD (TS-only), 11 boys with TS and ADHD (TS+ADHD), and 10 male controls. RESULTS: Latency of prosaccades was prolonged in boys with TS (both with and without ADHD) compared with controls. Variability in prosaccade latency was greater in the groups of boys with TS+ADHD compared with both the TS-only and control groups. Response inhibition errors on both the antisaccade task (directional errors) and memory-guided saccade task (anticipatory errors) were increased in boys with TS+ADHD compared with those with TS-only. There were no significant differences among the three groups in accuracy of memory-guided saccades. CONCLUSIONS: Oculomotor findings suggest that TS is associated with delay in initiation of motor response as evidenced by excessive latency on prosaccades. Signs of impaired response inhibition and variability in motor response appear to be associated with the presence of ADHD.
Asunto(s)
Trastorno por Déficit de Atención con Hiperactividad/epidemiología , Enfermedades del Nervio Oculomotor/diagnóstico , Enfermedades del Nervio Oculomotor/epidemiología , Síndrome de Tourette/epidemiología , Niño , Cuerpo Estriado/fisiopatología , Electrooculografía , Lóbulo Frontal/fisiopatología , Humanos , Masculino , Inhibición Neural/fisiología , Enfermedades del Nervio Oculomotor/fisiopatología , Prevalencia , Movimientos Sacádicos/fisiologíaRESUMEN
We review here the eye movements in patients with Huntington's disease (HD), concentrating upon saccades as they show the most prominent abnormalities. Inability to suppress reflexive glances to suddenly appearing novel visual stimuli and delayed initiation of voluntary saccades, including predictive saccades, are early and consistent findings. These two abnormalities can be interpreted in the context of a model, based upon the idea that the frontal lobes and basal ganglia contribute more to the control of voluntary than to reflexive types of saccades. Most patients eventually also show slow saccades but they are most prominent when the disease is early-onset. Slowing of saccades may reflect involvement of both the higher-level cerebral centers that trigger saccades and the areas in the brain stem that produce premotor saccade commands. The study of eye movements in HD has led to a fruitful interaction between basic science and clinical investigation, and has served as a paradigm for examining higher-level defects in saccadic eye movement control in patients with various degenerative, neurological diseases or with focal cerebral hemispheral lesions.
Asunto(s)
Enfermedad de Huntington/complicaciones , Trastornos de la Motilidad Ocular/etiología , Humanos , Enfermedad de Huntington/fisiopatología , Trastornos de la Motilidad Ocular/fisiopatología , Movimientos SacádicosRESUMEN
In five normal subjects, we analyzed uncalled for torsion (blips) during and after horizontal and vertical saccades. Torsion was defined as movement out of Listing's plane. During horizontal saccades in downward gaze the abducting eye extorted and the adducting eye intorted. The direction of the blips reversed in upward gaze. Peak torsional amplitudes (up to 1-2 deg) were always reached during saccades; drifts back to Listing's plane outlasted the saccades. Torsion of the extorting eye was larger than that of the intorting eye, producing a transient positive cyclovergence. Torsion and cyclovergence evoked by vertical saccades were also stereotyped in each eye, but showed idiosyncratic differences among subjects. We conclude that Listing's law is violated during saccades. Transient saccade-evoked torsion might reflect properties of the three-dimensional velocity-to-position integrator and/or the ocular plant.
Asunto(s)
Movimientos Oculares/fisiología , Fijación Ocular/fisiología , Movimientos Sacádicos/fisiología , Adulto , Algoritmos , Convergencia Ocular/fisiología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Modelos Biológicos , Rotación , Factores de TiempoRESUMEN
We compared saccadic eye movements in 21 patients with Huntington's disease (HD) and 21 normal subjects. In a predictive tracking task, HD patients were unable to anticipate normally the timing and location of a visual target that alternated its position predictably (+/- 10 degrees, 0.5 Hz; mean latency of +170 msec in HD and -78 msec in normal subjects). HD patients and normal subjects, however, showed comparable decreases in saccade latency (110 msec in HD, 124 msec in normal subjects) when the fixation target was turned off 200 msec before (gap task) versus 200 msec after (overlap task) the appearance of an unexpected peripheral stimulus. Taken together, these findings support the idea that HD patients show greater defects in initiating internally generated than in initiating externally triggered saccades. This dichotomy is likely due to involvement of frontal lobe--basal ganglia structures in HD, with relative sparing of parietal--superior collicular pathways.
Asunto(s)
Enfermedad de Huntington/fisiopatología , Movimientos Sacádicos/fisiología , Adulto , Electrooculografía , Humanos , Persona de Mediana Edad , Estimulación Luminosa , Tiempo de ReacciónRESUMEN
Eye movements were recorded from 20 mildly affected patients with Huntington's disease (HD) who were divided into two groups, 10 patients with onset of symptoms before age 30 and 10 with onset of symptoms after age 30. In the younger onset group (HD less than 30), peak saccade velocities were low (less than 255 deg/sec for 20-deg saccades) in six of the 10 patients, whereas none of the 10 patients in the older onset group (HD greater than 30) had peak saccade velocities lower than 300 deg/sec. Latencies for volitional saccades were greater than normal in the HD greater than 30 group, but were normal for the HD less than 30 group. The ability to maintain steady fixation in the face of a distracting visual stimulus was decreased, to the same degree, in both groups of HD patients. In addition, 70% of the HD less than 30 group had an affected father, while 70% of the HD greater than 30 group had an affected mother. These findings suggest that the pathophysiology of the slow saccades, initiation deficit, and excessive distractibility in HD are different.
Asunto(s)
Movimientos Oculares , Enfermedad de Huntington/fisiopatología , Movimientos Sacádicos , Adolescente , Adulto , Anciano , Humanos , Persona de Mediana Edad , Tiempo de Reacción , Índice de Severidad de la Enfermedad , Factores de TiempoRESUMEN
We recorded saccadic eye movements in patients mildly affected with Huntington's disease. Most showed an increase in saccade latencies that was greater for saccades made on command than to the sudden appearance of a visual target. All patients showed excessive distractibility during attempted fixation. They had particular difficulty suppressing a saccade to a suddenly appearing visual target when simultaneously trying to initiate a saccade in the opposite direction. Our results are compatible with a posited role of the basal ganglia in both the initiation of volitional saccades and in the maintenance of fixation. Saccade abnormalities--especially distractibility--are sensitive but probably not specific indicators of Huntington's disease.
Asunto(s)
Movimientos Oculares , Enfermedad de Huntington/fisiopatología , Movimientos Sacádicos , Adolescente , Adulto , Anciano , Atención/fisiología , Condicionamiento Psicológico/fisiología , Electrooculografía , Humanos , Persona de Mediana Edad , Tiempo de ReacciónRESUMEN
The maximum smooth pursuit eye velocity was determined in five human subjects. Eye movements were recorded with the d.c.-coupled EOG. On each trial the target moved in a ramp, at a constant velocity between 10 and 200 deg/sec. In four subjects eye velocity was approximately 90% of target velocity up to a target velocity of 100 deg/sec. Eye velocity then saturated with a large variability from trial to trial (standard deviation 16 deg/sec). The fifth subject had eye velocities only 60% of these values.
Asunto(s)
Movimientos Oculares , Seguimiento Ocular Uniforme , Adulto , Electrooculografía , Humanos , Masculino , Persona de Mediana Edad , Factores de TiempoRESUMEN
Optokinetic nystagmus (OKN), a periodic sawtooth movement of the eyes, is maximally elicited when a subject's entire visual field is moving. The most appropriate stimulus for the generation of OKN is an optokinetic drum that completely surrounds the subject. Such drums tend to be massive and can only be accelerated rapidly with a powerful motor. This report describes construction details of a drum designed especially to minimize moment of inertia and cost as well.
Asunto(s)
Nistagmo Fisiológico , Estimulación Luminosa/instrumentación , HumanosRESUMEN
Eye movements induced by head rotation were studied in 6 patients in acute coma, 4 patients in a persistent vegetative state, and 6 healthy, alert control subjects. Results from control subjects suggest that the oculocephalic response in the supine position is principally a vestibulo-ocular reflex. A position-step rotation of the head produced an initial oppositely directed eye movement, followed by a drift of the eyes back toward midline with a negative exponential time course. The time constant of this drift was greater than or equal to 10 seconds in control subjects but less than or equal to 1.5 seconds in unconscious patients and less than or equal to 0.5 seconds in vegetative patients. The rapid drift back of the eyes in unresponsive patients implies dysfunction of reticular and, possibly, cerebellar connections; the rate of this drift may indicate the severity and extent of brain injury. Sinusoidal head rotation produced slow and quick phases of nystagmus in normal subjects. Quick phases were absent in patients in acute coma; although present in vegetative patients, the quick phases did not keep the eyes close to primary position, as was the case in control subjects.
Asunto(s)
Coma/diagnóstico , Movimientos Oculares , Adulto , Anciano , Niño , Coma/fisiopatología , Femenino , Cabeza , Humanos , Masculino , Persona de Mediana Edad , Cuello/inervación , Propiocepción , Reflejo , Rotación , Pruebas de Función VestibularRESUMEN
We studied eye movements in 50 patients with Huntington's disease. Fixation was impaired in 73% of patients; such individuals had difficulty in suppressing saccades toward novel visual stimuli. Impaired initiation of saccades was manifest by increased reaction time (89%) and inability to make a saccade without head movement (89%) or blink (35%). Saccades and quick phases of nystagmus were slowed in 62%. Smooth pursuit was abnormal in 60%, and vergence in 33%. The vestibulo-ocular reflex and the ability to hold eccentric gaze were preserved even late in the disease.