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Fall injuries in people with Parkinson's disease (PD) are a major health problem. Increased sway while walking is a risk factor and further understanding of this destabilizing gait change may assist with rehabilitation and help prevent falls.Here, stride-to-stride head oscillations are used to help characterise different aspects of gait impairment in 10 people with PD on medication (67 years, SD 4), 10 healthy age-matched (HAM) participants (66 years, SD 7), and 10 young (30 years, SD 7). A wearable accelerometer was used to analyse head oscillations during five repeat 17 m walks by each participant.People with PD had significantly faster transverse plane head oscillations than the HAM or young groups; both along mediolateral (PD 47.2 cm s(-1), HAM 32.5 cm s(-1), and young 32.7 cm s(-1)) and anterioposterior axes (PD 33.3 cm s(-1), HAM 24.5 cm s(-1), and young 20.6 cm s(-1)). These differences were uncorrelated with reduced vertical oscillation velocity (PD 15.5 cm s(-1), HAM 18.8 cm s(-1), and young 20.1 cm s(-1)) and reduced walking speed (PD 1.2 m s(-1), HAM 1.4 m s(-1), and young 1.4 m s(-1)).Increased transverse plane head oscillations in people with PD may reflect motor impairment and the inability to respond sufficiently to perturbations while walking, which appears to be distinct from gait hyperkinesia, reduced vertical oscillations, step length, and walking speed.

Purpose To quantitatively characterize eye and head oscillations in patients with infantile nystagmus syndrome (INS). Methods Vertical and horizontal eye and head position in INS patients were measured simultaneously at a sampling frequency of 500 Hz. Eye and head movements were measured continuously for 180 seconds. The data was calibrated and converted to angular vectors, which were further analyzed with custom software. Results A total of 10 patients with INS were included: 3 with pseudo-jerk, 3 with pure-jerk, 2 with pseudo-pendular with foveating saccade form of jerk, 1 with bidirectional jerk, and 1 with asymmetric pendular nystagmus waveforms. None of the patients had periodic, aperiodic, or a superimposed latent nystagmus component. Two types of head oscillations were observed: one with a frequency of 1–3 Hz, present in all patients; and another with a frequency range of 5–8 Hz, present in only 7 patients. High-frequency oscillations were episodic, whereas low-frequency oscillations were constantly present. Peak velocity of the high-frequency head oscillations and eye velocity of nystagmus were not correlated, suggesting that these oscillations did not influence foveation. Conclusions Two types of head oscillations were found in INS patients: a constant, low-frequency and an episodic, high–frequency. Lack of correlation between the foveation period of nystagmus and peak head velocity during high-frequency oscillations suggests a coexisting pathological phenomenon rather than a compensatory mechanism used to improve the visual acuity.

This study measured the rate of acquisition of head and trunk postural control during the two early developmental periods of independent walking, as defined by global gait parameters. Gait parameters were observed longitudinally in four children. The maximum angular deviations of the trunk and head oscillations were computed in the frontal and sagittal planes. These decreased most dramatically during the first 10-15 weeks of independent walking, during the same period when global gait parameters changed rapidly. This head and trunk stabilization may be a fundamental process that help to maintain equilibrium during walking, and may be a necessary step prior to the development of fine posturo-motor control. Language: en

The apparent motion of a fixated spot stimulus during head oscillations (apparent concomitant motion, ACM) was measured before and after an adaptation period during which the fixation stimulus moved in synchrony with the head. During the adaptation period, the fixation stimulus moved either in the same (with) or the opposite (against) direction as did head movement. With adaptation increased ACM in the direction opposite head motion, whereas against adaptation increased ACM in the same direction as head motion. Pre- and postadaptation measures were obtained for .25-, .5-, 1.0-, and 2.0-Hz active head movements. Each of these frequencies was used in separate sessions as the adaptation frequency. ACM changes were greatest when the test and adaptation frequencies were the same, demonstrating frequency specificity of ACM adaptation. This frequency specificity, which is similar to that of the vestibulo-ocular reflex, indicates that ACM adaptation may reflect plasticity in oculomotor systems.

Congenital anomalies of the optic disc underlie many cases of decreased vision, strabismus, and nystagmus in childhood [54, 151]. A comprehensive evaluation necessitates an understanding of the ophthalmoscopic features, associated neuro-ophthalmologic findings, pathogenesis, and appropriate ancillary studies for each anomaly [46]. The subclassification of different forms of colobomatous defects on the basis of their ocular and systemic associations has further refined our ability to predict the likelihood of associated central nervous system (CNS) anomalies solely on the basis of the appearance of the optic disc [46]. The widespread availability of modern neuroimaging has refined the ability to identify subtle associated CNS anomalies and to prognosticate neurodevelopmental and endocrinological problems [46]. Genetic analysis has now advanced the understanding of some anomalies. It has been recognized [194, 218, 333] that many of these disorders are accompanied by some degree of peripheral retinal nonperfusion.

Healthy subjects use the vestibulo-ocular reflex (VOR) to stabilize gaze. Labyrinthine-defective humans without VOR still are, to some extent, able to maintain gaze stability during active eye-head movements. Here it is investigated whether this stabilization is due to anticipatory mechanisms or proprioceptive feedback. The head inertia was increased in humans who have undergone bilateral vestibulectomy (vestibular subjects) and in healthy controls during large gaze shifts. This leads to head oscillations in both groups. Whereas controls compensate for head oscillations and maintain gaze stability, vestibular subjects display gaze oscillations along with head oscillations. This indicates that vestibular subjects mainly use learned, anticipatory mechanisms, and not proprioception, to stabilize gaze.

Little is known of the functionality of the vestibulo-collic reflex (VCR) and cervico-collic reflex (CCR) during head and neck movements caused by perturbations of the trunk, previously, the authors formulated mathematical expressions for these neck reflexes and incorporated them into a model of horizontal plane head movements. The formalism of this neuromechanical model allowed the authors to examine separately the main components of head movement control. In the present study, they examine selected parameters within the main components of the model, and associate variations of these parameters with disease processes affecting head and neck movements, such as loss of sensory input or modification in central or motor function. The authors' simulations led them to several conclusions. First, the probable use of the VCR and CCR in yaw plane head movements is to tune the head response. In the time domain, they diminish natural head oscillations (head wobble) related to head mechanics. Equivalently, in the frequency domain, they reduce the amplitude of head wobble (resonances) around 2 Hz. Second, the authors' simulations suggest that the VCR is about ten times stronger than the CCR in normal humans. Moreover, this disproportion is associated with only very minor contributions from the CCR in yaw. Third, head oscillations (or instability) ran be generated by mechanical or neural changes in the head and neck system. Finally, readjustments of central nervous system dynamic operations could provide mechanisms to compensate for sensory and motor dysfunction caused by disease.

Postural sway during upright stance was analyzed in 12 patients with phobic postural vertigo (PPV) and in 12 age-matched healthy volunteers. Recordings were made under different conditions (with the eyes open or closed): when standing on a foam rubber pad with the head upright, turned 30 degrees to the right or left, or during 1 Hz horizontal head oscillations. Sway analysis included calculation of sway path, of root mean square values of sway and of the power spectrum of sway in fore/aft and lateral directions. There was a significant increase in sway activity in the 3.53-8 Hz frequency band in patients with PPV. This did not impair objective postural stability. Increase in higher frequency sway activity may simply reflect a change in postural strategy rather than a sensorimotor dysfunction. The patients' conscious control of stance may augment co-activation of anti-gravity muscles, a strategy applied by normal subjects when performing demanding balancing tasks.

Gaze functions under high-frequency head oscillations with large amplitudes were investigated in 12 normal subjects. Oscillation amplitude decreased as the frequency increased (31 degrees at 2 Hz to 11 degrees at 5 Hz on average). Maximum head velocity and acceleration were 170-200 degrees/s and 2,500-5,000 degrees/s2, respectively. At frequencies higher than 2 Hz, the mean ratio of eye amplitude to head amplitude reached high large values (1.2 at 2 Hz to 1.8 at 5 Hz, on average), whereas it dropped to extremely low values (0.5-0.6 at 3-5 Hz) in the 2 referred patients with bilateral labyrinthine loss. High ratio values, different from the previous reports, may result from a failure of compensation due to abnormally high-frequency and large head oscillations. The present study indicated that the frequency range of VOR influenced by gaze should correspond to that of daily-experienced oscillations, and that once head oscillations exceed the limit, compensation quickly deteriorates.

A variable proportion of albino rats 6-11 days old exhibit spontaneous and infrequent rotatory head-shaking episodes. This motor pattern is slightly anticipated and significantly increased in occurrence and duration by the administration of D-amphetamine (5 mg/Kg), with a maximal effect of the drug on the 9th day. The rate of amphetamine induced rhythmic head oscillations increases with age from below 5 cps on the 5th day to about 9 cps on the 10th day. The results are discussed in relation to maturation of both the underlying catecholaminergic pathways, activated by D-amphetamine, and the stretch reflex systems of the head and neck muscles participating in the rhythmic activity. Emphasis is placed on the difference between head-shaking and stereotyped activity.

The gain of the vestibulo-ocular reflex in the sagittal plane may be due to a cooperation between otoliths and the vertical semi-circular canals. The present space experiment was aimed at studying the influence of the absence of gravity stimulation on the otoliths, by comparing VOR gain and phase in space and on ground. Measurements were taken the 5th and the 7th day of flight, the subject being asked to perform, eyes closed, active head oscillations in pitch while fixating an imaginary target in front of him. No significant decrease of the VOR gain was found in space, but a change in phase was noted. A significant increase of the VOR gain was found 14 h after landing. Control experiments have been done on ground on several subjects. They indicate that pitch VOR gain during active head movements is about one, with eyes open in darkness at 1 Hz.