The Microbiota-Gut-Brain Axis in Neurological and Neuropsychiatric Disorders: A Literature Review

The gut-brain axis is a bidirectional communication network linking the GI tract and central nervous system via neural, immune, endocrine, and metabolic pathways. Growing evidence suggests that alterations in the gut microbiota are associated with the pathophysiology and clinical features of several neurological and neuropsychiatric disorders, including schizophrenia, autism spectrum disorder (ASD), Alzheimer’s disease (AD), Parkinson’s disease (PD), anxiety disorders, and amyotrophic lateral sclerosis (ALS). This narrative review used a structured search of PubMed/MEDLINE, ScienceDirect, SpringerLink, and Wiley Online Library to identify relevant literature published from January 1, 2010, through the final search date of June 25, 2026. Proposed mechanisms linking gut dysbiosis with neurological dysfunction include alterations in intestinal and blood-brain barrier (BBB) integrity, systemic inflammatory signaling, microglial activation, hypothalamic-pituitary-adrenal (HPA) axis dysregulation, changes in neurotransmitter pathways, and altered production of microbial metabolites such as short-chain fatty acids (SCFAs). Advanced profiling technologies, including 16S rRNA sequencing, whole-genome metagenomics, and metabolomics, have significantly enhanced the identification of disease-associated microbial signatures. These observations have stimulated interest in microbiome-targeted interventions, including probiotics, prebiotics, psychobiotics, synbiotics, fecal microbiota transplantation (FMT), live biotherapeutic products, and dietary modification; however, evidence supporting their clinical efficacy in neurological disorders remains limited and heterogeneous. Across the disorders reviewed, recurrent findings include alterations in microbial composition, intestinal barrier function, inflammatory signaling, and microbial metabolites. However, specific taxonomic signatures vary considerably among studies. Human evidence remains predominantly associative, while stronger mechanistic evidence is largely derived from animal and microbiota-transfer studies. Clinical studies of microbiome-targeted interventions remain limited and heterogeneous. Large-scale longitudinal studies and randomized controlled trials are critical to establishing causality, refining microbiome-targeted therapies, and developing personalized diagnostic tools for neurodegenerative and psychiatric diseases.