Sleep and oligodendrocyte functions

Revealing brain cell-stratified causality through dissecting causal variants according to their cell-type-specific effects on gene expression

The human brain has been implicated in the pathogenesis of several complex diseases. Taking advantage of single-cell techniques, genome-wide association studies (GWAS) have taken it a step further and revealed brain cell-type-specific functions for disease loci. However, genetic causal associations inferred by Mendelian randomization (MR) studies usually include all instrumental variables from GWAS, which hampers the understanding of cell-specific causality. Here, we developed an analytical framework, Cell-Stratified MR (csMR), to investigate cell-stratified causality through colocalizing GWAS signals with single-cell eQTL from different brain cells. By applying to obesity-related traits, our results demonstrate the cell-type-specific effects of GWAS variants on gene expression, and indicate the benefits of csMR to identify cell-type-specific causal effect that is often hidden from bulk analyses. We also found csMR valuable to reveal distinct causal pathways between different obesity indicators. These findings suggest the value of our approach to prioritize target cells for extending genetic causation studies.

Sleep disturbances, altered brain microstructure and chronic headache in youth

Chronic headache (persistent or recurrent headache for 3-months or longer) is highly prevalent among youth. While sleep disturbances have been associated with headache, their inter-relationship with brain connectivity remains unknown. This observational study examined whether self-report and actigraphy measures of sleep were associated with alterations to white matter tracts (i.e., uncinate fasciculus and cingulum) in youth with chronic headache versus healthy controls. Thirty youth aged 10-18 years with chronic headache and thirty controls underwent an MRI. Diffusion tensor images were obtained and mean fractional anisotropy values of the cingulum and uncinate were extracted. One-week prior to their MRI, youth wore an actigraph to obtain sleep duration, wake after sleep onset and sleep efficiency measures. Moreover, they completed questionnaires regarding their sleep quality and pain symptomatology. Linear regression was applied to examine the relationships between sleep (self-report and actigraphy), fractional anisotropy, and number of headache days per month. Self-report and actigraphy measures of sleep did not differ between patients and controls. However, poorer self-reported sleep quality was associated with lower fractional anisotropy values in the left uncinate (P = 0.05). Lower left uncinate fractional anisotropy was related to increased headache frequency (P = 0.002) in youth with chronic headache. Therefore, alterations to connectivity may be associated with the relationship between altered perceptions of sleep and headache chronicity.

Total Sleep Deprivation Increases Brain Age Prediction Reversibly in Multisite Samples of Young Healthy Adults

Sleep loss pervasively affects the human brain at multiple levels. Age-related changes in several sleep characteristics indicate that reduced sleep quality is a frequent characteristic of aging. Conversely, sleep disruption may accelerate the aging process, yet it is not known what will happen to the age status of the brain if we can manipulate sleep conditions. To tackle this question, we used an approach of brain age to investigate whether sleep loss would cause age-related changes in the brain. We included MRI data of 134 healthy volunteers (mean chronological age of 25.3 between the age of 19 and 39 years, 42 females/92 males) from five datasets with different sleep conditions. Across three datasets with the condition of total sleep deprivation (>24 h of prolonged wakefulness), we consistently observed that total sleep deprivation increased brain age by 1-2 years regarding the group mean difference with the baseline. Interestingly, after one night of recovery sleep, brain age was not different from baseline. We also demonstrated the associations between the change in brain age after total sleep deprivation and the sleep variables measured during the recovery night. By contrast, brain age was not significantly changed by either acute (3 h time-in-bed for one night) or chronic partial sleep restriction (5 h time-in-bed for five continuous nights). Together, the convergent findings indicate that acute total sleep loss changes brain morphology in an aging-like direction in young participants and that these changes are reversible by recovery sleep.SIGNIFICANCE STATEMENT Sleep is fundamental for humans to maintain normal physical and psychological functions. Experimental sleep deprivation is a variable-controlling approach to engaging the brain among different sleep conditions for investigating the responses of the brain to sleep loss. Here, we quantified the response of the brain to sleep deprivation by using the change of brain age predictable with brain morphologic features. In three independent datasets, we consistently found increased brain age after total sleep deprivation, which was associated with the change in sleep variables. Moreover, no significant change in brain age was found after partial sleep deprivation in another two datasets. Our study provides new evidence to explain the brainwide effect of sleep loss in an aging-like direction.

Differences in Gray Matter Volume in Cerebral Small Vessel Disease Patients with and without Sleep Disturbance

Recently, there has been increased interest in the relationship between cerebral small vessel disease (CSVD) and circadian rhythm disruption, particularly sleep disturbance. However, the neural mechanism of sleep disturbance in CSVD patients remains poorly understood. The purpose of this study is to explore the gray matter alterations in CSVD patients with and without sleep disturbance. 59 patients with CSVD and 40 healthy controls (HC) were recruited for the present study. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) questionnaire. CSVD patients were categorized into either the good sleepers group (CSVD-GS, n = 23) or the poor sleepers group (CSVD-PS, n = 36) based on PSQI score. Voxel-based morphometry (VBM) analysis was used to assess differences in gray matter volume (GMV) between groups. Multivariate regression analyses were performed to investigate the relationships between sleep quality, GMV, and white matter hyperintensities (WMH). We observed GMV differences between the three groups in the bilateral caudate, right thalamus, bilateral calcarine cortex, left precentral gyrus, right orbitofrontal cortex, left cingulate gyrus, and right sub-gyral temporal lobe. Additionally, the CSVD-PS group exhibited decreased GMV in the bilateral calcarine cortex yet increased GMV in the right caudate compared to the CSVD-GS group. In fully adjusted models, GMV of the right caudate and bilateral calcarine cortex was associated with sleep quality in CSVD patients. The present study revealed structural brain alterations in CSVD patients with sleep disturbance. These findings may provide novel insights into the neural mechanisms of sleep disturbance in CSVD.

Melatonin signalling in Schwann cells during neuroregeneration

It has widely been thought that in the process of nerve regeneration Schwann cells populate the injury site with myelinating, non–myelinating, phagocytic, repair, and mesenchyme–like phenotypes. It is now clear that the Schwann cells modify their shape and basal lamina as to accommodate re–growing axons, at the same time clear myelin debris generated upon injury, and regulate expression of extracellular matrix proteins at and around the lesion site. Such a remarkable plasticity may follow an intrinsic functional rhythm or a systemic circadian clock matching the demands of accurate timing and precision of signalling cascades in the regenerating nervous system. Schwann cells react to changes in the external circadian clock clues and to the Zeitgeber hormone melatonin by altering their plasticity. This raises the question of whether melatonin regulates Schwann cell activity during neurorepair and if circadian control and rhythmicity of Schwann cell functions are vital aspects of neuroregeneration. Here, we have focused on different schools of thought and emerging concepts of melatonin–mediated signalling in Schwann cells underlying peripheral nerve regeneration and discuss circadian rhythmicity as a possible component of neurorepair.

Endogenous Circadian Clock Machinery in Cortical NG2-Glia Regulates Cellular Proliferation

The molecular circadian clock can be found throughout the body and is essential for the synchronizing cellular physiology with the 24 h day. However, the role of the clock in regulating the regenerative potential of the brain has not been explored. We report here that murine NG2-glia, the largest population of proliferative cells in the mature central nervous system, rhythmically express circadian clock genes in a 24 h period, including the critical clock component Bmal1 RNA and BMAL1 protein. Interestingly, daily NG2-glia proliferation preferentially occurs during the time of day in which Bmal1 expression is high, while conditional knockout of Bmal1 decreases both cortical NG2-glia density and cellular proliferation. Furthermore, in a neurotrauma model, we show that pathology-induced NG2-glia proliferation is also dependent on Bmal1 expression. Because circadian rhythm disturbances are common in neurologic disorders across the life span, including in traumatic brain injury, these findings bear significant implications for cellular regeneration in brain injuries and disease.

Can measures of sleep quality or white matter structural integrity predict level of worry or rumination in adolescents facing stressful situations? Lessons from the COVID-19 pandemic

INTRODUCTION

COVID-19 has resulted in major life changes to the majority of the world population, particularly adolescents, with social-distancing measures such as home-based schooling likely to impact sleep quality. Increased worry is also likely considering the substantial financial, educational and health concerns accompanying COVID-19. White matter (WM) integrity has been shown to be associated with anxiety and depression symptoms, including worry, as well being closely associated with sleep quality. This study aimed to investigate the associations between pre-COVID sleep quality, WM structural integrity and levels of worry and rumination about COVID.

METHODS

N = 30 adolescent participants from Queensland, Australia, completed diffusion tensor imaging (DTI) scanning pre-COVID, the Pittsburgh Sleep Quality Index (PSQI) pre and during COVID, and 9 items designed to measure 3 constructs, perceived impact of COVID, general worry, and COVID-specific worry and rumination.

RESULTS

Sleep quality (PSQI total) was significantly poorer during COVID compared with pre-COVID. Sleep onset latency measured pre-COVID was significantly associated with COVID-specific worry and rumination. While the structural integrity of a number of WM tracts (measured pre-COVID) were found to be significantly associated with COVID-specific worry and rumination. Follow-up regression analysis using a model including pre-COVID sleep onset latency, structural integrity of the posterior limb of the internal capsule (PLIC), gender and change in PSQI explained a significant 47% of the variance in COVID-specific worry and rumination.

CONCLUSIONS

These findings suggest that adolescents with poor sleep quality and perturbed WM integrity may be at risk of heightened reactivity to future stressful events and interventions should focus on improving sleep onset latency.

The role of adolescent sleep quality in the development of anxiety disorders: A neurobiologically-informed model

In a series of cognitive and neuroimaging studies we investigated the relationships between adolescent sleep quality, white matter (WM) microstructural integrity and psychological distress. Collectively these studies showed that during early adolescence (12-14 years of age), sleep quality and psychological distress are significantly related. Sleep quality and the microstructure of the posterior limb of the internal capsule (PLIC), a WM tract that provides important connectivity between the cortex, thalamus and brain stem, were also shown to be significantly correlated as too were social connectedness and psychological distress. Longitudinally the uncinate fasciculus (UF), a WM tract that provides bidirectional connectivity between the amygdala and executive control centers in the Prefrontal cortex (PFC), was observed to be undergoing continued development during this period and sleep quality was shown to impact this development. Sleep latency was also shown to be a significant predictor of worry endured by early adolescents during future stressful situations. The current review places these findings within the broader literature and proposes an empirically supported model based in a theoretical framework. This model focuses on how fronto-limbic top-down control (or lack thereof) explains how poor sleep quality during early adolescence plays a crucial role in the initial development of anxiety disorders, and possibly in the reduced ability of anxiety disorder sufferers to benefit from cognitive reappraisal based therapies. While the findings outlined in these studies highlight the importance of sleep quality for WM development and in mitigating psychological distress, further research is required to further explicate the associations proposed within the model to allow causal inferences to be made.

Poor Self-Reported Sleep is Related to Regional Cortical Thinning in Aging but not Memory Decline-Results From the Lifebrain Consortium

We examined whether sleep quality and quantity are associated with cortical and memory changes in cognitively healthy participants across the adult lifespan. Associations between self-reported sleep parameters (Pittsburgh Sleep Quality Index, PSQI) and longitudinal cortical change were tested using five samples from the Lifebrain consortium (n = 2205, 4363 MRIs, 18–92 years). In additional analyses, we tested coherence with cell-specific gene expression maps from the Allen Human Brain Atlas, and relations to changes in memory performance. “PSQI # 1 Subjective sleep quality” and “PSQI #5 Sleep disturbances” were related to thinning of the right lateral temporal cortex, with lower quality and more disturbances being associated with faster thinning. The association with “PSQI #5 Sleep disturbances” emerged after 60 years, especially in regions with high expression of genes related to oligodendrocytes and S1 pyramidal neurons. None of the sleep scales were related to a longitudinal change in episodic memory function, suggesting that sleep-related cortical changes were independent of cognitive decline. The relationship to cortical brain change suggests that self-reported sleep parameters are relevant in lifespan studies, but small effect sizes indicate that self-reported sleep is not a good biomarker of general cortical degeneration in healthy older adults.

Short strides to important findings: A short interval longitudinal study of sleep quality, psychological distress and microstructure changes to the uncinate fasciculus in early adolescents

BACKGROUND

Developmental studies have shown adolescence is a period of ongoing white matter (WM) development, reduced sleep quality and the onset of many mental disorders. Findings indicate the WM development of the uncinate fasciculus (UF), a WM tract suggested to play a key role in mental disorders, continues throughout adolescence. While these studies provide valuable information, they are limited by long intervals between scans (1 to 4 years) leaving researchers and clinicians to infer what may be occurring between time-points. To allow inferences to be made regarding the impact that sleep quality may be having on WM development, longitudinal studies with much shorter between-scan intervals are required.

METHODS

The current study reports longitudinal data of self-reported sleep quality (PSQI), diffusion tensor imaging (DTI) measures of WM development and psychological distress (K10) for n = 64 early adolescents spanning the first twelve months (four time-points; Baseline, 4, 8, & 12 months) of the Longitudinal Adolescent Brain Study (LABS) study currently underway at the Thompson Institute.

RESULTS

Generalised Estimating Equation analysis showed a significant relationship between sleep quality and psychological distress over the four time-points. Reduced radial diffusivity and increased fractional anisotropy of the UF is also reported with increasing age suggesting that ongoing myelination is occurring. Adding sleep quality to the model, however, negatively impacted this myelination process.

CONCLUSION

These findings represent an important step towards elucidating how sleep, psychological distress and maturation of the UF may co-develop during early adolescence.

Sleep duration is associated with white matter microstructure and cognitive performance in healthy adults

Reduced sleep duration and sleep deprivation have been associated with cognitive impairment as well as decreased white matter integrity as reported by experimental studies. However, it is largely unknown whether differences in sleep duration and sleep quality might affect microstructural white matter and cognition. Therefore, the present study aims to examine the cross‐sectional relationship between sleep duration, sleep quality, and cognitive performance in a naturalistic study design, by focusing on the association with white matter integrity in a large sample of healthy, young adults. To address this, 1,065 participants, taken from the publicly available sample of the Human Connectome Project, underwent diffusion tensor imaging. Moreover, broad cognitive performance measures (NIH Cognition Toolbox) and sleep duration and quality (Pittsburgh Sleep Quality Index) were assessed. The results revealed a significant positive association between sleep duration and overall cognitive performance. Shorter sleep duration significantly correlated with fractional anisotropy (FA) reductions in the left superior longitudinal fasciculus (SLF). In turn, FA in this tract was related to measures of cognitive performance and was shown to significantly mediate the association of sleep duration and cognition. For cognition only, associations shift to a negative association of sleep duration and cognition for participants sleeping more than 8 hr a day. Investigations into subjective sleep quality showed no such associations. The present study showed that real‐world differences in sleep duration, but not subjective sleep quality are related to cognitive performance measures and white matter integrity in the SLF in healthy, young adults.

Investigating the association between sleep quality and diffusion-derived structural integrity of white matter in early adolescence

INTRODUCTION

Poor sleep quality has been linked to reduced neural connectivity through decreased white matter (WM) structural integrity. WM tract development has been shown to continue throughout adolescence with studies reporting positive correlations between diffusion-derived estimates of structural integrity and reduced sleep quality in adult samples. Few studies have investigated this relationship exclusively within a sample of young adolescents.

METHODS

N = 51 participants aged 12 years (M = 151.5 months, SD = 4 months) completed a self-report questionnaire which included the Pittsburgh Sleep Quality Index (PSQI) and underwent Diffusion Tensor Imaging (DTI) as part of their baseline assessment in the Longitudinal Adolescent Brain Study (LABS) being undertaken in Queensland, Australia. Fractional anisotropy (FA) were extracted using Tract-Based Spatial Statistics (TBSS) to investigate associations between sleep quality and WM integrity across the brain.

RESULTS

Significant correlations were found between the posterior limb of the internal capsule and the PSQI total sleep quality and sleep latency scores. There was also a significant difference in sleep duration between male and female participants.

CONCLUSION

These findings provide an important insight of the impact that sleep may have on early adolescent WM development. Ongoing longitudinal assessment of sleep on WM development across adolescence is likely to provide further important information about how WM maturation relates to variations in sleep quality as circadian rhythm changes occur during middle and late adolescence.

The prospective association of objectively measured sleep and cerebral white matter microstructure in middle-aged and older persons

STUDY OBJECTIVES

Poor sleep may destabilize axonal integrity and deteriorate cerebral white matter. In middle-aged and older adults sleep problems increase alongside structural brain changes, but the temporal relation between these processes is poorly understood. We studied longitudinal associations between sleep and cerebral white matter microstructure.

METHODS

One thousand one persons (59.3 ± 7.9 years, 55% women) were followed across 5.8 years (3.9-10.8). Total sleep time (TST, hours), sleep efficiency (SE, percentage), sleep onset latency (SOL, minutes), and wake after sleep onset (WASO, minutes) were measured at baseline using a wrist-worn actigraph. White matter microstructure (global and tract-specific fractional anisotropy [FA] and mean diffusivity [MD]) was measured twice with diffusion tensor imaging (DTI).

RESULTS

Poor sleep was associated with worse white matter microstructure up to 7 years later but did not predict trajectories of DTI over time. Longer TST was associated with higher global FA (β = 0.06, 95% CI: 0.01 to 0.12), but not with MD. Persons with higher SE had higher global FA (β = 0.01, 95% CI: 0.002 to 0.01) and lower MD (β = -0.01, 95% CI: -0.01 to -0.0004). Consistently, those with more WASO had lower global FA (β = -0.003, 95% CI: -0.005 to -0.001) and higher MD (β = 0.002, 95% CI: 0.0004 to 0.004). Global findings seemed to be driven by microstructural alterations in the cingulum, anterior forceps of corpus callosum, projection and association tracts.

CONCLUSIONS

Middle-aged and older persons with more WASO, lower SE and shorter TST have worse microstructure of cerebral white matter. Microstructural alterations are most pronounced projection and association tracts, in the cingulum, and in the anterior forceps of corpus callosum.

Connections Between Insomnia and Cognitive Aging

Insomnia is a common sleep disorder among older adults, and a risk factor for poor physical and mental health. However, the relationship between insomnia and cognitive health is not well understood. Here, we review observational studies that have investigated whether insomnia is associated with deficits in objective cognitive performance and an increased risk of dementia, magnetic resonance imaging studies that have assessed grey matter volumes and white matter microstructure, and interventional studies that have explored whether the treatment of insomnia can improve cognitive outcomes. There are inconsistent findings regarding impaired performance in objective cognitive tests and reduced grey matter volumes, and limited, emerging, evidence that suggests that insomnia is associated with an increased risk of dementia and reduced white matter integrity. Although the interventional literature is still in its infancy, there is some indication that treatment may have an impact on vigilance. Well-powered studies examining sources of heterogeneity are warranted.

The role of sleep and wakefulness in myelin plasticity

Myelin plasticity is gaining increasing recognition as an essential partner to synaptic plasticity, which mediates experience-dependent brain structure and function. However, how neural activity induces adaptive myelination and which mechanisms are involved remain open questions. More than two decades of transcriptomic studies in rodents have revealed that hundreds of brain transcripts change their expression in relation to the sleep-wake cycle. These studies consistently report upregulation of myelin-related genes during sleep, suggesting that sleep represents a window of opportunity during which myelination occurs. In this review, we summarize recent molecular and morphological studies detailing the dependence of myelin dynamics after sleep, wake, and chronic sleep loss, a condition that can affect myelin substantially. We present novel data about the effects of sleep loss on the node of Ranvier length and provide a hypothetical mechanism through which myelin changes in response to sleep loss. Finally, we discuss the current findings in humans, which appear to confirm the important role of sleep in promoting white matter integrity.

Sleep complaints and cerebral white matter: A prospective bidirectional study

Sleep complaints and brain changes co-occur in older adulthood, but the temporal relation between these processes is poorly understood. Poor sleep may destabilize axonal integrity and deteriorate white matter, but white matter pathology can also precede sleep complaints. Our objective was to explore a prospective, possibly bi-directional association between subjective sleep complaints and micro- and macro-structural properties of cerebral white matter. We assessed sleep complaints and brain magnetic resonance imaging at two time-points (2006-2008 and 2011-2014) in a population-based cohort including 2529 participants (56 ± 6 years old, 55% women). Sleep complaints were assessed with the Pittsburgh Sleep Quality Index. White matter lesion (WML) volume was assessed from fluid-attenuated inversion recovery images and global and tract-specific white matter microstructural integrity with diffusion tensor imaging. Sleep complaints at baseline were not associated with changes in WML volume or global white matter microstructure. In tract-specific analyses, however, sleep complaints were associated with reduced microstructural integrity in two white matter tracts projecting to the brainstem, but only when uncorrected for multiple testing. Likewise, we found no evidence for the reverse association; micro- or macro-structural properties of white matter were not related to changes in sleep complaints over time. This study provides evidence against the hypothesis that sleep complaints lead to white matter changes in the aging brain, and shows that white matter properties do not underlie sleep complaints in older persons. As subjective sleep complaints increase in later life, it is important to demonstrate that these are not etiologically related to cerebral white matter pathology.

Sleep quality can influence the outcome of patients with multiple sclerosis

OBJECTIVE

Sleep plays a role in some oligodendrocyte processes, including myelination. This study aimed to analyze the possible correlations between sleep quality and Multiple Sclerosis (MS) course.

METHODS

Forty patients with Relapsing-Remitting MS were admitted. Based on the score obtained by the Pittsburgh Sleep Quality Index (PSQI), they were divided into good sleepers (<5) and bad sleepers (≥5). A set of data was collected retrospectively for each patient to investigate whether PSQI scores correlated with EDSS score changes, the number and the duration of each relapse and the cumulative day-number of MS reactivations over a three-year period.

RESULTS

In a multivariate model, a PSQI score ≥5 independently and significantly correlated with an increase in number and duration of relapses (p = 0.000) and number of days of MS activity (p = 0.000) during the three-year retrospective observation period.

CONCLUSIONS

The results of this study show that the course of MS may be influenced by sleep quality. Assessment of sleep quality could be used to obtain reliable prognostic information in patients with relapsing-remitting MS. Further investigations are necessary to evaluate whether the correction of sleep disorders may be effective in improving the prognosis of MS patients.

Associations between self-reported sleep quality and white matter in community-dwelling older adults: A prospective cohort study

Both sleep disturbances and decline in white matter microstructure are commonly observed in ageing populations, as well as in age‐related psychiatric and neurological illnesses. A relationship between sleep and white matter microstructure may underlie such relationships, but few imaging studies have directly examined this hypothesis. In a study of 448 community‐dwelling members of the Whitehall II Imaging Sub‐Study aged between 60 and 82 years (90 female, mean age 69.2 ± 5.1 years), we used the magnetic resonance imaging technique diffusion tensor imaging to examine the relationship between self‐reported sleep quality and white matter microstructure. Poor sleep quality at the time of the diffusion tensor imaging scan was associated with reduced global fractional anisotropy and increased global axial diffusivity and radial diffusivity values, with small effect sizes. Voxel‐wise analysis showed that widespread frontal‐subcortical tracts, encompassing regions previously reported as altered in insomnia, were affected. Radial diffusivity findings remained significant after additional correction for demographics, general cognition, health, and lifestyle measures. No significant differences in general cognitive function, executive function, memory, or processing speed were detected between good and poor sleep quality groups. The number of times participants reported poor sleep quality over five time‐points spanning a 16‐year period was not associated with white matter measures. In conclusion, these data demonstrate that current sleep quality is linked to white matter microstructure. Small effect sizes may limit the extent to which poor sleep is a promising modifiable factor that may maintain, or even improve, white matter microstructure in ageing. Hum Brain Mapp 38:5465–5473, 2017. © 2017 Wiley Periodicals, Inc.

Rapid production of new oligodendrocytes is required in the earliest stages of motor-skill learning

We identified a novel marker of newly-forming oligodendrocytes – the ecto-enzyme Enpp6 – and used this to track oligodendrocyte differentiation in adult mice as they learned a motor skill (running on a wheel with unevenly spaced rungs). Production of Enpp6 - expressing immature oligodendrocytes was accelerated within just 2.5 hours exposure to the complex wheel in subcortical white matter and within 4 hours in motor cortex. Conditional deletion of Myelin regulatory factor (Myrf) in oligodendrocyte precursors blocked formation of new Enpp6⁺ oligodendrocytes and impaired learning within the same ~2-3 hour time frame. This very early requirement for oligodendrocytes suggests a direct and active role in learning, closely linked to synaptic strengthening. Running performance of normal mice continued to improve over the following week accompanied by secondary waves of oligodendrocyte precursor proliferation and differentiation. We conclude that new oligodendrocytes contribute to both early and late stages of motor skill learning.

Behavioral experiences as drivers of oligodendrocyte lineage dynamics and myelin plasticity

Many behavioral experiences are known to promote hippocampal neurogenesis. In contrast, the ability of behavioral experiences to influence the production of oligodendrocytes and myelin sheath formation remains relatively unknown. However, several recent studies indicate that voluntary exercise and environmental enrichment can positively influence both oligodendrogenesis and myelination, and that, in contrast, social isolation can negatively influence myelination. In this review we summarize studies addressing the influence of behavioral experiences on oligodendrocyte lineage cells and myelin, and highlight potential mechanisms including experience-dependent neuronal activity, metabolites, and stress effectors, as well as both local and systemic secreted factors. Although more study is required to better understand the underlying mechanisms by which behavioral experiences regulate oligodendrocyte lineage cells, this exciting and newly emerging field has already revealed that oligodendrocytes and their progenitors are highly responsive to behavioral experiences and suggest the existence of a complex network of reciprocal interactions among oligodendrocyte lineage development, behavioral experiences, and brain function. Achieving a better understanding of these relationships may have profound implications for human health, and in particular, for our understanding of changes in brain function that occur in response to experiences. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.