Olfactory ERPs in an odor/visual congruency task differentiate ApoE ε4 carriers from non-carriers

Studying the Alzheimer's disease continuum using EEG and fMRI in single-modality and multi-modality settings

Alzheimer's disease (AD) is a biological, clinical continuum that covers the preclinical, prodromal, and clinical phases of the disease. Early diagnosis and identification of the stages of Alzheimer's disease (AD) are crucial in clinical practice. Ideally, biomarkers should reflect the underlying process (pathological or otherwise), be reproducible and non-invasive, and allow repeated measurements over time. However, the currently known biomarkers for AD are not suitable for differentiating the stages and predicting the trajectory of disease progression. Some objective parameters extracted using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are widely applied to diagnose the stages of the AD continuum. While electroencephalography (EEG) has a high temporal resolution, fMRI has a high spatial resolution. Combined EEG and fMRI (EEG-fMRI) can overcome single-modality drawbacks and obtain multi-dimensional information simultaneously, and it can help explore the hemodynamic changes associated with the neural oscillations that occur during information processing. This technique has been used in the cognitive field in recent years. This review focuses on the different techniques available for studying the AD continuum, including EEG and fMRI in single-modality and multi-modality settings, and the possible future directions of AD diagnosis using EEG-fMRI.

Assessment and Scientific Progresses in the Analysis of Olfactory Evoked Potentials

The human sense of smell is important for many vital functions, but with the current state of the art, there is a lack of objective and non-invasive methods for smell disorder diagnostics. In recent years, increasing attention is being paid to olfactory event-related potentials (OERPs) of the brain, as a viable tool for the objective assessment of olfactory dysfunctions. The aim of this review is to describe the main features of OERPs signals, the most widely used recording and processing techniques, and the scientific progress and relevance in the use of OERPs in many important application fields. In particular, the innovative role of OERPs is exploited in olfactory disorders that can influence emotions and personality or can be potential indicators of the onset or progression of neurological disorders. For all these reasons, this review presents and analyzes the latest scientific results and future challenges in the use of OERPs signals as an attractive solution for the objective monitoring technique of olfactory disorders.

[Olfactory disorders as a multidisciplinary problem]

Olfactory dysfunction is a serious symptom that requires careful differential diagnosis. The article presents convincing evidence that dysosmia is not only a symptom of rinological pathology, but also a manifestation of various neurodegenerative diseases. Some patients with SARS-CoV-2 have neurological symptoms. Modern studies show that olfactory and gustatory dysfunctions are significant symptoms in the clinical presentation of the COVID-19 infection. The importance of olfactory diagnostics in relatives of patients with hereditary neurodegenerative diseases for the purpose of early detection of pathology is noted. We consider the possibility of introducing new methods for the diagnosis of olfactory dysfunction, which is a promising task both in the field of neurology and otorhinolaryngology, in order to prevent the development of neurodegenerative diseases at an early stage, improve the quality of life and social adaptation of patients.

Human APOE ɛ3 and APOE ɛ4 Alleles Have Differential Effects on Mouse Olfactory Epithelium

BACKGROUND

Alzheimer's disease (AD) is a progressive age-dependent disorder whose risk is affected by genetic factors. Better models for investigating early effects of risk factors such as apolipoprotein E (APOE) genotype are needed.

OBJECTIVE

To determine whether APOE genotype produces neuropathologies in an AD-susceptible neural system, we compared effects of human APOE ɛ3 (E3) and APOE ɛ4 (E4) alleles on the mouse olfactory epithelium.

METHODS

RNA-Seq using the STAR aligner and DESeq2, immunohistochemistry for activated caspase-3 and phosphorylated histone H3, glucose uptake after oral gavage of 2-[1,2-3H (N)]-deoxy-D-glucose, and Seahorse Mito Stress tests on dissociated olfactory mucosal cells.

RESULTS

E3 and E4 olfactory mucosae show 121 differentially abundant mRNAs at age 6 months. These do not indicate differences in cell type proportions, but effects on 17 odorant receptor mRNAs suggest small differences in tissue development. Ten oxidoreductases mRNAs important for cellular metabolism and mitochondria are less abundant in E4 olfactory mucosae but this does not translate into differences in cellular respiration. E4 olfactory mucosae show lower glucose uptake, characteristic of AD susceptibility and consistent with greater expression of the glucose-sensitive gene, Asns. Olfactory sensory neuron apoptosis is unaffected at age 6 months but is greater in E4 mice at 10 months.

CONCLUSION

Effects of human APOE alleles on mouse olfactory epithelium phenotype are apparent in early adulthood, and neuronal loss begins to increase by middle age (10 months). The olfactory epithelium is an appropriate model for the ability of human APOE alleles to modulate age-dependent effects associated with the progression of AD.

Apolipoprotein E ε4 allele impairs cortical activity in healthy aging and Alzheimer's disease

AIM

To investigate the influence of apolipoprotein E (APOE) genotype on cortical activity, using the event-related potential P300 in healthy older adults and individuals with Alzheimer's disease (AD).

METHODS

A cohort of 37 healthy older adults and 48 with AD participated in this study and completed an auditory oddball task using electroencephalographic equipment with 21 channels (10-20 system). APOE genotyping was obtained by real-time PCR.

RESULTS

AD presented increased P300 latency and lower P300 amplitude, compared to healthy older adults. AD APOE ε4 carriers presented increased P300 latency in F3 (420.7 ± 65.8 ms), F4 (412.0 ± 49.0 ms), C4 (413.0 ± 41.1 ms) and P3 (420.4 ± 55.7 ms) compared to non-carriers (F3 = 382.5 ± 56.8 ms, p < 0.01; F4 = 372.2 ± 56.7 ms, p < 0.01; C4 = 374.2 ± 51.7 ms, p < 0.01; P3 = 384.4 ± 44.4 ms, p < 0.01). Healthy older adults APOE ε4 carriers presented lower Fz amplitude (2.6 ± 1.5 μV) compared to non-carriers (4.9 ± 2.9 μV; p = 0.02). Linear regression analysis showed that being a carrier of APOE ε4 allele remained significantly associated with P300 latency even after adjusting for sex, age, and cognitive grouping. APOE ε4 allele increases P300 latency (95% CI 0.11-0.98; p = 0.02).

CONCLUSION

APOE ε4 allele negatively impacts cortical activity in both healthy older adults and AD individuals.

A Systematic Review of Altered P300 Event-Related Potential in Apolipoprotein E4 (APOE4) Carriers

BACKGROUND

Apolipoprotein ε4 allele (APOE4) is the strongest genetic risk factor for Alzheimer's disease and seems to be related to cognitive decline and damaged event-related potential P300, which is a sensitive measure to assess cognitive processing.

OBJECTIVE

This research aims to critically review the existing scientific evidence regarding the association between APOE4 and P300.

METHODS

A systematic review was carried out up to January 2020 on the following databases: Web of Science, Scopus and Medline/PubMed. Articles were considered for inclusion if they are original research that provided information regarding the association between APOE4 and P300, available in English, Spanish, or Portuguese, and available in full text. The methodological quality of the studies selected was evaluated using the quality assessment tool for observational cohort and cross-sectional studies recommended by Cochrane.

RESULTS

Out of 993 studies, 14 met the inclusion criteria. The results obtained showed that APOE4 is related to a longer P300 latency. However, the data supplied do not allow us to confirm if this relationship also occurs in amplitude measures. Moreover, it was observed that APOE genotype may influence P300 in different ages, from younger individuals to demented older people.

CONCLUSION

Evidence shows that APOE4 negatively influences cortical activities related to cognitive functions, as indicated by P300.

Do Food Odors Differently Influence Cerebral Activity Depending on Weight Status? An Electroencephalography Study of Implicit Olfactory Priming Effects on the Processing of Food Pictures

Attentional automatic processes and cerebral activity may differ between individuals with different weight statuses in the presence of food stimuli (e.g. odors, pictures). In the present study, we used an implicit olfactory priming paradigm to test the influence of non-attentively perceived food odors on the cerebral activity underlying the processing of food pictures, in normal-weight, overweight, and obese adults. A pear odor and a pound cake odor were used as primes, respectively priming sweet low-energy-density foods and high-energy-density foods. Event-related potentials were recorded while the participants passively watched pictures of sweet low and high-energy-density foods, under the two priming conditions plus an odorless control condition. The amplitude and latency of several peaks were measured (P100, N100, P200, N400). As a major result, we found that weight status influences the cerebral activity underlying the processing of food cues outside of consciousness, as early as the first detectable P100 peak.

A systematic review of cognitive event-related potentials in mild cognitive impairment and Alzheimer's disease

This systematic review examined whether event-related potentials (ERPs) during higher cognitive processing can detect subtle, early signs of neurodegenerative disease. Original, empirical studies retrieved from PsycINFO and PubMed were reviewed if they analyzed patterns in cognitive ERPs (≥150 ms post-stimulus) differentiating mild cognitive impairment (MCI), Alzheimer's disease (AD), or cognitively intact elders who carry AD risk through the Apolipoprotein-E ε4 allele (ε4+) from healthy older adult controls (HC). The 100 studies meeting inclusion criteria (MCI = 47; AD = 47; ε4+ = 6) analyzed N200, P300, N400, and occasionally, later components. While there was variability across studies, patterns of reduced amplitude and delayed latency were apparent in pathological aging, consistent with AD-related brain atrophy and cognitive impairment. These effects were particularly evident in advanced disease progression (i.e., AD > MCI) and in later ERP components measured during complex tasks. Although ERP studies in intact ε4+ elders are thus far scarce, a similar pattern of delayed latency was notable, along with a contrasting pattern of increased amplitude, consistent with compensatory neural activation. This limited work suggests ERPs might be able to index early neural changes indicative of future cognitive decline in otherwise healthy elders. As ERPs are also accessible and affordable relative to other neuroimaging methods, their addition to cognitive assessment might substantively enhance early identification and characterization of neural dysfunction, allowing opportunity for earlier differential diagnosis and targeting of intervention. To evaluate this possibility there is urgent need for well-powered studies assessing late cognitive ERPs during complex tasks, particularly in healthy elders at risk for cognitive decline.

Alzheimer's Disease: What Can We Learn From the Peripheral Olfactory System?

The sense of smell has been shown to deteriorate in patients with some neurodegenerative disorders. In Parkinson's disease (PD) and Alzheimer's disease (AD), decreased ability to smell is associated with early disease stages. Thus, olfactory neurons in the nose and olfactory bulb (OB) may provide a window into brain physiology and pathophysiology to address the pathogenesis of neurodegenerative diseases. Because nasal olfactory receptor neurons regenerate throughout life, the olfactory system offers a broad variety of cellular mechanisms that could be altered in AD, including odorant receptor expression, neurogenesis and neurodegeneration in the olfactory epithelium, axonal targeting to the OB, and synaptogenesis and neurogenesis in the OB. This review focuses on pathophysiological changes in the periphery of the olfactory system during the progression of AD in mice, highlighting how the olfactory epithelium and the OB are particularly sensitive to changes in proteins and enzymes involved in AD pathogenesis. Evidence reviewed here in the context of the emergence of other typical pathological changes in AD suggests that olfactory impairments could be used to understand the molecular mechanisms involved in the early phases of the pathology.

Visual Priming Influences Olfactomotor Response and Perceptual Experience of Smells

Whereas contextual influences in the visual and auditory domains have been largely documented, little is known about how chemical senses might be affected by our multisensory environment. In the present study, we aimed to better understand how a visual context can affect the perception of a rather pleasant (floral) and a rather unpleasant (damp) odor. To this end, 19 healthy participants performed a series of tasks including odor detection followed by perceptual evaluations of odor intensity, pleasantness, flowery, and damp characters of both odors presented at 2 different concentrations. A visual context (either congruent or incongruent with the odor; or a neutral control context) preceded odor stimulations. Olfactomotor responses as well as response times were recorded during the detection task. Results showed an influence of the visual context on semantic and motor responses to the target odors. First, congruency between context and odor increased the saliency of the olfactory feature of the memory trace, for the pleasant floral odor only (higher perceived flowery note). Clinical applications of this finding for olfactory remediation in dysosmic patients are proposed. Second, the unpleasant odor remained unaffected by visual primes, whatever the condition. In addition, incongruency between context and odor (regardless of odor type) had a disruptive effect on odor sampling behavior, which was interpreted as a protective behavior in response to expectancy violation. Altogether, this second series of effects may serve an adaptive function, especially the avoidance of, or simply vigilance toward, aversive and unpredictable stimuli.

Impact of Apolipoprotein E gene polymorphism during normal and pathological conditions of the brain across the lifespan

The central nervous system (CNS) is the cellular substrate for the integration of complex, dynamic, constant, and simultaneous interactions among endogenous and exogenous stimuli across the entire human lifespan. Numerous studies on aging-related brain diseases show that some genes identified as risk factors for some of the most common neurodegenerative diseases - such as the allele 4 of APOE gene (APOE4) for Alzheimer's disease (AD) - have a much earlier neuro-anatomical and neuro-physiological impact. The impact of APOE polymorphism appears in fact to start as early as youth and early-adult life. Intriguingly, though, those same genes associated with aging-related brain diseases seem to influence different aspects of the brain functioning much earlier actually, that is, even from the neonatal periods and earlier. The APOE4, an allele classically associated with later-life neurodegenerative disorders as AD, seems in fact to exert a series of very early effects on phenomena of neuroplasticity and synaptogenesis that begin from the earliest periods of life such as the fetal ones.We reviewed some of the findings supporting the hypothesis that APOE polymorphism is an early modifier of various neurobiological aspects across the entire human lifespan - from the in-utero to the centenarian life - during both normal and pathological conditions of the brain.

Intensity expectation modifies gustatory evoked potentials to sweet taste: Evidence of bidirectional assimilation in early perceptual processing

Expectations can affect subjective sensory and hedonic ratings of tastes, but it is unclear whether they also shape sensory experience at a perceptual level. The neural correlates of the taste‐expectancy relationship were explored through EEG analysis. Using a trial‐by‐trial cueing paradigm, lingual delivery of 0.05 M or 0.3 M sucrose solutions was preceded by congruent or incongruent visual cues designed to promote anticipation of either a low‐sweet or high‐sweet solution. When participants were cued to expect low‐sweet, but received high‐sweet (incongruent cue), intensity ratings for high‐sweet decreased. Likewise, expectation of high‐sweet increased intensity ratings of low‐sweet solutions. Taste‐dependent, right central‐parietal gustatory ERPs were detected, with greater P1 (associated with greater right insula activation) and P2 peak amplitudes for high‐sweet tastes. Valid cue‐taste pairings led to specific reduced right‐lateralized N400 responses (associated with an attenuation in right insula activation) compared with invalid cue‐taste pairings. Finally, P1 amplitudes following invalidly cued low‐sweet tastes closely matched those generated by expected high‐sweet tastes, and P1 amplitudes for invalidly cued high‐sweet tastes resembled those generated by low‐sweet tastes. We conclude that, as well as modifying subjective ratings toward the anticipated intensity level, expectations affect cortical activity in a top‐down manner to induce bidirectional assimilation in the early perceptual processing of sweet taste and modulate N400 ERP components not previously associated with gustatory stimulation.

Human Apolipoprotein E Genotype Differentially Affects Olfactory Behavior and Sensory Physiology in Mice

Apolipoprotein E (ApoE) is an important lipid carrier in both the periphery and the brain. The ApoE ε4 allele (ApoE4) is the single most important genetic risk-factor for Alzheimer's disease (AD) while the ε2 allele (ApoE2) is associated with a lower risk of AD-related neurodegeneration compared to the most common variant, ε3 (ApoE3). ApoE genotype affects a variety of neural circuits; however, the olfactory system appears to provide early biomarkers of ApoE genotype effects. Here, we directly compared olfactory behavior and olfactory system physiology across all three ApoE genotypes in 6-month- and 12-month-old mice with targeted replacement for the human ApoE2, ApoE3, or ApoE4 genes. Odor investigation and habituation were assessed, along with, olfactory bulb and piriform cortical local field potential activity. The results demonstrate that while initial odor investigation was unaffected by ApoE genotype, odor habituation was impaired in E4 relative to E2 mice, with E3 mice intermediate in function. There was also significant deterioration of odor habituation from 6 to 12 months of age regardless of the ApoE genotype. Olfactory system excitability and odor responsiveness were similarly determined by ApoE genotype, with an ApoE4 > ApoE3 > ApoE2 excitability ranking. Although motivated behavior is influenced by many processes, hyper-excitability of ApoE4 mice may contribute to impaired odor habituation, while hypo-excitability of ApoE2 mice may contribute to its protective effects. Given that these ApoE mice do not have AD pathology, our results demonstrate how ApoE affects the olfactory system at early stages, prior to the development of AD.

Apo E4 Alleles and Impaired Olfaction as Predictors of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia that affects more than 5 million Americans. It is the only disease among the 10 causes of death that cannot be slowed or cured, thus raising the need for identification of early preclinical markers that could be the focus of preventative efforts. Although evidence is escalating that abnormalities in olfactory structure and function precede AD development and early cognitive impairments by one or more decades, the importance of olfaction is largely overlooked in AD, and such testing is not routinely performed in neurology clinics. Nevertheless, research using the olfactory model, has begun to advance our understanding of the preclinical pathophysiology of AD. Notably, an interesting series of studies is beginning to illuminate the relationship between Apolipoprotein E (ApoE) ε4 polymorphism and olfactory dysfunction and late-onset Alzheimer's disease. In this article, we reviewed present research on the significance of ApoE and olfaction to AD, summarized current studies on the associations and mechanisms of ApoE and olfactory dysfunction, and highlighted important gaps for future work to further advance the translational application of the olfactory paradigm to early, preclinical diagnosis and treatment of AD.

Smell identification function and Alzheimer's disease: a selective review

PURPOSE OF REVIEW

To provide an update of the recent studies on the olfactory function in Alzheimer's disease, with a focus on the olfactory identification function.

RECENT FINDINGS

The studies reviewed here confirm previous reports on the poor olfactory function in Alzheimer's disease compared to health normal controls and also as a marker for conversion from mild cognitive impairment to Alzheimer's disease. Olfactory identification function has been associated with severity of illness, non-cognitive neuropsychiatric symptoms, and structural and functional MRI measures. There is a possible interaction of apolipoprotein E genotype with olfactory performance in Alzheimer's disease patients and those at risk for Alzheimer's disease. Usefulness of smell identification function in differentiating Alzheimer's disease patients from other types of dementia needs to be established.

SUMMARY

The need for simple, inexpensive and non-invasive procedures for aiding in the diagnosis and understanding of Alzheimer's disease has led to theories and procedures examining the role of olfactory functions in Alzheimer's disease. Although there is increasing evidence for olfactory dysfunction in general and impaired odour identification in particular in Alzheimer's disease, additional larger and methodologically sound research is needed for testing its clinical utility in day-to-day clinical practice for early, accurate and differential diagnosis of Alzheimer's disease.

A designated odor-language integration system in the human brain

Odors are surprisingly difficult to name, but the mechanism underlying this phenomenon is poorly understood. In experiments using event-related potentials (ERPs) and functional magnetic resonance imaging (fMRI), we investigated the physiological basis of odor naming with a paradigm where olfactory and visual object cues were followed by target words that either matched or mismatched the cue. We hypothesized that word processing would not only be affected by its semantic congruency with the preceding cue, but would also depend on the cue modality (olfactory or visual). Performance was slower and less precise when linking a word to its corresponding odor than to its picture. The ERP index of semantic incongruity (N400), reflected in the comparison of nonmatching versus matching target words, was more constrained to posterior electrode sites and lasted longer on odor-cue (vs picture-cue) trials. In parallel, fMRI cross-adaptation in the right orbitofrontal cortex (OFC) and the left anterior temporal lobe (ATL) was observed in response to words when preceded by matching olfactory cues, but not by matching visual cues. Time-series plots demonstrated increased fMRI activity in OFC and ATL at the onset of the odor cue itself, followed by response habituation after processing of a matching (vs nonmatching) target word, suggesting that predictive perceptual representations in these regions are already established before delivery and deliberation of the target word. Together, our findings underscore the modality-specific anatomy and physiology of object identification in the human brain.

Amyloid-aβ Peptide in olfactory mucosa and mesenchymal stromal cells of mild cognitive impairment and Alzheimer's disease patients

Patients with mild cognitive impairment (MCI) or Alzheimer's disease (AD) might develop olfactory dysfunction that correlates with progression of disease. Alteration of olfactory neuroepithelium associated with MCI may be useful as predictor of cognitive decline. Biomarkers with higher sensitivity and specificity would allow to understand the biological progression of the pathology in association with the clinical course of the disease. In this study, magnetic resonance images, apolipoprotein E (ApoE) load, Olfactory Connecticut test and Montreal Cognitive Assessment (MoCA) indices were obtained from noncognitive impaired (NCI), MCI and AD patients. We established a culture of patient-derived olfactory stromal cells from biopsies of olfactory mucosa (OM) to test whether biological properties of mesenchymal stromal cells (MSC) are concurrent with MCI and AD psychophysical pathology. We determined the expression of amyloid Aβ peptides in the neuroepithelium of tissue sections from MCI and AD, as well as in cultured cells of OM. Reduced migration and proliferation of stromal (CD90(+) ) cells in MCI and AD with respect to NCI patients was determined. A higher proportion of anosmic MCI and AD cases were concurrent with the ApoE ε4 allele. In summary, dysmetabolism of amyloid was concurrent with migration and proliferation impairment of patient-derived stem cells.

Electroencephalogram and Alzheimer's disease: clinical and research approaches

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by cognitive deficits, problems in activities of daily living, and behavioral disturbances. Electroencephalogram (EEG) has been demonstrated as a reliable tool in dementia research and diagnosis. The application of EEG in AD has a wide range of interest. EEG contributes to the differential diagnosis and the prognosis of the disease progression. Additionally such recordings can add important information related to the drug effectiveness. This review is prepared to form a knowledge platform for the project entitled "Cognitive Signal Processing Lab," which is in progress in Information Technology Institute in Thessaloniki. The team tried to focus on the main research fields of AD via EEG and recent published studies.

Time to smell: a cascade model of human olfactory perception based on response-time (RT) measurement

The timing of olfactory behavioral decisions may provide an important source of information about how the human olfactory-perceptual system is organized. This review integrates results from olfactory response-time (RT) measurements from a perspective of mental chronometry. Based on these findings, a new cascade model of human olfaction is presented. Results show that main perceptual decisions are executed with high accuracy within about 1~s of sniff onset. The cascade model proposes the existence of distinct processing stages within this brief time-window. According to the cascade model, different perceptual features become accessible to the perceiver at different time-points, and the output of earlier processing stages provides the input for later processing stages. The olfactory cascade starts with detecting the odor, which is followed by establishing an odor object. The odor object, in turn, triggers systems for determining odor valence and edibility. Evidence for the cascade model comes from studies showing that RTs for odor valence and edibility assessment are predicted by the shorter RTs needed to establish the odor object. Challenges for future research include innovative task designs for olfactory RT experiments and the integration of the behavioral processing sequence into the underlying cortical processes using complementary RT measures and neuroimaging methods.

Age and apolipoprotein E ε4 effects on neural correlates of odor memory

Alzheimer's disease (AD) affects 5.4 million Americans. Evidence suggests that individuals who are positive for the apolipoprotein E (ApoE) ε4 allele are at higher risk for developing the disease. Studies have also shown that the ε4 allele is linked to olfactory decline. Olfactory functioning may be investigated using olfactory event-related potentials (OERPs). The high temporal resolution of OERPs enables an understanding of the neural correlates of olfactory processing and functioning. This study investigated the effects of age, ApoE ε4 status, response type, and electrode site on OERP latency and amplitude during encoding and retrieval in an odor recognition memory task. The 60 participants were equally divided into 3 age groups matched on ε4 status: younger, middle, and older. Odors were presented using a computer-controlled olfactometer. Participants were notified during encoding that this was a task of odor memory. Results indicated differences in OERP activity as a function of age, ApoE ε4 status, response type, and electrode site. These findings highlight the potential of OERPs to distinguish ε4- and ε4+ individuals and to contribute to an earlier diagnosis of AD.

Early Alzheimer's and Parkinson's disease pathology in urban children: Friend versus Foe responses--it is time to face the evidence

Chronic exposure to particulate matter air pollution is known to cause inflammation leading to respiratory- and cardiovascular-related sickness and death. Mexico City Metropolitan Area children exhibit an early brain imbalance in genes involved in oxidative stress, inflammation, and innate and adaptive immune responses. Early dysregulated neuroinflammation, brain microvascular damage, production of potent vasoconstrictors, and perturbations in the integrity of the neurovascular unit likely contribute to progressive neurodegenerative processes. The accumulation of misfolded proteins coincides with the anatomical distribution observed in the early stages of both Alzheimer's and Parkinson's diseases. We contend misfolding of hyperphosphorylated tau (HPπ), alpha-synuclein, and beta-amyloid could represent a compensatory early protective response to the sustained systemic and brain inflammation. However, we favor the view that the chronic systemic and brain dysregulated inflammation and the diffuse vascular damage contribute to the establishment of neurodegenerative processes with childhood clinical manifestations. Friend turns Foe early; therefore, implementation of neuroprotective measures to ameliorate or stop the inflammatory and neurodegenerative processes is warranted in exposed children. Epidemiological, cognitive, structural, and functional neuroimaging and mechanistic studies into the association between air pollution exposures and the development of neuroinflammation and neurodegeneration in children are of pressing importance for public health.