SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A visual target was mloved left and right in exact synchrony with vertical movements of the head. A few minutes' exposure to this novel head-movement feedback led to a change in the visual discrimlination of head movement from object movement. The critical factor in the adaptation is the novel correlation of eye and head movement elicited during the period of exposure.
The experiment reported here explores 3-month-old infants' ability to recognize a human face from a specific motion pattern lacking static facial features. A woman's face was covered with black makeup and numerous white triangles. It was videotaped while the woman was pretending to interact with a baby. A soft rubber mask was prepared likewise and was videotaped while being moved and deformed by hand. In one condition, the face or mask showed facial movement only, while in a second condition there was internal movement plus head movement. The two stimuli were presented either in upright or in upside-down orientation. Results of 48 subjects indicate that the discrimination of face and mask was easier when the stimuli were presented upright. The absence of head movements did not influence the discriminability. These results suggest that 3-month-old infants organize the moving triangles on the face in the upright orientation into a coherent facelike structure.
Abnormal head movements have been studied in a variety of diseases using objective recording techniques and the data analysed with respect to the frequency content of the movement. Flopping, nodding, tic, chorea, myoclonic jerks, and most head tremors involve frequencies of approximately 2 and 4 Hz which correspond to the natural fundamental and second harmonic resonances of the head as determined by the mechanical properties of the head/neck system. These findings provide a basis for classification of abnormal head movements as well as an explanation of the characteristics of those arising from hypotonia of the neck muscles. The similarities between tremor frequencies and natural resonances suggest that in the case of the head, tremor arises from disorders of neural mechanisms normally responsible for the fine control of voluntary head movement and for stabilisation of the head during disturbance of posture. Head movements in cases of congenital nystagmus were found to be of two types. Some were of bizarre waveform, in no way assisted vision, and were taken to be of primarily pathological origin and classified as tremors. Others were learned adaptive responses which assisted vision either by interrupting the nystagmus, as in the case of spasmus nutans, or by compensating for the nystagmus with an inverse waveform and were called nodding. A prerequisite for true compensatory nodding is modified vestibulo-ocular reflex.
1. In the companion article, a variety of head movements were elicited by stimulation in, and adjacent to, the gigantocellular reticular nucleus (Cowie and Robinson 1994). We refer to this area, caudal to the abducens nucleus, as the gigantocellular head movement region. In the present paper, the anatomical connections of this region, as determined by injections of wheat-germ agglutinin conjugated horseradish peroxidase (WGA-HRP), are reported. The majority of efferent and afferent connections were with areas related to head movements. 2. Efferent fibers from the region projected via two paths to the caudal medulla and upper cervical spinal cord. Labeled fibers descended in the anterolateral funiculus of the ipsilateral spinal cord to terminate in lateral parts of the ventral horn. A second pathway descended bilaterally in the medial longitudinal fasciculus to the anterior funiculi and medial portions of the ventral gray. These efferents paralleled the head-movement topography demonstrated physiologically. Other projections included efferents to the interstitial nucleus of Cajal, caudal field H of Forel, paramedian pontine reticular formation, and caudal vestibular nuclei. Other efferent fibers projected to the trigeminal, facial, and hypoglossal nuclei, as well as to the parvocellular reticular field, which contains interneurons for these motor groups. However, no efferent or afferent labeling involved the ocular motor nuclei. 3. Afferents to the gigantocellular head movement region arose mainly from head-movement areas. In all animals, labeled cells were found in the intermediate and deep layers of the caudal superior colliculus. Labeled neurons also were found in the caudal field H of Forel, interstitial nucleus of Cajal, pontine medial tegmentum including the pontine paramedian reticular formation, nucleus subcoeruleus, and vestibular nuclear complex. Caudally, filled cells were located in the parvocellular, magnocellular, dorsal, and ventral reticular nuclei, the supraspinal nucleus, and the upper cervical ventral horn. 4. In one animal, the ipsilateral frontal cortex contained retrogradely labeled neurons. These cells were found in layer V of cortical areas 4 and 6. Other afferent cells were found consistently in the periventricular and periaqueductal gray matter. 5. A control injection into the caudal vestibular nuclear complex showed projections to the gigantocellular reticular formation and labeled cells in the vestibular and parvocellular reticular nuclei. These observations show that the connections of the gigantocellular region are not typical of all head movement sites. 6. These data indicate that the gigantocellular head-movement region has the requisite efferent and afferent connections to function in the subcortical control of head, but not eye, movements.(ABSTRACT TRUNCATED AT 400 WORDS)
Single unit activities were recorded in Forel's field H (FFH) at the mesodiencephalic junction during orienting head movements in two alert cats under head-free conditions. Recordings were made of 63 neurons of which 20 showed phasic firing that preceded the onset of head movements by 20-100 ms and was temporally related to the dynamic phase of the orienting head movement. Nineteen of these neurons showed a preference for upward movements, while the remaining neuron preferred downward movements. Activities during orienting movements in eight different directions (each separated by 45 degrees) were systematically analyzed for 12 of the 19 upward-preferring neurons. The activities were broadly tuned; in most of the neurons, maximum activity was observed for direct upward movements (+90 degrees), but significant activity was also observed for ipsilateral and contralateral oblique upward movements (+45 degrees and +135 degrees). In these cases, the increase in activity preceded the onset of the movement. Some increase in activity was also observed for ipsilateral and contralateral horizontal, oblique downward and downward movements. However, the increase in activity in the latter cases occurred simultaneously with or lagged behind the onset of the movement and was often preceded by a decrease in activity. The same pattern of directional tuning was observed in the EMG of the biventer cervicis muscle, a target of FFH neurons. The preferred directions of the 12 upward-preferring neurons were estimated by calculating the vector sum of the activity and were distributed between +68 degrees and +108 degrees. The same amount of activity was observed for ipsilateral and contralateral oblique upward movements, suggesting that FFH neurons on both sides of the brainstem are equally activated even during oblique orienting. Input from the ipsilateral superior colliculus was investigated in 18 neurons, all of which were orthodromically activated with a latency of 0.8-1.8 ms, suggestive of a mono- or disynaptic excitatory connection. Seven neurons were identified as descending projection neurons by antidromic activation from the ipsilateral medullary reticular formation. Repetitive microstimulation of unilateral FFH induced oblique upward head movements and an accompanying torsional component, while simultaneous bilateral stimulation at comparable stimulus strength induced purely upward head movements. These results strongly suggest that the vertical component of orienting head movements is encoded by equal bilateral activation of the FFH.
Rotational eye and head movements were recorded with great precision with scleral and cranial search coils in a rotating magnetic field. Compensatory eye movements were recorded in light and darkness during active as well as passive head movements in the frequency range 0.33-1.33 Hz. From the recorded, nominal gaze movements the effective gaze was reconstructed taking into account magnification or reduction factors of corrective spectacles. Effective gain was calculated as the ratio between the velocities of the effective corrective eye movements and the head movements. In the light, effective gain of compensatory eye movements during active head motion was mostly between 0.97 and 1.03. It was never precisely unity and differed systematically between subjects and between the two eyes of each subject. During passive head motion in the light, gain was lower by about 3% than during active motion. During active head movement in the dark, gain was mostly between 0.92 and 1.00; values were about 5% lower than during active motion in the light. During passive head movement in the dark, gain was about 13% lower than during active motion, and the variability of the oculomotor response increased. Adaptation of these base-line conditions was induced by fitting the subjects with magnifying or reducing spectacles for periods of 40 min to 24 h. The largest required change in amplitude of eye movements was 36%. When active head movements were made, the amplitude of compensatory eye movements in the light as well as in the dark adjusted rapidly. Most of the adaptation of the vestibulo-ocular reflex in the dark was completed in about 30 min. This rate is much faster than that found in previous experiments requiring larger adaptive changes. Differential adaptation to unequal demands for the two eyes proved to be very hard or impossible. In a mild conflict situation the system adjusted to an intermediate level, distributing the error symmetrically between the eyes. When the discrepancy was large, the adaptive process of both eyes was controlled by the one eye which provided the most meaningful information. It is concluded that the system generating compensatory eye movements performs best during active rather than passive head movements, and that adaptation to moderate changes in optimal gain are made very rapidly.
Electrical stimulation of the superior colliculus (SC) in alert cats free to move their head, evoked coordinate eye and head movements. The characteristics of these movements as well as their mode of coordination differed according to the collicular region being explored. Three zones were distinguished. In the anterior zone, evoked eye saccades were retinotopic and the accompanying head movements were slow and small in amplitude. The vestibular slow phase velocity signal was continuously added to the eye saccadic command so that the evoked gaze shift was identical, with the head fixed or free. In the intermediate zone, evoked eye saccades were goal-directed and the synchronous head movements fast and of large amplitude. The vestibular slow phase signal was cancelled during the eye saccade so that the evoked gaze shift was the result of the eye plus head angular displacement. In the posterior zone, the evoked head movements were goal-directed. The pattern of eye movements was similar to a vestibular nystagmus. This zone probably directly commands body orienting movements. A model of SC function in gaze orienting behavior is proposed, calling upon at least two different modes of eye-head coordination.
Eye-head coordination during the shift of gaze is investigated. Dynamic trajectories of eye movements and head movements were measured for exploring the control mechanism of the head movement in eye-head coordination. The experimental results revealed the dual mode control of the head movement in eye-head coordination: a linear control for small amplitude movement (less than 30 degree), and a Bang-Bang control for larger amplitude.
Eye and head movements of ten mentally retarded (MR) children and ten normal school children were recorded. Each was directed to look to one side or the other in response to verbal commands, to gestural directions, or to the appearance of illuminated fixation targets. Under these conditions: 1. Large gaze movements of MR subjects were accompanied by head movements more frequently than those of the normal subjects. Furthermore, for similar gaze deviations, head movement of MR subjects tended to be larger than those of normal subjects. 2. Head movements of normal subjects rarely began before eye movement, but those of MR subjects often did so. This "abnormal" MR eye-head movement pattern was more frequent in response to verbal or gestural commands than in response elicited by illumination of fixation targets.
Compensatory horizontal eye movements of head restrained rats were compared with compensatory horizontal eye-head movements of partially restrained rats (head movements limited to the horizontal plane). Responses were evoked by constant velocity optokinetic and vestibular stimuli (10-60 degrees/s) and recorded with search coils in a rotating magnetic field. Velocity and position components of eye and head responses were analysed. The velocity gains of optokinetic and vestibular responses of partially restrained and of head restrained rats were similarly high (between 0.8 and 1.0). Eye movements in partially restrained rats also contributed most (about 80%) to the velocity components of the responses. At stimulus velocities above 10 degrees/s, the "beating field" of the evoked optokinetic and vestibular nystagmus was shifted transiently in the direction of ocular quick phases. The amplitude of this shift of the line of sight was about 3-10 degrees in head restrained and about 20-30 degrees in partially head restrained rats. Most of this large, transient gaze shift (about 80%) was accomplished by head movements. We interpret this gaze shift as an orienting response, and conclude that the recruitment of the ocular and the neck motor systems can be independent and task specific: head movements are primarily used to orient eye, ear and nose towards a sector of particular relevance, whereas eye movements provide the higher frequency dynamics for image stabilization and vergence movements.
Eye-head coordination was measured in patients with Parkinson's disease as they made horizontal gaze shifts in response to predictable and unpredictable target steps and to targets moving smoothly with either constant or sinusoidally varying velocity. Patients preferred not to move their heads for both large and small amplitude gaze shifts. Both eye and head movement reaction times were prolonged. Saccades were hypometric and, frequently, slow. Head movements were also slow, hypometric, and varied in amplitude for target shifts of a given amplitude. Compensatory eye movements (CEMs) that normally stabilize gaze direction during head movement varied in gain from zero to greater than unity, and often drove the eyes off target. CEM abnormalities occurred most commonly in patients with abnormal vestibulo-ocular reflex (VOR) gain in darkness. We attribute these abnormalities of programming combined eye-head saccades to dysfunction of striatonigralcollicular circuits. Smooth gaze pursuit gain, the ratio of gaze velocity to target velocity, was lowered in patients while tracking sinusoidal targets at 0.3, 0.5 and 1.0 Hz. Some patients could track these targets with the head fixed but not with the head free. We attribute this to abnormal suppression of the vestibuloocular reflex. The results indicate that Parkinson's disease impairs motor programming of coordinated eye-head gaze saccades and disrupts normal interaction between head movement and the VOR.
1. Saccadic eye movements during walking were studied in chickens using cinematography. 2. Saccades were made during about 80% of the thrust phases of head bobbing, and not made in the hold phases. 3. The coordination of saccades with head movements maintains clear vision for the largest possible proportion of the time. 4. The absence of saccades in hold phases and in some thrusts is probably not the result of insufficient time to organize a saccade.
Head movement of normal subjects and patients with peripheral vestibular disorders while stepping was recorded using three accelerometers, a multi-channel telemeter and a microcomputer. The head movement registered from normal subjects was stable at a stepping speed of 1.2 or 1.4 steps/sec. Patients with peripheral vestibular disorders (except for BPPV) showed significantly greater head movement values in all three directions and smaller ratios of anteroposterior component to lateral component in the head movement, as compared with those of normal subjects.
We have investigated the relationships among the firing frequency B(t) of inhibitory burst neurons (IBNs) and the metrics and dynamics of the eye, head, and gaze (eye + head) movements generated during voluntary combined eye-head gaze shifts in monkey. The same IBNs were characterized during head-fixed saccades in our first of three companion papers. In head-free gaze shifts, the number of spikes (NOS) in a burst was, for 82% of the neurons, better correlated with gaze amplitude than with the amplitude of either the eye or head components of the gaze shift. A multiple regression analysis confirmed that NOS was well correlated to the sum of head and eye amplitudes during head-free gaze shifts. Furthermore, the mean slope of the relationship between NOS and gaze amplitude was significantly less for head-free gaze shifts than for head-fixed saccades. NOS is a global parameter. To refine we used system identification techniques to evaluate a series of dynamic models in which IBN spike trains were related to gaze or eye movements. We found that gaze- and eye-based models predicted the discharges of IBNs equally well. However, the bias values required by gaze-based models were comparable to those required in our head-fixed models whereas those required by eye-based models were significantly larger. The difference in biases between gaze- and eye-based models was very strongly correlated to the mean head velocity () during gaze shifts [R = -0.93 +/- 0.15 (SD)]. This result suggested that the increased bias required by the eye-based models reflected an unmodeled input onto these cells. To pursue this argument further we investigated a series of dynamic models that included both eye velocity () and terms and this confirmed the importance of these two terms. As in our head-fixed analysis of companion paper I, the most valuable model formulation also included an eye saccade amplitude term (DeltaE) and was given by B(t) = r0 + r1DeltaE + b1 + g1 where r0, r1, b1, and g1 are constants. The amplitude of the head velocity coefficient was significantly less than that of the eye velocity coefficient. Furthermore, in our population long-lead IBNs tended to have a smaller head velocity coefficients than short-lead IBNs. We conclude that during head-free gaze shifts, the head velocity signal carried to the abducens nucleus by primate excitatory burst neurons (EBNs; if EBNs and IBNs carry similar signals) must be offset by other premotor cells.
Gaze is shifted by means of eye saccades which, in most instances, are synchronized with head rotations. During eye-head movements performed by cats in the dark, most of the rapid eye movements start after the head has begun to move (mean time lag was 45 msec). This pattern resembles that observed when the cat, as a whole, is suddenly rotated passively and consists of a short lasting vestibularly induced slow phase component followed by a rapid eye movement that takes the eye in the same direction as the head. We have compared the passively and actively induced eye-head movements. The rapid eye movements are similar in both cases in that they terminate at a fixed position ("goal") in the orbit irrespective of the eye's starting position. They differ primarily in the fact that the eccentricity of the "goal" during active head rotations increases much more rapidly with velocity than it does during the passive condition. The results suggest that the rapid eye movement that accompanies an active head movement in the dark is not simply a vestibularly induced quick phase.
When the head rotates, vestibulocollic reflexes counteract the rotation by causing contraction of the neck muscles that pull against the imposed motion. With voluntary head rotations, these same muscles contract and assist the movement of the head. The purpose of this study was to determine if an infinite variety of muscle activation patterns are available to generate a particular head movement, of if the CNS selects a consistent and unique muscle pattern for the same head movement whether performed in a voluntary or reflex mode. The relationship of neck muscle activity to reflex and voluntary head movements was examined by recording intramuscular EMG activity from six neck muscles in three alert cats during sinusoidal head rotations about 24 vertical and horizontal axes. The cats were trained to voluntarily follow a water spout with their heads. Vestibulocollic reflex (VCR) responses were recorded in the same cats by rotating them in an equivalent set of planes with the head stabilized to the trunk so that only the vestibular labyrinths were stimulated. Gain and phase of the EMG responses were calculated, and data analyzed to determine the directions of rotation for which specific muscles produced their greatest EMG output. Each muscle exhibited preferential activation for a unique direction of rotation, and weak responses during rotations orthogonal to that preferred direction. The direction of maximal activation could differ for reflex and voluntary responses. Also, the best excitation of the muscle was not always in the direction that would produce a maximum mechanical advantage for the muscle based on its line of pull. The results of this study suggest that a unique pattern of activity is selected for VCR and tracking responses in any one animal. Patterns for the two behaviors differ, indicating that the CNS can generate movements in the same direction using different muscle patterns.
Visually guided head movement was studied in the African chameleon. Within certain ranges of frequencies and amplitudes, the chameleons followed horizontal, sinusoidal cricket (bait) movement with sinusoidal head movement and no apparent eye movement. Although head movement lagged behind bait movement, the chameleons used head amplitudes that minimized the motion of the bait relative to the head.
Head movement propensity-the pattern of head saccades dependent on methods of target presentation-varies among individuals. The present group of 9 young adults was previously ranked in a visual saccadic task according to this propensity. The present report examines how and why this propensity changes if the saccades are made to auditory targets. 1) Spatially identical, interleaved, auditorily and visually elicited horizontal saccadic gaze shifts (jumps) differed in amplitude and in starting and/or ending position. The jumps were executed in two head movement modes: first, the non-aligned mode was a standard reaction-time single gaze step between two points. Second, the head-aligned mode required alignment of the head with the fixation (starting) point; thereafter both modes were identical. All results in the auditory task are expressed relative to the visual results. 2) In the non-aligned mode, head movement amplitudes were increased on average by 15% (for example, an 80 degrees jump elicited a 12 degrees larger head movement), and velocity decreased by 12%, reflecting the increased demands of the auditory task. More importantly, the differences between subjects was narrowed; that is, head movement propensity was homogenized in the auditory task. In the visual task, head-movers willingly move their heads off and across the midline, whereas non-movers are unwilling to leave the midline from eccentric starting points or to eccentric ending points. This is called the midline attraction effect and was previously linked to spatial reference frames. The homogenization in the auditory task was characterized by head-movers increasing, and non-movers decreasing, their midline attraction, suggesting altered spatial reference frames. 3) For heuristic purposes, the ideal head-mover is defined by a gain of 1.0 in the visual task, and by external earth-fixed reference frames. Similarly, the ideal non-mover has a gain of 0.0 and has a bias toward body (or some par of the body)-fixed reference frames. In the auditory task these gains (and reference frames) in head movers and non-movers are homogenized (close to 0.5), either by the participation of the head (movement of the ears in space) in sensory acquisition or by differences in central nervous processing of the two modalities, or both.