Effect of vision, touch and stance on cerebellar vermian-related sway and tremor: a quantitative physiological and MRI study

Contributions of cerebral white matter hyperintensities, age, and pedal perception to postural sway in people with HIV

OBJECTIVE

With aging, people with HIV (PWH) have diminishing postural stability that increases liability for falls. Factors and neuromechanisms contributing to instability are incompletely known. Brain white matter abnormalities seen as hyperintense (WMH) signals have been considered to underlie instability in normal aging and PWH. We questioned whether sway-WMH relations endured after accounting for potentially relevant demographic, physiological, and HIV-related variables.

DESIGN

Mixed cross-sectional/longitudinal data were acquired over 15 years in 141 PWH and 102 age-range matched controls, 25-80 years old.

METHODS

Multimodal structural MRI data were quantified for seven total and regional WMH volumes. Static posturography acquired with a force platform measured sway path length separately with eyes closed and eyes open. Statistical analyses used multiple regression with mixed modeling to test contributions from non-MRI and nonpath data on sway path-WMH relations.

RESULTS

In simple correlations, longer sway paths were associated with larger WMH volumes in PWH and controls. When demographic, physiological, and HIV-related variables were entered into multiple regressions, the sway-WMH relations under both vision conditions in the controls were attenuated when accounting for age and two-point pedal discrimination. Although the sway-WMH relations in PWH were influenced by age, 2-point pedal discrimination, and years with HIV infection, the sway-WMH relations endured for five of the seven regions in the eyes-open condition.

CONCLUSION

The constellation of age-related increasing instability while standing, degradation of brain white matter integrity, and peripheral pedal neuropathy is indicative of advancing fraility and liability for falls as people age with HIV infection.

Contributions of Cerebral White Matter Hyperintensities to Postural Instability in Aging with and without Alcohol Use Disorder

BACKGROUND

Postural instability and brain white matter hyperintensities (WMH) are both noted markers of normal aging and alcohol use disorder (AUD). Here, we questioned what variables contribute to sway path/WMH relations in individuals with AUD and healthy control participants.

METHOD

The data comprised 404 balance platform sessions, yielding sway path length and MRI acquired cross-sectionally or longitudinally, in 102 control and 158 AUD participants, ages 25-80 years. Balance sessions were typically conducted on the same day as MRI FLAIR acquisitions, permitting WMH volume quantification. Factors considered in multiple regression analyses as potential contributors to relations between WMH volumes and postural instability were age, sex, socioeconomic status, education, pedal 2-point discrimination, systolic and diastolic blood pressure, body mass index, depressive symptoms, total alcohol consumed in the past year, and race.

RESULTS

Initial analysis identified diagnosis, age, sex, and race as significant contributors to observed sway path/WMH relations. Inclusion of these factors as predictors in multiple regression analysis substantially attenuated the sway/WMH relations in both AUD and healthy control groups. Women, irrespective of diagnosis or race, had shorter sway paths than men. Black participants, irrespective of diagnosis or sex, had shorter sway paths than non-Black participants despite having modestly larger WMH volumes than non-Black participants, possibly a reflection of the younger age of the Black sample.

DISCUSSION

Longer sway paths were related to larger WMH volumes in healthy men and women, with and without AUD. Critically, however, age nearly fully accounted for these relations.

Internal models of self-motion: neural computations by the vestibular cerebellum

The vestibular cerebellum plays an essential role in maintaining our balance and ensuring perceptual stability during activities of daily living. Here I examine three key regions of the vestibular cerebellum: the floccular lobe, anterior vermis (lobules I-V), and nodulus and ventral uvula (lobules X-IX of the posterior vermis). These cerebellar regions encode vestibular information and combine it with extravestibular signals to create internal models of eye, head, and body movements, as well as their spatial orientation with respect to gravity. To account for changes in the external environment and/or biomechanics during self-motion, the neural mechanisms underlying these computations are continually updated to ensure accurate motor behavior. To date, studies on the vestibular cerebellum have predominately focused on passive vestibular stimulation, whereas in actuality most stimulation is the result of voluntary movement. Accordingly, I also consider recent research exploring these computations during active self-motion and emerging evidence establishing the cerebellum's role in building predictive models of self-generated movement.

The 'Postural Rhythm' of the Ground Reaction Force during Upright Stance and Its Conversion to Body Sway-The Effect of Vision, Support Surface and Adaptation to Repeated Trials

The ground reaction force (GRF) recorded by a platform when a person stands upright lies at the interface between the neural networks controlling stance and the body sway deduced from centre of pressure (CoP) displacement. It can be decomposed into vertical (VGRF) and horizontal (HGRF) vectors. Few studies have addressed the modulation of the GRFs by the sensory conditions and their relationship with body sway. We reconsidered the features of the GRFs oscillations in healthy young subjects (n = 24) standing for 90 s, with the aim of characterising the possible effects of vision, support surface and adaptation to repeated trials, and the correspondence between HGRF and CoP time-series. We compared the frequency spectra of these variables with eyes open or closed on solid support surface (EOS, ECS) and on foam (EOF, ECF). All stance trials were repeated in a sequence of eight. Conditions were randomised across different days. The oscillations of the VGRF, HGRF and CoP differed between each other, as per the dominant frequency of their spectra (around 4 Hz, 0.8 Hz and <0.4 Hz, respectively) featuring a low-pass filter effect from VGRF to HGRF to CoP. GRF frequencies hardly changed as a function of the experimental conditions, including adaptation. CoP frequencies diminished to <0.2 Hz when vision was available on hard support surface. Amplitudes of both GRFs and CoP oscillations decreased in the order ECF > EOF > ECS ≈ EOS. Adaptation had no effect except in ECF condition. Specific rhythms of the GRFs do not transfer to the CoP frequency, whereas the magnitude of the forces acting on the ground ultimately determines body sway. The discrepancies in the time-series of the HGRF and CoP oscillations confirm that the body's oscillation mode cannot be dictated by the inverted pendulum model in any experimental conditions. The findings emphasise the robustness of the VGRF "postural rhythm" and its correspondence with the cortical theta rhythm, shed new insight on current principles of balance control and on understanding of upright stance in healthy and elderly people as well as on injury prevention and rehabilitation.

Postural instability in HIV infection: relation to central and peripheral nervous system markers

OBJECTIVES

Determine the independent contributions of central nervous system (CNS) and peripheral nervous system (PNS) metrics to balance instability in people with HIV (PWH) compared with people without HIV (PWoH).

METHODS

Volumetric MRI (CNS) and two-point pedal discrimination (PNS) were tested as substrates of stance instability measured with balance platform posturography.

DESIGN

125 PWH and 88 PWoH underwent balance testing and brain MRI.

RESULTS

The PWH exhibited stability deficits that were disproportionately greater with eyes closed than eyes open compared with PWoH. Further analyses revealed that greater postural imbalance measured as longer sway paths correlated with smaller cortical and cerebellar lobular brain volumes known to serve sensory integration; identified brain/sway path relations endured after accounting for contributions from physiological and disease factors as potential moderators; and multiple regression identified PNS and CNS metrics as independent predictors of postural instability in PWH that differed with the use of visual information to stabilize balance. With eyes closed, temporal volumes and two-point pedal discrimination were significant independent predictors of sway; with eyes open, occipital volume was an additional predictor of sway. These relations were selective to PWH and were not detected in PWoH.

CONCLUSION

CNS and PNS factors were independent contributors to postural instability in PWH. Recognizing that myriad inputs must be detected by peripheral systems and brain networks to integrate sensory and musculoskeletal information for maintenance of postural stability, age- or disease-related degradation of either or both nervous systems may contribute to imbalance and liability for falls.

Vestibular motor control

The vestibular system is an essential sensory system that generates motor reflexes that are crucial for our daily activities, including stabilizing the visual axis of gaze and maintaining head and body posture. In addition, the vestibular system provides us with our sense of movement and orientation relative to space and serves a vital role in ensuring accurate voluntary behaviors. Neurophysiological studies have provided fundamental insights into the functional circuitry of vestibular motor pathways. A unique feature of the vestibular system compared to other sensory systems is that the same central neurons that receive direct input from the afferents of the vestibular component of the 8th nerve can also directly project to motor centers that control vital vestibular motor reflexes. In turn, these reflexes ensure stabilize gaze and the maintenance of posture during everyday activities. For instance, a direct three-neuron pathway mediates the vestibulo-ocular reflex (VOR) pathway to provide stable gaze. Furthermore, recent studies have advanced our understanding of the computations performed by the cerebellum and cortex required for motor learning, compensation, and voluntary movement and navigation. Together, these findings have provided new insights into how the brain ensures accurate self-movement during our everyday activities and have also advanced our knowledge of the neurobiological mechanisms underlying disorders of vestibular processing.

Disruption of cerebellar-cortical functional connectivity predicts balance instability in alcohol use disorder

BACKGROUND

A neural substrate of alcohol-related instability of gait and balance is the cerebellum. Whether disruption of neural communication between cerebellar and cortical brain regions exerts an influence on ataxia in alcohol use disorder (AUD) was the focus of this study.

METHODS

Study groups comprised 32 abstinent AUD participants and 22 age- and sex-matched healthy controls (CTL). All participants underwent clinical screening, motor testing, and resting-state functional MR imaging analyzed for functional connectivity (FC) among 90 regions across the whole cerebrum and cerebellum. Ataxia testing quantified gait and balance with the Fregly-Graybiel Ataxia Battery conducted with and without vision.

RESULTS

The AUD group achieved lower scores than the CTL group on balance performance, which was disproportionately worse for eyes open than eyes closed in the AUD relative to the CTL group. Differences in ataxia were accompanied by differences in FC marked by cerebellar-frontal and cerebellar-parietal hyperconnectivity and cortico-cortical hypoconnectivity in the AUD relative to the control group. Lifetime alcohol consumption correlated significantly with AUD-related FC aberrations, which explained upwards of 69% of the AUD ataxia score variance.

CONCLUSION

Heavy, chronic alcohol consumption is associated with disorganized neural communication among cerebellar-cortical regions and contributes to ataxia in AUD. Ataxia, which is known to accelerate with age and be exacerbated with AUD, can threaten functional independence. Longitudinal studies are warranted to address whether extended sobriety quells ataxia and normalizes aberrant FC contributing to instability.

Distinct representations of body and head motion are dynamically encoded by Purkinje cell populations in the macaque cerebellum

The ability to accurately control our posture and perceive our spatial orientation during self-motion requires knowledge of the motion of both the head and body. However, while the vestibular sensors and nuclei directly encode head motion, no sensors directly encode body motion. Instead, the integration of vestibular and neck proprioceptive inputs is necessary to transform vestibular information into the body-centric reference frame required for postural control. The anterior vermis of the cerebellum is thought to play a key role in this transformation, yet how its Purkinje cells transform multiple streams of sensory information into an estimate of body motion remains unknown. Here, we recorded the activity of individual anterior vermis Purkinje cells in alert monkeys during passively applied whole-body, body-under-head, and head-on-body rotations. Most Purkinje cells dynamically encoded an intermediate representation of self-motion between head and body motion. Notably, Purkinje cells responded to both vestibular and neck proprioceptive stimulation with considerable heterogeneity in their response dynamics. Furthermore, their vestibular responses were tuned to head-on-body position. In contrast, targeted neurons in the deep cerebellar nuclei are known to unambiguously encode either head or body motion across conditions. Using a simple population model, we established that combining responses of~40-50 Purkinje cells could explain the responses of these deep cerebellar nuclei neurons across all self-motion conditions. We propose that the observed heterogeneity in Purkinje cell response dynamics underlies the cerebellum’s capacity to compute the dynamic representation of body motion required to ensure accurate postural control and perceptual stability in our daily lives.

Effects of unhealthy alcohol use on brain morphometry and neurocognitive function among people with HIV

Individual impacts of alcohol misuse and HIV on brain structure and function have been well demonstrated; however, the potential compounded effect of these conditions is seldom considered, despite the high prevalence of alcohol use in HIV infection. We aimed to determine the effects of unhealthy alcohol use on brain morphometry and cognitive function amongst people with HIV (PWH). In 27 (50.9%) HIV-positive users of alcohol and 26 (49.1%) HIV-positive abstainers from alcohol, results revealed significant differences for left and right amygdala (p < 0.01), left and right hippocampus (p = 0.05), left and right posterior cingulate (p < 0.01), left and right precuneus (p < 0.01), left insula (p < 0.01), left and right caudate (p < 0.01), right thalamus (p < 0.01), and corpus callosum (p < 0.05). Mean volume of these regions was significantly smaller in HIV-positive alcohol users compared to HIV-positive abstainers. Homogeneity of slopes ANCOVA revealed significant associations between anterior cingulate cortex, precuneus, amygdala, hippocampus, and insula volumes and cognitive function in the domains of learning and delayed recall, motor function, speed of information processing, executive function, attention/working memory, and language. Among PWH, unhealthy alcohol use is associated with negative effects on brain structure and cognitive function.

A review of center of pressure (COP) variables to quantify standing balance in elderly people: Algorithms and open-access code

Postural control is often quantified by recording the trajectory of the center of pressure (COP)-also called stabilogram-during human quiet standing. This quantification has many important applications, such as the early detection of balance degradation to prevent falls, a crucial task whose relevance increases with the aging of the population. Due to the complexity of the quantification process, the analyses of sway patterns have been performed empirically using a number of variables, such as ellipse confidence area or mean velocity. This study reviews and compares a wide range of state-of-the-art variables that are used to assess the risk of fall in elderly from a stabilogram. When appropriate, we discuss the hypothesis and mathematical assumptions that underlie these variables, and we propose a reproducible method to compute each of them. Additionally, we provide a statistical description of their behavior on two datasets recorded in two elderly populations and with different protocols, to hint at typical values of these variables. First, the balance of 133 elderly individuals, including 32 fallers, was measured on a relatively inexpensive, portable force platform (Wii Balance Board, Nintendo) with a 25-s open-eyes protocol. Second, the recordings of 76 elderly individuals, from an open access database commonly used to test static balance analyses, were used to compute the values of the variables on 60-s eyes-open recordings with a research laboratory standard force platform.

Trajectories of brain development reveal times of risk and factors promoting resilience to alcohol use during adolescence

Alcohol use disorder (AUD) is recognized as harmful for the developing brain. Numerous studies have sought environmental and genetic risk factors that predict the development of AUD, but recently identified resilience factors have emerged as protective. This chapter reviews normal processes of brain development in adolescence and emerging adulthood, delineates disturbed growth neurotrajectories related to heavy drinking, and identifies potential endogenous, experiential, and time-linked brain markers of resilience. For example, concurrent high dorsolateral prefrontal activation serving inhibitory control and low nucleus accumbens activation serving reward functions engender positive adaptation and low alcohol use. Also discussed is the role that moderating factors have in promoting risk for or resilience to AUD. Longitudinal research on the effects of all levels of alcohol drinking on the developing brain remains crucial and should be pursued in the context of resilience, which is a promising direction for identifying protective biomarkers against developing AUDs.

Korsakoff syndrome: An overlook (Review)

This review aimed to analyze the latest neurobiological findings regarding Korsakoff syndrome, since alcoholism is the most prevalent addiction worldwide. In addition, we analyzed the optimal treatment that can be administered in order to minimize the symptoms and improve the outcome of these patients. The disruption of memory circuits within the brain of alcoholic patients results in the amnestic syndrome known as Korsakoff syndrome. It is generally characterized by a chronic neuropsychiatric syndrome caused by vitamin B1 (thiamine) deficiency. Other categories of patients can develop Korsakoff syndrome without consuming alcohol such as AIDS patients, terminally ill cancer patients, or patients with chronic infections and malnutrition. Vitamin B1 is required in the Krebs cycle for production of adenosine triphosphate (ATP). It is also a cofactor in the production of acetylcholine and certain neurotransmitters. Alcohol consumption can decrease the intake, gastrointestinal absorption and cellular utilization of vitamin B1. Treatment of alcohol withdrawal along with high doses of vitamin B1 can improve the general outcome of patients. A small percentage of patients can recover from Wernicke's encephalopathy with no permanent brain damage. The onset of Korsakoff syndrome darkens the prognosis. Alcohol abstinence is an absolute recommendation and prevents the extension of neural damage.

Disturbed sensory physiology underlies poor balance and disrupts activities of daily living in alcohol use disorder

Postural stability is a multi-factorial skill maintained implicitly. Components of quiet standing can decline with Alcohol Use Disorder (AUD), cause instability, and disrupt activities of daily living (ADL). To examine how stability factors contribute to ADL and balance, 638 force platform testing sessions measured sway paths acquired during quiet standing in 151 AUD and 96 control men and women, age 25-75. Structural equation (seq) path analysis estimated contributions from age, diagnosis, and sensory perception to sway and measures of ADL and roadside ataxia testing. Whether eyes were open or closed, older AUD and control participants had longer sway paths than younger ones; older men had longer sway paths than older women. Although each sensory ability tested declined with aging, different factor constellations influenced ADL, ataxia scores, or sway path. Seq-path analysis indicated that ADL was strongly dependent on sensory (but not cognitive) systems with sway-path length accounting for upwards of 25% of variance. Within the AUD group, an index of historically-experienced withdrawal symptoms was a common predictor of stability regardless of vision condition. The greatest variance measured by the seq-path model was for predicting platform sway and simple ataxia testing of one-leg standing even though these measures were affected by different predictor variables: strong predictors of one-leg standing were diagnosis and age (R²  = 39.6%-43.2%), whereas strong predictors of sway-path length were sensory factors and withdrawal index (R²  = 22.0%-22.9%). These findings present evidence for appreciating selective factors that contribute to declining postural stability and to liability for compromised quality of life in AUD.

3-Hz Postural Tremor in MSA-C and SCA: Revisiting an Old but Underestimated Cerebellar Sign by Posturography

The aim of this study is to evaluate the prevalence and electrophysiological features of 3-Hz postural tremor in multiple system atrophy-cerebellar type and spinocerebellar ataxia. A static posturography examination was administered to 37 persons with spinocerebellar ataxia, 58 others with the cerebellar type of multiple system atrophy, and 53 healthy controls. During the sensory organization tests of 5 multiple system atrophy patients, surface electromyograms were recorded from bilateral tibialis anterior and medial gastrocnemius muscles. The patients with multiple system atrophy had, on average, significantly higher scores on the International Cooperative Ataxia Rating Scale and significantly greater prevalence of cross sign. Almost 80% of them fell during the posturography testing compared with two-thirds of the spinocerebellar ataxia patients. Twenty-seven percent of the spinocerebellar ataxia patients and 82.8% of those with multiple system atrophy displayed postural tremor with a frequency of approximately 3 Hz. The tremor's frequency tended to be lower in the spinocerebellar ataxia patients. The surface electromyography revealed highly coherent tremor activity at about 3 Hz in the patients' bilateral tibialis anterior and alternating firing in the bilateral antagonist muscles. Combining cross sign with a subject's static score of the International Cooperative Ataxia Rating Scale and occurrence of the tremor produced an indicator able to differentiate the two conditions with a sensitivity of 87.9% and a specificity of 89.2%. The area under the receiver operating characteristics curve for the indicator was 0.942. Three-hertz postural tremor is relatively characteristic of cerebellar type of multiple system atrophy and appears at an early stage of the disease. Identification of the tremor by posturography will facilitate its diagnosis.

Accelerated aging and motor control deficits are related to regional deformation of central cerebellar white matter in alcohol use disorder

The World Health Organization estimates a 12-month prevalence rate of 8+% for an alcohol use disorder (AUD) diagnosis in people age 15 years and older in the United States and Europe, presenting significant health risks that have the potential of accelerating age-related functional decline. According to neuropathological studies, white matter systems of the cerebellum are vulnerable to chronic alcohol dependence. To pursue the effect of AUD on white matter structure and functions in vivo, this study used T1-weighted, magnetic resonance imaging (MRI) to quantify the total corpus medullare of the cerebellum and a finely grained analysis of its surface in 135 men and women with AUD (mean duration of abstinence, 248 d) and 128 age- and sex-matched control participants; subsets of these participants completed motor testing. We identified an AUD-related volume deficit and accelerated aging in the total corpus medullare. Novel deformation-based surface morphometry revealed regional shrinkage of surfaces adjacent to lobules I-V, lobule IX, and vermian lobule X. In addition, accelerated aging was detected in the regional surface areas adjacent to lobules I-V, lobule VI, lobule VIIB, and lobules VIII, IX, and X. Sex differences were not identified for any measure. For both volume-based and surface-based analyses, poorer performance in gait and balance, manual dexterity, and grip strength were linked to greater regional white matter structural deficits. Our results suggest that local deformation of the corpus medullare has the potential of identifying structurally and functionally segregated networks affected in AUD.

Disturbed Cerebellar Growth Trajectories in Adolescents Who Initiate Alcohol Drinking

BACKGROUND

The cerebellum is a target of alcoholism-related brain damage in adults, yet no study has prospectively tracked deviations from normal cerebellar growth trajectories in adolescents before and after initiating drinking.

METHODS

Magnetic resonance imaging tracked developmental volume trajectories of 10 cerebellar lobule and vermis tissue constituents in 548 no/low drinking youths age 12 to 21 years at induction into this 5-site, NCANDA (National Consortium on Alcohol and NeuroDevelopment in Adolescence) study. Over the 3- to 4-year longitudinal examination yielding 2043 magnetic resonance imaging scans, 328 youths remained no/low drinkers, whereas 220 initiated substantial drinking after initial neuroimaging.

RESULTS

Normal growth trajectories derived from no/low drinkers indicated that gray matter volumes of lobules V and VI, crus II, lobule VIIB, and lobule X declined faster with age in male youths than in female youths, whereas white matter volumes in crus I and crus II and lobules VIIIA and VIIIB expanded faster in female youths than in male youths; cerebrospinal fluid volume expanded faster in most cerebellar regions of male youths than female youths. Drinkers exhibited accelerated gray matter decline in anterior lobules and vermis, accelerated vermian white matter expansion, and accelerated cerebrospinal fluid volumes expansion of anterior lobules relative to youths who remained no/low drinkers. Analyses including both alcohol and marijuana did not support an independent role for marijuana in alcohol effects on cerebellar gray matter trajectories.

CONCLUSIONS

Alcohol use-related cerebellar growth trajectory differences from normal involved anterior lobules and vermis of youths who initiated substantial drinking. These regions are commonly affected in alcohol-dependent adults, raising the possibility that cerebellar structures affected by youthful drinking may be vulnerable to age-alcohol interactions in later adulthood.

Cerebellar Morphometry and Cognition in the Context of Chronic Alcohol Consumption and Cigarette Smoking

BACKGROUND

Cerebellar atrophy (especially involving the superior-anterior cerebellar vermis) is among the most salient and clinically significant effects of chronic hazardous alcohol consumption on brain structure. Smaller cerebellar volumes are also associated with chronic cigarette smoking. The present study investigated effects of both chronic alcohol consumption and cigarette smoking on cerebellar structure and its relation to performance on select cognitive/behavioral tasks.

METHODS

Using T1-weighted Magnetic Resonance Images (MRIs), the Cerebellar Analysis Tool Kit segmented the cerebellum into bilateral hemispheres and 3 vermis parcels from 4 participant groups: smoking (s) and nonsmoking (ns) abstinent alcohol-dependent treatment seekers (ALC) and controls (CON) (i.e., sALC, nsALC, sCON, and nsCON). Cognitive and behavioral data were also obtained.

RESULTS

We found detrimental effects of chronic drinking on all cerebellar structural measures in ALC participants, with largest reductions seen in vermis areas. Furthermore, both smoking groups had smaller volumes of cerebellar hemispheres but not vermis areas compared to their nonsmoking counterparts. In exploratory analyses, smaller cerebellar volumes were related to lower measures of intelligence. In sCON, but not sALC, greater smoking severity was related to smaller cerebellar volume and smaller superior-anterior vermis area. In sALC, greater abstinence duration was associated with larger cerebellar and superior-anterior vermis areas, suggesting some recovery with abstinence.

CONCLUSIONS

Our results show that both smoking and alcohol status are associated with smaller cerebellar structural measurements, with vermal areas more vulnerable to chronic alcohol consumption and less affected by chronic smoking. These morphometric cerebellar deficits were also associated with lower intelligence and related to duration of abstinence in sALC only.

Brain-behavior relations and effects of aging and common comorbidities in alcohol use disorder: A review

OBJECTIVE

Alcohol use disorder (AUD) is a complex, dynamic condition that waxes and wanes with unhealthy drinking episodes and varies in drinking patterns and effects on brain structure and function with age. Its excessive use renders chronically heavy drinkers vulnerable to direct alcohol toxicity and a variety of comorbidities attributable to nonalcohol drug misuse, viral infections, and accelerated or premature aging. AUD affects widespread brain systems, commonly, frontolimbic, frontostriatal, and frontocerebellar networks.

METHOD AND RESULTS

Multimodal assessment using selective neuropsychological testing and whole-brain neuroimaging provides evidence for AUD-related specific brain structure-function relations established with double dissociations. Longitudinal study using noninvasive imaging provides evidence for brain structural and functional improvement with sustained sobriety and further decline with relapse. Functional imaging suggests the possibility that some alcoholics in recovery can compensate for impairment by invoking brain systems typically not used for a target task but that can enable normal-level performance.

CONCLUSIONS

Evidence for AUD-aging interactions, indicative of accelerated aging, together with increasing alcohol consumption in middle-age and older adults, put aging drinkers at special risk for developing cognitive decline and possibly dementia. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Convergence of three parcellation approaches demonstrating cerebellar lobule volume deficits in Alcohol Use Disorder

Recent advances in robust and reliable methods of MRI-derived cerebellar lobule parcellation volumetry present the opportunity to assess effects of Alcohol Use Disorder (AUD) on selective cerebellar lobules and relations with indices of nutrition and motor functions. In pursuit of this opportunity, we analyzed high-resolution MRI data acquired in 24 individuals with AUD and 20 age- and sex-matched controls with a 32-channel head coil using three different atlases: the online automated analysis pipeline volBrain Ceres, SUIT, and the Johns Hopkins atlas. Participants had also completed gait and balance examination and hematological analysis of nutritional and liver status, enabling testing of functional meaningfulness of each cerebellar parcellation scheme. Compared with controls, each quantification approach yielded similar patterns of group differences in regional volumes: All three approaches identified AUD-related deficits in total tissue and total gray matter, but only Ceres identified a total white matter volume deficit. Convergent volume differences occurred in lobules I-V, Crus I, VIIIB, and IX. Coefficients of variation (CVs) were <20% for 46 of 56 regions measured and in general were graded: Ceres<SUIT<Hopkins. The most robust correlations were identified between poorer stability in balancing on one leg and smaller lobule VI and Crus I volumes from the Ceres atlas. Lower values of two essential vitamins-thiamine (vitamin B1) and serum folate (vitamin B9)-along with lower red blood cell count, which are dependent on adequate levels of B vitamins, correlated with smaller gray matter volumes of lobule VI and Crus I. Higher γ-glutamyl transferase (GGT) levels, possibly reflecting compromised liver function, correlated with smaller volumes of lobules VI and X. These initial results based on high resolution data produced with clinically practical imaging procedures hold promise for expanding our knowledge about the relevance of focal cerebellar morphology in AUD and other neuropsychiatric conditions.

Relations between cognitive and motor deficits and regional brain volumes in individuals with alcoholism

Despite the common co-occurrence of cognitive impairment and brain structural deficits in alcoholism, demonstration of relations between regional gray matter volumes and cognitive and motor processes have been relatively elusive. In pursuit of identifying brain structural substrates of impairment in alcoholism, we assessed executive functions (EF), episodic memory (MEM), and static postural balance (BAL) and measured regional brain gray matter volumes of cortical, subcortical, and cerebellar structures commonly affected in individuals with alcohol dependence (ALC) compared with healthy controls (CTRL). ALC scored lower than CTRL on all composite scores (EF, MEM, and BAL) and had smaller frontal, cingulate, insular, parietal, and hippocampal volumes. Within the ALC group, poorer EF scores correlated with smaller frontal and temporal volumes; MEM scores correlated with frontal volume; and BAL scores correlated with frontal, caudate, and pontine volumes. Exploratory analyses investigating relations between subregional frontal volumes and composite scores in ALC yielded different patterns of associations, suggesting that different neural substrates underlie these functional deficits. Of note, orbitofrontal volume was a significant predictor of memory scores, accounting for almost 15% of the variance; however, this relation was evident only in ALC with a history of a non-alcohol substance diagnosis and not in ALC without a non-alcohol substance diagnosis. The brain-behavior relations observed provide evidence that the cognitive and motor deficits in alcoholism are likely a result of different neural systems and support the hypothesis that a number of identifiable neural systems rather than a common or diffuse neural pathway underlies cognitive and motor deficits observed in chronic alcoholism.

Balance and the brain: A review of structural brain correlates of postural balance and balance training in humans

BACKGROUND

Balance challenges are associated with not only the aging process but also a wide variety of psychiatric and neurological disorders. However, relatively little is known regarding the neural basis of balance and the effects of balance interventions on the brain.

RESEARCH QUESTION

This review synthesizes the existing literature to answer the question: What are the key brain structures associated with balance?

METHODS

This review examined 37 studies that assessed brain structures in relation to balance assessment or intervention. These studies provided 234 findings implicating 71 brain structures. The frequency of implication for each structure was examined based upon specific methodological parameters, including study design (assessment/intervention), type of balance measured (static/dynamic), population (clinical/non-clinical), and imaging analysis technique (region of interest [ROI]/voxel-based morphometry [VBM]).

RESULTS

Although a number of structures were associated with balance across the brain, the most frequently implicated structures included the cerebellum, basal ganglia, thalamus, hippocampus, inferior parietal cortex, and frontal lobe regions. Findings in the cerebellum and brainstem were most common in studies with clinical populations, studies that used an ROI approach, and studies that measured dynamic balance. Findings in the frontal, occipital, and parietal regions were also more common in studies that measured dynamic compared to static balance.

SIGNIFICANCE

While balance appears to be a whole-brain phenomenon, a subset of structures appear to play a key role in balance and are likely implicated in balance disorders. Some of these structures (i.e., the cerebellum, basal ganglia and thalamus) have a well-appreciated role in balance, whereas other regions (i.e., hippocampus and inferior parietal cortex) are not commonly thought to be associated with balance and therefore may provide alternative explanations for the neural basis of balance. Key avenues for future research include understanding the roles of all regions involved in balance across the lifespan and in different clinical populations.

Effects of Light Touch on Balance in Patients with Stroke

Light touch is the combination of cutaneous and kinesthetic inputs. The literature suggests that light touch compensates for a reduced amount of center of pressure information in older peoples, blind subjects and patients with neurological disorder. This study investigated the effects of light touch applied to an external bar, on the postural sway in individuals with hemiparetic stroke. We used a cross sectional study, fifteen individuals with stroke and 15 healthy age-matched adults stood as still as possible on a force plate. Experimental trials (duration, 30 s) included two visual conditions (open eyes and closed eyes), two somatosensory conditions (no touch and light touch) and two support surface conditions (firm and foam surfaces). The area of center of pressure (COP) and the mean velocity of COP in the medio-lateral and anterior-posterior directions were assessed. For both groups, COP velocity and area decreased with light touch regardless of the visual or surface conditions. The effects of light touch were similar in both groups. In addition, results show that the effectiveness of light touch in reducing postural sway was greater on a foam surface than on a firm surface. Our findings indicate that light touch could be beneficial in postural control for individuals with hemi-paretic stroke

Quantification of trunk segmental coordination and head stability in laterally unstable sitting identifies aging and cerebellar ataxia

BACKGROUND

We quantified trunk segmental coordination and head stability in unstable sitting and investigated whether it can discriminate postural control, age-related differences and presence of coordination disorder.

METHODS

Subjects were a healthy younger group (n = 7), a healthy elderly group (n = 7), and a cerebellar ataxia group (n = 8). The motion sensors and surface electrodes were located on the trunk and/or head segments to measure angle displacements, acceleration and electromyograms in unstable sitting during a lateral tilt task. Trunk lateral angle cross-correlation and electromyogram cross-correlation for the trunk segmental coordination, head root mean square (RMS) for the head stability, clinical performance scales, and gait parameters (velocity, coefficient of variation, and RMS ratio) were analyzed.

FINDINGS

Trunk lateral angle cross-correlation showed a significantly negative correlation in the healthy younger group compared with the two other groups (p < 0.01). Head RMS showed a significantly larger value in the cerebellar ataxia group compared with the two other groups (p < 0.01). Trunk lateral angle cross-correlation had moderate correlation with the clinical performance scale of ataxia and gait parameters; however, it was not correlated with head RMS. Classification using trunk lateral angle cross-correlation and head RMS was validated by discriminant analysis and hierarchical cluster analysis.

INTERPRETATION

We found that trunk lateral angle cross-correlation reflected age-related differences and head RMS characterized the pathology of cerebellar ataxia. Trunk segmental coordination and head stability, as two aspects of sitting postural control, can be used to discriminate the degree of aging and cerebellar ataxia.

Novel Machine Learning Identifies Brain Patterns Distinguishing Diagnostic Membership of Human Immunodeficiency Virus, Alcoholism, and Their Comorbidity of Individuals

The incidence of alcohol use disorder (AUD) in human immunodeficiency virus (HIV) infection is twice that of the rest of the population. This study documents complex radiologically identified, neuroanatomical effects of AUD+HIV comorbidity by identifying structural brain systems that predicted diagnosis on an individual basis. Applying novel machine learning analysis to 549 participants (199 control subjects, 222 with AUD, 68 with HIV, 60 with AUD+HIV), 298 magnetic resonance imaging brain measurements were automatically reduced to small subsets per group. Significance of each diagnostic pattern was inferred from its accuracy in predicting diagnosis and performance on six cognitive measures. While all three diagnostic patterns predicted the learning and memory score, the AUD+HIV pattern was the largest and had the highest predication accuracy (78.1%). Providing a roadmap for analyzing large, multimodal datasets, the machine learning analysis revealed imaging phenotypes that predicted diagnostic membership of magnetic resonance imaging scans of individuals with AUD, HIV, and their comorbidity.

A Pivotal Role for Thiamine Deficiency in the Expression of Neuroinflammation Markers in Models of Alcohol-Related Brain Damage

BACKGROUND

Alcohol-related brain damage (ARBD) is associated with neurotoxic effects of heavy alcohol use and nutritional deficiency, in particular thiamine deficiency (TD), both of which induce inflammatory responses in brain. Although neuroinflammation is a critical factor in the induction of ARBD, few studies have addressed the specific contribution(s) of ethanol (EtOH) versus TD.

METHODS

Adult rats were randomly divided into 6 conditions: chronic EtOH treatment (CET) where rats consumed a 20% v/v solution of EtOH for 6 months; CET with injections of thiamine (CET + T); severe pyrithiamine-induced TD (PTD); moderate PTD; moderate PTD during CET; and pair-fed controls. After the treatments, the rats were split into 3 recovery phase time points: the last day of treatment (time point 1), acute recovery (time point 2: 24 hours posttreatment), and delayed recovery (time point 3: 3 weeks posttreatment). At these time points, vulnerable brain regions (thalamus, hippocampus, frontal cortex) were collected and changes in neuroimmune markers were assessed using a combination of reverse transcription polymerase chain reaction and protein analysis.

RESULTS

CET led to minor fluctuations in neuroimmune genes, regardless of the structure being examined. In contrast, PTD treatment led to a profound increase in neuroimmune genes and proteins within the thalamus. Cytokine changes in the thalamus ranged in magnitude from moderate (3-fold and 4-fold increase in interleukin-1β [IL-1β] and IκBα) to severe (8-fold and 26-fold increase in tumor necrosis factor-α and IL-6, respectively). Though a similar pattern was observed in the hippocampus and frontal cortex, overall fold increases were moderate relative to the thalamus. Importantly, neuroimmune gene induction varied significantly as a function of severity of TD, and most genes displayed a gradual recovery across time.

CONCLUSIONS

These data suggest an overt brain inflammatory response by TD and a subtle change by CET alone. Also, the prominent role of TD in the immune-related signaling pathways leads to unique regional and temporal profiles of induction of neuroimmune genes.

Efficacy of Balance and Eye-Movement Exercises for Persons With Multiple Sclerosis (BEEMS)

Objective

To determine whether a multifaceted vestibular-related rehabilitation program (Balance and Eye-Movement Exercises for Persons with Multiple Sclerosis; BEEMS) improves balance in persons with MS and whether there are differences in outcomes based on brainstem/cerebellar lesion involvement.

Methods

A 2-arm, examiner-blinded, stratified (involvement vs no involvement of brainstem/cerebellar structures), randomized controlled trial was implemented. Eighty-eight participants were allocated to BEEMS or no treatment control. Computerized Dynamic Posturography-Sensory Organization Test (CDP-SOT) measured balance control. The Dizziness Handicap Inventory (DHI), Modified Fatigue Impact Scale (MFIS), and Short Form-36 Health Status Questionnaire (SF-36) were also administered. Linear mixed models were used to investigate the primary and secondary aims.

Results

From baseline to 6 weeks, BEEMS participants experienced greater improvements compared to control participants in CDP-SOT composite (model-estimated difference in change 4.9, 95% confidence interval 1.39–8.38, p = 0.006), DHI total (−13.5, −17.7 to −7.25, p < 0.0001), MFIS total (−11.4, −15.7 to −7.0, p < 0.0001), SF-36 Mental (5.6, 2.43–8.71, p = 0.0006), and SF-36 Physical (3.5, 1.12–5.81, p = 0.004) scores and from baseline to 14 weeks in CDP-SOT composite (8.3, 4.73–11.9, p < 0.0001), DHI total (−13.9, −19.3 to −8.62, p < 0.0001), MFIS total (−12.3, −16.7 to −7.79, p < 0.0001), SF-36 Mental (3.9, 0.70–7.16, p = 0.02), and SF-36 Physical (3.2, 0.79–5.62, p = 0.01) scores. From baseline to 6 weeks, BEEMS participants with brainstem/cerebellar lesion involvement experienced greater improvements compared to those without in CDP-SOT composite (5.26, 0.34–10.2, p = 0.04) and MFIS total (−7.6, −14.0 to −1.33, p = 0.02) scores.

Conclusion

BEEMS improved multiple outcomes regardless of whether brainstem/cerebellar lesions were present, supporting the generalizability of BEEMS for ambulatory people with MS who have at least minimally impaired balance and fatigue.

Clinical trials.gov identifier

NCT01698086.

Classification of evidence

This study provides Class I evidence that BEEMS training improves dynamic posturography-based balance, dizziness, fatigue, and quality of life in persons with MS.

Contributions to Understanding the Neuropsychology of Alcoholism: An INS Legacy

Alcohol use disorder (AUD) has been a major cause of family, social, and personal strife for centuries, with current prevalence estimates of 14% for 12-month and 29% lifetime AUD. Neuropsychological testing of selective cognitive, sensory, and motor functions complemented with in vivo brain imaging has enabled tracking the consequences of AUD, which follows a dynamic course of development, maintenance, and recovery or relapse. Controlled studies of alcoholism reviewed herein provide evidence for disruption of selective functions involving executive, visuospatial, mnemonic, emotional, and attentional processes, response inhibition, prosody, and postural stability and brain systems supporting these functions. On a hopeful front, longitudinal study provides convincing evidence for improvement in brain structure and function following sustained sobriety. These discoveries have a strong legacy in the International Neuropsychological Society (INS), starting from its early days when assumptions regarding which brain regions were disrupted relied solely on patterns of functional sparing and impairment deduced from testing. This review is based on the symposium presentation delivered at the 2017 annual North American meeting of the INS in celebration of the 50th anniversary since its institution in 1967. In the spirit of the meeting's theme, "Binding the Past and Present," the lecture and this review recognized the past by focusing on early, rigorous neuropsychological studies of alcoholism and their influence on research currently conducted using imaging methods enabling hypothesis testing of brain substrates of observed functional deficits. (JINS, 2017, 23, 843-859).

Roles of the Declive, Folium, and Tuber Cerebellar Vermian Lobules in Sportspeople

The cerebellum plays vital roles in balance control and motor learning, including in saccadic adaptation and coordination. It consists of the vermis and two hemispheres and is anatomically separated into ten lobules that are designated as I–X. Although neuroimaging and clinical studies suggest that functions are compartmentalized within the cerebellum, the function of each cerebellar lobule is not fully understood. Electrophysiological and lesion studies in animals as well as neuroimaging and lesion studies in humans have revealed that vermian lobules VI and VII (declive, folium, and tuber) are critical for controlling postural balance, saccadic eye movements, and coordination. In addition, recent structural magnetic resonance imaging studies have revealed that these lobules are larger in elite basketball and short-track speed skaters. Furthermore, in female short-track speed skaters, the volume of this region is significantly correlated with static balance. This article reviews the function of vermian lobules VI and VII, focusing on the control of balance, eye movements, and coordination including coordination between the eyes and hands and bimanual coordination.

Body Sway Increases After Functional Inactivation of the Cerebellar Vermis by cTBS

Balance stability correlates with cerebellar vermis volume. Furthermore, the cerebellum is involved in precise timing of motor processes by fine-tuning the sensorimotor integration. We tested the hypothesis that any cerebellar action in stance control and in timing of visuomotor integration for balance is impaired by continuous theta-burst stimulation (cTBS) of the vermis. Ten subjects stood quietly and underwent six sequences of 10-min acquisition of center of foot pressure (CoP) data after cTBS, sham stimulation, and no stimulation. Visual shifts from eyes closed (EC) to eyes open (EO) and vice versa were presented via electronic goggles. Mean anteroposterior and mediolateral CoP position and oscillation, and the time delay at which body sway changed after visual shift were calculated. CoP position under both EC and EO condition was not modified after cTBS. Sway path length was greater with EC than EO and increased in both visual conditions after cTBS. CoP oscillation was also larger with EC and increased under both visual conditions after cTBS. The delay at which body oscillation changed after visual shift was longer after EC to EO than EO to EC, but unaffected by cTBS. The time constant of decrease or increase of oscillation was longer in EC to EO shifts, but unaffected by cTBS. Functional inactivation of the cerebellar vermis is associated with increased sway. Despite this, cTBS does not detectably modify onset and time course of the sensorimotor integration process of adaptation to visual shifts. Cerebellar vermis normally controls oscillation, but not timing of adaptation to abrupt changes in stabilizing information.

Perspectives on fronto-fugal circuitry from human imaging of alcohol use disorders

Descriptions of the cognitive functions affected by alcohol use disorders (AUD) often highlight dysfunction of executive processes such attention, inhibitory control, working memory, and cognitive flexibility. Such complex cognitive functions have historically been ascribed to the prefrontal cortex. AUD, however, disrupts extensive areas of the brain. Structural and functional MRI studies suggest a central role for degradation of circuitry originating in the prefrontal cortex including nodes in widespread brain regions. This review features fronto-fugal circuits affected by AUD including frontocerebellar, frontolimbic, and frontostriatal networks and their relations to the salient, enduring, and debilitating cognitive and motor deficits reported in AUD. This article is part of the Special Issue entitled "Alcoholism".

Structural and microstructral imaging of the brain in alcohol use disorders

Magnetic resonance imaging (MRI), by enabling rigorous in vivo study of the longitudinal, dynamic course of alcoholism through periods of drinking, sobriety, and relapse, has enabled characterization of the effects of chronic alcoholism on the brain in the human condition. Importantly, MRI has distinguished alcohol-related brain effects that are permanent versus those that are reversible with abstinence. In support of postmortem neuropathologic studies showing degeneration of white matter, MRI has shown a specific vulnerability of brain white matter to chronic alcohol exposure by demonstrating white-matter volume deficits, yet not leaving selective gray-matter structures unscathed. Diffusion tensor imaging (DTI), by permitting microstructural characterization of white matter, has extended MRI findings in alcoholics. This review focuses on MRI and DTI findings in common concomitants of alcoholism, including Wernicke's encephalopathy, Korsakoff's syndrome, hepatic encephalopathy, central pontine myelinolysis, alcoholic cerebellar degeneration, alcoholic dementia, and Marchiafava-Bignami disease as a framework for findings in so-called "uncomplicated alcoholism," and also covers findings in abstinence and relapse.

Associations Between Cerebellar Subregional Morphometry and Alcoholism History in Men and Women

BACKGROUND

Alcoholism has been linked to deficits in cognitive, behavioral, and emotional functions, and the cerebellum is important for optimal functioning of these abilities. However, little is known about how individual differences such as gender and drinking history might influence regional cerebellar abnormalities.

METHODS

Volumetric analyses of the cerebellum and its subregions were performed in relation to the interaction of gender and measures of drinking history. Structural magnetic resonance imaging scans of 44 alcoholic individuals (23 men) and 39 nonalcoholic controls (18 men) were obtained. In addition to measuring total cerebellar gray and white matter volumes, we measured 64 individual cerebellar parcellation units, as well as functionally defined a priori regions of interest that have been shown to correspond to functions impaired in alcoholism.

RESULTS

Total cerebellar white matter volume was smaller in alcoholic relative to nonalcoholic participants. Moreover, volumes of parcellation units varied with drinking history, showing negative associations between years of heavy drinking and the anterior lobe, the vestibulocerebellar lobe, and the spinocerebellar subdivision. The negative association between anterior volume and years of heavy drinking was driven primarily by alcoholic men. Additionally, we observed larger white and gray matter volumes for alcoholic women than for alcoholic men.

CONCLUSIONS

The identification of drinking-related abnormalities in cerebellar subregions lays a foundation that can be utilized to inform how cerebro-cerebellar networks are perturbed in this pathological condition. These results also provide estimates of how gender and individual differences in drinking history can predict cerebellar volumes.

Psychological and Neurobiological Precursors of Alcohol Use Disorders in High Risk Youth

It has long been known that Alcohol Use Disorders (AUDs) run in families with substantial heritability. Determining the specific genetic underpinnings of these disorders has been challenging because of the clinical heterogeneity and variable expression across the lifespan. The search for endophenotypic biological variation associated with the AUD and related substance use disorder (SUD) phenotypes is based on the belief that an endophenotype is more proximal to the causative gene. Identification of genes conferring increased susceptibility has important implications for treatment through the potential development of medications that target specific genetic pathways. High risk family designs that contrast offspring with and without a familial/genetic background have provided valuable insights into the psychological characteristics (executive control, affective regulation, decision making and social cognition) that differentiate such individuals. The current chapter will review these with a focus on brain morphology of specific regions, the coordinated activity of neural networks, and developmental trajectories of electrophysiological activity.

Cognitive demands during quiet standing elicit truncal tremor in two frequency bands: differential relations to tissue integrity of corticospinal tracts and cortical targets

The ability to stand quietly is disturbed by degradation of cerebellar systems. Given the complexity of sensorimotor integration invoked to maintain upright posture, the integrity of supratentorial brain structures may also contribute to quiet standing and consequently be vulnerable to interference from cognitive challenges. As cerebellar system disruption is a common concomitant of alcoholism, we examined 46 alcoholics and 43 controls with a force platform to derive physiological indices of quiet standing during cognitive (solving simple, mental arithmetic problems) and visual (eyes closed) challenges. Also tested were relations between tremor velocity and regional gray matter and white matter tissue quality measured with the diffusion tensor imaging (DTI) metric of mean diffusivity (MD), indexing disorganized microstructure. Spectral analysis of sway revealed greater tremor in alcoholic men than alcoholic women or controls. Cognitive dual-tasking elicited excessive tremor in two frequency bands, each related to DTI signs of degradation in separate brain systems: tremor velocity at a low frequency (2–5 Hz/0–2 Hz) correlated with higher MD in the cerebellar hemispheres and superior cingulate bundles, whereas tremor velocity at a higher frequency (5–7 Hz) correlated with higher MD in the motor cortex and internal capsule. These brain sites may represent “tremorgenic networks” that, when disturbed by disease and exacerbated by cognitive dual-tasking, contribute to postural instability, putting affected individuals at heightened risk for falling.

Preliminary evidence of an effect of cerebellar volume on postural sway in FMR1 premutation males

Recent evidence suggests that early changes in postural control may be discernible among females with premutation expansions (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene at risk of developing fragile X-associated tremor ataxia syndrome (FXTAS). Cerebellar dysfunction is well described in males and females with FXTAS, yet the interrelationships between cerebellar volume, CGG repeat length, FMR1 messenger RNA (mRNA) levels and changes in postural control remain unknown. This study examined postural sway during standing in a cohort of 22 males with the FMR1 premutation (ages 26-80) and 24 matched controls (ages 26-77). The influence of cerebellar volume, CGG repeat length and FMR1 mRNA levels on postural sway was explored using multiple linear regression. The results provide preliminary evidence that increasing CGG repeat length and decreasing cerebellar volume were associated with greater postural sway among premutation males. The relationship between CGG repeat length and postural sway was mediated by a negative association between CGG repeat size and cerebellar volume. While FMR1 mRNA levels were significantly elevated in the premutation group and correlated with CGG repeat length, FMR1 mRNA levels were not significantly associated with postural sway scores. These findings show for the first time that greater postural sway among males with the FMR1 premutation may reflect CGG repeat-mediated disruption in vulnerable cerebellar circuits implicated in postural control. However, longitudinal studies in larger samples are required to confirm whether the relationships between cerebellar volume, CGG repeat length and postural sway indicate greater risk for neurological decline.

Thalamic abnormalities are a cardinal feature of alcohol-related brain dysfunction

Two brain networks are particularly affected by the harmful effect of chronic and excessive alcohol consumption: the circuit of Papez and the frontocerebellar circuit, in both of which the thalamus plays a key role. Shrinkage of the thalamus is more severe in alcoholics with Korsakoff's syndrome (KS) than in those without neurological complication (AL). In accordance with the gradient effect of thalamic abnormalities between AL and KS, the pattern of brain dysfunction in the Papez's circuit results in anterograde amnesia in KS and only mild-to-moderate episodic memory disorders in AL. On the opposite, dysfunction of the frontocerebellar circuit results in a similar pattern of working memory and executive deficits in the AL and KS. Several hypotheses, mutually compatible, can be drawn to explain that the severe thalamic shrinkage observed in KS has different consequences in the neuropsychological profile associated with the two brain networks.

Methods of association and dissociation for establishing selective brain-behavior relations

Methods for identifying and understanding brain structure-function relations have evolved over the past century, from astute observations of selective impairments associated with focal brain damage to dissociations measured by combining quantitative neuropsychologic assessment and brain imaging. Enhanced spatial and temporal resolution in brain imaging modalities has led to refined visualization and quantification of the brain's substructures, microstructural integrity, and functional connectivity of neural networks. The double dissociation model has been a gold standard used to demonstrate that a particular cognitive, emotional, sensory, or motor process is selectively related to a particular brain region or neural network and not to others. This model has provided a fruitful means for testing hypotheses of functional localization and enabled examination and establishment of component processes contributing to complex cognitive and motor functions, parsing multifactorial behaviors and identifying brain regions, and networks subserving these complex abilities. In this chapter we discuss the evolution of the dissociation model and highlight how the modifications of this model are used presently to establish selective brain-behavior relationships in disorders such as chronic alcoholism with a neuropathologic signature but no localizable, space-occupying lesion.

Perspectives on the neuroscience of alcohol from the National Institute on Alcohol Abuse and Alcoholism

Mounting evidence over the last 40 years clearly indicates that alcoholism (alcohol dependence) is a disorder of the brain. The National Institute on Alcohol Abuse and Alcoholism (NIAAA) has taken significant steps to advance research into the neuroscience of alcohol. The Division of Neuroscience and Behavior (DNB) was formed within NIAAA in 2002 to oversee, fund, and direct all research areas that examine the effects of alcohol on the brain, the genetic underpinnings of alcohol dependence, the neuroadaptations resulting from excessive alcohol consumption, advanced behavioral models of the various stages of the addiction cycle, and preclinical medications development. This research portfolio has produced important discoveries in the etiology, treatment, and prevention of alcohol abuse and dependence. Several of these salient discoveries are highlighted and future areas of neuroscience research on alcohol are presented.

Motor systems and postural instability

Acute alcohol intoxication and chronic alcohol dependence alter the neurologic control of posture and motor function. Ethanol delays the conduction of electric signals from the central nervous system to the muscles controlling posture and impairs the integration of sensory inputs required for maintaining vertical stance. Consequently, alcohol intoxication delays the ability to detect postural changes and enact the appropriate response. Common signs of acute alcohol intoxication include spinocerebellar and vestibulocerebellar ataxia, oculomotor changes, and increased reliance on visuospatial clues. Chronic alcoholism results in postural tremors and excessive sway during quiet stance that can persist even after sobriety is achieved. Underlying neurologic changes due to chronic alcoholism have been found to be associated with these characteristic postural changes and include decreased volume of the anterior superior vermis of the cerebellum, decreased connectivity within the corpus callosum, and overall cortical atrophy. Severity of motor impairments and other symptoms from alcoholism relate to a variety of factors, including duration of alcoholism, age, sex, and other health determinants and comorbidities. Imaging studies highlight the potential for partial recovery from neurologic and motor deficits caused by alcoholism. Emerging evidence on the motor and neurologic changes caused by alcohol dependence may allow for improved treatment and prevention of the morbidities associated with alcoholism.

Imaging studies in focal dystonias: a systems level approach to studying a systems level disorder

Focal dystonias are dystonias that affect one part of the body, and are sometimes task-specific. Brain imaging and transcranial magnetic stimulation techniques have been valuable in defining the pathophysiology of dystonias in general, and are particularly amenable to studying focal dystonias. Over the past few years, several common themes have emerged in the imaging literature, and this review summarizes these findings and suggests some ways in which these distinct themes might all point to one common systems-level mechanism for dystonia. These themes include (1) the role of premotor regions in focal dystonia, (2) the role of the sensory system and sensorimotor integration in focal dystonia, (3) the role of decreased inhibition/increased excitation in focal dystonia, and (4) the role of brain imaging in evaluating and guiding treatment of focal dystonias. The data across these themes, together with the features of dystonia itself, are consistent with a hypothesis that all dystonias reflect excessive output of postural control/stabilization systems in the brain, and that the mechanisms for dystonia reflect amplification of an existing functional system, rather than recruitment of the wrong motor programs. Imaging is currently being used to test treatment effectiveness, and to visually guide treatment of dystonia, such as placement of deep brain stimulation electrodes. In the future, it is hoped that imaging may be used to individualize treatments across behavioral, pharmacologic, and surgical domains, thus optimizing both the speed and effectiveness of treatment for any given individual with focal dystonia.

Gait and balance in treatment-naïve active alcoholics with and without a lifetime drug codependence

BACKGROUND

Disturbed gait and balance are among the most consistent sequelae of chronic alcoholism. However, although a majority of alcoholics have never sought treatment, most investigations showing ataxia in alcohol-dependent individuals have relied on samples drawn from treated populations. In addition, few studies have addressed the associations of codependence on other drugs with alcoholic gait and balance disturbance.

METHODS

This study employed the Walk-a-Line Ataxia Battery (Fregly et al. Alcohol Clin Exp Res 1972;43:395-399) to assess gait and balance in treatment-naïve, actively drinking alcohol-dependent men and women (TNA; n = 69) who were dependent on alcohol only (ALC; n = 43), or who also had a lifetime drug dependence (ALC + DRG; n = 26; i.e., methamphetamine, cocaine, opiates, and/or marijuana), compared with nonsubstance abusing controls (NSAC; n = 74).We also examined associations between lifetime alcohol use and age with gait and balance measures.

RESULTS

Our main findings were (i) no evidence of disturbed gait and balance in ALC versus NSAC and (ii) significantly disturbed gait and balance in ALC + DRG, relative to both NSAC and ALC, along with steeper age-associated decline in gait and balance performance in ALC versus ALC + DRG.

CONCLUSIONS

Our results provide evidence consistent with previous studies that TNA (without a lifetime drug codependence) may represent a population that is different and less impaired (including in gait and balance) than treated alcoholics. Additionally, we provide evidence that ALC + DRG, with greater alcohol use and family drinking density than ALC, have an accelerated effect of age on gait and balance disturbance compared with both NSAC and ALC. The ALC + DRG group likely represents a subset of TNA with different characteristics than ALC.

Resting state cortico-cerebellar functional connectivity networks: a comparison of anatomical and self-organizing map approaches

The cerebellum plays a role in a wide variety of complex behaviors. In order to better understand the role of the cerebellum in human behavior, it is important to know how this structure interacts with cortical and other subcortical regions of the brain. To date, several studies have investigated the cerebellum using resting-state functional connectivity magnetic resonance imaging (fcMRI; Krienen and Buckner, 2009; O'Reilly et al., 2010; Buckner et al., 2011). However, none of this work has taken an anatomically-driven lobular approach. Furthermore, though detailed maps of cerebral cortex and cerebellum networks have been proposed using different network solutions based on the cerebral cortex (Buckner et al., 2011), it remains unknown whether or not an anatomical lobular breakdown best encompasses the networks of the cerebellum. Here, we used fcMRI to create an anatomically-driven connectivity atlas of the cerebellar lobules. Timecourses were extracted from the lobules of the right hemisphere and vermis. We found distinct networks for the individual lobules with a clear division into “motor” and “non-motor” regions. We also used a self-organizing map (SOM) algorithm to parcellate the cerebellum. This allowed us to investigate redundancy and independence of the anatomically identified cerebellar networks. We found that while anatomical boundaries in the anterior cerebellum provide functional subdivisions of a larger motor grouping defined using our SOM algorithm, in the posterior cerebellum, the lobules were made up of sub-regions associated with distinct functional networks. Together, our results indicate that the lobular boundaries of the human cerebellum are not necessarily indicative of functional boundaries, though anatomical divisions can be useful. Additionally, driving the analyses from the cerebellum is key to determining the complete picture of functional connectivity within the structure.

Differential effect of alcoholism and HIV infection on visuomotor procedural learning and retention

BACKGROUND

Selective declarative memory processes are differentially compromised in chronic alcoholism (ALC) and HIV infection (HIV) and likely reflect neuropathology associated with each condition: frontocerebellar dysfunction in ALC and frontostriatal dysfunction in HIV infection. Evidence for disease overlap derives from observed exacerbated impairments in these declarative memory processes in ALC-HIV comorbidity. Less is known about nondeclarative memory processes in these disease conditions. Examination of visuomotor learning in chronic ALC and HIV infection could provide insight into the differential and combined contribution of selective disease-related injury to visuomotor procedural memory processes.

METHODS

We examined component processes of visuomotor learning and retention on the rotary pursuit task in 29 ALC, 23 HIV, 28 ALC + HIV, and 20 control subjects. Participants were given 4 rotary pursuit learning sessions over 2 testing days, typically separated by 1 week, to assess visuomotor learning and retention patterns. Ancillary measures of simple motor, psychomotor, explicit memory, and balance abilities were administered to test which component processes independently predicted visuomotor learning.

RESULTS

All clinical groups showed visuomotor learning across rotary pursuit testing sessions, despite impairment in visuomotor speed in the HIV groups and impairment in explicit memory and psychomotor speed in the alcohol groups. The 2 alcoholic groups showed retention and consolidation over time (i.e., improved performance without further training), whereas the HIV-infected group showed learning and retention but no consolidation effect. The comorbid group shared impairments associated with the ALC-only group (explicit memory and psychomotor speed) and the HIV-only group (visuomotor speed), although there was no clear compounded effect of alcohol and HIV infection on visuomotor learning performance.

CONCLUSIONS

This study supports the hypothesis that ALC and HIV infection exert differential effects on components of visuomotor procedural learning. Further, the results provide behavioral evidence for dissociable influences of frontocerebellar and frontostriatal disruption to visuomotor procedural learning and retention.

Gait and balance deficits in chronic alcoholics: no improvement from 10 weeks through 1 year abstinence

BACKGROUND

Disturbed gait and balance are common and important sequelae of chronic alcoholism. We present longitudinal data on recovery of gait and balance in alcoholics 6 to 15 weeks abstinent at baseline assessment through follow-up assessment 4 to 16 months after baseline.

METHODS

We performed a follow-up assessment (4 to 16 months after baseline) of gait and balance functioning in 37 short-term (6 to 15 weeks) abstinent alcoholics (STAA), 25 of whom remained abstinent through the follow-up period. Fourteen non-substance-abusing controls (NSAC) were also brought back for a follow-up assessment to examine practice effects.

RESULTS

Alcoholics showed gait and balance impairment versus controls at both the initial and follow-up assessments, showing no improvement in gait and balance measures over the follow-up period. At follow-up, NSAC showed improvement on the Walk on Floor eyes closed measure, possibly representing a practice effect not present in STAA.

CONCLUSIONS

This study finds no improvement from about 10 weeks to about 1 year of abstinence in chronic alcoholics. The study is silent with regard to gait and balance recovery that occurs prior to 10 weeks abstinence, and after the first year of abstinence. Other studies suggest some recovery of gait and balance prior to 10 weeks abstinence, and our recent cross-sectional study (Smith and Fein, 2011, Alcohol Clin Exp Res 35:2184-2192) suggests that significant additional recovery occurs in the ensuing years.

Neuroanatomy and neuropathology associated with Korsakoff's syndrome

Although the neuropathology of Korsakoff's syndrome (KS) was first described well over a century ago and the characteristic brain pathology does not pose a diagnostic challenge to pathologists, there is still controversy over the neuroanatomical substrate of the distinctive memory impairment in these patients. Cohort studies of KS suggest a central role for the mammillary bodies and mediodorsal thalamus, and quantitative studies suggest additional damage to the anterior thalamus is required. Rare cases of KS caused by pathologies other than those of nutritional origin provide support for the role of the anterior thalamus and mammillary bodies. Taken together the evidence to date shows that damage to the thalamus and hypothalamus is required, in particular the anterior thalamic nucleus and the medial mammillary nucleus of the hypothalamus. As these nuclei form part of wider memory circuits, damage to the inter-connecting white matter tracts can also result in a similar deficit as direct damage to the nuclei. Although these nuclei and their connections appear to be the primary site of damage, input from other brain regions within the circuits, such as the frontal cortex and hippocampus, or more distant regions, including the cerebellum and amygdala, may have a modulatory role on memory function. Further studies to confirm the precise site(s) and extend of brain damage necessary for the memory impairment of KS are required.