Oculomotor function in the rhesus monkey after deafferentation of the extraocular muscles

The function of extraocular muscle proprioception in the control of eye movements remains uncertain. In this study, we examined the effect of bilateral proprioceptive deafferentation of the extraocular muscles on eye movements in two rhesus monkeys. Before and after deafferentation, we analyzed baseline ocular alignment, saccades, pursuit, and vestibular eye movements. We also examined visually mediated adaptation of ocular alignment, saccades, and pursuit. Deafferentation of the eye muscles did not affect baseline ocular motor control, either acutely or over a 5-week period of study. Furthermore, visually mediated adaptation of the eye movement subtypes was also unaffected by deafferentation. These results suggest that ocular proprioception in primates is not used in the immediate, on-line control of eye movements and does not interact with visual cues in the adaptive modification of ocular motor function. We conclude that the efferent command (efference copy) provides sufficient information about eye kinematics to the brain for accurate eye movement control in normal monkeys, and that this information is modified by visual feedback independently of proprioception. We hypothesize that proprioception may be used to calibrate the efference copy during development and in response to perturbations by signaling potential mismatches between eye movement information derived from the efferent command and the actual motion of the eye transduced by the proprioceptive organs.

Cerebellar lesions impair context-dependent adaptation of reaching movements in primates

To produce accurate movements when conditions change suddenly, the brain must be capable of learning multiple versions of a given motor task and must be able to access the appropriate program using sensory information linked to the context of the movement. The neural basis for context-dependent motor learning is uncertain, but the cerebellum is thought to play a fundamental role. In this study, we examined the effect of lesions of the dorsal vermal and paravermal cerebellar cortex on the adaptation of reaching movements produced by modified visual feedback and accessed with a visual cue. Two rhesus monkeys were trained to point to targets displayed on a video monitor while viewing monocularly with either eye. During the experimental sessions, visual information received by one eye (the "modified" eye) was displaced horizontally, while the information received by the other ("normal") eye remained unaltered. In the first set of experiments (noncontextual paradigm), the animals pointed to targets while viewing with the modified eye. This paradigm resulted in a gradual improvement in pointing accuracy when viewing with that eye, but also produced a shift in pointing responses of equivalent size when viewing with the normal eye. In the second set of experiments (contextual paradigm), the animals alternated six blocks of reaches while viewing monocularly with the modified eye with six blocks viewing with the normal eye. This paradigm improved the pointing accuracy when viewing with the modified eye, but produced only a small shift in pointing responses when viewing with the normal eye. After the dorsal vermal and paravermal cerebellar cortex were resected, no change occurred in the pattern of adaptation produced by the noncontextual paradigm. The contextual paradigm, however, no longer selectively adapted pointing responses for each eye, but rather produced a pointing shift of equivalent size when viewing with either eye. The results indicate that pointing responses can be differentially adapted for each viewing eye, which is a form of context-dependent motor learning. This capability was lost after focal lesions of the dorsal vermal and paravermal cerebellar cortex, suggesting that these regions of cerebellar cortex are required to learn or store multiple representations of a movement, or to retrieve the appropriate motor program in a given sensory context.

Ocular motor dysfunction in Lesch-Nyhan disease

Eye movements were assessed in 22 patients with varying degrees of hypoxanthine-guanine phosphoribosyltransferase deficiency. Ocular motility was clinically normal in seven patients with moderate enzyme deficiency but grossly abnormal in 15 patients with severe enzyme deficiency. In patients with severe deficiency, fixation was interrupted by frequent unwanted saccades toward minor visual distractions. Voluntary saccades were associated with an initial head movement and/or eyeblink in all of these patients. When head motion was prevented, voluntary saccades were often delayed and sometimes absent. In contrast, saccade speed, reflexive saccades, and other reflexive eye movements appeared clinically normal. Four patients with severe enzyme deficiency also experienced mild blepharospasm, and two had ocular tics. These disturbances of ocular motility are consistent with dysfunction of the basal ganglia or its connections with ocular motor centers in the prefrontal cortex or midbrain.

Comparison of diameter and perimeter methods for tumor volume calculation

PURPOSE

Lesion volume is often used as an end point in clinical trials of oncology therapy. We sought to compare the common method of using orthogonal diameters to estimate lesion volume (the diameter method) with a computer-assisted planimetric technique (the perimeter method).

METHODS

Radiologists reviewed 825 magnetic resonance imaging studies from 219 patients with glioblastoma multiforme. Each study had lesion volume independently estimated via the diameter and perimeter methods. Cystic areas were subtracted out or excluded from the outlined lesion. Inter- and intrareader variability was measured by using multiple readings on 48 cases. Where serial studies were available in noncystic cases, a mock response analysis was used.

RESULTS

The perimeter method had a reduced interreader and intrareader variability compared with the diameter method (using SD of differences): intrareader, 1.76 mL v 7.38 mL (P < .001); interreader, 2.51 mL v 9.07 mL (P < .001) for perimeter and diameter results, respectively. Of the 121 noncystic cases, 23 had serial data. In six (26.1%) of those 23, a classification difference occurred when the perimeter method was used versus the diameter method.

CONCLUSION

Variability of measurements was reduced with the computer-assisted perimeter method compared with the diameter method, which suggests that changes in volume can be detected more accurately with the perimeter method. The differences between these techniques seem large enough to have an impact on grading the response to therapy.

Hypoperfusion of inferior frontal brain regions in abstinent alcoholics: a pilot SPECT study

OBJECTIVE

This pilot study evaluated hypotheses concerning the relationship between cerebral hypoperfusion and residual deficits in the functioning of frontal brain systems in abstinent long-term alcoholics.

METHOD

The participants (N = 22) were 10 healthy, abstinent alcoholics (9 men) and 12 age-equivalent nonalcoholic controls (10 men). Cerebral blood flow was observed through the use of regionally specific computer-derived quantitative analysis of single photon emission computed tomography (SPECT) perfusion images. Measures of alcohol use, abstinence and neuropsychological functioning were also obtained to relate to SPECT findings.

RESULTS

A positive relationship was observed between perfusion levels in the left inferior frontal brain region and years of sobriety. Alcoholics with less than 4 years of sobriety had significantly reduced left inferior frontal perfusion compared with both nonalcoholic controls and alcoholics having longer periods of sobriety.

CONCLUSIONS

The findings support the hypothesis that frontal brain abnormalities in alcoholics may subside with extended abstinence.

Ocular motor abnormalities in ataxia telangiectasia

Although abnormal eye movements are a prominent feature of ataxia telangiectasia, the characteristics of the oculomotor dysfunction in the disease have been reported only in small groups of patients. We have examined eye movements clinically in 56 patients with ataxia telangiectasia, and obtained electrooculographic recordings of eye movements in 33 subjects. Deficits were observed in the eye movement systems that stabilize images on the retina, including pursuit, gaze holding, convergence, vestibular and optokinetic slow phases, and cancellation of vestibular slow phases. Abnormalities in the systems that maintain fixation and shift gaze were also prominent, including abnormal reflexive and voluntary saccades (characterized by prolonged latency, hypometric amplitude, and the use of head movements to initiate gaze shifts), impaired fixation, and a reduction in vestibular and optokinetic quick phases. The abnormalities in image stabilization most likely result from dysfunction in the cerebellar flocculus and paraflocculus. The basis of the saccadic and fixation disturbance is less certain but may be the result of abnormal supranuclear control of the superior colliculus resulting from dysfunction in the cerebellar vermis or the basal ganglia.

Reduced basal ganglia blood flow and volume in pre-symptomatic, gene-tested persons at-risk for Huntington's disease

The aim of this study was to examine basal ganglia volumes and regional cerebral blood flow in asymptomatic subjects at-risk for Huntington's disease who had undergone genetic testing. We determined which measures were the best 'markers' for the presence of the mutation and for the onset of symptoms. Twenty subjects who were Huntington's disease gene mutation-positive and 24 Huntington's disease gene mutation-negative participants, all of whom had a parent with genetically confirmed Huntington's disease, and were therefore 50% at-risk for inheriting the Huntington's disease gene mutation, were included in the study. To evaluate basal ganglia structure and function, MRI and single photon emission computed tomography (SPECT) were used. Quantitative measures of regional volumes and relative measures of regional perfusion were calculated. SPECT and MRI scans were co-registered so that MRI anatomy could be used accurately to place SPECT regions. Estimated years-to-onset in the mutation-positive subjects was calculated based on a regression formula that included gene (CAG)(n) repeat length and parental age of onset. Changes in imaging measures in relation to estimated years-to-onset were assessed. The imaging measure that was most affected in mutation-positive subjects was putamen volume. This was also the measure that correlated most strongly with approaching onset. In subjects >/=7 years from estimated onset age, the putamen volume measures were similar to those of the mutation-negative subjects. However, in subjects </=6 years from estimated onset age, there were dramatic reductions in putamen volume, resulting in >90% discrimination from both the far-from-onset and the mutation-negative subjects. Caudate volume and bicaudate ratio also showed a significant decline in the close-to-onset subjects, although to a lesser degree than putamen volume reductions. Furthermore, SPECT basal ganglia perfusion deficits were observed in mutation-positive subjects. Imaging markers of neuropathological decline preceding clinical onset are important for assessing the effects of treatments aimed at slowing the course of Huntington's disease. The current study suggests that quantitative assessment of basal ganglia may provide a means to track early signs of decline in individuals with the Huntington's disease gene mutation prior to clinical onset.

Proprioceptive and retinal afference modify postsaccadic ocular drift

Drift of the eyes after saccades produces motion of images on the retina (retinal slip) that degrades visual acuity. In this study, we examined the contributions of proprioceptive and retinal afference to the suppression of postsaccadic drift induced by a unilateral ocular muscle paresis. Eye movements were recorded in three rhesus monkeys with a unilateral weakness of one vertical extraocular muscle before and after proprioceptive deafferentation of the paretic eye. Postsaccadic drift was examined in four visual states: monocular viewing with the normal eye (4-wk period); binocular viewing (2-wk period); binocular viewing with a disparity-reducing prism (2-wk period); and monocular viewing with the paretic eye (2-wk period). The muscle paresis produced vertical postsaccadic drift in the paretic eye, and this drift was suppressed in the binocular viewing condition even when the animals could not fuse. When the animals viewed binocularly with a disparity-reducing prism, the drift in the paretic eye was suppressed in two monkeys (with superior oblique pareses) but generally was enhanced in one animal (with a tenotomy of the inferior rectus). When drift movements were enhanced, they reduced the retinal disparity that was present at the end of the saccade. In the paretic-eye-viewing condition, postsaccadic drift was suppressed in the paretic eye and was induced in the normal eye. After deafferentation in the normal-eye-viewing state, there was a change in the vertical postsaccadic drift of the paretic eye. This change in drift was idiosyncratic and variably affected the amplitude and velocity of the postsaccadic drift movements of the paretic eye. Deafferentation of the paretic eye did not affect the postsaccadic drift of the normal eye nor did it impair visually mediated adaptation of postsaccadic drift. The results demonstrate several new findings concerning the roles of visual and proprioceptive afference in the control of postsaccadic drift: disconjugate adaptation of postsaccadic drift does not require binocular fusion; slow, postsaccadic drift movements that reduce retinal disparity but concurrently increase retinal slip can be induced in the binocular viewing state; postsaccadic drift is modified by proprioception from the extraocular muscles, but these modifications do not serve to minimize retinal slip or to correct errors in saccade amplitude; and visually mediated adaptation of postsaccadic drift does not require proprioceptive afference from the paretic eye.

Hypoperfusion of the cerebellum and aging effects on cerebral cortex blood flow in abstinent alcoholics: a SPECT study

BACKGROUND

This study evaluated hypotheses concerning alcoholism, aging, and the relationship between cerebral hypoperfusion and residual deficits in the functioning of cerebellar and neocortical brain systems.

METHODS

The participants were 10 healthy abstinent alcoholics (9 men, 1 woman) and 12 nonalcoholic controls (10 men, 2 women) ranging in age from 35 to 67 years. Cerebral blood flow was observed through the use of regionally specific computer-derived quantitative analysis of single photon emission computed tomography (SPECT) perfusion images. Cerebellar perfusion was measured and compared with cerebral cortex perfusion in age-equivalent subgroups of alcoholics and controls (under 55 years; 55 years and over).

RESULTS

In abstinent alcoholics under age 55, cerebellar perfusion ratios were significantly reduced compared with the controls. In alcoholics and nonalcoholic controls 55 years old and older, this relationship was reversed, probably as a result of diminished cortical perfusion with aging in the alcoholics and of cerebellar decline in the controls.

CONCLUSIONS

The findings support hypotheses that the residual effects of alcoholism include cerebellar brain abnormalities and that aging combined with long-term alcoholism leads to cerebral cortical decline.

Group C streptococci isolated from throat swabs: a laboratory and clinical study

AIMS

To determine the prevalence of beta haemolytic, Lancefield group C streptococci in throat swabs taken in routine clinical practice, and correlate the species identified with presenting clinical features.

METHODS

One year, laboratory based prospective study, using a questionnaire to elicit clinical information.

RESULTS

4.4% of throat swabs yielded group C streptococci, of which 38% belonged to S equisimilis and 53% to S anginosus-milleri group (SAM). Pyrexia was more common in patients with S equisimilis, but other clinical features did not differ significantly between the two groups. No S zooepidemicus was isolated.

CONCLUSIONS

Species identification of group C streptococci from throat swabs does not appear to be clinically useful in this patient population. However, the prevalence and spectrum of organisms is similar to that reported in N America, where studies suggest a possible role in some cases of severe pharyngitis. Observational studies such as this lack power to resolve the issue of pathogenicity, for which a placebo controlled trial of antibiotic treatment is ideally required.

Disconjugate adaptation of saccades: contribution of binocular and monocular mechanisms

We studied the effects of prism-induced disparity on static and intrasaccadic alignment in six normal human subjects. A ten diopter base-out prism, calling for convergence, was placed in front of the central field of the right eye, so that at the center the eye viewed through the prism; at left and right, outside the prism. During 15 min of training, subjects made repetitive saccades solely in the right field of vision (C-R-C sequence). This paradigm required relative divergence for centrifugal (C-R) saccades and relative convergence for centripetal (R-C) saccades, as well as increase of the amplitude for all saccades made by the right eye. We found that during training, all subjects incorporated the necessary change in alignment into the saccades. After training the resultant intrasaccadic disconjugacy persisted when tested during monocular viewing, indicating that motor learning had occurred. Subjects demonstrated increased divergence for C-R and increased convergence for R-C saccades, in accordance with the change acquired during adaptation to the prism. In addition, five subjects developed increased divergence for C-L saccades, for which they did not train. Smaller and less consistent divergence was also observed for L-C saccades. Changes in intrasaccadic alignment were accompanied by changes in the relative velocities of the two eyes' saccades and slowing of the peak velocities in both eyes during training. Static alignment showed a general tendency toward convergence that did not parallel the changes in the intrasaccadic alignment, suggesting that saccade adaptation is system-specific. The pattern of transfer of the intrasaccadic disconjugacy to saccades in the untrained field and the changes in the relative speeds of the two eyes cannot be explained by monocular adjustment of the saccades. Our results indicate that both a binocular mechanism--saccade-vergence interaction--and monocular adaptation contribute to disconjugate adaptation of saccades.

Dynamic susceptibility contrast MR imaging of regional cerebral blood volume in Alzheimer disease: a promising alternative to nuclear medicine

BACKGROUND AND PURPOSE

The goal of our study was to evaluate the sensitivity and specificity for Alzheimer disease of semiquantitative dynamic susceptibility contrast (DSC) MR imaging as compared with results of qualitative single-photon emission computed tomography (SPECT) in the same patients and with previously published semiquantitative SPECT results.

METHODS

Fifty subjects were studied: 19 patients with probable Alzheimer disease with moderate cognitive impairment, eight mildly impaired patients with possible or probable Alzheimer disease, 18 group-matched elderly healthy comparison subjects, and five elderly comparison patients with psychiatric diagnoses. Relative values of temporoparietal regional cerebral blood volume (rCBV) were measured as a percentage of cerebellar rCBV, and group classification was assessed with logistic regression. The DSC MR imaging results were compared with SPECT scans in these same subjects and with previously published semiquantitative SPECT data.

RESULTS

Temporoparietal rCBV ratios were reduced 20% bilaterally in the patients with Alzheimer disease. Using left and right temporoparietal rCBV as index measures, sensitivity was 95% in moderately affected patients with Alzheimer disease and 88% in patients with mild cases. Specificity was 96% in healthy comparison subjects and in psychiatric comparison subjects. Sensitivity with DSC MR imaging was considerably better than with visual clinical readings of SPECT scans (74% in moderate and 50% in mild Alzheimer disease cases), and was similar to previous published SPECT temporoparietal measurements (90%). Specificity with SPECT was 100% visually and 87% based on previous temporoparietal measurements.

CONCLUSIONS

DSC MR imaging of rCBV is promising as a safe, potentially lower-cost alternative to nuclear medicine imaging for the evaluation of patients with dementia.

Efference copy provides the eye position information required for visually guided reaching

The contribution of extraocular muscle (EOM) proprioception to the eye position signal used to transform retinotopic visual information to a craniotopic reference frame remains uncertain. In this study we examined the effects of unilateral and bilateral proprioceptive deafferentation of the EOMs on the accuracy of reaching movements directed to visual targets. No significant changes occurred in the mean accuracy (constant error) or variance (variable error) of pointing after unilateral or bilateral deafferentation. We concluded that in normal animals efference copy provides sufficient information about orbital eye position to code space in craniotopic coordinates.

Functional magnetic resonance imaging of alprazolam-induced changes in humans with familial alcoholism

This study sought to identify whether subjects with a family history (FH + ) of alcoholism had changes in regional cerebral blood volume (rCBV) after an alprazolam challenge which distinguished them from subjects without a family history (FH -) of alcoholism using functional MRI (fMRI). Twelve FH + and eight FH - subjects were challenged with 1 mg of alprazolam or placebo in a double-blind crossover design. FMRI scans were obtained at baseline, 1 and 2 h after the challenge using the dynamic susceptibility contrast method with gadolinium. Mood scales, the Tufts Addiction Research Center Inventory-Morphine Benzedrine Group Scale and the drug liking scale, were administered every 30 min to assess drug effects. Global analysis of CBV showed a treatment by time decrease on alprazolam relative to placebo, but no effect by family history. The FH + group showed rCBV decreases at 1 h in the left caudate and left inferior prefrontal region, while the FH - group showed rCBV decreases at 2 h in the right inferior prefrontal region and anterior cingulate in response to alprazolam relative to placebo. FH + subjects reported more mood enhancement with alprazolam. This fMRI technique detected global and regional CBV changes induced by alprazolam. The location and rate of alprazolam-induced rCBV changes differed between FH + and FH - subjects. These changes may be related to the increased mood enhancement found in subjects genetically predisposed to alcoholism.

Dynamic susceptibility contrast magnetic resonance imaging in neuropsychiatry: present utility and future promise

Dynamic susceptibility contrast magnetic resonance imaging (DSC MRI) provides a noninvasive means to create high resolution maps of the regional distribution of cerebral blood volume (CBV). Most DSC MRI studies conducted to date have focused on the evaluation of patients with cerebral neoplasms, ischemia or infarction, and epilepsy. However, preliminary work suggests that DSC MRI may also provide clinically important information for the evaluation of patients with neuropsychiatric disorders, especially dementia and schizophrenia. Additionally, with appropriate modification, DSC MRI may be used to reliably evaluate the effects of pharmacological challenges on cerebral hemodynamics. As pharmacotherapy is an important component in the treatment of a range of psychiatric disorders, the dynamic assessment of changes in cerebral perfusion associated with drug administration may ultimately lead to the development of "brain function tests" for a wide range of disorders.

Influence of advanced recipient and donor age on the outcome of corneal transplantation. Australian Corneal Graft Registry

AIMS

The aims of this study were to examine the influence of advanced recipient and donor age on the long term outcome of corneal transplantation.

METHODS

Records of 1036 penetrating corneal grafts in recipients aged > or = 80 years at surgery (defined as the elderly subset) and 8092 donor corneas used for transplantation were obtained from the Australian Corneal Graft Register database, Kaplan-Meier graft survival plots were compared using log rank statistics.

RESULTS

Elderly recipients constituted 15% of the recipient pool. The major indication for corneal transplantation in the elderly was bullous keratopathy. Graft survival fell with increasing recipient age (p < 0.00001); the major cause of graft failure was rejection (33%). The desired outcome in 51% of cases was to improve vision and in 42% of cases to relieve pain; 23% of elderly recipients achieved a Snellen acuity of 6/18 or better in the grafted eye and 66% recorded improved acuity after transplantation. Elderly recipients suffered more complications and comorbidities in the grafted eye than did younger recipients. Donor age (stratified in 10 year intervals) did not influence corneal graft survival significantly (p = 0.10).

CONCLUSIONS

Elderly graft recipients fared less well after corneal transplantation than did younger recipients, but outcomes in terms of long term graft survival and visual rehabilitation were still good. Donor age did not affect graft survival.

Predictive power of duplex ultrasonography in asymptomatic carotid disease

BACKGROUND

Duplex ultrasonography is considered a valid measure of stenosis of the carotid arteries, but the prognostic value of repeated ultrasonographic examinations is unknown.

OBJECTIVE

To determine the ability of serial ultrasonographic measurements to predict cerebrovascular events in patients with asymptomatic carotid disease.

DESIGN

Secondary analysis of data from a natural history study of asymptomatic carotid disease.

PATIENTS

Asymptomatic patients with cervical bruits.

MEASUREMENTS

Duplex ultrasonography of the carotid arteries was done at study enrollment and biannually thereafter. Multivariable Cox proportional hazards models with fixed and time-dependent covariates were used for analysis.

RESULTS

61 transient ischemic attacks (TIAs) and 38 strokes occurred in 715 participants over a mean follow-up period of 3.2 years; 4 strokes were disabling, and no deaths from stroke occurred. Sixty percent of strokes occurred in persons who did not have severe stenosis. One fifth of participants had stenosis progression. Baseline carotid stenosis was a significant predictor of the outcome "TIA or stroke" (relative risk, 1.5 [95% CI, 1.2 to 1.7]) and retained its predictive ability for more than 3 years. Progression of stenosis to 80% or more significantly increased the risk for cerebrovascular events and death. The sensitivity and positive predictive value of progression as an independent predictor of TIA or stroke were low.

CONCLUSION

Severe carotid stenosis is associated with a higher risk for cerebrovascular events, but the power of repeated ultrasonography to predict ischemic events is limited by low incidence rates and low rates of progression. The evidence does not support the routine use of serial ultrasonography to determine the risk for stroke in unselected patients with asymptomatic carotid disease.

Regional cerebral blood volume measured by dynamic susceptibility contrast MR imaging in Alzheimer's disease: a principal components analysis

Dynamic susceptibility contrast (DSC) MRI is an alternative to positron emission tomography (PET) and single photon emission computed tomography (SPECT) for the evaluation of cerebral hemodynamics in patients with Alzheimer's disease. DSC MRI allows the construction of high resolution images of cerebral blood volume (CBV) without the use of radionuclides or ionizing radiation. In this study, DSC MRI data were collected from 16 patients with probable Alzheimer's disease and 16 age-matched control subjects. Characteristic patterns of regional CBV variation were found using principal component analysis. Three such patterns were identified: a global variation pattern, an anterior-to-posterior CBV gradient, and a temporoparietal pattern. Group differences in the principal component scores associated with the global and temporoparietal patterns (P = .08 and P = .007, respectively) suggest that these deficits reflect characteristic CBV abnormalities in Alzheimer's disease. Using only these two scores, the Alzheimer's disease group was classified with a sensitivity of 81% and a specificity of 88%. Additionally, disease severity, as measured by the Mini-Mental State Examination (MMSE), was correlated significantly with the third principal component score (Pearson's r = .50, P = .05).

Dynamic susceptibility contrast MRI of regional cerebral blood volume in Alzheimer's disease

OBJECTIVE

The purpose of this study was to investigate the potential effectiveness of dynamic susceptibility contrast magnetic resonance imaging (MRI) to discriminate elderly patients with Alzheimer's disease from normal matched comparison subjects.

METHOD

Images of regional cerebral blood volume (CBV) were generated from echo-planar MRI with the dynamic susceptibility contrast method in 13 Alzheimer's disease patients and 13 comparison subjects group-matched on age and gender.

RESULTS

Temporoparietal cerebral blood volume, expressed as a percentage of the cerebellum value, was reduced 17% bilaterally in the patients with Alzheimer's disease. Blood volume in sensorimotor regions was reduced only 8.5% in the patients. Discriminant function analysis based on left and right temporoparietal measures correctly classified 88.5% of the subjects as patients or comparison subjects. Temporoparietal CBV was reduced even in mildly affected Alzheimer's disease patients (Mini-Mental State scores > 24).

CONCLUSIONS

Dynamic susceptibility contrast MRI of regional CBV is promising as a nonradioactive, potentially lower-cost alternative to other functional neuroimaging methods for evaluating Alzheimer's disease.

Vertigo: some uncommon causes of a common problem

Vertigo, an extremely common symptom, may be caused by numerous disorders affecting the central or peripheral vestibular systems. Patients can usually be categorized into four groups based on the clinical presentation: monophasic, prolonged episodes of vertigo due to acute unilateral vestibular hypofunction; recurrent episodes of vertigo, due to transient vestibular dysfunction; vertigo provoked by changes in head position with respect to gravity (positional vertigo); and bilateral vestibulopathies, which present with imbalance and oscillopsia. Although each clinical syndrome is usually caused by a limited number of disorders, many less common entities must be considered in the differential diagnosis. This article reviews the clinical presentation of the less common causes of vestibular syndromes and discusses their medical and nonmedical management.

The Digit Vigilance Test: reliability, validity, and sensitivity to diazepam

The Digit Vigilance Test (DVT), a measure of sustained attention and psychomotor speed, was evaluated in terms of test-retest and alternate-form reliability as well as sensitivity to a single dose of diazepam (10 mg). A one-page version was compared to the standard two-page format. Forty undergraduates, randomly assigned in a double-blind manner to either drug or placebo condition, were tested three times in two sessions (1 week apart). Both Page 1 and Total Time scores were found to be highly reliable across time and forms. Repeated measures ANOVAs revealed the Total Time score, but not the Page 1 score, to be significant in discriminating diazepam from placebo across time, supporting the use of the complete DVT for measuring drug effects. Findings based on convergent measures also help to validate the DVT as a measure of sustained attention.

Regulation of static and dynamic ocular alignment in patients with trochlear nerve pareses

Ocular alignment and saccades were studied in seven patients with trochlear nerve pareses, before and after strabismus surgery. Prior to surgery, a position-dependent vertical ocular misalignment was present, and downward saccades were hypometric in the paretic eye. Strabismus surgery reduced the magnitude and position-dependence of the static misalignment. Saccade conjugacy improved in the patients with congenital pareses, and in the patient with a gradual-onset acquired paresis, but less improvement occurred in subjects with traumatic pareses. The post-operative change in saccade conjugacy relative to the change in static alignment correlated with pre-operative vertical vergence, suggesting that changes in saccade yoking depend on an interaction between saccades and vertical vergence.

How successful is corneal transplantation? A report from the Australian Corneal Graft Register

Corneal graft outcome was assessed within a large, prospectively collected database of 4499 records. Penetrating corneal graft survival was 91% at 1 year, 72% at 5 years and 69% at 7 years. The three most common indications for graft were keratoconus (30%), bullous keratopathy (25%) and failed previous graft (18%); the three most common causes of graft failure were rejection (34%), infection (18%) and glaucoma (9%). The vast majority of grafts were performed for improved visual acuity. About four-fifths of recipients achieved at least one line of better acuity on the Snellen chart post-operatively; of the remainder with unchanged or worse acuity, only 21% had failed grafts. Overall, 43% of recipients achieved a best corrected Snellen acuity of 6/12 or better, 52% achieved 6/18 or better, and 20% had acuitities of less than 6/60. Reasons for poor post-operative acuity (recorded as less than 6/60) included graft failure (41%) and comorbidities in the grafted eye (43%). A number of risk factors for graft failure were examined: in most instances, there was little room for decision-making or expert intervention.

The Gravitational Plant Physiology Facility--description of equipment developed for biological research in Spacelab

In January 1992, the NASA Shuttle mission STS 42 carried a facility designed to perform experiments on plant gravi- and photo-tropic responses. This equipment, the Gravitational Plant Physiology Facility (GPPF) was made up of a number of interconnected units mounted within a Spacelab double rack. The details of these units and the plant growth containers designed for use in GPPF are described. The equipment functioned well during the mission and returned a substantial body of time-lapse video data on plant responses to tropistic stimuli under conditions of orbital microgravity. GPPF is maintained by NASA Ames Research Center, and is flight qualifiable for future Spacelab missions.

Extraocular muscle proprioception functions in the control of ocular alignment and eye movement conjugacy

1. The function of extraocular muscle proprioception in the control of eye movements is uncertain. We tested the hypothesis that proprioception contributes to the long-term regulation of ocular alignment and eye movement conjugacy. 2. Eye movements were recorded in monkeys with unilateral extraocular muscle palsies, before and after proprioceptive deafferentation of the paretic eye. Following deafferentation, ocular alignment and saccade conjugacy gradually worsened over several weeks. In contrast, disconjugate adaptation induced by habitual binocular viewing with a prism (disparity-mediated adaptation) occurred normally after deafferentation. 3. These results provide the first evidence that proprioception functions in the control of eye movements in primates, and indicate that proprioception contributes to the long-term adaptive mechanisms that regulate ocular alignment during fixation and saccades. The error signal used in this process may be derived from a mismatch between the efference copy and proprioceptive afference.

Abnormal spatial localization with trigeminal-oculomotor synkinesis. Evidence for a proprioceptive effect

We examined spatial localization, using open-loop pointing to visual targets, in a patient with a congenital trigeminal-oculomotor synkinesis. This patient demonstrated abnormal co-activation of the left medial rectus muscle when the left lateral pterygoid contracted. Because one eye could be deviated in the absence of a normal oculomotor innervational command, the efference copy (derived from monitoring of central oculomotor commands) could be dissociated from the proprioceptive afferent signal (determined by the mechanical state of the extraocular muscles). Under conditions of monocular viewing with the normal right eye, when the covered left eye was adducted by the aberrant trigeminal innervation, the patient pointed to the left of the actual position of the target. This finding indicates that proprioceptive afference from the adducted, covered left eye was used in the process of spatial localization. While synkinetic adduction produced a shift in pointing in the opposite direction of rotation of the non-viewing eye, previous studies using passive deviation of the non-viewing eye in normal subjects reported a shift in pointing in the same direction as eye rotation (Gauthier et al., 1990; Bridgeman and Stark, 1991). We propose that this discrepancy is due to the different effects of passive eye rotation and active muscle contraction on the tendon organs of the extraocular muscles. On this basis, we hypothesize that the tendon organs, rather than the muscle spindles, are primarily responsible for the transduction of proprioceptive information about eye position in the orbit.

Evaluating the effects of drugs on behavior and quality of life: An alternative strategy for clinical trials

Conventional clinical trials involve tests of hypotheses with statistics computed from values of dependent variables alone. An alternative is to test hypotheses with statistics computed from benefit/harm scores that measure longitudinal associations between dose and values of the dependent variables. The proposed standardized measure of benefit/harm quantifies the strength of evidence that a patient did either better or worse while on treatment. A benefit/harm score, particularly when obtained from a randomized, N-of-1 trial, indicates a beneficial or harmful treatment effect for the individual. Benefit/harm scores from samples of patients are evaluated with standard statistical tests, with or without group comparisons, to make inferences about populations. The proposed alternative strategy can yield within-patient indicators of treatment effect that are more reliable, valid, comprehensive, and detailed. This, in turn, could help make many population-based clinical trials more informative, cost-effective, and clinically useful for participants.

Ten-year changes in birthweight distributions of black and white infants, South Carolina

The birthweight distributions of Black and White infants in South Carolina were compared for the paired-year periods 1975-76 and 1985-86. No discernible changes in birthweight distributions between the two time periods were observed especially among Black infants. The distributions among White infants reflected an overall improvement in birthweight most noticeably above 2500g.

Circumnutations of sunflower hypocotyls in satellite orbit

The principal objective of the research reported here was to determine whether a plant's periodic growth oscillations, called circumnutations, would persist in the absence of a significant gravitational or inertial force. The definitive experiment was made possible by access to the condition of protracted near weightlessness in an earth satellite. The experiment, performed during the first flight of Spacelab on the National Aeronautics and Space Administration shuttle, Columbia, in November and December, 1983, tested a biophysical model, proposed in 1967, that might account for circumnutation as a gravity-dependent growth response. However, circumnutations were observed in microgravity. They continued for many hours without stimulation by a significant g-force. Therefore, neither a gravitational nor an inertial g-force was an absolute requirement for initiation [correction of initation] or continuation of circumnutation. On average, circumnutation was significantly more vigorous in satellite orbit than on earth-based clinostats. Therefore, at least for sunflower (Helianthus annuus L.) circumnutation, clinostatting is not the functional equivalent of weightlessness.

Independence of Intrapericardial Right and Left Ventricular Performance in Septic Pulmonary Hypertension

To study the effect of septic pulmonary hypertension on right/left ventricular intrapericardial interactions thirteen trauma patients, seven septic and six non-septic controls, were compared. Ventricular volumes were derived from firstpass or gated equilibrium radionuclide angiocardiography, and related to body surface area. Systemic and pulmonary pressures were measured invasively. Pulmonary arterial pressure was significantly increased in the sepsis group. Although right ventricular end-diastolic volumes were higher in sepsis, left ventricular end-diastolic volumes were not decreased. In terms of intrapericardial right/left ventricular interactions these results indicate that the right and left ventricles operate independently in septic pulmonary hypertension.

Beta-haemolytic streptococci from the female genital tract: clinical correlates and outcome of treatment

Clinical features, treatment and outcome were assessed retrospectively by means of a questionnaire in 174 patients in general practice whose vaginal swabs yielded beta-haemolytic streptococci. These were compared with 96 patients whose swabs yielded no recognized microbial pathogens. Patients with group B streptococci did not differ in any of these parameters from the control group, but those with group A streptococci were more likely to have vaginal soreness, a purulent discharge, and to respond to anti-streptococcal antibiotics. Implications for laboratory reporting are discussed.

Medicare risk contracting. Lessons from an unsuccessful demonstration

The Tax Equity and Fiscal Responsibility Act of 1982 provided a full-risk Medicare capitation financing option for health maintenance organizations and competitive medical plans. Two rounds of demonstrations were conducted, followed by the publication of final regulations in January 1985. The first-round demonstration at Marshfield, Wis, was operational for 28 months. Thirty-seven percent of all resident beneficiaries enrolled. Aggregate losses exceeded $3 million (11.6% of revenue). Management implemented increasingly more stringent utilization review. Overall hospital utilization declined 261.7 days per 1000 from fiscal year 1981 to 1982; nonetheless, federal reimbursement was insufficient to meet program costs and the demonstration was terminated. The central reimbursement method used in Medicare risk contracting (adjusted average per capita cost) does not adequately control for enrollment selection, unmet medical need, or recent regional cost variations. Reimbursement set at 95% of estimated fee-for-service costs does not recognize, and in the long run will not support, an efficiently operating delivery system.

A new hospital library in San Diego: planning and construction

A new library building at the University of California Medical Center, San Diego provides 7,100 net square feet, seating for 100 readers, and a stack capacity of 23,000 volumes. The building contains three split-level floors with conventional reference and circulation services, a combination of group and single seating, rapid copying machines, audiovisual facilities, a public elevator, and an electronic security system for the protection of library materials. The library, intended primarily for the use of health care professionals and students in their third and fourth years of medical school, serves a teaching hospital and its associated research facilities.

Neuropsychological test performances of paranoid schizophrenic and brain-damaged patients

Predicted that simple tests that require attention and motor speed would be able to differentiate paranoid schizophrenics from brain-damaged patients better than more complex, problem-solving neuropsychological tests. The strategy was to improve discrimination between schizophrenic and brain-damaged patients by selecting a schizophrenic subgroup with a recognized cognitive strong point. Fourteen organic, 14 paranoid schizophrenic, and 14 nonpsychotic psychiatric patients matched for sex, education, and IQ were tested. As predicted, the attention and speed measures differentiated the brain-damaged and paranoid groups, while the four more complex measures from the Halstead-Reitan Battery did not separate the groups. There were no significant differences between the two psychiatric groups.