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Although the pull of gravity, primarily detected by the labyrinth, is the fundamental input for our sense of upright, vision and proprioception must also be integrated with vestibular information into a coherent perception of spatial orientation. Here, we used transcranial magnetic stimulation (TMS) to probe the role of the cortex at the temporal parietal junction (TPJ) of the right cerebral hemisphere in the perception of upright. We measured the perceived vertical orientation of a visual line; that is, the subjective visual vertical (SVV), after a short period of continuous theta burst stimulation (cTBS) with the head upright. cTBS over the posterior aspect of the supramarginal gyrus (SMGp) in 8 right-handed subjects consistently tilted the perception of upright when tested with the head tilted 20° to either shoulder (right: 3.6°, left: 2.7°). The tilt of SVV was always in the direction opposite to the head tilt. On the other hand, there was no significant tilt after sham stimulation or after cTBS of nearby areas. These findings suggest that a small area of cerebral cortex--SMGp--has a role in processing information from different sensory modalities into an accurate perception of upright.

Background Perception of upright is often assessed by aligning a luminous line to the subjective visual vertical (SVV). Objective Here we investigated the effects of visual line rotation and viewing eye on SVV responses and whether there was any change with head tilt. Methods SVV was measured using a forced-choice paradigm and by combining the following conditions in 22 healthy subjects: head position (20° left tilt, upright and 20° right tilt), viewing eye (left eye, both eyes and right eye) and direction of visual line rotation (clockwise [CW] and counter clockwise [CCW]). Results The accuracy and precision of SVV responses were not different between the viewing eye conditions in all head positions (P> 0.05, Kruskal-Wallis test). The accuracy of SVV responses was % significantly different between the CW and CCW line rotations (p ≈ 0.0001; Kruskal-Wallis test) and SVV was tilted in the same direction as the line rotation. This effect of line rotation was however not consistent across head tilts and was only present in the upright and right tilt head positions. The accuracy of SVV responses showed a higher variability among subjects in the left head tilt position with no significant difference between the CW and CCW line rotations (P> 0.05; post-hoc Dunn's test). Conclusions In spite of the challenges to the estimate of upright with head tilt, normal subjects did remarkably well irrespective of the viewing eye. The physiological significance of the asymmetry in the effect of line rotation between the head tilt positions is unclear but it %may suggest suggests a lateralizing effect of head tilt on the visual perception of upright.

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

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 (± 45Âř) 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 ±45Âř vs. −45Âř (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/ f & b e t a ; 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 ± 45Âř indicates that the brain has limited ability to estimate oblique angles.

To examine patterns of executive and oculomotor control in a group of both boys and girls with attention-deficit/hyperactivity disorder (ADHD).Cross-sectional study of 120 children aged 8 to 12 years, including 60 with ADHD (24 girls) and 60 typically developing controls (29 girls). Oculomotor paradigms included visually guided saccades (VGS), antisaccades, memory-guided saccades, and a go/no-go test, with variables of interest emphasizing response preparation, response inhibition, and working memory.As a group, children with ADHD demonstrated significant deficits in oculomotor response preparation (VGS latency and variability) and response inhibition but not working memory. Girls, but not boys with ADHD, had significantly longer VGS latencies, even after controlling for differences in ADHD symptom severity. The ADHD subtypes did not differ on response preparation or inhibition measures; however, children with the Inattentive subtype were less accurate on the working memory task than those with the Combined subtype.Sex differences in children with ADHD extend beyond symptom presentation to the development of oculomotor control. Saccade latency may represent a specific deficit among girls with ADHD.

Fragile X and Turner syndromes are two X-chromosome-related disorders associated with executive function and visual spatial deficits. In the present study, we used ocular motor paradigms to examine evidence that disruption to different neurological pathways underlies these deficits. We tested 17 females with fragile X, 19 females with Turner syndrome, and 40 females with neither disorder who comprised the comparison group. Group differences emerged for both the fragile X and Turner syndrome groups, each relative to the comparison group: Females with fragile X had deficits in generating memory-guided saccades, predictive saccades, and saccades made in the overlap condition of a gap/overlap task. Females with Turner syndrome showed deficits in generating memory-guided saccades, but not during either the predictive saccade or gap/overlap task. Females with Turner syndrome, but not females with fragile X, showed deficits in visually guided saccades and anti-saccades. These findings indicate that different brain regions are affected in the two disorders, and suggest that different pathways lead to the similar cognitive phenotypes described for fragile X and Turner syndromes.

Torsional eye movements are rotations of the eye around the line of sight. Measuring torsion is essential to understanding how the brain controls eye position and how it creates a veridical perception of object orientation in three dimensions. Torsion is also important for diagnosis of many vestibular, neurological, and ophthalmological disorders. Currently, there are multiple devices and methods that produce reliable measurements of horizontal and vertical eye movements. Measuring torsion, however, noninvasively and reliably has been a longstanding challenge, with previous methods lacking real-time capabilities or suffering from intrusive artifacts. We propose a novel method for measuring eye movements in three dimensions using modern computer vision software (OpenCV) and concepts of iris recognition. To measure torsion, we use template matching of the entire iris and automatically account for occlusion of the iris and pupil by the eyelids. The current setup operates binocularly at 100 Hz with noise

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.

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.

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.

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.

Studies of eye movements in patients with Huntington's disease (HD) have suggested that frontal lobe-basal ganglia structures are more involved in HD than the parietal lobes. To test this hypothesis further we compared the ability of HD patients and normal subjects to direct “covert” visual attention, using saccade latency and thumb press reaction time tasks that have been shown to be sensitive to parietal lobe dysfunction. Subjects were instructed to move their eyes or to press a button when a peripheral target was illuminated. The peripheral stimulus appeared at various intervals after the appearance of a central arrow(s) that pointed in the direction of the target (valid cue), in the opposite direction (invalid cue), or pointed simultaneously in both directions (neutral cue). For both saccade and thumb press paradigms, the difference in the latencies for trials with invalid and valid cues was the same in HD patients and normals. These findings suggest that the ability to direct visual attention is normal in HD and are compatible with the hypothesis that in HD, frontal-basal ganglia circuits are more affected than parietal lobe pathways.

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.

Previously we have shown that repetitive predictive saccades to alternating visual targets are mediated by an internal clock. That is, when subjects track a periodic visual stimulus alternating at a high rate (a small inter-stimulus interval, ISI, of 500 or 833ms), they use an internal estimate of stimulus timing to pre-program the eye movement timing. Auditory pacing tones at the same rate also generate predictive saccades. It is natural to ask if an identical internal clock is used to generate the predictive saccades in each case. We hypothesized that if subjects can use auditory information to establish an internal estimate of stimulus timing—as we demonstrated can be done with visual targets—then the distributions of predictive inter-saccade intervals should demonstrate the well-known “Scalar Property” for either Auditory Cued or Visual Cued stimuli: inter-saccade interval histograms should be almost identical when each is divided by its mean. However, when making reactive saccades to a pacing stimulus (at a low rate), there should be a difference in the timing statistics between Auditory and Visual pacing, due to differences in sensory processing. We report here that the variances of inter-saccade intervals at three predictive pacing rates (ISIs of 500, 833, and 1000ms) are equivalent, whereas the variance for Auditory Cued Pacing was greater than that for Visual Cued Pacing during reactive saccades at two reactive pacing rates (ISIs of 1667 and 2500ms). When the inter-saccade interval histograms at the predictive pacing rates were normalized, the distributions were nearly identical for both Visual and Auditory Cued Pacing, which means that the Scalar Property holds for predictive saccades from either pacing stimulus. These results suggest that (1) an internal timing reference (clock) can be established by either auditory or visual information and (2) during predictive tracking the variability in saccade timing is due to the variability in the internal timing representation, while during reactive tracking the variability in saccade timing depends on the sensory modality used to trigger the saccades.

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.

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 (latency100 ms), predictive (-200 mslatency100 ms), or anticipatory (latency-200 ms). We also calculated arrival time (saccade latency+saccade duration). Instructions had a striking effect on predictive performance. The effects were greatest with the longest ISIs (1000 and 2000 ms) and the largest target displacement (40 degrees ). With the active instruction there were more predictive and anticipatory saccades and with the passive instruction more reflexive saccades. Furthermore, with the active instruction subjects could take into account the duration of the impending saccade so that the eyes would arrive closer to the appearance of the target no matter what the amplitude of the required saccade. In sum, cognitive set, as determined by the specific instructions given to the subject, has a striking effect on predictive saccade behavior, which has important implications for interpreting physiological and imaging correlates of predictive behavior in normals and in patients with neurological disease.

For the past decade, federal judges have been obligated to serve as gatekeepers and keep scientifically unreliable and irrelevant expert testimony out of the courtroom. The exacting evidentiary standards set forth in the landmark Daubert decision have had a significant impact on numerous areas of legal dispute. Toxic tort litigation, in particular, has been transformed by the standards. This Article reviews the Supreme Court's adoption of the scientific method as the standard for admissibility of expert testimony. It analyzes how a court's proper understanding of the scientific method can guide it in evaluating the different types of causation evidence presented in toxic tort litigation, both with respect to general and specific causation. Throughout this discussion and in the concluding section, the Article reflects the authors' firm's experience as national defense counsel in a series of product liability cases involving the prescription drug Parlodel, in which these evidentiary issues have been analyzed extensively.

Patients with neurofibromatosis 1 show neurocognitive deficits including abnormal visuospatial performance, but oculomotor behavior has not been studied. We recorded saccades in neurofibromatosis 1 and normal children, ages 6 to 12 years. Patients showed increased latency and diminished amplitude to more eccentric targets for both visually guided and memory-guided saccades. Subtracting the latencies of visually guided saccades from memory-guided saccades produced no differences between groups. For predictive saccades (0.5 Hz), patients with neurofibromatosis 1 generated fewer anticipatory saccades than normal subjects, but patients with neurofibromatosis 1 made more direction errors in an antisaccade task. Patients with neurofibromatosis 1 show saccade abnormalities that are not easily ascribed to dysfunction within single cortical areas. Rather, the findings likely reflect (1) partial involvement of different components of a widely distributed cerebral network that controls saccades, (2) impaired visuomotor maturation in a brain abnormal early in development, and (3) excessive γ-aminobutyric acid—mediated inhibition, which could influence basal ganglia pathways that modulate superior colliculus activity. ( J Child Neurol 2003;18:348—355).

To establish an objective Hess screen test that allows a simultaneous and binocular analysis of all three axes of eye rotation.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.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.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.

Within-lineage repeated-pair isonymy is calculated as RPW = sigma [Sij(Sij - 1)]/sigma [Si(Si - 1)], in which Sij is the number of a combination of two surnames in marriages (for total RPW, in both orders, brides first and also grooms first) and Si is the corresponding number of individuals of each surname (for total RPW of both sexes). In St. Ouen the 3479 native Jersey marriages between 1634 and 1914 yield a mean total RPW of 0.03314, which can be compared with a random isonymy (Ir) of 0.02205 and a marital isonymy (Im) of 0.04942. In the most recent time periods (1830-1914) there was an increase in RPW, but the increase is small if all marriages are considered rather than only native Jersey ones. In the Scilly Isles 2827 marriages between 1725 and 1975 yield a mean total RPW of 0.05127, which compares with a mean Ir of 0.01960 and an Im of 0.05238. In each kind of isonymy there is a decline over 1850-1975 caused by increased migration to the Scilly Isles. In the Scilly Isles RPW consistently approximately equals Im, so the nonrandom component of inbreeding is fully accounted for by factors that affect marital choice in the whole lineage. In St. Ouen, however, RPW is intermediate in value between Ir and Im, so the nonrandom component of inbreeding is only partly a lineage phenomenon and is also affected by other (individual) factors in choice of spouses.

Measurements of 133 adult offspring of exogamous matings and of 347 adult offspring of endogamous matings in a Mexican community were standardized for sex and prior international migration. The offspring of the exogamous matings were larger than those of the endogamous matings in 3 of 26 anthropometric dimensions. The probability of 3 or more in 26 dimensions at the 0.05 level is p = 0.14, not statistically significant. Comparisons of offspring of exogamous and endogamous unions in populations of this kind do not consistently provide evidence of heterosis.

For the neurologist, examination of eye movements at the bedside is a traditional mainstay of anatomic localization and often provides diagnostic certainty in complicated clinical problems. For the basic neuroscientist, recording and analysis of eye movements, both in behaving monkeys and in normal humans, have become powerful tools to understand normal ocular motor control and to probe higher-level cerebral mechanisms that underlie attention, memory, and decision making. The antisaccade task is an example of such a useful eye movement paradigm.1–3⇓⇓ In this task, the subject has to cancel willfully a “reflexive” saccade to a suddenly appearing visual stimulus (i.e., …

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.

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.

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.

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.

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.

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.

Article abstract-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 30) had peak saccade velocities lower than 300 deg/sec. Latencies for volitional saccades were greater than normal in the HD > 30 group, but were normal for the HD 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. NEUROLOGY 1988;38427-431 In a recent study of eye movements in mildly affected patients with Huntington’s disease (HD), we found abnormalities of both the initiation of saccades as well as the ability to hold steady fixation.’ Most patients showed an increase in saccade latencies that was greater for saccades made on command (voluntary saccades) than for saccades made to the sudden appearance of a visual stimulus (reflexive saccades). All patients showed excessive distractibility; they had difficulty in suppressing a saccade to a suddenly appearing visual target even though they were instructed either to maintain straight-ahead fixation or to make a saccade in the direction opposite to the visual target. We attributed these abnormalities to involvement of the frontal eye fields or basal ganglia in HD. In the present study, we report further abnormalities of eye movements-saccade slowing andsaccade dysmetria-in the same group of patients, and compare these findings with their deficits in saccade initiation and in holding steady fixation. Slow saccades have been noted in patients with HD with a reported prevalence of 18% to 100%.2-10 While one study did seem to show a correlation between the age of the patient and the saccade ~elocity,~ few attempts have been made to correlate saccade slowing with other saccade abnormalities in HD or with patient age or severity or duration of illne~s.~J~J~ In contrast to the saccade initiation and the fixation deficits, which have been attributed to involvement of the basal ganglia or cerebral hemispheres, saccade slowing has usually been attributed to direct pathologic involvement of the intrinsic brainstem structures that generate the immediate premotor commands for saccadic eye movement~.~-~ Accordingly, to better understand the eye movement abnormalities in HD, we compared disor

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.