Modulation of gut microbiome in the treatment of neurodegenerative diseases: A systematic review.

BACKGROUND AND AIMS: Microbiota plays an essential role in maintaining body health, through positive influences on metabolic, defensive, and trophic processes and on intercellular communication. Imbalance in intestinal flora, with the proliferation of harmful bacterial species (dysbiosis) is consistently reported in chronic illnesses, including neurodegenerative diseases (ND). Correcting dysbiosis can have a beneficial impact on the symptoms and evolution of ND. This review examines the effects of microbiota modulation through administration of probiotics, prebiotics, symbiotics, or prebiotics' metabolites (postbiotics) in patients with ND like multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). METHODS: PubMed, Web of Science, Medline databases and ClinicalTrials.gov registry searches were performed using pre-/pro-/postbiotics and ND-related terms. Further references were obtained by checking relevant articles. RESULTS: Although few compared to animal studies, the human studies generally show positive effects on disease-specific symptoms, overall health, metabolic parameters, on oxidative stress and immunological markers. Therapy with probiotics in various forms (mixtures of bacterial strains, fecal microbiota transplant, diets rich in fermented foods) exert favorable effects on patients' mental health, cognition, and quality of life, targeting pathogenetic ND mechanisms and inducing reparatory mechanisms at the cellular level. More encouraging results have been observed in prebiotic/postbiotic therapy in some ND. CONCLUSIONS: The effects of probiotic-related interventions depend on the patients' ND stage and pre-existing allopathic medication. Further studies on larger cohorts and long term comprehensive neuropsychiatric, metabolic, biochemical testing, and neuroimaging monitoring are necessary to optimize therapeutic protocols in ND.

Neuroanatomical correlates of negative emotionality-related traits: A systematic review and meta-analysis.

Two central traits present in the most influential models of personality characterize the response to positive and, respectively, negative emotional events. Negative emotionality (NE)-related traits are linked to vulnerability to mood and anxiety disorders; this has fuelled a special interest in examining stable differences in brain morphology associated to these traits. Structural imaging methods including voxel-based morphometry, cortical thickness analysis and diffusion tensor imaging (DTI) have yielded inconclusive and sometimes contradictory results. This review summarizes the findings reported to date through these methods and discusses them in relation to the functional imaging results. To detect topographic convergence between studies showing positive and, respectively, negative grey matter associations with NE-traits, activation likelihood estimation (ALE) meta-analyses of VBM studies were performed. Individuals scoring high on NE-related traits show consistent morphological differences in a left-lateralized circuit: higher grey matter volume (GMV) in amygdala and anterior parahippocampal gyrus and lower GMV in the orbitofrontal cortex extending into perigenual anterior cingulate cortex. Most DTI studies indicate reduced white matter integrity in various brain regions and tracts, particularly in the uncinate fasciculus and in cingulum bundle. These results show that the behavioural phenotype associated to NE traits is reflected in structural differences within the cortico-limbic system, suggesting alterations in information processing and transmission. The results are discussed from the perspective of neuron-glia interactions. Future directions are outlined based on recent developments in structural imaging techniques.

Neural substrate of the cognitive and emotional interference processing in healthy adolescents.

Emotion regulation is essential for adaptive functioning and social integration. However, it is not clear to what extent the responsible brain mechanisms are similar to those invoked in cognitive control in a non-emotional context. The aim of this study was to compare the neural circuitry of cognitive and emotional interference resolution in healthy adolescents, employing variants of the counting Stroop task. Cognitive and emotional interference processing engaged predominantly brain regions belonging to the dorsal- and the ventral attentional systems, respectively, and commonly the inferior frontal gyrus, IFG (Broca's area, left BA 45, but also right BA 45). These results suggest that BA 45 is a bridge of interaction between the dorsal- and the ventral attentional systems implicated in top-down orienting of attention and, respectively, in bottom-up processing of salient stimuli. Reaction time data showed that some participants tend to respond faster, while others respond slower to negative emotional compared to neutral trials. The emotional interference maps revealed that fast responders recruit the right temporo-parietal junction and to a larger extent the right BA 45 and the bilateral cuneus, suggesting that they engage more efficient cognitive control mechanisms to override the attentional bias. No anterior cingulate (ACC) activation was observed in either cognitive, or emotional interference; this supports the view that ACC is not involved specifically in mediating Stroop selection.

The complex minds of teenagers: neuroanatomy of personality differs between sexes.

Extraversion and neuroticism influence behaviour and mood. Extreme expressions of these personality traits may predispose individuals to developing chronic functional pains and mood disorders that predominantly affect women. We acquired anatomical MRI scans and personality scores from healthy male and female adolescents and measured gray matter volume (GMV) and cortical thickness to test the hypothesis that neuroticism and extraversion contribute to sex differences in fronto-limbic cortical development during a crucial period of social and biological maturation. In females, extraversion correlated negatively with medial frontal gyrus GMV and neuroticism correlated positively with subgenual anterior cingulate cortex GMV and cortical thickness. Interestingly, correlations between GMV and personality in males showed an opposite effect. Given the association of these cortical areas with social cognition and emotional processing, we suggest that a neuro-maturational divergence during adolescence accounts for the higher prevalence of specific chronic pains and mood disorders in females.