Author

Mohammad I. K. Hamad

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#small language model Review Open access Sep 2026

Paired neuronal-haemodynamic neurovascular coupling measures and cognitive performance in vascular pathology: protocol for a systematic review and meta-analysis

Neurovascular coupling (NVC) links neuronal activity to haemodynamic responses. Altered NVC may contribute to cognitive impairment in vascular pathology, but evidence is limited by inconsistent definitions and by the conflation of paired neuronal–haemodynamic NVC measures with haemodynamic-only, model-derived, or imaging-derived proxy measures. The primary aim is to evaluate the association between paired neuronal–haemodynamic NVC measures and cognitive performance in middle-aged and older adults with vascular pathology. Secondarily, we will compare paired neuronal–haemodynamic NVC measures between patients with vascular pathology and age-matched controls without vascular pathology, determine whether predefined pathology strata show distinct impairment profiles, and examine whether the NVC–cognition association varies across cognitive domains. As an exploratory objective, we will synthesise evidence on the prognostic utility of paired neuronal–haemodynamic NVC measures in predicting future cognitive decline. Collectively, these objectives address critical gaps in a fragmented literature characterised by heterogeneous methodologies, populations, and assessment techniques, as well as methodological limitations including small samples, cross-sectional designs, and inadequate confounder control. This review will systematically synthesise existing findings, identify remaining knowledge gaps, and outline priorities for future research. This protocol follows PRISMA-P guidance and is registered with PROSPERO (CRD420261351976). We searched five electronic databases from inception to 28 July 2026 for peer-reviewed English-language studies. Eligible studies include middle-aged and older adults with vascular pathology and/or participants from relevant comparator groups and report paired neuronal–haemodynamic NVC measures based on independently acquired neuronal and haemodynamic or vascular signals. The primary synthesis will evaluate associations between paired neuronal–haemodynamic NVC measures and cognitive performance, with meta-analysis conducted only for synthesis strata that meet prespecified feasibility criteria.

V. Abramova, Marta Estrada, Veronica Egovtseva et al. · Systematic Reviews · 0 citations

Review Open access Jul 2026

From association to causality: mechanistic pathways linking the gut microbiome to psychiatric disorders.

The microbiota-gut-brain axis (MGBA) has emerged as a key framework for understanding how peripheral biological systems influence brain function and behaviour. However, despite extensive associative evidence linking gut microbiome to psychiatric disorders, robust causal and mechanistic insights remain limited. This review critically evaluates current evidence to determine whether microbiome alterations contribute to psychiatric pathophysiology and inform therapeutic strategies. We outline methodological frameworks for causal inference, highlighting the limitations of cross-sectional designs and the need for convergent evidence from longitudinal studies, experimental models, and human genetic approaches. We then synthesize mechanistic pathways linking the microbiota to brain function, including immune signaling, neuroendocrine regulation via the hypothalamic-pituitary-adrenal (HPA) axis, neural communication through vagal and enteric pathways, and intestinal and blood-brain barrier (BBB) integrity. Across these systems, microbial metabolites and immune mediators emerge as key mediators, although direct causal mechanisms in humans remain incompletely established. Disorder-specific evaluation across major depressive disorder (MDD), anxiety disorders, bipolar disorder (BD), schizophrenia (SCZ), and post-traumatic stress disorder (PTSD) reveals heterogeneous but converging evidence for microbiome involvement. Although preclinical and interventional studies support biological plausibility, human evidence remains constrained by confounding, variability, and limited mechanistic validation. Translational strategies, including psychobiotics, dietary interventions, fecal microbiota transplantation (FMT), and microbiome-based biomarkers, show promise but remain methodologically limited. Overall, the gut microbiome represents a biologically plausible and modifiable contributor to psychiatric disorders. Advancing toward clinical application will require integrative, longitudinal, and mechanism-driven research to enable precision psychiatry grounded in causal evidence.

Sultan Almarzooqi, Lidya K. Yassin, Fatima Alnuaimi et al. · Translational Psychiatry · 0 citations