Racial/ethnic differences in the association between transgender-related U.S. state policies and self-rated health of transgender women

BACKGROUND

Policy protections for transgender adults in the United States are consistently associated with positive health outcomes. However, studies over-represent non-Latinx White transgender people and obscure variation in policies' intended goals. This study examined racial differences in the relationship between transgender-related policies and transgender women's self-rated health. Guided by Critical Race Theory, we hypothesized that policies conferring access to resources (e.g., healthcare) would be associated with better self-rated health among all participants while policies signifying equality (e.g., nondiscrimination laws) would be associated with better self-rated health only for White participants.

METHODS

Using cross-sectional data collected between March 2018-December 2020 from 1566 transgender women, we analyzed 7 state-level 'access policies,' 5 'equality policies,' and sum indices of each. Participants represented 29 states, and 54.7% were categorized as people of color. We fit a series of multilevel ordinal regression models predicting self-rated health by each policy. Multivariate models were adjusted for relevant covariates at the individual- and state-level. We then tested moderation by race/ethnicity using interaction terms and generated stratified predicted probability plots.

RESULTS

In bivariate models, 4 access policies, 2 equality policies, and both indices were associated with better self-rated health, but associations did not persist in adjusted models. Results from the multivariable models including interaction terms indicated that policies concerning private insurance coverage of gender-affirming care, private insurance nondiscrimination, credit nondiscrimination, and both indices were statistically significantly associated with better self-rated health for White participants and worse self-rated health for participants of color.

CONCLUSIONS

The policies included in this analysis do not mitigate racism's effects on access to resources, indicating they may be less impactful for transgender women of color than White transgender women. Future research and policy advocacy efforts promoting transgender women's health must center racial equity as well as transgender people of color's priorities.

Inequities in the distribution of adverse childhood experiences and their association with health among transgender people of color

BACKGROUND

Racism and cisgenderism expose transgender people of color to adversity across the life course. However, little is known about the prevalence of adverse childhood experiences (ACEs) in this population or their association with health in comparison to other groups.

OBJECTIVE

Guided by the structural trauma framework, we examined race/ethnicity/gender group differences in the prevalence of ACEs and their association with adult mental and physical health.

PARTICIPANTS AND SETTING

2019-2021 Behavioral Risk Factor Surveillance Survey.

METHODS

Transgender participants (n = 551) were matched with two cisgender men (n = 1102) and two cisgender women (n = 1102) on key covariates. We compared age-adjusted predicted probabilities of nine ACEs by race/ethnicity/gender group. We then fit adjusted logistic regression models predicting poor mental and physical health by each ACE and compared marginal effects between groups.

RESULTS

Transgender people of color had higher age-adjusted probabilities of six ACEs than at least one other group; for example, household incarceration was 0.16 (95 % CI: 0.11-0.22) compared to 0.09 (95 % CI: 0.06-0.13) for cisgender men of color (p = 0.032). The relationship between five ACEs and poor mental health was greater for transgender people of color than at least one other group. For instance, the marginal effect of household alcoholism on poor mental health was 0.28 (95 % CI: 0.11-0.45) compared to 0.07 (0.01-0.14) for White cisgender men (p = 0.031). There were no statistically significant differences regarding effects on poor physical health.

CONCLUSIONS

ACEs inequitably impact transgender people of color, reflecting the need to restructure the interlocking systems that drive adversity among transgender children of color and exacerbate ACEs' health effects among adults.

Structural vulnerability as a conceptual framework for transgender health research: findings from a community needs assessment of transgender women of colour in Detroit

The concept of structural vulnerability explains how systems of oppression drive health inequities by reducing access to survival resources (e.g. food, housing) for marginalised populations. Indicators of structural vulnerability such as housing instability, violent victimisation and poverty are often interconnected and result from intersectional oppression. We sought to demonstrate the utility of the structural vulnerability framework for transgender health research by examining patterns of structural vulnerability indicators among transgender women of colour in Detroit. We conducted latent class analysis and tested associations between classes and mental health and substance use outcomes. Membership to the Lowest Vulnerability class was negatively associated with post-traumatic stress disorder (PTSD) (aOR = 0.10, 95% CI: 0.02-0.59). High Economic Vulnerability membership was associated with daily marijuana use (aOR = 4.61, 95% CI: 1.31-16.16). Complex Multi-Vulnerability membership was associated with PTSD (aOR = 9.75, 95% CI: 2.55-37.29), anxiety (aOR = 4.12, 95% CI: 1.22-13.97), suicidality (aOR = 6.20, 95% CI: 1.39-27.70), and club drug use (aOR = 4.75, 95% CI: 1.31-17.29). Substantively different findings emerged when testing relationships between each indicator and each outcome, highlighting the value of theoretically grounded quantitative approaches to understanding health inequities. Community-driven interventions and policy changes that reduce structural vulnerability may improve mental health and substance use outcomes among structurally vulnerable trans women of colour.

Community-Led Response to Address Economic Vulnerability due to COVID-19 with, for, and by Transgender Women of Color: A Qualitative Pilot Evaluation

Purpose

Intersectional stigma fuels inequities among transgender women of color, which have been exacerbated by coronavirus disease 2019 (COVID-19). This study evaluated a community-led emergency assistance program for transgender women of color.

Methods

We conducted a pilot program evaluation (n=8).

Results

Retention was 87.5% over the follow-up. Funds were primarily used for bills, food, and housing. Requesting and receiving funds was described as "somewhat to extremely easy." Participants identified the need for economic empowerment components in future programming, specifically gender affirmation, skill-building for education and employment, and entrepreneurial opportunities.

Conclusion

Findings highlight the need to invest in community-led strategies to address inequities experienced by transgender women of color.

Structural Needs, Substance Use, and Mental Health Among Transgender and Nonbinary Young Adults in the San Francisco Bay Area: Findings from the Phoenix Study

Transgender and nonbinary (trans) young adults report high rates of substance use and adverse mental health outcomes; however, few studies have examined how social, economic, and legal factors may contribute to health inequities in this population. Guided by the structural vulnerability framework, this study sought to explore structural needs and whether these needs were associated with substance use and mental health outcomes among trans young adults. Between 2019 and 2021, 215 trans young adults aged 18-29 from San Francisco Bay Area were recruited into a longitudinal study. Baseline data were used to examine bivariate and multivariable associations between structural needs and substance use and mental health outcomes. There were bivariate differences in the number of structural needs by education, income source, incarceration history, and ethnicity, and the number of unmet structural needs was associated with education and income source. After adjusting for sociodemographics, the number of structural needs was associated with daily marijuana use (AOR 1.29, 95% CI: 1.10-1.49) and suicidal ideation (AOR 1.24, 95% CI: 1.06-1.45), and the number of unmet structural needs was associated with daily marijuana use (AOR 1.30, 95% CI: 1. 10-1.55) and depressive symptoms (β 2.00, 95% CI: 1.00-3.00). Additionally, both numbers of structural needs and unmet structural needs mediated the relationship between income source (traditional employment vs. other income only) and depressive symptoms (TIE β 2.51, 95% CI: 0.99-4.04; β 1.37, 95% CI: 0.23-2.52, respectively). Findings highlight a need for multisector efforts to address structural vulnerabilities among trans young adults.

Improving Access to Legal Gender Affirmation for Transgender Women Involved in the Criminal-Legal System

Transgender women of color experience interlocking systems of oppression rooted in racism and transphobia, which fuel economic vulnerability and overrepresentation in the criminal-legal system. Legal gender affirmation, which refers to changing one's name and gender marker on official documents, has the potential to mitigate these issues by improving access to employment, housing, education, health care, and social services. These services are particularly important for transgender women of color with criminal records, a history of incarceration, or other legal infractions; however, 23 states have policies that restrict access to legal gender affirmation for these individuals. Alongside eliminating restrictive policies to obtain legal gender affirmation, medical-legal partnerships in these states may address recidivism and health inequities among transgender women of color.

A Scoping Review of Health Outcomes Among Transgender Migrants

Purpose

Transgender people constitute diverse populations who experience a range of adverse health outcomes. Despite increasing awareness of adverse health outcomes among migrant populations, there has been a dearth of studies focused on the health of transgender migrants. The goal of this scoping review was to describe common themes and empirical trends in research on the health of transgender migrants and identify gaps for future research and programming.

Methods

Using a systematic review protocol, we searched PubMed, Embase, Scopus, PsycINFO, CINAHL, and Web of Science with a combination of terms to identify empirical articles that examined health outcomes among transgender migrants. The search included studies published as of May 2019.

Results

Twenty of 1666 identified records met inclusion criteria. All studies were cross-sectional, and 50% were quantitative designs, 45% were qualitative designs, and 5% were mixed-methods designs. The majority reported on sexually transmitted infections (55%), violence (40%), and mental health (35%). Qualitative studies were generally high quality, while many quantitative studies had high risk of bias. While some adverse health outcomes may abate, stigmatizing social conditions continue to impact transgender migrant's health postmigration.

Conclusions

Anti-transgender and anti-immigrant stigma may contribute to adverse health outcomes for transgender migrants. Additional research using rigorous inclusive methods to survey a broader range of health domains is needed. The lives of transgender migrants are continuously upended by oppressive policies; therefore, it is vital to continue to expand the breadth of transgender health research.

US Black-White Differences in Mortality Risk Among Transgender and Cisgender People in Private Insurance, 2011-2019

Objectives. To compare survival by gender and race among transgender and cisgender people enrolled in private insurance in the United States between 2011 and 2019. Methods. We examined Optum's Clinformatics Data Mart Database. We identified transgender enrollees using claims related to gender-affirming care. Our analytic sample included those we identified as transgender and a 10% random sample of cisgender enrollees. We limited our sample to those 18 years or older who were non-Hispanic Black or White. We identified 18 033 transgender and more than 4 million cisgender enrollees. We fit Kaplan-Meier survival curves and calculated standardized mortality ratios while adjusting for census region. Results. Black transfeminine and nonbinary people assigned male sex at birth were 2.73 times more likely to die than other Black transgender people and 2.38 and 3.34 times more likely than Black cisgender men and women, respectively; similar results were found when White transfeminine and nonbinary people assigned male sex at birth were compared with White cisgender cohorts. Conclusions. Our findings highlight glaring inequities in mortality risks among Black transfeminine and nonbinary people assigned male sex at birth and underscore the need to monitor mortality risks in transgender populations and address the social conditions that increase these risks. (Am J Public Health. 2022;112(10):1507-1514. https://doi.org/10.2105/AJPH.2022.306963).

State-Level Policy Stigma and Non-Prescribed Hormones Use among Trans Populations in the United States: A Mediational Analysis of Insurance and Anticipated Stigma

BACKGROUND

Medical gender affirmation (i.e., hormone use) is one-way transgender (trans) people affirm their gender and has been associated with health benefits. However, trans people face stigmatization when accessing gender-affirming healthcare, which leads some to use non-prescribed hormones (NPHs) that increase their risk for poor health.

PURPOSE

We examined whether healthcare policy stigma, as measured by state-level trans-specific policies, was associated with NPHs use and tested mediational paths that might explain these associations. Because stigmatizing healthcare policies prevent trans people from participation in healthcare systems and allow for discrimination by healthcare providers, we hypothesized that healthcare policy stigma would be associated with NPHs use by operating through three main pathways: skipping care due to anticipated stigma in healthcare settings, skipping care due to cost, and being uninsured.

METHODS

We conducted analyses using data from the 2015 U.S. Transgender Survey. The analytic sample included trans adults using hormones (N = 11,994). We fit a multinomial structural equation model to examine associations.

RESULTS

Among trans adults using hormones, we found that healthcare policy stigma was positively associated with NPHs use and operated through insurance coverage and anticipating stigma in healthcare settings. The effect sizes on key predictor variables varied significantly between those who use supplemental NPHs and those who only use NPHs suggesting the need to treat NPHs use as distinct from those who use supplemental NPHs.

CONCLUSIONS

Our work highlights the importance of healthcare policy stigma in understanding health inequities among trans people in the USA, specifically NPHs use.

Differences in All-Cause Mortality Among Transgender and Non-Transgender People Enrolled in Private Insurance

Few studies have analyzed mortality rates among transgender (trans) populations in the United States and compared them to the rates of non-trans populations. Using private insurance data from 2011 to 2019, we estimated age-specific all-cause mortality rates among a subset of trans people enrolled in private insurance and compared them to a 10% randomly selected non-trans cohort. Overall, we found that trans people were nearly twice as likely to die over the period as their non-trans counterparts. When stratifying by gender, we found key disparities within trans populations, with people on the trans feminine to nonbinary spectrum being at the greatest risk of mortality compared to non-trans males and females. While we found that people on the trans masculine to nonbinary spectrum were at a similar risk of overall mortality compared to non-trans females, their overall mortality rate was statistically smaller than that of non-trans males. These findings provide evidence that some trans and non-trans populations experience substantially different mortality conditions across the life course and necessitate further study.

Stigma Experienced by Transgender Women of Color in Their Dating and Romantic Relationships: Implications for Gender-based Violence Prevention Programs

Although transgender women of color, specifically Black and Latina experience gender-based violence in a variety of contexts, one of the most consistently reported is from a dating or romantic partner. This qualitative study sought to understand the manifestations and consequences of stigma experienced by transgender women of color in their dating or romantic relationships. Between January and February 2019, we purposively recruited 33 transgender women of color to participate in five focus group discussions and complete a brief survey. We employed both inductive and deductive approaches to coding and thematic analysis. We identified different forms of anti-transgender interpersonal stigma experienced by transgender women of color seeking romantic relationships and by those in romantic relationships. For those dating and seeking relationships, anti-transgender interpersonal stigma took the form of dehumanizing stereotypes and sexual objectification. While these manifestations of anti-transgender interpersonal stigma persisted for some within relationships, concealment behaviors from partners was the predominant type of anti-transgender interpersonal stigma. Each of these forms of anti-transgender interpersonal stigma had significant gender-based violence consequences, specifically encountering physical violence, experiencing psychological trauma, and engaging in survival strategies. In the current climate of COVID-19, which is exacerbating risks of gender-based violence, there is an urgent need to understand and address the nuanced manifestations of stigma in relationships and their consequences on the lives of transgender women of color. Culturally grounded gender-based violence prevention policies and programs with transgender women should address these forms of stigma and build on community strengths. Findings also highlight the importance of future research and gender-based violence prevention programming with cisgender men in/seeking partnerships with transgender women of color.

Behavioral and social interventions to promote optimal HIV prevention and care continua outcomes in the United States

PURPOSE OF REVIEW

This review reports on trends in behavioral and social intervention research in the United States published over the past year (2020-2021) investigating HIV prevention and care outcomes, organized by the level of intervention focus - individual, dyadic, and organizational.

RECENT FINDINGS

Researchers have continued to develop and evaluate behavioral and social interventions to reduce HIV acquisition risk and disease progression. With few exceptions, social and behavioral interventions have primarily focused on individuals as the unit of behavior change. Interventions operating at the individual-, dyadic-, and organizational-level have made strides to reduce HIV transmission risk and disease progressing by addressing mental health, substance use, stigma, peer and romantic relationships, and, to some extent, structural vulnerabilities.

SUMMARY

Social and behavioral interventions continue to be critical in addressing HIV inequities in the United States. An important gap in the literature is the need for multilevel interventions designed and implemented within existing community-based organizations and local healthcare settings. We call on researchers to continue to attend to the structural, environmental, and economic vulnerabilities that shape HIV inequities in the development of multilevel approaches necessary to realize the full potential of existing and emerging HIV prevention and care strategies.

A "tax" on gender affirmation and safety: costs and benefits of intranational migration for transgender young adults in the San Francisco Bay area

Many transgender (trans) young adults migrate to urban enclaves with known infrastructures to fulfil gender affirmation needs such as obtaining trans-inclusive healthcare and support. This study sought to explore experiences of intranational migration (i.e. migration within a single country) for gender affirmation among trans young adults who relocated to San Francisco. A convenience sample of 61 trans young adults aged 18 to 29 (32% nonbinary, 28% trans women, and 40% trans men; 84% identified as a person of colour) participated in a one-time qualitative interview as part of a larger study. Thematic analysis was used to develop and refine the codes and themes. Three overarching themes became apparent regarding intranational migration and gender affirmation needs: (1) access to basic gender affirmation needs; (2) safety; and (3) the price of gender affirmation. Migration for gender affirmation and safety placed informants at risk for structural vulnerabilities including homelessness, unemployment and racism. Despite these structural vulnerabilities, participants were willing to "pay" the price in order to gain gender affirmation and safety. Findings underscore the importance of moving beyond individual-level risk factors to understand how unmet gender affirmation needs may place trans young adults in structurally vulnerable positions that can affect health and wellness.

Exploring Multiple Forms of Intimate Partner Violence in a Gender and Racially/Ethnically Diverse Sample of Transgender Adults

Intimate partner violence (IPV) is highly prevalent in transgender (trans) populations in the United States; however, details about its manifestations and correlates have not been well captured. Using data from the 2015 U.S. Transgender Survey, we analyzed weighted data from 23,999 adult transgender participants to estimate the prevalence and explore correlates of five IPV subtypes: psychological IPV, physical IPV, trans-related IPV, stalking, and forced sex committed by an intimate partner. Regression models examined race/ethnicity, gender identity, past-year incarceration, past-year sex work, and lifetime homelessness, and adjusted for annual household income, highest level of education, age, birthplace, Census region, and relationship status. The sample was racially/ethnically diverse (62.6% White, 0.7% Alaskan Native/American Indian, 4.7% Asian/Native Hawaiian/Pacific Islander, 12.7% Black/African American, 16.5% Latinx/Hispanic, 0.4% Middle Eastern/North African, 2.5% Multiracial/Not Listed), and comprised of 31.2% transgender men, 34.2% transgender women, 27.5% assigned-female-at-birth nonbinary participants, and 7.1% assigned-male-at-birth nonbinary participants. Rates of IPV were high, with variability by IPV subtype: 42.0% endorsed psychological IPV, 39.9% endorsed physical IPV, 30.4% endorsed trans-related IPV, 18.0% endorsed stalking, and 21.5% endorsed forced sex by an intimate partner. We observed disparities in IPV subtypes by race/ethnicity, gender identity, and experiences of social marginalization. Results highlight the need for targeted, trans-inclusive IPV screening practices and interventions. Future studies should examine the syndemic effects of IPV, social marginalization, and health outcomes related to HIV, substance use, and mental health in trans populations.

A Scoping Review Examining Social and Legal Gender Affirmation and Health Among Transgender Populations

Purpose: Transgender (trans) populations experience health inequities. Gender affirmation refers to psychological, social, legal, and medical validation of one's gender and is a key social determinant of trans health. The majority of research has focused on medical affirmation; however, less is known about the role of social and legal affirmation in shaping trans health. This review aimed to (1) examine how social and legal gender affirmation have been defined and operationalized and (2) evaluate the association between these forms of gender affirmation and health outcomes among trans populations in the United States. Methods: We conducted a systematic search of LGBT Life, PsycInfo, and PubMed using search strings targeting transgender populations and gender affirmation. This review includes 24 of those articles as well as 1 article retrieved through hand searching. We used a modified version of the National Institute of Health Quality Assessment Tool to evaluate study quality. Results: All studies relied on cross-sectional data. Studies measured and operationalized social and legal gender affirmation inconsistently, and some measures conflated social gender affirmation with other constructs. Health outcomes related to mental health, HIV, smoking, and health care utilization, and studies reported mixed results regarding both social and legal gender affirmation. The majority of studies had serious methodological limitations. Conclusion: Despite conceptual and methodological limitations, social and legal gender affirmation were related to several health outcomes. Study findings can be used to develop valid and reliable measures of these constructs to support future multilevel interventions that improve the health of trans communities.

Transgender stigma: A critical scoping review of definitions, domains, and measures used in empirical research

RATIONALE

A growing body of transgender (trans) health research has explored the relationship between stigma and health; yet, studies have conceptualized and operationalized anti-trans stigma in multiple ways.

OBJECTIVE

This scoping review aims to critically analyze quantitative measures of anti-trans stigma in the U.S. using a socioecological framework.

METHOD

We organized and appraised measures from 126 included articles according to socioecological level: structural, interpersonal, or individual.

RESULTS

Of the identified articles, 36 measured anti-trans stigma at the structural level (i.e., institutional structures and policies), 102 measured anti-trans at the interpersonal level (i.e., community interactions), and 44 measured anti-trans stigma at the individual level (i.e., internalized or anticipated stigma). Definitions of anti-trans stigma varied substantially across articles. Most measures were adapted from measures developed for other populations (i.e., sexual minorities) and were not previously validated for trans samples.

CONCLUSIONS

Studies analyzing anti-trans stigma should concretely define anti-trans stigma. There is a need to develop measures of anti-trans stigma at all socioecological levels informed by the lived experiences of trans people.

Intense noise exposure alters peripheral vestibular structures and physiology

The otolith organs play a critical role in detecting linear acceleration and gravity to control posture and balance. Some afferents that innervate these structures can be activated by sound and are at risk for noise overstimulation. A previous report demonstrated that noise exposure can abolish vestibular short-latency evoked potential (VsEP) responses and damage calyceal terminals. However, the stimuli that were used to elicit responses were weaker than those established in previous studies and may have been insufficient to elicit VsEP responses in noise-exposed animals. The goal of this study was to determine the effect of an established noise exposure paradigm on VsEP responses using large head-jerk stimuli to determine if noise induces a stimulus threshold shift and/or if large head-jerks are capable of evoking VsEP responses in noise-exposed rats. An additional goal is to relate these measurements to the number of calyceal terminals and hair cells present in noise-exposed vs. non-noise-exposed tissue. Exposure to intense continuous noise significantly reduced VsEP responses to large stimuli and abolished VsEP responses to small stimuli. This finding confirms that while measurable VsEP responses can be elicited from noise-lesioned rat sacculi, larger head-jerk stimuli are required, suggesting a shift in the minimum stimulus necessary to evoke the VsEP. Additionally, a reduction in labeled calyx-only afferent terminals was observed without a concomitant reduction in the overall number of calyces or hair cells. This finding supports a critical role of calretinin-expressing calyceal-only afferents in the generation of a VsEP response.NEW & NOTEWORTHY This study identifies a change in the minimum stimulus necessary to evoke vestibular short-latency evoked potential (VsEP) responses after noise-induced damage to the vestibular periphery and reduced numbers of calretinin-labeled calyx-only afferent terminals in the striolar region of the sacculus. These data suggest that a single intense noise exposure may impact synaptic function in calyx-only terminals in the striolar region of the sacculus. Reduced calretinin immunolabeling may provide insight into the mechanism underlying noise-induced changes in VsEP responses.

Vestibular short-latency evoked potential abolished by low-frequency noise exposure in rats

The vestibular system plays a critical role in detection of head movements and is essential for normal postural control. Because of their anatomical proximity to the cochlea, the otolith organs are selectively exposed to sound pressure and are at risk for noise overstimulation. Clinical reports suggest a link between noise exposure and balance problems, but the structural and physiological basis for this linkage is not well understood. The goal of this study was to determine the effects of low-frequency noise (LFN) on the otolith organs by correlating changes in vestibular short-latency evoked potentials (VsEPs) with changes in saccular afferent endings following noise exposure. LFN exposure transiently abolished the VsEP and reduced the number of stained calyces within the sacculus. Although some recovery of the VsEP waveform could be observed within 3 days after noise, at 3 wk recovery was only partial in most animals, consistent with a reduced number of afferents with calyceal endings. These data show that a single intense noise exposure is capable of causing a vestibular deficit that appears to mirror the synaptic deficit associated with hidden hearing loss after noise-induced cochlear injury. NEW & NOTEWORTHY This is the first study to explore the effects of low-frequency high-intensity noise on vestibular short-latency evoked potential (VsEP) responses, which shows a linkage between attenuated noise-induced VsEPs and pathological changes to otolith organ afferents. This finding suggests a potential limitation of the VsEP for evaluation of vestibular dysfunction, since the VsEP measurement may assess the activity of a specific class rather than all afferents.

Scaling of compensatory eye movements during translations: virtual versus real depth

Vestibulo-ocular reflexes are the fastest compensatory reflex systems. One of these is the translational vestibulo-ocular reflex (TVOR) which stabilizes the gaze at a given fixation point during whole body translations. For a proper response of the TVOR the eyes have to counter rotate in the head with a velocity that is inversely scaled to viewing distance of the target. It is generally assumed that scaling of the TVOR is automatically coupled to vergence angle at the brainstem level. However, different lines of evidence also argue that in humans scaling of the TVOR also depends on a mechanism that pre-sets gain on a priori knowledge of target distance. To discriminate between these two possibilities we used a real target paradigm with vergence angle coupled to distance and a virtual target paradigm with vergence angle dissociated from target distance. We compared TVOR responses in six subjects who underwent lateral sinusoidal whole-body translations at 1 and 2 Hz. Real targets varied between distance of 50 and 22.4 cm in front of the subjects, whereas the virtual targets consisting of a green and red light emitting diode (LED) were physically located at 50 cm from the subject. Red and green LED's were dichoptically viewed. By shifting the red LED relative to the green LED we created a range of virtual viewing distances where vergence angle changed but the ideal kinematic eye velocity was always the same. Eye velocity data recorded with virtual targets were compared to eye velocity data recorded with real targets. We also used flashing targets (flash frequency 1 Hz, duration 5 ms). During the real, continuous visible targets condition scaling of compensatory eye velocity with vergence angle was nearly perfect. During viewing of virtual targets, and with flashed targets compensatory eye velocity only weakly correlated to vergence angle, indicating that vergence angle is only partially coupled to compensatory eye velocity during translation. Our data suggest that in humans vergence angle as a measure of target distance estimation has only limited use for automatic TVOR scaling.

Getting ahead of oneself: anticipation and the vestibulo-ocular reflex

Compensatory counter-rotations of the eyes provoked by head turns are commonly attributed to the vestibulo-ocular reflex (VOR). A recent study in guinea pigs demonstrates, however, that this assumption is not always valid. During voluntary head turns, guinea pigs make highly accurate compensatory eye movements that occur with zero or even negative latencies with respect to the onset of the provoking head movements. Furthermore, the anticipatory eye movements occur in animals with bilateral peripheral vestibular lesions, thus confirming that they have an extra vestibular origin. This discovery suggests the possibility that anticipatory responses might also occur in other species including humans and non-human primates, but have been overlooked and mistakenly identified as being produced by the VOR. This review will compare primate and guinea pig vestibular physiology in light of these new findings. A unified model of vestibular and cerebellar pathways will be presented that is consistent with current data in primates and guinea pigs. The model is capable of accurately simulating compensatory eye movements to active head turns (anticipatory responses) and to passive head perturbations (VOR induced eye movements) in guinea pigs and in human subjects who use coordinated eye and head movements to shift gaze direction in space. Anticipatory responses provide new evidence and opportunities to study the role of extra vestibular signals in motor control and sensory-motor transformations. Exercises that employ voluntary head turns are frequently used to improve visual stability in patients with vestibular hypofunction. Thus, a deeper understanding of the origin and physiology of anticipatory responses could suggest new translational approaches to rehabilitative training of patients with bilateral vestibular loss.

Galvanic stimulation of the vestibular periphery in guinea pigs during passive whole body rotation and self-generated head movement

Irregular vestibular afferents exhibit significant phase leads with respect to angular velocity of the head in space. This characteristic and their connectivity with vestibulospinal neurons suggest a functionally important role for these afferents in producing the vestibulo-collic reflex (VCR). A goal of these experiments was to test this hypothesis with the use of weak galvanic stimulation of the vestibular periphery (GVS) to selectively activate or suppress irregular afferents during passive whole body rotation of guinea pigs that could freely move their heads. Both inhibitory and excitatory GVS had significant effects on compensatory head movements during sinusoidal and transient whole body rotations. Unexpectedly, GVS also strongly affected the vestibulo-ocular reflex (VOR) during passive whole body rotation. The effect of GVS on the VOR was comparable in light and darkness and whether the head was restrained or unrestrained. Significantly, there was no effect of GVS on compensatory eye and head movements during volitional head motion, a confirmation of our previous study that demonstrated the extravestibular nature of anticipatory eye movements that compensate for voluntary head movements.

Anticipatory eye movements stabilize gaze during self-generated head movements

Visual acuity and motion perception are degraded during head movements unless the eyes counter-rotate so as to stabilize the line of sight and the retinal image. The vestibulo-ocular reflex (VOR) is assumed to produce this ocular counter-rotation. Consistent with this assumption, oscillopsia is a common complaint of patients with bilateral vestibular weakness. Shanidze et al. recently described compensatory eye movements in normal guinea pigs that appear to anticipate self-generated head movements. These responses effectively stabilize gaze and occur independently of the vestibular system. These new findings suggest that the VOR stabilizes gaze during passive perturbations of the head in space, but anticipatory responses may supplement or even supplant the VOR during actively generated head movements. This report reviews these findings, potential neurophysiological mechanisms, and their potential application to human clinical treatment of patients with vestibular disease.

Binocular coordination of eye movements--Hering's Law of equal innervation or uniocular control?

The neurophysiological basis for binocular control of eye movements in primates has been characterized by a scientific controversy that has its origin in the historical conflict of Hering and Helmholtz in the 19th century. This review focuses on two hypotheses, linked to that conflict, that seek to account for binocular coordination - Hering's Law vs. uniocular control of each eye. In an effort to manage the length of the review, the focus is on extracellular single-unit studies of premotor eye movement cells and extraocular motoneurons. In the latter half of the 20th century, these studies provided a wealth of neurophysiological data pertaining to the control of vergence and conjugate eye movements. The data were initially supportive of Hering's Law. More recent data, however, have provided support for uniocular control of each eye consistent with Helmholtz's original idea. The controversy is far from resolved. New anatomical descriptions of the disparate inputs to multiply and singly innervated extraocular muscle fibers challenge the concept of a 'final common pathway' as they suggest there may be separate groups of motoneurons involved in vergence and conjugate control of eye position. These data provide a new challenge for interpretation of uniocular premotor control networks and how they cooperate to produce coordinated eye movements.

Eye-head coordination in the guinea pig I. Responses to passive whole-body rotations

Vestibular reflexes act to stabilize the head and eyes in space during locomotion. Head stability is essential for postural control, whereas retinal image stability enhances visual acuity and may be essential for an animal to distinguish self-motion from that of an object in the environment. Guinea pig eye and head movements were measured during passive whole-body rotation in order to assess the efficacy of vestibular reflexes. The vestibulo-ocular reflex (VOR) produced compensatory eye movements with a latency of approximately 7 ms that compensated for 46% of head movement in the dark and only slightly more in the light (54%). Head movements, in response to abrupt body rotations, also contributed to retinal stability (21% in the dark; 25% in the light) but exhibited significant variability. Although compensatory eye velocity produced by the VOR was well correlated with head-in-space velocity, compensatory head-on-body speed and direction were variable and poorly correlated with body speed. The compensatory head movements appeared to be determined by passive biomechanical (e.g., inertial effects, initial tonus) and active mechanisms (the vestibulo-collic reflex or VCR). Chemically induced, bilateral lesions of the peripheral vestibular system abolished both compensatory head and eye movement responses.

Orthopedic outcomes of long-term daily corticosteroid treatment in Duchenne muscular dystrophy

OBJECTIVE

To document the effects of long-term daily corticosteroid treatment on a variety of orthopedic outcomes in boys with Duchenne muscular dystrophy.

METHODS

We reviewed the charts of 159 boys with genetically confirmed dystrophinopathies followed at the Ohio State University Muscular Dystrophy Clinic between 2000 and 2003. Charts were reviewed for ambulation status, type and duration of steroid treatment (if any), and orthopedic complications including presence and location of long bone fractures, vertebral compression fractures, and the presence and degree of scoliosis.

RESULTS

The cohort consisted of 143 boys (16 boys with Becker dystrophy were excluded); 75 had been treated with steroids for at least 1 year, whereas 68 boys had never been treated or had received only a brief submaximal dose. The mean duration of daily steroid treatment was 8.04 years. Treated boys ambulated independently 3.3 years longer than the untreated group (p < 0.0001) and had a lower prevalence of scoliosis than the untreated group (31 vs 91%; p < 0.0001). The average scoliotic curve was also milder in the treated group (11.6 degrees) compared with the untreated group (33.2 degrees; p < 0.0001). Vertebral compression fractures occurred in 32% of the treated group, whereas no vertebral fractures were discovered in the steroid naive group (p = 0.0012). Long bone fractures were 2.6 times greater in steroid-treated patients.

CONCLUSIONS

Although boys with Duchenne muscular dystrophy on long-term corticosteroid treatment have a significantly decreased risk of scoliosis and an extension of more than 3 years' independent ambulation, they are at increased risk of vertebral and lower limb fractures compared with untreated boys.

Responses of monkey vestibular-only neurons to translation and angular rotation

Single-unit recordings were obtained from central vestibular neurons in three monkeys during passive head movements. Neurons that discharged in relation to head translation or changes in head orientation, but not eye movement ("vestibular-only," n = 154), were examined in detail. Neuronal discharge rates were analyzed during four stimulus conditions: sinusoidal head translation in the horizontal plane (0.2-4 Hz, 0.2 g peak acceleration), static head tilt in the vertical plane (+/-20 degrees ), oscillatory head tilt (0.5-2 Hz), and sinusoidal angular rotation about an earth-vertical axis (0.5 or 1 Hz). Vestibular-only cells were divided into two groups based on the regularity of their spontaneous discharge rates (CV*). One group (low-sensitivity units) exhibited regular discharge rates (CV* < 0.2), weak discharge modulation during head translation (<25 spikes . s(-1) . g(-1) at f = 1 Hz), and persistent discharge rates related to static head tilt (0.68 spikes . s(-1) . degrees (-1) of head tilt). The second group (high sensitivity neurons) exhibited irregular discharge rates (CV* > 0.2), strong discharge modulation during head translation ( approximately 100 spikes . s(-1) . g(-1) at f = 1 Hz), and little or no change in discharge rate during static head tilt (0.32 spikes . s(-1) . degrees (-1)). The firing rates of some neurons in both groups were modulated during rotation about an earth-vertical axis (42%), but the modulation was greater for neurons classified as high sensitivity units. Previous reports have described neurons similar to the high sensitivity group; however, the low sensitivity or tilt neurons have not previously been characterized. Significantly, recent theoretical models have predicted neurons with discharge patterns similar to those of low- and high-sensitivity neurons.

NT-3 promotes nerve regeneration and sensory improvement in CMT1A mouse models and in patients

BACKGROUND

Xenografts from patients with Charcot-Marie-Tooth type 1A (CMT1A) have shown delayed myelination and impaired regeneration of nude mice axons passing through the grafted segments. Neurotrophin-3 (NT-3), an important component of the Schwann cell (SC) autocrine survival loop, could correct these deficiencies.

OBJECTIVE

To assess the efficacy of NT-3 treatment in preclinical studies using animal models of CMT1A and to conduct a double-blind, placebo-controlled, randomized, pilot clinical study to assess the efficacy of subcutaneously administered NT-3 in patients with CMT1A.

METHODS

Nude mice harboring CMT1A xenografts and Trembler(J) mice with a peripheral myelin protein 22-point mutation were treated with NT-3, and the myelinated fiber (MF) and SC numbers were quantitated. Eight patients received either placebo (n = 4) or 150 microg/kg NT-3 (n = 4) three times a week for 6 months. MF regeneration in sural nerve biopsies before and after treatment served as the primary outcome measure. Additional endpoint measures included the Mayo Clinic Neuropathy Impairment Score (NIS), electrophysiologic measurements, quantitative muscle testing, and pegboard performance.

RESULTS

The NT-3 treatment augmented axonal regeneration in both animal models. For CMT1A patients, changes in the NT-3 group were different from those observed in the placebo group for the mean number of small MFs within regeneration units (p = 0.0001), solitary MFs, (p = 0.0002), and NIS (p = 0.0041). Significant improvements in these variables were detected in the NT-3 group but not in the placebo group. Pegboard performance was significantly worsened in the placebo group. NT-3 was well tolerated.

CONCLUSION

Neurotrophin-3 augments nerve regeneration in animal models for CMT1A and may benefit patients clinically, but these results need further confirmation.

Vestibulo-collic reflex (VCR) in mice

The vestibulo-collic reflex (VCR) attempts to stabilize head position in space during motion of the body. Similar to the better-studied vestibulo-ocular reflex, the VCR is subserved by relatively direct, as well as indirect pathways linking vestibular nerve activity to cervical motor neurons. We measured the VCR using an electromagnetic technique often employed to measure eye movements; we attached a loop of wire (head coil) to an animal's head using an adhesive; then the animal was gently restrained with its head free to move within an electromagnetic field, and was subjected to sinusoidal (0.5-3 Hz) or abrupt angular acceleration (peak velocity approximately 200 degrees/s). Head rotation opposite in direction to body rotation was assumed to be driven by the VCR. To confirm that the compensatory head movements were in fact vestibular in origin, we plugged the horizontal canal unilaterally and then retested the animals 2, 8 and 15 days after the lesion. Two days after surgery, the putative VCR was almost absent in response to abrupt or sinusoidal rotations. Recovery commenced by day 8 and was nearly complete by day 15. We conclude that the compensatory head movements are vestibular in origin produced by the VCR. Similar to other species, there are robust compensatory mechanisms that restore the VCR following peripheral lesions.

Rapid motor learning in the translational vestibulo-ocular reflex

Motor learning was induced in the translational vestibulo-ocular reflex (TVOR) when monkeys were repeatedly subjected to a brief (0.5 sec) head translation while they tried to maintain binocular fixation on a visual target for juice rewards. If the target was world-fixed, the initial eye speed of the TVOR gradually increased; if the target was head-fixed, the initial eye speed of the TVOR gradually decreased. The rate of learning acquisition was very rapid, with a time constant of approximately 100 trials, which was equivalent to <1 min of accumulated stimulation. These learned changes were consolidated over >or=1 d without any reinforcement, indicating induction of long-term synaptic plasticity. Although the learning generalized to targets with different viewing distances and to head translations with different accelerations, it was highly specific for the particular combination of head motion and evoked eye movement associated with the training. For example, it was specific to the modality of the stimulus (translation vs rotation) and the direction of the evoked eye movement in the training. Furthermore, when one eye was aligned with the heading direction so that it remained motionless during training, learning was not expressed in this eye, but only in the other nonaligned eye. These specificities show that the learning sites are neither in the sensory nor the motor limb of the reflex but in the sensory-motor transformation stage of the reflex. The dependence of the learning on both head motion and evoked eye movement suggests that Hebbian learning may be one of the underlying cellular mechanisms.

Neural basis of disjunctive eye movements

New evidence has challenged a widely accepted interpretation of Hering's law of equal innervation, which states that disjunctive saccades are produced by the linear addition of conjugate and vergence innervation commands produced by independent oculomotor subsystems. We hypothesize, instead, that saccades are produced by a monocular premotor control network. A model, based on this hypothesis and consistent with known brain-stem anatomy, simulates realistic disjunctive saccades including initial and late slow vergence movements.

Attentional sensitivity and asymmetries of vertical saccade generation in monkey

The first goal of this study was to systematically document asymmetries in vertical saccade generation. We found that visually guided upward saccades have not only shorter latencies, but higher peak velocities, shorter durations and smaller errors. The second goal was to identify possible mechanisms underlying the asymmetry in vertical saccade latencies. Based on a recent model of saccade generation, three stages of saccade generation were investigated using specific behavioral paradigms: attention shift to a visual target (CUED paradigm), initiation of saccade generation (GAP paradigm) and release of the motor command to execute the saccade (DELAY paradigm). Our results suggest that initiation of a saccade (or "ocular disengagement") and its motor release contribute little to the asymmetry in vertical saccade latency. However, analysis of saccades made in the CUED paradigm indicated that it took less time to shift attention to a target in the upper visual field than to a target in the lower visual field. These data suggest that higher attentional sensitivity to targets in the upper visual field may contribute to shorter latencies of upward saccades.

Randomized, double-blind, placebo-controlled trial of albuterol in facioscapulohumeral dystrophy

BACKGROUND/OBJECTIVES

Animal and human studies suggest that beta(2)-adrenergic agonists exert anabolic effects on muscles, inducing and preventing atrophy after a variety of insults. Based on data from an open-label trial of albuterol in 15 patients with facioscapulohumeral dystrophy (FSHD), the authors conducted a randomized, double-blind, placebo-controlled trial of sustained-release albuterol in this disease.

METHODS

Ninety patients were randomized to three groups: placebo; 8.0 mg albuterol twice daily; or 16.0 mg albuterol twice daily. Patients were treated for 1 year with assessments at baseline and weeks 13, 26, and 52. The primary outcome was the 52-week change in global strength by maximum voluntary isometric contraction testing (MVICT). Secondary outcomes included changes at 52 weeks in strength by manual muscle testing (MMT), grip strength, functional testing, and muscle mass assessed by dual energy x-ray absorptiometry (DEXA).

RESULTS

Eighty-four patients completed the study. The mean changes in composite MVICT scores were not significantly different between the groups (mean +/- SD: placebo 0.20 +/- 0.91; low dose -0.04 +/- 0.84; high dose 0.08 +/- 0.98). Similarly, there were no differences in the mean MMT change (placebo 0.04 +/- 0.16; low dose -0.03 +/- 0.13; high dose 0.00 +/- 0.15). Grip improved in both treatment groups compared to placebo (placebo -0.53 +/- 4.13, low dose +1.90 +/- 3.34 [p = 0.02], high dose +1.70 +/- 4.13 [p = 0.03]). The high-dose group had a significant increase in lean mass by DEXA (+1.57 +/- 1.71 kg) compared to placebo (0.25 +/- 2.24; p = 0.007). Albuterol was well tolerated; side effects included cramps, tremors, insomnia, and nervousness.

CONCLUSIONS

Although albuterol did not improve global strength or function in patients with FSHD, it did increase muscle mass and improve some measures of strength.

Responses of rostral fastigial neurons to linear acceleration in an alert monkey

Vestibular-only neuronal responses to angular acceleration have been systematically characterized in the rostral fastigial nucleus (FN) by several studies. However, responses of these neurons to linear acceleration have not been examined. In this study, we recorded single-unit activity of vestibular-only neurons in an alert monkey during pure sinusoidal linear acceleration along different directions in the horizontal plane. Spatiotemporal response properties were quantified by computing two-dimensional response ellipses in the horizontal plane. Based on this analysis, neurons were classified as narrowly or broadly tuned. About 29% (5/17) of neurons were broadly tuned. The other 71% (12/17) were narrowly tuned. Unlike vestibular nuclei neurons, all recorded FN neurons exhibited irregular resting discharge rates (CV*0.2). Based on studies of linear motion-sensitive neurons in the vestibular nuclei, the data suggest that irregular neurons in the rostral FN and the vestibular nuclei have similar responses to linear acceleration in behaving monkeys.

A randomized efficacy and safety trial of oxandrolone in the treatment of Duchenne dystrophy

BACKGROUND

A pilot study suggested that oxandrolone, an anabolic steroid, improved strength in boys with Duchenne dystrophy (DD) and indicated the need for a more definitive study.

METHODS

A 6-month, randomized, double-blind, placebo-controlled study of oxandrolone in boys with an established diagnosis of DD, using the change from baseline to 6 months in the average muscle strength score (MMT) as the primary efficacy measure.

RESULTS

The mean change from baseline for the oxandrolone group was +0.035 and that for the placebo group was -0.140. Although the oxandrolone group did not get worse and the placebo patients showed some deterioration in strength, the difference was not significant (p = 0.13). The average of the four quantitative muscle tests (QMT) showed a significant improvement in the oxandrolone-treated boys as compared with placebo. No adverse reactions attributable to oxandrolone were recorded.

CONCLUSIONS

Although oxandrolone did not produce a significant change in the average manual muscle strength score as compared with placebo, the mean change in QMT was significant. Because oxandrolone is safe, accelerates linear growth, and may have some beneficial effect in slowing the progress of weakness, it may be useful before initiating corticosteroid therapy.

Anatomical risk factors for phonological dyslexia

Successful behavioral genetic studies require precise definition of a homogenous phenotype. This study searched for anatomical markers that might restrict variability in the reading disability phenotype. The subjects were 15 college students (8 male/7 female) diagnosed with a reading disability (RD) and 15 controls (8 males/7 females). All subjects completed a cognitive and reading battery. Only 11 of the RD subjects had a phonological deficit [phonological dyslexia (PD): pseudo word decoding scores < 90 (27th percentile)]. Thirteen RD (9 PD) and 15 controls received a volumetric MRI scan. Four anatomical measures differentiated the PD group from the remainder of the subjects: (i) marked rightward cerebral asymmetry, (ii) marked leftward asymmetry of the anterior lobe of the cerebellum, (ii) combined leftward asymmetry of the planum and posterior ascending ramus of the sylvian fissure, and (iv) a large duplication of Heschl's gyrus on the left. When these four measures were normalized and summed, the resulting variable predicted short- and long-term phonological memory. By contrast, oral and written comprehension skills were predicted by a different anatomical variable: low cerebral volume. These findings provide neurobiological support for an RD phenotype characterized by phonological deficits in the presence of normal or superior comprehension. The study of individual variation in cortical structure may provide a useful link between genotype and behavior.

New ideas about binocular coordination of eye movements: is there a chameleon in the primate family tree?

Many animals with laterally placed eyes, such as chameleons, move their eyes independently of one another. In contrast, primates with frontally placed eyes and binocular vision must move them together so that both eyes are aimed at the same point in visual space. Is binocular coordination an innate feature of how our brains are wired, or have we simply learned to move our eyes together? This question sparked a controversy in the 19(th) century between two eminent German scientists, Ewald Hering and Hermann von Helmholtz. Hering took the position that binocular coordination was innate and vigorously challenged von Helmholtz's view that it was learned. Hering won the argument and his hypothesis, known as Hering's Law of Equal Innervation, became generally accepted. New evidence suggests, however, that similar to chameleons, primates may program movements of each eye independently. Binocular coordination is achieved by a neural network at the motor periphery comprised of motoneurons and specialized interneurons located near or in the cranial nerve nuclei that innervate the extraocular muscles. It is assumed that this network must be trained and calibrated during infancy and probably throughout life in order to maintain the precise binocular coordination characteristic of primate eye movements despite growth, aging effects, and injuries to the eye movement neuromuscular system. Malfunction of this network or its ability to adaptively learn may be a contributing cause of strabismus.

Stereotactic posterioventral pallidotomy improves balance control as assessed by computerized posturography

Postural instability is arguably the most debilitating symptom of Parkinson's disease (PD). Recently, posterioventral pallidotomy/pallidoansotomy (PVP) has been advocated to improve a multitude of symptoms associated with PD. Dyskinesias, rigidity and bradykinesia are the most talked about improved symptoms, but posture and gait are also affected after PVP. To analyze the effect of PVP on postural control, 14 patients with PD were prospectively studied using a computerized dynamic posturography machine. Seven males and 7 females underwent a total of 18 procedures, 6 left PVP, 6 right PVP, 2 bilateral and 2 had Vim thalamotomies in addition to PVP. Data were collected pre- and postoperatively after a 12-hour drug-free interval ('off' period) and 1-2 h after medications ('on' period). Postoperative analyses were performed between 1 and 3 months postoperatively. As a group, patients' balance, in the off period, improved after surgery in a dynamic setting. Prior to surgery, patients' anterior-posterior sway exceeded their stability limits (patient fell) on 31% of the trials. After surgery, the fall rate decreased to 23%. Anterior-posterior sway decreased significantly (p < 0.05) postoperatively when the platform was sway referenced. In comparing the effect of surgery in decreasing sway with that of medication preoperatively, improvement after surgery (off period) was better than the preoperative on period (p < 0.05). Patients also improved in ostoperative off state when compared to preoperative off state with the platform sway referenced (p < 0.05), controlling for improvement in dyskinesia-induced imbalance. In conclusion, PVP improves standing balance performance better than that achieved with medications preoperatively. Since central input parameters were improved, the mechanism of PVP may be centralized.

Influence of speech stimuli intensity on the activation of auditory cortex investigated with functional magnetic resonance imaging

Understanding the impact of variations in the acoustic signal is critical for the development of auditory and language fMRI as an experimental tool. We describe the dependence of the BOLD signal and speech intelligibility on the intensity of auditory stimuli. Eighteen subjects were imaged on a 1.5-T MRI scanner. Speech stimuli were English monosyllabic words played at five intensity levels. Intrasubject reproducibility was measured on one subject by presenting the stimulus five times at the same intensity level. Intelligibility was measured during data acquisition as subjects signaled when hearing two targets. Each functional trial consisted of four cycles (30 s off-30 s on). Five oblique slices covering primary and association auditory areas were imaged. Activated voxels were identified by cross-correlation analysis and their percent signal change (delta S) was measured. Intersubject differences in activation extent, asymmetry, and dependence on intensity were striking. Volume of activation was significantly greater in the left than in the right hemisphere. Intrasubject reproducibility for delta S was higher than for volume of activation. delta S and intelligibility showed a similar dependence on intensity suggesting that not only intensity but also intelligibility affect the fMRI signal.

Premotor commands encode monocular eye movements

Binocular coordination of eye movements is essential for stereopsis (depth perception) and to prevent double vision. More than a century ago, Hering and Helmholtz debated the neural basis of binocular coordination. Helmholtz believed that each eye is controlled independently and that binocular coordination is learned. Hering believed that both eyes are innervated by common command signals that yoke the eye movements (Hering's law of equal innervation). Here we provide evidence that Hering's law is unlikely to be correct. We show that premotor neurons in the paramedian pontine reticular formation that were thought to encode conjugate velocity commands for saccades (rapid eye movements) actually encode monocular commands for either right or left eye saccades. However, 66% of the abducens motor neurons, which innervate the ipsilateral lateral rectus muscle, fire as a result of movements of either eye. The distribution of sensitivity to ipsilateral and contralateral eye movements across the abducens motor neuron pool may provide a basis for learning binocular coordination in infancy and adapting it throughout life.

Pilot trial of albuterol in facioscapulohumeral muscular dystrophy. FSH-DY Group

BACKGROUND/OBJECTIVE

Facioscapulohumeral muscular dystrophy (FSHD) is currently untreatable, and there have been few therapeutic trials of any agent in the disease. Animal studies have demonstrated that beta2-adrenergic agonists induce muscle hypertrophy and prevent atrophy after a variety of physical and biochemical insults, and two human studies have shown that these agents increase certain measures of strength in healthy volunteers. We conducted an open-label pilot trial of a beta2-agonist (albuterol) in patients with FSHD.

METHODS

Fifteen FSHD patients were given sustained-release albuterol (16.0 mg/day) for 3 months. The primary outcome measure was lean body mass, which was assessed through dual energy X-ray absorptiometry (DEXA). Strength was evaluated through maximal voluntary isometric contraction testing (MVICT) and manual muscle testing.

RESULTS

Albuterol significantly increased DEXA lean body mass (the skeletal muscle compartment) by 1.29 +/- 1.18 kg (mean +/- SD, p = 0.001). Strength assessed through composite MVICT scores also increased by an average of 0.33 +/- 0.60 (p = 0.05), representing an overall 12% improvement in strength.

CONCLUSIONS

These encouraging results suggest that beta2-agonists may have a role in treating FSHD and possibly other neuromuscular diseases. The effects of albuterol in FSHD are currently being evaluated in a larger, randomized, double-blind, placebo-controlled trial lasting 1 year.

Binocular eye movements not coordinated during REM sleep

Rapid eye movements (REMs) are a defining characteristic of REM sleep during which vivid dreams occur. It has been suggested that REMs may be binocularly coordinated and related to "watching" dream images. For the first time, binocular eye movements were recorded during natural REM sleep in monkeys to test the conjugate nature of the oculomotor system and the "scanning hypothesis" of REMs during sleep. During REM sleep, the lines of sight of the two eyes are frequently misaligned up to 30 degrees horizontally and/or vertically. Since the lines of sight usually don't intersect, there is no fixation point. Instead, each eye is aimed at a different part of the visual field during REM sleep. Furthermore, REMs are not usually conjugate, but are disjunctive or even monocular in horizontal or vertical directions. These data argue against the idea that REMs actually "track" dream images, unless each eye is watching its own dream! Binocular misalignment and disjunctive (even monocular) REMs during sleep suggest that separate left eye and right eye pathways generate saccades in each eye and control the position of each eye. Binocular coordination cannot be the passive result of anatomical connectivity as has been argued previously, but instead must result from a high-level process associated with the awake state that coordinates activity in left-eye and right-eye pathways. Hering's law of equal innervation is not consistent with these data.

Deficits in auditory temporal and spectral resolution in language-impaired children

Between 3 and 6 per cent of children who are otherwise unimpaired have extreme difficulties producing and understanding spoken language. This disorder is typically labelled specific language impairment. Children diagnosed with specific language impairment often have accompanying reading difficulties (dyslexia), but not all children with reading difficulties have specific language impairment. Some researchers claim that language impairment arises from failures specific to language or cognitive processing. Others hold that language impairment results from a more elemental problem that makes affected children unable to hear the acoustic distinctions among successive brief sounds in speech. Here we report the results of psychophysical tests employing simple tones and noises showing that children with specific language impairment have severe auditory perceptual deficits for brief but not long tones in particular sound contexts. Our data support the view that language difficulties result from problems in auditory perception, and provide further information about the nature of these perceptual problems that should contribute to improving the diagnosis and treatment of language impairment and related disorders.

Behavior and physiology of the macaque vestibulo-ocular reflex response to sudden off-axis rotation: computing eye translation

The vestibulo-ocular reflex (VOR) has historically been considered a computationally simple reflex: to stabilize images on the retina against imposed head rotation, the eyes must be counterrotated by an equal amount in the opposite direction. During almost any head rotation, however, the eyes are also translated. We show that the VOR compensates for 90% of this translation, and suggest a computational scheme by which this is done, based on a temporal dissection of the VOR response to sudden head rotation. An initial response that corrects only for imposed rotation is refined by a series of three temporally delayed corrections of increasing complexity. The first correction takes only head rotation and viewing distance into account; the second, head rotation, viewing distance, and otolith translation; and the third, head rotation, viewing distance, otolith translation, and translation of the eyes relative to the otoliths. Responses of type I gaze velocity Purkinje (GVP) cells in the cerebellar flocculus and ventral paraflocculus of rhesus monkeys were recorded during sudden head rotation. We show that cell discharge was modulated both by axis location and by viewing distance, suggesting that GVP cells play a role in the VOR response to rotation-induced eye translation.

Initiation of disjunctive smooth pursuit in monkeys: evidence that Hering's law of equal innervation is not obeyed by the smooth pursuit system

Monkeys generated disjunctive smooth pursuit eye movements when they tracked visual targets that moved toward or away from them. Eye acceleration was computed during the initial 100 msec of pursuit (the open-loop interval) for various target trajectories. The initial acceleration of either eye was a function of the target's motion with respect to that eye, regardless of whether or not the pursuit was conjugate or disjunctive, or performed with one eye occluded. Eye movements produced by fusional vergence could be separated temporally from eye movements produced by smooth pursuit using step-ramp paradigms. The separation of the two responses demonstrates that the fusional vergence system operates in parallel with the smooth pursuit system, presumably to minimize disparity, but not to generate disjunctive components of smooth pursuit eye movements.

Eye position signals in the abducens and oculomotor nuclei of monkeys during ocular convergence

Many neurons in oculomotor pathways encode signals related to eye position. For example, motoneurons in the third, fourth, and sixth cranial nuclei discharge at highly regular rates during fixation intervals. During fixations of far targets, their tonic discharge is linearly related to conjugate eye position. Previous studies provided evidence that premotor cells in brainstem pathways also encoded conjugate eye position. McConville et al. (this volume), however, measured eye movements during binocular fixations when the eyes were converged and concluded that the position signal encoded by premotor position-vestibular-pause (PVP) cells in the vestibular nuclei is related to monocular (right or left) eye position rather than to conjugate eye position. This surprising relationship would not have been noticed in earlier studies that measured the movements of only one eye (using a single eye coil) or that measured only the conjugate movements of the two eyes (using bitemporal EOG electrodes). How general a feature of oculomotor signal processing is this finding? In this paper, we re-examine the eye position signal in abducens and oculomotor neurons when the movements of the two eyes are conjugate and when they are disjunctive and therefore disassociated. The data suggest that abducens neurons (AMNs and AINs) and oculomotor neurons (putative medial rectus motoneurons), unlike PVP cells, are not monocular but encode mixtures of right and left eye position signals.

Eye position signals in the vestibular nuclei: consequences for models of integrator function

Recordings from neurons in the vestibular nuclei indicate that the cells that carry eye position signals encode the position of a single eye (either ipsilateral or contralateral) during both conjugate and vergence eye movements. The fact that the vestibular nuclei are aware of the positions of each eye is not surprising as the otolith-based linear vestibulo-ocular reflex is known to change its behaviour as a function of uniocular eye position. This result suggests that the signal coming from the oculomotor velocity-to-position integrator specifies the position of each eye during vergence movements and thus must receive a vergence velocity input along with its conjugate velocity inputs. As there is no vergence system in laterally eyed animals, we have proposed two possible models of integrator arrangement that could have developed from conjugate directional (rather than uniocular) integrators in lower animals without frontally mounted eyes. Both of these models explain the existence of near-response cells and produce the required bidirectional gaze paretic nystagmus following unilateral lesions of one integrator. The models also make specific and different predictions concerning the effects of unilateral integrator lesions on the behaviour of the vergence system and thus make suggestions for further experiments.