To explore the mechanism of tobacco addiction using structural and functional MRI: a preliminary study of the role of the cerebellum-striatum circuit.

Previous studies have found that the striatum and the cerebellum played important roles in nicotine dependence, respectively. In heavy smokers, however, the effect of resting-state functional connectivity of cerebellum-striatum circuits in nicotine dependence remained unknown. This study aimed to explore the role of the circuit between the striatum and the cerebellum in addiction in heavy smokers using structural and functional magnetic resonance imaging. The grey matter volume differences and the resting-state functional connectivity differences in cerebellum-striatum circuits were investigated between 23 heavy smokers and 23 healthy controls. The cigarette dependence in heavy smokers and healthy controls were evaluated by using Fagerström Test. Then, we applied mediation analysis to test whether the resting-state functional connectivity between the striatum and the cerebellum mediates the relationship between the striatum morphometry and the nicotine dependence in heavy smokers. Compared with healthy controls, the heavy smokers' grey matter volumes decreased significantly in the cerebrum (bilateral), and increased significantly in the caudate (bilateral). Seed-based resting-state functional connectivity analysis showed significantly higher resting-state functional connectivity among the bilateral caudate, the left cerebellum, and the right middle temporal gyrus in heavy smokers. The cerebellum-striatum resting-state functional connectivity fully mediated the relationship between the striatum morphometry and the nicotine dependence in heavy smokers. Heavy smokers showed abnormal interactions and functional connectivity between the striatum and the cerebellum, which were associated with the striatum morphometry and nicotine dependence. Such findings could provide new insights into the neural correlates of nicotine dependence in heavy smokers.

Deep Semantic Segmentation Feature-Based Radiomics for the Classification Tasks in Medical Image Analysis.

Recently, an emerging trend in medical image classification is to combine radiomics framework with deep learning classification network in an integrated system. Although this combination is efficient in some tasks, the deep learning-based classification network is often difficult to capture an effective representation of lesion regions, and prone to face the challenge of overfitting, leading to unreliable features and inaccurate results, especially when the sizes of the lesions are small or the training dataset is small. In addition, these combinations mostly lack an effective feature selection mechanism, which makes it difficult to obtain the optimal feature selection. In this paper, we introduce a novel and effective deep semantic segmentation feature-based radiomics (DSFR) framework to overcome the above-mentioned challenges, which consists of two modules: the deep semantic feature extraction module and the feature selection module. Specifically, the extraction module is utilized to extract hierarchical semantic features of the lesions from a trained segmentation network. The feature selection module aims to select the most representative features by using a novel feature similarity adaptation algorithm. Experiments are extensively conducted to evaluate our method in two clinical tasks: the pathological grading prediction in pancreatic neuroendocrine neoplasms (pNENs), and the prediction of thrombolytic therapy efficacy in deep venous thrombosis (DVT). Experimental results on both tasks demonstrate that the proposed method consistently outperforms the state-of-the-art approaches by a large margin.

Fully Automated Segmentation of Lower Extremity Deep Vein Thrombosis Using Convolutional Neural Network.

OBJECTIVE: Deep vein thrombosis (DVT) is a disease caused by abnormal blood clots in deep veins. Accurate segmentation of DVT is important to facilitate the diagnosis and treatment. In the current study, we proposed a fully automatic method of DVT delineation based on deep learning (DL) and contrast enhanced magnetic resonance imaging (CE-MRI) images. METHODS: 58 patients (25 males; 28~96 years old) with newly diagnosed lower extremity DVT were recruited. CE-MRI was acquired on a 1.5 T system. The ground truth (GT) of DVT lesions was manually contoured. A DL network with an encoder-decoder architecture was designed for DVT segmentation. 8-Fold cross-validation strategy was applied for training and testing. Dice similarity coefficient (DSC) was adopted to evaluate the network's performance. RESULTS: It took about 1.5s for our CNN model to perform the segmentation task in a slice of MRI image. The mean DSC of 58 patients was 0.74± 0.17 and the median DSC was 0.79. Compared with other DL models, our CNN model achieved better performance in DVT segmentation (0.74± 0.17 versus 0.66±0.15, 0.55±0.20, and 0.57±0.22). CONCLUSION: Our proposed DL method was effective and fast for fully automatic segmentation of lower extremity DVT.

Perceived burden in adherence of antiretroviral treatment in rural China.

To determine the level of antiretroviral treatment adherence and explore the correlated factors of perceived burden of taking antiretroviral medications among people living with HIV (PLH) in a rural area of China. Data were collected from 66 PLH who were currently receiving antiretroviral treatment. Face-to-face interviews were conducted during August to October, 2009. Approximately 18.2% of participants failed to adhere to antiretroviral treatment in the previous 30 days. A majority of PLH reported that taking antiretroviral medications posed a burden to them. Those who perceived a higher level of burden were more likely to be women, to have lower annual income, and to report a high level of depressive symptoms, poor physical health, and strained family interactions. Findings suggest that future programs in promoting adherence to antiretroviral treatment should address issues related to psychosocial well-being and PLH's interactions with their family members.

Parents living with HIV and children's stress and delinquent behaviors in China.

OBJECTIVE: The current study aims to explore the association of parents living with HIV (PLHs) and their children's self-esteem, everyday stress, and delinquent behaviors. DESIGN: The study samples included 79 families with 79 PLHs and 79 children. METHODS: Multiple regression analysis was used on baseline data collected in 2009 from a pilot study in Anhui Province, China. RESULTS: The results indicated that children from a family with both parents infected with HIV or children from families having multiple children were more likely to report a higher level of everyday stress. Male PLHs have significant influence on their children's everyday stress compared with female PLHs. Children reporting a lower level of parental care and lower self-esteem were significantly more likely to report a higher level of delinquent behaviors. In addition, we have found a strong positive correlation between families with multiple children and their children's delinquent behaviors. CONCLUSIONS: The findings indicate that the severity of psychological and behavioral problems of children living in different HIV-affected families may be dependent not only on factors related to the children but also on factors related to their parents and families. Therefore, parental and family level factors should be considered when providing care and support to children living in HIV-affected families.

A multilevel intervention for HIV-affected families in China: Together for Empowerment Activities (TEA).

This article analyzes the efficacy of the Together for Empowerment Activities (TEA) intervention in decreasing depressive symptoms and improving social support for persons living with HIV (PLH) and their family members. A total of 79 families, consisting of 88 PLH and 79 family members, were recruited from Anhui province, China, and randomized to the TEA intervention (n = 38) or a control condition (n = 41). The intervention was delivered at three levels: 1) TEA Gathering (small group for PLH and family members); 2) TEA Time (home-based family activities with children that accompany each TEA Gathering); and 3) TEA Garden (community events that build social integration). Face-to-face interviews were administered at baseline, 3, and 6 months. Mixed-effects regression models and kernel density estimation were used for data analysis. PLH and their family members in the intervention reported significant improvements in depressive symptoms, social support, and family functioning at the 3-month and 6-month follow-up assessments compared to those in the control condition. Heterogeneous intervention effects on social support and family functioning were indicated at the 6-month follow-up. The intervention could have various effect patterns for different subgroups within the intervention condition. This study provides preliminary data to support the feasibility and efficacy of a multilevel intervention.

Functional anatomy of the extraocular muscles during vergence.

Magnetic resonance imaging (MRI) now enables precise visualisation of the mechanical state of the living human orbit, enabling inferences about the effects of mechanical factors on ocular kinematics. We used 3-dimensional (3D) magnetic search coil recordings and MRI to investigate the mechanical state of the orbit during vergence in humans. Horizontal convergence of 23 degrees from a remote to a near target aligned on one eye was geometrically ideal, and was associated with lens thickening and extorsion of the rectus pulley array of the aligned eye with superior oblique muscle relaxation and inferior oblique muscle contraction. There was no rectus muscle co-contraction. Subjective fusion through a 1 degree vertical prism caused a clockwise (CW) torsion in both eyes, as well as variable vertical and horizontal vergences that seldom corresponded to prism amount or direction. MRI under these conditions did not show consistent torsion of the rectus pulley array, but a complex pattern of changes in rectus extraocular muscle (EOM) crossections, consistent with co-contraction. Binocular fusion during vergence is accomplished by complex, 3D eye rotations seldom achieving binocular retinal correspondence. Vergence eye movements are sometimes associated with changes in rectus EOM pulling directions, and may sometimes be associated with co-contraction. Thus, extraretinal information about eye position would appear necessary to interpret binocular correspondence, and to avoid diplopia.

Unilateral deafferentation and eye position misdirect the initial vestibulo-ocular reflex: a model-based study.

PURPOSE: Orbital eye position and vestibular sensitivity have both been postulated to influence vestibulo-ocular reflex (VOR) axis direction. The interaction of these factors in unilateral vestibular deafferentation (UVD) was examined. METHODS: Initial VOR direction and magnitude were examined in six normal human subjects and five with UVD during transient whole-body yaw at 2800 deg/s(2). The effect of eye position was evaluated by computing the tilt angle ratio (TAR), the ratio of change in VOR axis orientation relative to change in target direction for targets 20 degrees up or down. RESULTS: Gain during the initial 50 ms in UVD subjects was 0.66 +/- 0.13 (mean +/- SD) during contralesional, and 0.30 +/- 0.16 during ipsilesional rotation, but 0.87 +/- 0.02 in normal control subjects. In control subjects VOR axis direction was independent of stimulus direction. During ipsilesional rotation, subjects with UVD had a significant (P < 0.01) initial forward VOR axis tilt relative to contralesional rotation averaging 9.5 +/- 4.9 degrees , which was evident 20 ms after rotation. Initial TAR was 0.18 +/- 0.08 in control subjects and 0.32 +/- 0.08 in subjects with UVD. Since Listing's Law (LL) requires 0.5 TAR, whereas a VOR axis perfectly aligned with head axis requires 0, the observed intermediate TAR implies a compromise between the two criteria. In the interval 150 to 200 ms after rotation onset, subjects with UVD had 0.21 +/- 0.06 TAR during contralesional rotation and 0.50 +/- 0.11 during ipsilesional rotation, suggesting late synergy between the VOR and visual pursuit. CONCLUSIONS: A vector-based model accounts for observed axis tilt based on semicircular canal directional sensitivity and response saturation. Overall, the deviating effect of eye position on VOR axis is not influenced by UVD, but canal nonlinearity and geometric orientation account for the additional VOR axis error.

Three dimensional kinematics of rapid compensatory eye movements in humans with unilateral vestibular deafferentation.

Saccades executed with the head stationary have kinematics conforming to Listing's law (LL), confining the ocular rotational axis to Listing's plane (LP). In unilateral vestibular deafferentation (UVD), the vestibulo-ocular reflex (VOR), which does not obey LL, has at high head acceleration a slow phase that has severely reduced velocity during ipsilesional rotation, and mildly reduced velocity during contralesional rotation. Studying four subjects with chronic UVD using 3D magnetic search coils, we investigated kinematics of stereotypic rapid eye movements that supplement the impaired VOR. We defined LP with the head immobile, and expressed eye and head movements as quaternions in LP coordinates. Subjects underwent transient whole body yaw at peak acceleration 2,800 degrees /s(2) while fixating targets centered, or 20 degrees up or down prior to rotation. The VOR shifted ocular torsion out of LP. Vestibular catch-up saccades (VCUS) occurred with mean latency 90 +/- 44 ms (SD) from ipsilesional rotation onset, maintained initial non-LL torsion so that their quaternion trajectories paralleled LP, and had velocity axes changing by half of eye position. During contralesional rotation, rapid eye movements occurred at mean latency 135 +/- 36 ms that were associated with abrupt decelerations (ADs) of the horizontal slow phase correcting 3D deviations in its velocity axis, with quaternion trajectories not paralleling LP. Rapid eye movements compensating for UVD have two distinct kinematics. VCUS have velocity axis dependence on eye position consistent with LL, so are probably programmed in 2D by neural circuits subserving visual saccades. ADs have kinematics that neither conform to LL nor match the VOR axis, but appear instead programmed in 3D to correct VOR axis errors.

Shifts in listing's plane produced by vertical axis rotation: sustained ocular torsion due to semicircular canal stimulation.

PURPOSE: With the head upright and stationary, ocular torsion is confined by Listing's Law (LL), so that three-dimensional eye rotational axes form Listing's plane (LP). During head rotation, the vestibulo-ocular reflex violates LL by driving ocular torsion opposite to head torsion, sometimes out of LP. Saccades originating from non-Listing's initial torsional positions remain in a plane offset from, but parallel to, the original LP. The present study was conducted to determine whether whole-body yaw alters the position and orientation of LP. METHODS: Eight normal subjects and six with unilateral vestibular deafferentation (UVD) underwent binocular eye and head movement recordings with 3-D magnetic search coils. Visual fixations were used to define LP, after which subjects underwent whole-body yaw rotation of 30 degrees or 70 degrees , at peak accelerations from 125 deg/s(2) to 2800 deg/s(2). Gaze during rotation was either central or 20 degrees up. After rotation, a dynamic LP (DLP) was defined during fixations. RESULTS: Orientation and thickness of the DLP did not vary significantly from the previously defined LP; however, DLP was offset an average of 4 degrees +/- 4 degrees (mean +/- SD), 87% of head torsion relative to LP. Stimulus intensity, UVD, and starting vertical gaze direction had no effect on DLP offset or orientation. The DLP torsional offset declined toward the original LP with a time constant of approximately 1 minute, suggesting mediation by neural integration. CONCLUSIONS: Yaw rotation can cause stable torsional offsets in the location of Listing's Plane.

Temporal dynamics of semicircular canal and otolith function following acute unilateral vestibular deafferentation in humans.

Dynamic changes of deficits in canal and otolith vestibulo-ocular reflexes (VORs) to high acceleration, eccentric yaw rotations were investigated in five subjects aged 25-65 years before and at frequent intervals 3-451 days following unilateral vestibular deafferentation (UVD) due to labyrinthectomy or vestibular neurectomy. Eye and head movements were recorded using magnetic search coils during transients of directionally random, whole-body rotation in darkness at peak acceleration 2,800 degrees/s2. Canal VORs were characterized during rotation about a mid-otolith axis, viewing a target 500 cm distant until rotation onset in darkness. Otolith VOR responses were characterized by the increase in VOR gain during identical rotation about an axis 13 cm posterior to the otoliths, initially viewing a target 15 cm distant. Pre-UVD canal gain was directionally symmetrical, averaging 0.87 +/- 0.02 (+/-SEM). Contralesional canal gain declined from pre-UVD by an average of 22% in the first 3-5 days post-UVD, before recovering to an asymptote of close 90% of pre-UVD level at 1-3 months. This recovery corresponded to resolution of spontaneous nystagmus. Ipsilesional gain declined to 59%, and showed no consistent recovery afterwards. Pre-UVD otolith gain was directionally symmetrical, averaging 0.56 +/- 0.02. Immediately after UVD, the contralesional otolith gain declined to 0.30 +/- 0.02, and did not recover. Ipsilesional otolith gain declined profoundly to 0.08 +/- 0.03 (P < 0.01), and never recovered. In contrast to the modest and directionally symmetrical effect of UVD on the human otolith VOR during pure translational acceleration, otolith gain during eccentric yaw rotation exhibited a profound and lasting deficit that might be diagnostically useful in lateralizing otolith pathology. Most recovery of the human canal gain to high acceleration transients following UVD is for contralesional head rotation, occurring within 3 months as spontaneous nystagmus resolves.

Effect of unilateral vestibular deafferentation on the initial human vestibulo-ocular reflex to surge translation.

Transient whole-body surge (fore-aft) translation at 0.5 G peak acceleration was administered to six subjects with unilateral vestibular deafferentation (UVD), and eight age-matched controls. Subjects viewed eccentric targets to determine if linear vestibulo-ocular reflex (LVOR) asymmetry might lateralize otolith deficits. Eye rotation was measured using magnetic search coils. Immediately before surge, subjects viewed a luminous target 50 cm away, centered or displaced 10 degrees horizontally or vertically. The target was extinguished during randomly directed surges. LVOR gain relative to ideal velocity in subjects with UVD for the contralesional horizontally eccentric target (0.59 +/- 0.08, mean +/- SEM) did not differ significantly from normal (0.50 +/- 0.04), but gain for the ipsilesional eccentric target (0.35 +/- 0.02) was significantly less than normal (0.48 +/- 0.03, P < 0.05). Normal subjects had mean gain asymmetry for horizontally eccentric targets of 0.17 +/- 0.03, but asymmetry in UVD was significantly increased to 0.35 +/- 0.05 (P < 0.05). Four of six subjects with UVD had maximum gain asymmetry outside normal 95% confidence limits. Asymmetry did not correlate with UVD duration. Gain for 10 degrees vertically eccentric targets averaged 0.38 +/- 0.14 for subjects with UVD, insignificantly lower than the normal value of 0.75 +/- 0.15 (P > 0.05). Surge LVOR latency was symmetrical in UVD, and did not differ significantly from normal. There was no significant difference in response between dark and visible target conditions until 200 ms after surge onset. Chronic human UVD, on average, significantly impairs the surge LVOR for horizontally eccentric targets placed ipsilesionally, but this asymmetry is small relative to interindividual variation.

Temporal dynamics of ocular position dependence of the initial human vestibulo-ocular reflex.

PURPOSE: While an ideal vestibulo-ocular reflex (VOR) generates ocular rotations compensatory for head motion, during visually guided movements, Listing's Law (LL) constrains the eye to rotational axes lying in Listing's Plane (LP). The present study was conducted to explore the recent proposal that the VOR's rotational axis is not collinear with the head's, but rather follows a time-dependent strategy intermediate between LL and an ideal VOR. METHODS: Binocular LPs were defined during visual fixation in eight normal humans. The VOR was evoked by a highly repeatable transient whole-body yaw rotation in darkness at a peak acceleration of 2800 deg/s2. Immediately before rotation, subjects regarded targets 15 or 500 cm distant located at eye level, 20 degrees up, or 20 degrees down. Eye and head responses were compared with LL predictions in the position and velocity domains. RESULTS: LP orientation varied both among subjects and between individual subject's eyes, and rotated temporally with convergence by 5 +/- 5 degrees (+/-SEM). In the position domain, the eye compensated for head displacement even when the head rotated out of LP. Even within the first 20 ms from onset of head rotation, the ocular velocity axis tilted relative to the head axis by 30% +/- 8% of vertical gaze position. Saccades increased this tilt. Regardless of vertical gaze position, the ocular rotation axis tilted backward 4 degrees farther in abduction than in adduction. There was also a binocular vertical eye velocity transient and lateral tilt of the ocular axis. CONCLUSIONS: These disconjugate, short-latency axis perturbations appear intrinsic to the VOR and may have neural or mechanical origins.

Vestibulo-ocular reflex to transient surge translation: complex geometric response ablated by normal aging.

The linear vestibulo-ocular reflex (LVOR) to surge (fore-aft) translation has complex kinematics varying with target eccentricity and distance. To determine normal responses and aging changes, 9 younger [age, 28 +/- 2 (SE) yr] and 11 older subjects (age, 69 +/- 2 yr) underwent 0.5 g whole body surge transients while wearing binocular scleral search coils. Linear chair position and head acceleration were measured with a potentiometer and accelerometer. Subjects viewed centered and 10 degrees horizontally and vertically eccentric targets 50, 25, or 15 cm distant before unpredictable onset of randomly directed surge in darkness (LVOR) and light (V-LVOR). Response directions were kinematically appropriate to eccentricity in all subjects, but there were significantly more measurable LVOR and V-LVOR responses (63-79%) in younger than older subjects (38-44%, P < 0.01). Minimal LVOR latency averaged 48 +/- 4 ms for younger and significantly longer at 70 +/- 6 ms for older subjects. In the interval 200-300 ms after surge onset, horizontal LVOR gain (relative to ideal velocity) of younger subjects averaged over all target distances was 0.55 +/- 0.04 and was significantly reduced in older subjects to 0.33 +/- 0.04. Horizontal V-LVOR gain was 0.58 +/- 0.04 in younger and significantly lower at 0.35 +/- 0.06 in older subjects. Vertical gains did not differ significantly between groups. Target visibility had no effect in either group during the initial 200 ms. The LVOR and V-LVOR were augmented by saccades in younger more than older subjects. Aging thus decreases LVOR velocity gain, response rate, and saccade augmentation, but prolongs latency.

Kinematics of vertical saccades during the yaw vestibulo-ocular reflex in humans.

PURPOSE: Listing's law (LL) constrains the rotational axes of saccades and pursuit eye movements to Listing's plane (LP). In the velocity domain, LL is ordinarily equivalent to a tilt in the ocular velocity axis equal to half the change in eye position, giving a tilt angle ratio (TAR) of 0.5. This study was undertaken to investigate vertical saccade behavior after the yaw vestibulo-ocular reflex (VOR) had driven eye torsion out of LP, an initial condition causing the position and velocity domain formulations of LL to differ. METHODS: Binocular eye and head motions were recorded with magnetic search coils in eight humans. With the head immobile, LP was determined for each eye, and mean TAR was 0.50 +/- 0.07 (mean +/- SD) for horizontal and 0.45 +/- 0.11 for vertical saccades. The VOR was evoked by transient, whole-body yaw at 2800 deg/s2 peak acceleration, capable of evoking large, uninterrupted VOR slow phases. Before rotation, subjects viewed a target at eye level, 20 degrees up, or 20 degrees down. In two thirds of the trials, the target moved upward or downward at systematically varying times, triggering a vertical saccade during the horizontal VOR slow phase. RESULTS: Because the head rotation axis was generally misaligned with LP, the eye averaged 3.6 degrees out of LP at vertical saccade onset. During the saccade, eye position continued to depart LP by an average 0.8 degrees. The horizontal TAR at saccade onset was 0.29 +/- 0.07. At peak saccade velocity 35 +/- 3 ms later, the vertical TAR was 0.45 +/- 0.07, statistically similar to that of head fixed saccades. Saccades did not return to LP. CONCLUSIONS: Although they did not observe the position domain formulation of LL, vertical saccades, during the VOR, observed the half-angle velocity domain formulation of LL.

Human angular vestibulo-ocular reflex axis disconjugacy: relationship to magnetic resonance imaging evidence of globe translation.

Magnetic resonance imaging (MRI) demonstrates that the lateral rectus pulley shifts 0.5 mm inferiorly relative to the medial rectus in 20 degrees upgaze, but 0.5 mm superiorly in 20 degrees downgaze, whereas the globe translates 0.7 mm nasally in adduction and 0.2 mm nasally in abduction. If pulleys influence ocular kinematics, these effects would predict disconjugate alterations of the yaw vestibulo-ocular reflex (VOR) rotational axes. Binocular eye and head movements were recorded using three-dimensional search coils in 8 humans (age 24 +/- 2 years, mean +/- SE) undergoing directionally randomized, transient, whole-body yaw (2800 degrees /s2 peak) in darkness while fixating straight ahead, as well as +/- 18 degrees vertically. Eye and head rotational velocity axes were expressed as quaternions in Listing coordinates. In the initial 70 ms, the ocular axis varied with vertical gaze by one-quarter the angle of target elevation, but this effect summed significantly with a disconjugate effect of horizontal duction. In central gaze, the mean adducting eye (AD) rotational axis tilted 3.4 +/- 0.8 degrees forward relative to the head axis, while that of the abducting eye (AB) tilted 0.6 +/- 0.8 degrees backward. In downgaze, the AD rotational axis tilted 8.6 +/- 1.0 degrees forward, and AB 5.7 +/- 1.2 degrees forward. In upgaze, the AD rotational axis tilted backward by 0.1 +/- 0.7 degrees, and AB backward 3.4 +/- 0.9 degrees. We suggest that nasal globe translation relative to the fixed trochlea produces binocular extorsion accounting for yaw VOR axis disconjugacy, and thus a horizontal duction dependence in VOR rotational axis summating with classic dependence of VOR axis on vertical gaze. Confirmation of predicted duction-dependent VOR disconjugacy supports the idea that rectus pulleys influence kinematics for all eye movements.

Human angular vestibulo-ocular reflex initiation: relationship to Listing's law.

An ideal vestibulo-ocular reflex (VOR) generates ocular rotations compensatory for head motion. During visually guided movements, Listing's law (LL) constrains eye rotation to axes in Listing's plane (LP). Recently, it has been reported that the VOR axis is not collinear with the rotation axis of the head, but is influenced by eye position in the orbit. Elaborate models have been proposed suggesting dynamic neural control of the VOR axis. By examining the variability and time course of changes in VOR axis orientation, we sought to test plausibility of these models. Binocular LPs were defined in eight humans. The VOR was evoked by a highly repeatable, transient, whole-body yaw rotation in darkness at peak acceleration 2800 deg/s2. Immediately prior to rotation, subjects regarded targets at eye level, 20 degrees up, or 20 degrees down. Eye and head positions were expressed in LP coordinates for comparison with LL. Eye position generally followed head position and departed LP when the head axis tilted out of LP. In the velocity domain the VOR axis tilted 28 +/- 9% of the change in vertical eye position, but there was significant intrasubject variation (14% to 41%). This roughly "quarter-angle" behavior began with the earliest detectable VOR. Given the brief latency and marked interindividual variability of the eye position dependence of the VOR rotational axis, and the small deviation of the VOR from LL in the position domain, it is speculated that this behavior is largely due to orbital mechanics interacting with the basic neural commands that initiate the VOR.

Human surge linear vestibulo-ocular reflex during tertiary gaze viewing.

The otolith-mediated linear vestibulo-ocular reflex (IVOR) was studied in 9 normal humans undergoing transient whole-body surges at 0.5 g peak acceleration while viewing targets eccentrically placed in tertiary positions that combined horizontal and vertical eccentricities at distance of 15, 25, or 50 cm both in darkness and light. Mean velocity gain (+/-SEM) for the horizontal component was 0.61 +/- 0.04 in darkness and increased to 0.72 +/- 0.03 for visible targets (P < 0.05), and for the vertical component was 0.54 +/- 0.02 in darkness, not significantly different from horizontal component gain. For visible targets, vertical component gain significantly increased to 0.63 +/- 0.04 (P < 0.05) with visible targets, but remained significantly less than horizontal component gain.

Initiation and cancellation of the human heave linear vestibulo-ocular reflex after unilateral vestibular deafferentation.

The effect of unilateral vestibular deafferentation (UVD) on the linear vestibulo-ocular reflex (LVOR) was studied in 11 humans an average of 52 months following surgical UVD. Controls consisted of seven healthy age-matched subjects. The LVOR was evoked by directionally random, transient whole body interaural (heave) translation with a peak acceleration of 0.5 g while subjects viewed earth-fixed (LVOR) and head-fixed (cancellation) targets 15, 25, and 200 cm distant. The magnitude of the LVOR slow phase was inversely proportional to target distance for both subject groups. Neither latency nor the magnitude of the LVOR significantly differed in the ipsi- vs contralesional directions (P>0.1) in UVD. When the target disappeared at heave onset, subjects with UVD had LVOR slow phase displacement 100 ms later that was 5% of ideal at 15 cm, 6% at 25 cm, and 16% at 200 cm. This was significantly less than corresponding control values of 41, 43, and 50%. During cancellation the LVOR magnitude 100 ms from heave onset was reduced at all target distances by an average of 40+/-4%, and the relative reduction did not significantly differ between controls and subjects with UVD (P>0.1). Cancellation latency did not vary significantly among target distances or subject groups. It is concluded that after UVD, the LVOR is bilaterally and symmetrically reduced but remains modulated by viewing distance and cancellation effort.

Vestibular catch-up saccades augmenting the human transient heave linear vestibulo-ocular reflex.

Vestibular catch-up saccades (VCUS) cued by the semicircular canals can supplement the deficient angular vestibulo-ocular reflex during transient rotations to stabilize gaze in people with unilateral vestibular deafferentation (Tian et al. 2000). However, a possible analogous role for VCUS to augment a deficient linear vestibulo-ocular reflex (LVOR) has not been carefully studied. We investigated VCUS in 9 younger, 8 older normal, and 12 vestibulopathic subjects undergoing directionally random heave (interaural) translations at 0.5 g peak acceleration. Eye and head movements were sampled at 1200 Hz using magnetic search coils and a cranial accelerometer. Subjects fixated visible targets 200, 50, or 15 cm distant immediately before unpredictable onset of translation in either darkness or light. Evoked slow phase eye rotations opposite to the direction of head translation accounted for only 19-70% of ideal eye position, being less for nearer targets, and VCUS commonly occurred to augment the deficiency. Eye position error relative to geometric ideal was highly correlated to VCUS amplitude ( P<0.001). This error was systematically corrected by VCUS whose latency decreased, and speed and frequency increased, with decreasing target distance. When targets remained visible, nearly all subjects made VCUS for nearer targets. In darkness, VCUS for the nearest target were significantly less common for older normal and vestibulopathic subjects than in younger normal subjects ( P<0.001). In older and vestibulopathic subjects, VCUS latency was significantly prolonged. We conclude that otolith-mediated VCUS calibrated to target distance assist LVOR slow phases, but the ability to generate VCUS in darkness is impaired in older normal and vestibulopathic subjects. In the presence of visual information, VCUS can be generated in older and vestibulopathic subjects, albeit at prolonged latency perhaps indicating visual augmentation of deficient vestibular input.