Creating cognitive normative data for rural Indian population.

Neurodegenerative disorders (NDDs) represent one of the most pressing biomedical challenges of the twenty-first century, not only because of their rising prevalence but also due to their striking heterogeneity in onset, progression, and clinical expression. Individuals exposed to seemingly similar genetic risks and environmental influences often follow markedly different neurocognitive trajectories. This variability suggests that disease vulnerability may be shaped by modulatory systems operating beyond classical protein aggregation paradigms (; ). Increasingly, attention has shifted toward systemic and environmental contributors that influence how the central nervous system (CNS) responds to stress across the lifespan. Among these, peripheral immune perturbations and intestinal ecosystem dynamics have emerged as important determinants of neuroinflammatory tone (). The gut–brain axis has reshaped contemporary understanding of brain–body communication. The brain is no longer viewed as an isolated organ. Instead, it operates within a bidirectional network involving immune mediators, metabolic intermediates, microbial metabolites, and neural circuits. The intestinal microbiota represents a dynamic ecological system that can influence host physiology far beyond digestion (). Early research in this field mainly focused on compositional differences in microbial taxa associated with neurological disease. However, a more functional perspective is now emerging. This perspective emphasizes regulatory and metabolic interactions rather than taxonomy alone (). In parallel with advances in microbiome research, the concept of immune programming has gained importance. Peripheral inflammatory events, whether triggered by infection, barrier dysfunction, or systemic immune activation, may not only generate transient cytokine responses. Instead, evidence suggests that these events can recalibrate immune responsiveness even after the initial stimulus has resolved. This recalibration may occur through mechanisms that alter transcriptional accessibility, reshape signaling thresholds, or modify the balance between pro- and anti-inflammatory pathways (). Within this framework, the key question is no longer whether peripheral inflammation affects the brain. Instead, it is whether repeated or unresolved immune perturbations can establish durable neuroimmune set-points that influence vulnerability to later-life pathology. One potential mediator of these long-term effects is epigenetic regulation. Chromatin architecture provides a biologically plausible mechanism through which environmental signals can be encoded without changing DNA sequence. Modifications in histone acetylation, methylation, and enhancer accessibility allow cells to adjust gene expression in response to external stimuli (; ). Importantly, these regulatory layers are dynamic but also capable of persistence. This allows prior exposures to shape future cellular responses. In immune cells, including tissue-resident macrophages, chromatin remodeling has been linked to innate immune memory. This memory can bias subsequent inflammatory responses. Whether similar mechanisms operate in infection-associated microbial disturbances and neurodegenerative susceptibility remains an open question (; ). Microglia are long-lived resident immune cells of the CNS. They continuously survey the brain microenvironment. They also integrate signals from systemic circulation, metabolic status, and neuronal activity. Experimental studies show that peripheral immune challenges can alter microglial inflammatory thresholds and cytokine responses later in life (; ). These findings suggest that microglial priming may represent a cumulative record of peripheral immune history. Microglia may therefore not act only as passive responders to neuronal pathology. Instead, they may actively shape neurodegenerative trajectories through state-dependent inflammatory regulation. At the level of the intestinal ecosystem, systemic infection has been associated with reproducible changes in microbial balance and barrier integrity. These changes can increase exposure to microbial-derived products (). Such peripheral disturbances suggest that infection-driven dysbiosis may influence regulatory networks beyond the gut. Moreover, microbial metabolites, including short-chain fatty acids (SCFAs) and tryptophan-derived compounds, can interact with chromatin-modifying enzymes and transcriptional regulators under defined experimental conditions (; ). Most mechanistic evidence comes from peripheral tissues. However, these findings suggest that microbiota-derived signals may intersect with host epigenetic systems that regulate immune responsiveness across tissues and time. Preclinical models of neurodegeneration have also investigated whether targeted modulation of microbial communities can influence synaptic resilience and inflammatory signaling (; ). Although these findings are context-dependent and require careful interpr