Neural correlates of cerebellar-mediated timing during finger tapping in children with fetal alcohol spectrum disorders

Recent breakthroughs in understanding the cerebellum's role in fetal alcohol spectrum disorder: A systematic review

Exposure to alcohol during fetal development can lead to structural and functional abnormalities in the cerebellum, a brain region responsible for motor coordination, balance, and specific cognitive functions. In this systematic review, we comprehensively analyze a vast body of research conducted on vertebrate animals and humans over the past 13 years. We identified studies through PubMed and screened them following PRISMA guidelines. Data extraction and quality analysis were conducted using Covidence systematic review software. A total of 108 studies met our inclusion criteria, with the majority (79 studies) involving vertebrate animal models and 29 studies focusing on human subjects. Animal models included zebrafish, mice, rats, sheep, and non-human primates, investigating the impact of ethanol on cerebellar structure, gene/protein expression, physiology, and cerebellar-dependent behaviors. Additionally, some animal studies explored potential therapeutic interventions against ethanol-induced cerebellar damage. The human studies predominantly adopted cohort designs, exploring the effects of prenatal alcohol exposure on cerebellar structure and function. Certain human studies delved into innovative cerebellar-based diagnostic approaches for fetal alcohol spectrum disorder (FASD). The collective findings from these studies clearly indicate that the cerebellum is involved in various neurophysiological deficits associated with FASD, emphasizing the importance of evaluating both cerebellar structure and function in the diagnostic process for this condition. Moreover, this review sheds light into potential therapeutic strategies that can mitigate prenatal alcohol exposure-induced cerebellar damage.

Validity of automated FreeSurfer segmentation compared to manual tracing in detecting prenatal alcohol exposure-related subcortical and corpus callosal alterations in 9- to 11-year-old children

In recent years a number of semi-automated and automated segmentation tools and brain atlases have been developed to facilitate morphometric analyses of large MRI datasets. These tools are much faster than manual tracing and demonstrate excellent test-retest reliabilities. Reliabilities of automated segmentations relative to "gold standard" manual tracings have, however, been shown to vary by brain region and in different cohorts. It remains uncertain to what extent smaller brain volumes and potential changes in grey/white matter contrasts in paediatric brains impact on the performance of automated methods, and how pathology may influence performance. This study examined whether using data from automated FreeSurfer segmentation would alter our ability, compared to manual segmentation, to detect prenatal alcohol exposure (PAE)-related volume changes in subcortical regions and the corpus callosum (CC) in pre-adolescent children. High-resolution T1-weighted images were acquired, using a sequence optimized for morphometric neuroanatomical analysis, on a Siemens 3T Allegra MRI scanner in 71 right-handed, 9- to 11-year-old children (27 fetal alcohol syndrome (FAS) and partial FAS (PFAS), 25 non-syndromal heavily exposed (HE) and 19 non-exposed controls) from a high-risk community in Cape Town, South Africa. Data from timeline follow-back interviews administered to the mothers prospectively during pregnancy were used to quantify the amount of alcohol (in ounces absolute alcohol per day, AA/day) that the children had been exposed to prenatally. Volumes of corpus callosum (CC) and bilateral caudate nuclei, hippocampi and nucleus accumbens (NA) were obtained by manual tracing and automated segmentation using both FreeSurfer versions 5.1 and 6.0. Reliability across methods was assessed using intraclass correlation (ICC) estimates for consistency and absolute agreement, and Cronbach's α. Ability to detect regions showing PAE effects was assessed separately for each segmentation method using ANOVA and linear regression of regional volumes with AA/day. Our results support findings from other studies showing excellent reliability across methods for easy-to-segment structures, such as the CC and caudate nucleus. Volumes from FreeSurfer 6.0 were smaller than those from version 5.1 in all regions except the right caudate, for which they were similar, and right hippocampus and CC, for which they were larger. Despite poor absolute agreement between methods in the NA and hippocampus, all three segmentation methods detected dose-dependent volume reductions in regions for which reliabilities on ICC consistency across methods reached at least 0.70, namely the CC, and bilateral caudate nuclei and hippocampi. PAE-related changes in the NA for which ICC consistency did not reach this minimum were inconsistent across methods and should be interpreted with caution. This is the first study to demonstrate in a pre-adolescent cohort the ability of automated segmentation with FreeSurfer to detect regional volume changes associated with pathology similar to those found using manual tracing.

Weak correlations between cerebellar tests

Eyeblink conditioning, finger tapping, and prism adaptation are three tasks that have been linked to the cerebellum. Previous research suggests that these tasks recruit distinct but partially overlapping parts of the cerebellum, as well as different extra-cerebellar networks. However, the relationships between the performances on these tasks remain unclear. Here we tested eyeblink conditioning, finger tapping, and prism adaptation in 42 children and 44 adults and estimated the degree of correlation between the performance measures. The results show that performance on all three tasks improves with age in typically developing school-aged children. However, the correlations between the performance measures of the different tasks were consistently weak and without any consistent directions. This reinforces the view that eyeblink conditioning, finger tapping, and prism adaptation rely on distinct mechanisms. Consequently, performance on these tasks cannot be used separately to assess a common cerebellar function or to make general conclusions about cerebellar dysfunction. However, together, these three behavioral tasks have the potential to contribute to a nuanced picture of human cerebellar functions during development.

Graded Cerebellar Lobular Volume Deficits in Adolescents and Young Adults with Fetal Alcohol Spectrum Disorders (FASD)

The extensive prenatal developmental growth period of the cerebellum renders it vulnerable to unhealthy environmental agents, especially alcohol. Fetal alcohol spectrum disorders (FASD) is marked by neurodysmorphology including cerebral and cerebellar volume deficits, but the cerebellar lobular deficit profile has not been delineated. Legacy MRI data of 115 affected and 59 unaffected adolescents and young adults were analyzed for lobular gray matter volume and revealed graded deficits supporting a spectrum of severity. Graded deficits were salient in intracranial volume (ICV), where the fetal alcohol syndrome (FAS) group was smaller than the fetal alcohol effects (FAE) group, which was smaller than the controls. Adjusting for ICV, volume deficits were present in VIIB and VIIIA of the FAE group and were more widespread in FAS and included lobules I, II, IV, V, VI, Crus II, VIIB, and VIIIA. Graded deficits (FAS < FAE) were consistently present in lobules VI; neither group showed volume deficits in Crus I or IX. Neuroradiological readings blind to diagnosis identified 20 anomalies, 8 involving the cerebellum, 5 of which were in the FAS group. We speculate that the regional cerebellar FASD-related volume deficits may contribute to diagnostically characteristic functional impairment involving emotional control, visuomotor coordination, and postural stability.

Efficacy of Maternal Choline Supplementation During Pregnancy in Mitigating Adverse Effects of Prenatal Alcohol Exposure on Growth and Cognitive Function: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

BACKGROUND

We recently demonstrated the acceptability and feasibility of a randomized, double-blind choline supplementation intervention for heavy drinking women during pregnancy. In this study, we report our results relating to the efficacy of this intervention in mitigating adverse effects of prenatal alcohol exposure (PAE) on infant growth and cognitive function.

METHODS

Sixty-nine Cape Coloured (mixed ancestry) heavy drinkers in Cape Town, South Africa, recruited in mid-pregnancy, were randomly assigned to receive a daily oral dose of either 2 g of choline or placebo from time of enrollment until delivery. Each dose consisted of an individually wrapped packet of powder that, when mixed with water, produced a sweet tasting grape-flavored drink. The primary outcome, eyeblink conditioning (EBC), was assessed at 6.5 months. Somatic growth was measured at birth, 6.5, and 12 months, recognition memory and processing speed on the Fagan Test of Infant Intelligence, at 6.5 and 12 months.

RESULTS

Infants born to choline-treated mothers were more likely to meet criterion for conditioning on EBC than the placebo group. Moreover, within the choline arm, degree of maternal adherence to the supplementation protocol strongly predicted EBC performance. Both groups were small at birth, but choline-treated infants showed considerable catch-up growth in weight and head circumference at 6.5 and 12 months. At 12 months, the infants in the choline treatment arm had higher novelty preference scores, indicating better visual recognition memory.

CONCLUSIONS

This exploratory study is the first to provide evidence that a high dose of choline administered early in pregnancy can mitigate adverse effects of heavy PAE on EBC, postnatal growth, and cognition in human infants. These findings are consistent with studies of alcohol-exposed animals that have demonstrated beneficial effects of choline supplementation on classical conditioning, learning, and memory.

An fMRI study of finger tapping in children and adults

Functional brain imaging studies have characterized the neural bases of voluntary movement for finger tapping in adults, but equivalent information for children is lacking. When contrasted to adults, one would expect children to have relatively greater activation, reflecting compensation for an underdeveloped motor system combined with less experience in the execution of voluntary movement. To test this hypothesis, we acquired functional magnetic resonance imaging (fMRI) data on 17 healthy right-handed children (7.48 ± 0.66 years) and 15 adults (24.9 ± 2.9 years) while they performed an irregularly paced finger-tapping task in response to a visual cue (left- and right-hand examined separately). Whole-brain within-group analyses revealed that finger tapping in either age group and for either hand activated contralateral SM1, SMA, ipsilateral anterior cerebellum, and occipital cortices. We used an ANOVA factorial design to test for main effects of Age Group (children vs adults), Hand (left vs. right), and their interactions. For main effects of Age Group, children showed relatively greater activity in left SM1 (extending into bilateral SMA), and, surprisingly, adults exhibited relatively greater activity in right pre-SMA/SMA (extending into left pre-SMA/SMA), right lateral globus pallidus, left putamen, and right anterior cerebellum. The interaction of Age Group × Hand revealed that while both groups activated right SM1 during left finger tapping and exhibited signal decreases (i.e., below fixation baseline) during right finger tapping, both these responses were attenuated in children relative to adults. These data provide an important foundation by which to study children with motor disorders.

Sensorimotor network alterations in children and youth with prenatal alcohol exposure

Children with prenatal alcohol exposure (PAE) often have impaired sensorimotor function. While altered brain structure has been noted in sensorimotor areas, the functional brain alterations remain unclear. This study aims to investigate sensorimotor brain networks in children and youth with PAE using resting-state functional magnetic resonance imaging (rs-fMRI). A parcellation-based network analysis was performed to identify brain networks related to hand/lower limb and face/upper limb function in 59 children and youth with PAE and 50 typically developing controls. Participants with PAE and controls had similar organization of the hand and face areas within the primary sensorimotor cortex, but participants with PAE had altered functional connectivity (FC) between the sensorimotor regions and the rest of the brain. The sensorimotor regions in the PAE group showed less connectivity to certain hubs of the default mode network and more connectivity to areas of the salience network. Overall, our results show that despite similar patterns of organization in the sensorimotor network, subjects with PAE have increased FC between this network and other brain areas, perhaps suggesting overcompensation. These alterations in the sensorimotor network lay the foundation for future studies to evaluate interventions and treatments to improve motor function in children with PAE.

Reductions in Corpus Callosum Volume Partially Mediate Effects of Prenatal Alcohol Exposure on IQ

Disproportionate volume reductions in the basal ganglia, corpus callosum (CC) and hippocampus have been reported in children with prenatal alcohol exposure (PAE). However, few studies have investigated these reductions in high prevalence communities, such as the Western Cape Province of South Africa, and only one study made use of manual tracing, the gold standard of volumetric analysis. The present study examined the effects of PAE on subcortical neuroanatomy using manual tracing and the relation of volumetric reductions in these regions to IQ and performance on the California Verbal Learning Test-Children's Version (CVLT-C), a list learning task sensitive to PAE. High-resolution T1-weighted images were acquired, using a sequence optimized for morphometric neuroanatomical analysis, on a Siemens 3T Allegra MRI scanner from 71 right-handed, 9- to 11-year-old children [9 fetal alcohol syndrome (FAS), 19 partial FAS (PFAS), 24 non-syndromal heavily exposed (HE) and 19 non-exposed controls]. Frequency of maternal drinking was ascertained prospectively during pregnancy using timeline follow-back interviews. PAE was examined in relation to volumes of the CC and left and right caudate nuclei, nucleus accumbens and hippocampi. All structures were manually traced using Multitracer. Higher levels of PAE were associated with reductions in CC volume after adjustment for TIV. Although the effect of PAE on CC was confounded with smoking and lead exposure, additional analyses showed that it was not accounted for by these exposures. Amongst dysmorphic children, smaller CC was associated with poorer IQ and CVLT-C scores and statistically mediated the effect of PAE on IQ. In addition, higher levels of PAE were associated with bilateral volume reductions in caudate nuclei and hippocampi, effects that remained significant after control for TIV, child sex and age, socioeconomic status, maternal smoking during pregnancy, and childhood lead exposure. These data confirm previous findings showing that PAE is associated with decreases in subcortical volumes and is the first study to show that decreases in callosal volume may play a role in fetal alcohol-related impairment in cognitive function seen in childhood.

Radiological studies of fetal alcohol spectrum disorders in humans and animal models: An updated comprehensive review

Fetal Alcohol Spectrum Disorders encompass a wide range of birth defects in children born to mothers who consumed alcohol during pregnancy. Typical mental impairments in FASD include difficulties in life adaptation and learning and memory, deficits in attention, visuospatial skills, language and speech disabilities, mood disorders and motor disabilities. Multimodal imaging methods have enabled in vivo studies of the teratogenic effects of alcohol on the central nervous system, giving more insight into the FASD phenotype. This paper offers an up-to-date comprehensive review of radiological findings in the central nervous system in studies of prenatal alcohol exposure in both humans and translational animal models, including Magnetic Resonance Imaging, Computed Tomography, Positron Emission Tomography, Single Photon Emission Tomography and Ultrasonography.

Ethanol exposure during development reduces GABAergic/glycinergic neuron numbers and lobule volumes in the mouse cerebellar vermis

Cerebellar alterations are a hallmark of Fetal Alcohol Spectrum Disorders and are thought to be responsible for deficits in fine motor control, motor learning, balance, and higher cognitive functions. These deficits are, in part, a consequence of dysfunction of cerebellar circuits. Although the effect of developmental ethanol exposure on Purkinje and granule cells has been previously characterized, its actions on other cerebellar neuronal populations are not fully understood. Here, we assessed the impact of repeated ethanol exposure on the number of inhibitory neurons in the cerebellar vermis. We exposed pregnant mice to ethanol in vapor inhalation chambers during gestational days 12-19 and offspring during postnatal days 2-9. We used transgenic mice expressing the fluorescent protein, Venus, in GABAergic/glycinergic neurons. Using unbiased stereology techniques, we detected a reduction in Venus positive neurons in the molecular and granule cell layers of lobule II in the ethanol exposed group at postnatal day 16. In contrast, ethanol produced a more widespread reduction in Purkinje cell numbers that involved lobules II, IV-V and IX. We also found a reduction in the volume of lobules II, IV-V, VI-VII, IX and X in ethanol-exposed pups. These findings indicate that second and third trimester-equivalent ethanol exposure has a greater impact on Purkinje cells than interneurons in the developing cerebellar vermis. The decrease in the volume of most lobules could be a consequence of a reduction in cell numbers, dendritic arborizations, or axonal projections.

Fetal Alcohol Spectrum Disorders: An Overview from the Glia Perspective

Alcohol consumption during pregnancy can produce a variety of central nervous system (CNS) abnormalities in the offspring resulting in a broad spectrum of cognitive and behavioral impairments that constitute the most severe and long-lasting effects observed in fetal alcohol spectrum disorders (FASD). Alcohol-induced abnormalities in glial cells have been suspected of contributing to the adverse effects of alcohol on the developing brain for several years, although much research still needs to be done to causally link the effects of alcohol on specific brain structures and behavior to alterations in glial cell development and function. Damage to radial glia due to prenatal alcohol exposure may underlie observations of abnormal neuronal and glial migration in humans with Fetal Alcohol Syndrome (FAS), as well as primate and rodent models of FAS. A reduction in cell number and altered development has been reported for several glial cell types in animal models of FAS. In utero alcohol exposure can cause microencephaly when alcohol exposure occurs during the brain growth spurt a period characterized by rapid astrocyte proliferation and maturation; since astrocytes are the most abundant cells in the brain, microenchephaly may be caused by reduced astrocyte proliferation or survival, as observed in in vitro and in vivo studies. Delayed oligodendrocyte development and increased oligodendrocyte precursor apoptosis has also been reported in experimental models of FASD, which may be linked to altered myelination/white matter integrity found in FASD children. Children with FAS exhibit hypoplasia of the corpus callosum and anterior commissure, two areas requiring guidance from glial cells and proper maturation of oligodendrocytes. Finally, developmental alcohol exposure disrupts microglial function and induces microglial apoptosis; given the role of microglia in synaptic pruning during brain development, the effects of alcohol on microglia may be involved in the abnormal brain plasticity reported in FASD. The consequences of prenatal alcohol exposure on glial cells, including radial glia and other transient glial structures present in the developing brain, astrocytes, oligodendrocytes and their precursors, and microglia contributes to abnormal neuronal development, reduced neuron survival and disrupted brain architecture and connectivity. This review highlights the CNS structural abnormalities caused by in utero alcohol exposure and outlines which abnormalities are likely mediated by alcohol effects on glial cell development and function.

Aberrant development of post-movement beta rebound in adolescents and young adults with fetal alcohol spectrum disorders

Dependent on maternal (e.g. genetic, age) and exposure (frequency, quantity, and timing) variables, the effects of prenatal alcohol exposure on the developing fetus are known to vary widely, producing a broad range of morphological anomalies and neurocognitive deficits in offspring, referred to as fetal alcohol spectrum disorders (FASD). Maternal drinking during pregnancy remains a leading risk factor for the development of intellectual disabilities in the US. While few functional findings exist today that shed light on the mechanisms responsible for the observed impairments in individuals with FASD, animal models consistently report deleterious effects of early alcohol exposure on GABA-ergic inhibitory pathways. The post-motor beta rebound (PMBR), a transient increase of 15-30 Hz beta power in the motor cortex that follows the termination of movement, has been implicated as a neural signature of GABA-ergic inhibitory activity. Further, PMBR has been shown to be a reliable predictor of age in adolescents. The present study sought to investigate any differences in the development of PMBR between FASD and control groups. Beta event-related de-synchronization (ERD) and movement-related gamma synchronization (MRGS), although not clearly linked to brain maturation, were also examined. Twenty-two participants with FASD and 22 age and sex-matched controls (12-22 years old) underwent magnetoencephalography scans while performing an auditory oddball task, which required a button press in response to select target stimuli. The data surrounding the button presses were localized to the participants' motor cortices, and the time courses from the locations of the maximally evoked PMBR were subjected to wavelet analyses. The subsequent analysis of PMBR, ERD, and MRGS revealed a significant interaction between group and age in their effects on PMBR. While age had a significant effect on PMBR in the controls, no simple effects of age were detected in the FASD group. The FASD group additionally displayed decreased overall ERD levels. No group or age effects on MRGS were detected. The described findings provide further evidence for broad impairments in inhibitory processes in adolescents with FASD, possibly related to aberrant development of GABA-ergic pathways.

Conflict anticipation in alcohol dependence - A model-based fMRI study of stop signal task

Background

Our previous work characterized altered cerebral activations during cognitive control in individuals with alcohol dependence (AD). A hallmark of cognitive control is the ability to anticipate changes and adjust behavior accordingly. Here, we employed a Bayesian model to describe trial-by-trial anticipation of the stop signal and modeled fMRI signals of conflict anticipation in a stop signal task. Our goal is to characterize the neural correlates of conflict anticipation and its relationship to response inhibition and alcohol consumption in AD.

Methods

Twenty-four AD and 70 age and gender matched healthy control individuals (HC) participated in the study. fMRI data were pre-processed and modeled with SPM8. We modeled fMRI signals at trial onset with individual events parametrically modulated by estimated probability of the stop signal, p(Stop), and compared regional responses to conflict anticipation between AD and HC. To address the link to response inhibition, we regressed whole-brain responses to conflict anticipation against the stop signal reaction time (SSRT).

Results

Compared to HC (54/70), fewer AD (11/24) showed a significant sequential effect — a correlation between p(Stop) and RT during go trials — and the magnitude of sequential effect is diminished, suggesting a deficit in proactive control. Parametric analyses showed decreased learning rate and over-estimated prior mean of the stop signal in AD. In fMRI, both HC and AD responded to p(Stop) in bilateral inferior parietal cortex and anterior pre-supplementary motor area, although the magnitude of response increased in AD. In contrast, HC but not AD showed deactivation of the perigenual anterior cingulate cortex (pgACC). Furthermore, deactivation of the pgACC to increasing p(Stop) is positively correlated with the SSRT in HC but not AD. Recent alcohol consumption is correlated with increased activation of the thalamus and cerebellum in AD during conflict anticipation.

Conclusions

The current results highlight altered proactive control that may serve as an additional behavioral and neural marker of alcohol dependence.

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We addressed the neural correlates of conflict anticipation in AD and HC in an SST.

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AD showed greater activation in preSMA and less deactivation in pgACC.

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Deactivation in pgACC inversely correlated with SSRT in HC but not AD.

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Alcohol use is correlated with greater thalamic and cerebellar activations in AD.

Eyeblink Classical Conditioning in Alcoholism and Fetal Alcohol Spectrum Disorders

Alcoholism is a debilitating disorder that can take a significant toll on health and professional and personal relationships. Excessive alcohol consumption can have a serious impact on both drinkers and developing fetuses, leading to long-term learning impairments. Decades of research in laboratory animals and humans have demonstrated the value of eyeblink classical conditioning (EBC) as a well-characterized model system to study the neural mechanisms underlying associative learning. Behavioral EBC studies in adults with alcohol use disorders and in children with fetal alcohol spectrum disorders report a clear learning deficit in these two patient populations, suggesting alcohol-related damage to the cerebellum and associated structures. Insight into the neural mechanisms underlying these learning impairments has largely stemmed from laboratory animal studies. In this mini-review, we present and discuss exemplary animal findings and data from patient and neuroimaging studies. An improved understanding of the neural mechanisms underlying learning deficits in EBC related to alcoholism and prenatal alcohol exposure has the potential to advance the diagnoses, treatment, and prevention of these and other pediatric and adult disorders.