Unisensory and Multisensory Responses in Fetal Alcohol Spectrum Disorders (FASD): Effects of Spatial Congruence

The effect of developmental alcohol exposure on multisensory integration is larger in deeper cortical layers

Fetal Alcohol Spectrum Disorders (FASD) are one of the most common causes of mental disability in the world. Despite efforts to increase public awareness of the risks of drinking during pregnancy, epidemiological studies indicate a prevalence of 1-6% in all births. There is growing evidence that deficits in sensory processing may contribute to social problems observed in FASD. Multisensory (MS) integration occurs when a combination of inputs from two sensory modalities leads to enhancement or suppression of neuronal firing. MS enhancement is usually linked to processes that facilitate cognition and reaction time, whereas MS suppression has been linked to filtering unwanted sensory information. The rostral portion of the posterior parietal cortex (PPr) of the ferret is an area that shows robust visual-tactile integration and displays both MS enhancement and suppression. Recently, our lab demonstrated that ferrets exposed to alcohol during the "third trimester equivalent" of human gestation show less MS enhancement and more MS suppression in PPr than controls. Here we complement these findings by comparing in vivo electrophysiological recordings from channels located in shallow and deep cortical layers. We observed that while the effects of alcohol (less MS enhancement and more MS suppression) were found in all layers, the magnitude of these effects were more pronounced in putative layers V-VI. These findings extend our knowledge on the sensory deficits of FASD.

Brain Volume in Fetal Alcohol Spectrum Disorders Over a 20-Year Span

Importance

Anomalous brain development and mental health problems are prevalent in fetal alcohol spectrum disorders (FASD), but there is a paucity of longitudinal brain imaging research into adulthood. This study presents long-term follow-up of brain volumetrics in a cohort of participants with FASD.

Objective

To test whether brain tissue declines faster with aging in individuals with FASD compared with control participants.

Design, Setting, and Participants

This cohort study used magnetic resonance imaging (MRI) data collected from individuals with FASD and control individuals (age 13-37 years at first magnetic resonance imaging [MRI1] acquired 1997-2000) compared with data collected 20 years later (MRI2; 2018-2021). Participants were recruited for MRI1 through the University of Washington Fetal Alcohol Syndrome (FAS) Follow-Up Study. For MRI2, former participants were recruited by the University of Washington Fetal Alcohol and Drug Unit. Data were analyzed from October 2022 to August 2023.

Main Outcomes and Measures

Intracranial volume (ICV) and regional cortical and cerebellar gray matter, white matter, and cerebrospinal fluid volumes were quantified automatically and analyzed, with group and sex as between-participant factors and age as a within-participant variable.

Results

Of 174 individuals with MRI1 data, 48 refused participation, 36 were unavailable, and 24 could not be located. The remaining 66 individuals (37.9%) were rescanned for MRI2, including 26 controls, 18 individuals with nondysmorphic heavily exposed fetal alcohol effects (FAE; diagnosed prior to MRI1), and 22 individuals with FAS. Mean (SD) age was 22.9 (5.6) years at MRI1 and 44.7 (6.5) years at MRI2, and 35 participants (53%) were male. The FAE and FAS groups exhibited enduring stepped volume deficits at MRI1 and MRI2; volumes among control participants were greater than among participants with FAE, which were greater than volumes among participants with FAS (eg, mean [SD] ICV: control, 1462.3 [119.3] cc at MRI1 and 1465.4 [129.4] cc at MRI2; FAE, 1375.6 [134.1] cc at MRI1 and 1371.7 [120.3] cc at MRI2; FAS, 1297.3 [163.0] cc at MRI1 and 1292.7 [172.1] cc at MRI2), without diagnosis-by-age interactions. Despite these persistent volume deficits, the FAE participants and FAS participants showed patterns of neurodevelopment within reference ranges: increase in white matter and decrease in gray matter of the cortex and decrease in white matter and increase in gray matter of the cerebellum.

Conclusions and Relevance

The findings of this cohort study support a nonaccelerating enduring, brain structural dysmorphic spectrum following prenatal alcohol exposure and a diagnostic distinction based on the degree of dysmorphia. FASD was not a progressive brain structural disorder by middle age, but whether accelerated decline occurs in later years remains to be determined.

Effects of developmental alcohol exposure on cortical multisensory integration

Fetal alcohol spectrum disorder (FASD) is one of the most common causes of mental disabilities in the world with a prevalence of 1%-6% of all births. Sensory processing deficits and cognitive problems are a major feature in this condition. Because developmental alcohol exposure can impair neuronal plasticity, and neuronal plasticity is crucial for the establishment of neuronal circuits in sensory areas, we predicted that exposure to alcohol during the third trimester equivalent of human gestation would disrupt the development of multisensory integration (MSI) in the rostral portion of the posterior parietal cortex (PPr), an integrative visual-tactile area. We conducted in vivo electrophysiology in 17 ferrets from four groups (saline/alcohol; infancy/adolescence). A total of 1157 neurons were recorded after visual, tactile and combined visual-tactile stimulation. A multisensory (MS) enhancement or suppression is characterized by a significantly increased or decreased number of elicited spikes after combined visual-tactile stimulation compared to the strongest unimodal (visual or tactile) response. At the neuronal level, those in infant animals were more prone to show MS suppression whereas adolescents were more prone to show MS enhancement. Although alcohol-treated animals showed similar developmental changes between infancy and adolescence, they always 'lagged behind' controls showing more MS suppression and less enhancement. Our findings suggest that alcohol exposure during the last months of human gestation would stunt the development of MSI, which could underlie sensory problems seen in FASD.

Decreased resting-state alpha peak frequency in children and adolescents with fetal alcohol spectrum disorders or prenatal alcohol exposure

Prenatal alcohol exposure (PAE) can result in long-lasting changes to physical, behavioral, and cognitive functioning in children. PAE might result in decreased white matter integrity, corticothalamic tract integrity, and alpha cortical oscillations. Previous investigations of alpha oscillations in PAE/fetal alcohol spectrum disorder (FASD) have focused on average spectral power at specific ages; therefore, little is known about alpha peak frequency (APF) or its developmental trajectory making this research novel. Using resting-state MEG data, APF was determined from parietal/occipital regions in participants with PAE/FASD or typically developing controls (TDC). In total, MEG data from 157 infants, children, and adolescents ranging in age from 6 months to 17 years were used, including 17 individuals with PAE, 61 individuals with an FASD and 84 TDC. In line with our hypothesis, we found that individuals with PAE/FASD had significantly reduced APF relative to TDC. Both age and group were significantly related to APF with differences between TDC and PAE/FASD persisting throughout development. We did not find evidence that sex or socioeconomic status had additional impact on APF. Reduced APF in individuals with an FASD/PAE may represent a long-term deficit and demonstrates the detrimental impact prenatal alcohol exposure can have on neurophysiological processes.

Persistent myelin abnormalities in a third trimester-equivalent mouse model of fetal alcohol spectrum disorder

BACKGROUND

Abnormal diffusion within white matter (WM) tracts has been linked to cognitive impairment in children with fetal alcohol spectrum disorder. Whether changes to myelin organization and structure underlie the observed abnormal diffusion patterns remains unknown. Using a third trimester-equivalent mouse model of alcohol exposure, we previously demonstrated acute loss of oligodendrocyte lineage cells with persistent loss of myelin basic protein and lower fractional anisotropy (FA) in the corpus callosum (CC). Here, we tested whether these WM deficits are accompanied by changes in: (i) axial diffusion (AD) and radial diffusion (RD), (ii) myelin ultrastructure, or (iii) structural components of the node of Ranvier.

METHODS

Mouse pups were exposed to alcohol or air vapor for 4 h daily from postnatal day (P)3 to P15 (BEC: 160.4 ± 12.0 mg/dl; range = 128.2 to 185.6 mg/dl). Diffusion tensor imaging (DTI) and histological analyses were performed on brain tissue isolated at P50. Diffusion parameters were measured with Paravision™ 5.1 software (Bruker) following ex vivo scanning in a 7.0 T MRI. Nodes of Ranvier were identified using high-resolution confocal imaging of immunofluorescence for Nav 1.6 (nodes) and Caspr (paranodes) and measured using Imaris™ imaging software (Bitplane). Myelin ultrastructure was evaluated by calculating the G-ratio (axonal diameter/myelinated fiber diameter) on images acquired using transmission electron microscopy.

RESULTS

Consistent with our previous study, high resolution DTI at P50 showed lower FA in the CC of alcohol-exposed mice (p = 0.0014). Here, we show that while AD (diffusion parallel to CC axons) was similar between treatment groups (p = 0.30), RD (diffusion perpendicular to CC axons) in alcohol-exposed subjects was significantly higher than in controls (p = 0.0087). In the posterior CC, where we identified the highest degree of abnormal diffusion, node of Ranvier length did not differ between treatment groups (p = 0.41); however, the G-ratio of myelinated axons was significantly higher in alcohol-exposed animals than controls (p = 0.023).

CONCLUSIONS

High resolution DTI revealed higher RD at P50 in the CC of alcohol-exposed animals, suggesting less myelination of axons, particularly in the posterior regions. In agreement with these findings, ultrastructural analysis of myelinated axons in the posterior CC showed reduced myelin thickness in alcohol-exposed animals, evidenced by a higher G-ratio.

Examining the effects of prenatal alcohol exposure on corticothalamic connectivity: A multimodal neuroimaging study in children

Children with a fetal alcohol spectrum disorder (FASD) experience a range of cognitive and behavioral effects. Prior studies have demonstrated white matter changes in children with FASD relative to typically developing controls (TDC) and these changes relate to behavior. Our prior MEG study (Candelaria-Cook et al. 2020) demonstrated reduced alpha oscillations during rest in FASD relative to TDC and alpha power is correlated with behavior. However, little is known about how brain structure influences brain function. We hypothesized that alpha power was related to corticothalamic connectivity. Children 8–13 years of age (TDC: N = 25, FASD: N = 24) underwent rest MEG with eyes open or closed and MRI to collect structural and diffusion tensor imaging data. MEG spectral analysis was performed for sensor and source data. We estimated mean fractional anisotropy in regions of interest (ROIs) that included the corticothalamic tracts. The FASD group had reduced mean FA in three of the corticothalamic ROIs. FA in these tracts was significantly correlated with alpha power at the sensor and source level. The results support the hypothesis that integrity of the corticothalamic tracts influences cortical alpha power. Further research is needed to understand how brain structure and function influence behavior.

Dynamics of microglia and dendritic spines in early adolescent cortex after developmental alcohol exposure

Fetal alcohol spectrum disorder patients suffer from many cognitive disabilities. These include impaired auditory, visual, and tactile sensory information processing, making it more difficult for these patients to learn to navigate social scenarios. Rodent studies have shown that alcohol exposure during the brain growth spurt (BGS) can lead to acute neuronal apoptosis and an immunological response by microglia in the somatosensory cortex. Since microglia have critical physiological functions, including the support of excitatory synapse remodeling via interactions with dendritic spines, we sought to understand whether BGS alcohol exposure has long-term effects on microglial or dendritic spine dynamics. Using in vivo two-photon microscopy in 4-5 week old mice, we evaluated microglial functions such as process motility, the response to tissue injury, and the dynamics of physical interactions between microglial processes and dendritic spines. We also investigated potential differences in the morphology, density, or dynamics of dendritic spines in layer I/II primary sensory cortex of control and BGS alcohol exposed mice. We found that microglial process motility and contact with dendritic spines were not altered after BGS alcohol exposure. While the response of microglial processes toward tissue injury was not significantly altered by prior alcohol exposure, there was a trend suggesting that alcohol early in life may prime microglia to respond more quickly to secondary injury. Spine density, morphology, stability, and remodeling over time were not perturbed after BGS alcohol exposure. We demonstrate that after BGS alcohol exposure, the physiological functions of microglia and excitatory neurons remain intact in early adolescence.

Covariation Between Brain Function (MEG) and Structure (DTI) Differentiates Adolescents with Fetal Alcohol Spectrum Disorder from Typically Developing Controls

The behavioral, cognitive, and sensory difficulties experienced by individuals exposed to alcohol prenatally currently fail to provide early identification for fetal alcohol spectrum disorder (FASD). Attempting to advance this pursuit through a multivariate analysis, we collected magnetoencephalography (MEG) data during auditory, somatosensory, visual paradigms, DTI, and behavior in adolescents ages 12-21 years (FASD: N = 13; HC: N = 20). We assessed the relationship between brain function (MEG) and structure (fractional anisotropy (FA)) utilizing joint independent component analysis (jICA), and examined how this measure relates to behavior. We identified 5 components that reveal group differences in co-variation between MEG and FA. For example, component 5 (t = 3.162, p = 0.003, Hedges' g = 1.13) contained MEG activity corresponding to all three sensory modalities, most robustly in occipital lobes, and DTI-derived cerebellar FA, underlying the role of the cerebellum in sensory processing. Further, in HCs component 5's loading factor was positively correlated with verbal ability (r = 0.646, p = 0.002), indicating higher covariation was associated with better verbal performance. Interestingly, this relationship is lacking in FASD (r = 0.009, p = 0.979). Also, component 5 loading factor negatively correlated with impulsivity (r = -0.527, p = 0.002), indicating that stronger function-structure associations were associated with individuals with lower impulsivity. These findings suggest that multimodal integration of MEG and FA provides novel associations between structure and function that may help differentiate adolescents with FASD from HC.